- Email: [email protected]
Environmental impact assessment of sediment dumping in the southern Baltic Sea using meiofaunal indicators
Journal of Marine Systems 75 (2009) 430–440
Contents lists available at ScienceDirect
Journal of Marine Systems j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j m a r s y s
Environmental impact assessment of sediment dumping in the southern Baltic Sea using meiofaunal indicators Peter Frenzel a,⁎, Corinna Borrmann a, Beate Lauenburg a, Björn Bohling b, Jan Bartholdy c a b c
Meeresbiologie, Institut für Biowissenschaften, Universität Rostock, Albert-Einstein-Str. 3, 18051 Rostock, Germany Christian-Albrechts-Universität zu Kiel, Institut für Geowissenschaften, AG Sedimentologie, Küsten-und Schelfgeologie, Otto-Hahn-Platz 1, 24118 Kiel, Germany Bredereicher Str. 17, 16798 Fürstenberg, Germany
a r t i c l e
i n f o
Article history: Received 7 April 2006 Received in revised form 8 January 2007 Accepted 9 January 2007 Available online 24 April 2008 Keywords: Foraminifera (Protista) Ostracoda (Crustacea) Environmental micropalaeontology Brackish water Halocline oscillation Germany Mecklenburg-Vorpommern Mecklenburg Bight 54.2°N 11.9°E
a b s t r a c t An experimental sediment dumping was carried out in the southern part of the Mecklenburg Bight in June 2001. Foraminiferans and ostracods from superficial sandy sediment were studied in a time series from before dumping until March 2004 in order to assess changes in associations and recolonization patterns of both groups. Additionally, an area sampling covering the dumping site and its surroundings from 15.5 to 20.7 m water depth made it possible to compare associations inside and outside the dumping area as well as the water depth dependent distribution of foraminiferans and ostracods. Salinity values vary within the high alpha-mesohaline and low polyhaline range. The dominating species are Ammotium cassis (Foraminifera) and Sarsicytheridea bradii (Ostracoda). The diversity is low (Fisher alpha index from 0.4 to 3.2 for foraminiferans and 1.0 to 2.5 for ostracods), but higher within the dumping site samples. These higher values are explainable by input of allochthonous tests and valves representing additional species. After the sediment dumping it took two and a half years to reestablish the total foraminiferan association and the total foraminifer/ostracod ratio within the dumping site. Total foraminiferan abundance increases remarkably with water depth (mean 83 tests in 100 ml) driven by higher nutrient availability and more suitable salinity and temperature values within the zone of the oscillating halocline. The distribution of shallow water species such as Cribroelphidium excavatum, Eucythere argus and Hirschmannia viridis, within the transient water layer A. cassis, Nodulina dentaliniformis, S. bradii and Palmoconcha laevata and below Eggerella scabra indicate the depth position of the halocline. Water depth and sediment dumping influence are the main driving factors for the distribution of foraminifer and ostracod associations within the study area. However, a significant sedimentological difference between samples inside and outside the dumping area is not recognizable. © 2008 Elsevier B.V. All rights reserved.
1. Introduction A frequently discussed anthropogenic impact on the marine environment is the dumping of dredged material. International conventions on the protection of the sea demand
⁎ Corresponding author. Present address: Institute of Geosciences, University of Jena, Burgweg 11, 07749 Jena, Germany. Tel.: +49 3641 948619; fax: +49 3641 948622. E-mail addresses: [email protected] (P. Frenzel), [email protected] (C. Borrmann), [email protected] (B. Lauenburg), [email protected] (B. Bohling), [email protected] (J. Bartholdy). 0924-7963/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2007.01.016
minimizing of environmental damage by dumping dredged material (e. g. HELCOM Recommendations 13/1 for the Baltic Sea, compare HELCOM, 1992). In the German Baltic Sea coastal area annually about 2.0 up to 2.5 million m3 dredged material is generated (Netzband, 2002). The majority of this material is not contaminated (Koch, 1994). The dumping of these uncontaminated sediments can cause environmental problems only in terms of the volume of deposits laid down on the sea floor, in the additional turbidity of the coastal waters near the discharge point, and in the possible establishment of unstable deposits on the sea floor (Gorsline, 1979). From the biological point of view especially the burial of benthic organisms is a
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
crucial effect of the dumping procedure. This study deals with the impact of sediment dumping in a south-western Baltic Sea site on two meiofaunal groups (Foraminifera and Ostracoda). They are classical microfossils in paleontology as well and possess easily preservable hard parts. In a previous study (Bohling, 2005a) it was not possible to detect unambiguous effects of a test dumping on the sedimentology around a dumping field in this selected study area. Thus the question arises, whether the meiofauna/”microfossils” may serve as a possible indicator for dumping effects or even large scale natural sediment displacements. Unfortunately, our knowledge about the foraminiferans and ostracods of the Mecklenburg Bight is rather limited. It is based on general occurrence of foraminiferans in the Mecklenburg Bight and its coast (Frenzel et al., 2005b) and on general remarks (Klie, 1938) and data about shallow water forms (Frenzel et al., 2005a) for the ostracods. The detailed and substantial studies by Rosenfeld (1977) on ostracods and Lutze (1965) on foraminiferans touch the Mecklenburg Bight in the northernmost part only. Hence, a baseline study of the distribution patterns of both meiofaunal groups in the area around the dumping site also had to be carried out.
431
Table 1 Abiotic factors for the studied samples
2. Study area The Baltic Sea has an estuarine circulation pattern with water body stratification. The bottom water shows higher salinity with general lower and less variable temperature and an upper water body with lower salinity and more variable temperature conditions (Matthäus, 1996). The stratification may cause oxygen deficiency during longer periods of lacking water intrusion from the North Sea. A tidal influence is not remarkable in the inner Baltic Sea (Lass and Margaard, 1996). The Mecklenburg Bight is situated in the south-western Baltic Sea. The study area lies in the southern part of the Mecklenburg Bight, north of Bad Doberan in north-eastern Germany (Fig. 1). All samples derive from water depths from 15 to 21 m. The depth level of the layer of discontinuity (halocline) is here 10–15 m to about 20 m oscillating over the year (personal communication H. U. Lass, Institute of Baltic Sea Research Warnemünde). Salinity shows about 12–14 psu in the surface water and 19–21 psu in the deeper water (Niedermeyer et al., 1995). The mean water temperature varies between 3 °C in winter and 17 °C in summer within the upper water layer and is about 13 °C in deeper water in summer (personal communication H. U. Lass). Near-bottom
The samples from within the dumping site area are highlighted with two double lined frames. Full sample numbers (IOW designation) were given with highlighted numbers as used in the present paper.
water temperatures and salinities at the dumping site varied between 9.1 to 14.2 °C and 13.5 to 18.8 PSU respectively at the sampling occasions between June, 2000 and July, 2003 (Powilleit et al., 2006). The sediment at the sea floor of the study area is well sorted fine sand (Bohling, 2005b). Only the south-western and south-eastern edge of the sampled area is covered with medium to coarse sand. The sediment type distribution in the Mecklenburg Bight can be considered as stable (Bohling, 2005b). The macrofauna of the disposal site area prior to the dumping in June, 2001 could be characterised as a well-established soft bottom community typically found in the western Baltic Sea with the dominant bivalve species Arctica islandica, Macoma balthica, the cumacean Diastylis rathkei, and the polychaete Nephtys hombergii (Powilleit et al., 2006). 3. Material and methods
Fig. 1. The Mecklenburg Bight in the southern Baltic Sea and grid of sampled stations with isobaths (October, 2002). The black framed square in the overview indicates the study area.
An experimental dumping of sediment was executed in the study area within the DYNAS project (compare Harff, 2003) in April, 2001. The used sediment derives from a close to shore site in front of the Warnow estuary about 12 km to the west. Several distinct sediment mounds with diameters of
432
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Fig. 2. Plots of sedimentological parameters against water depth with trend lines. Dumping site samples are indicated by hollow circles. The mean grain size of the sandy sediment decreases with increasing water depth, showing a lower variance in grain size distribution and higher silt proportions which causes higher organic contents (TOC) and higher water contents of the sediment.
up to 28 m and heights of up to 1.5 m were created by the experimental dumping. The dumping site was observed during the next 3 years in intervals of some months for documenting impact on macrofauna and sedimentology as well as recolonialization of the site (Bohling, 2005a; Powilleit et al., 2006). Five sediment samples were used for the present study. The material derives from the uppermost 1–2 cm sediment and was freeze-dried immediately after winning. Because of other studies the volume left for meiofaunal analysis varies around only 30 cm3. An area sampling (twelve samples) was done on October 14, 2002, one and a half years after dumping. Only one station lies within the dumping field, all the others group in a grid around (Fig. 1). The used sampling device was a box core sampler as in the time series. Again, 1–2 cm superficial sediment were taken, but fixed immediately in 70% ethanol with Bengal Rose stain following Lutze (1964) in order to identify living specimens in the lab. Each sample contained about 70 cm3 to 100 cm3 sediment volume. Because of the sandy sediment character, we concentrated foraminiferan tests and ostracods by repeated (five times) flotation of dried sediment in water. The floating material was given on a 200 µm and 63 µm sieve and afterwards dried in an oven at 60 °C. Measured sediment parameters were mean grain size, sorting (Trask) and sand and silt content (all measured by sieving) as well as water content and total organic carbon by loss on ignition method. Foraminiferans and ostracods from both sample series (time and area sampling) were picked completely from the 200 µm size fraction. The smaller fraction and the flotation
residues were spot checked for larger quantities of shells, what was not the case. We distinguished between living and dead foraminiferans on the base of stained tests (compare Lutze and Altenbach, 1991). Well preserved tests, i.e. complete and not corroded or abraded, with a stained lumen in one or more chambers were regarded as living individuals. Agglutinated tests had to be wetted before examining the chamber lumen under the microscope. Here, stained residues of pseudopodia and catched detritus around the aperture often indicated activity during sampling. Living ostracods were counted if stained and well preserved carapaces with soft body were present (compare Uffenorde, 1972 and Rosenfeld,
Fig. 3. Dendrogram of a cluster analysis (complete linkage) on sediment parameters (mean grain size, silt content, sorting, water content, TOC). The dumping site (asterisk) lies within the main group of samples, whereas samples with coarse grain size and low TOC values are grouped outside.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440 Table 2 Living and dead Foraminifera and Ostracoda from the study area Taxon
Species
Foraminifera Ammonia batavus Hofker, 1951 Ammoscalaria runiana (Heron-Allen and Earland, 1916) Ammotium cassis (Parker, 1870) Astrammina sphaerica (Heron-Allen and Earland, 1932) Cribroelphidium albiumbilicatum (Weiss, 1954) Cribroelphidium excavatum (Terquem, 1875) Cribroelphidium gerthi (Van Voorthuysen, 1957) Cribroelphidium incertum (Williamson, 1858) Cribroelphidium williamsoni (Haynes, 1973) Eggerella scabra (Williamson, 1858) Haynesina germanica (Ehrenberg, 1840) Miliammina fusca (Brady, 1870) Nodulina dentaliniformis (Brady, 1881) Ophthalmina kilianensis Rhumbler, 1936 Subreophax aduncus (Brady, 1882) Ostracoda Candona candida (O. F. Müller, 1776) Cyprideis torosa (Jones, 1850) f. littoralis Cyprideis torosa (Jones, 1850) f. torosa Cytheropteron latissimum (Norman, 1865) Cytherura atra (Sars, 1865) Eucythere argus (Sars, 1865) Hirschmannia viridis (O. F. Müller, 1785) Leptocythere baltica (Klie, 1929) Leptocythere pellucida (Baird, 1850) Leptocythere psammophila (Guillaume, 1976) Neocytherideis crenulata (Klie, 1929) Palmoconcha guttata (Norman, 1865) Palmoconcha laevata (Norman, 1865) Paracyprideis fennica (Hirschmann, 1909) Robertsonites tuberculatus (Sars, 1865) Sarsicytheridea bradii (Norman, 1865) Sarsicytheridea punctillata (Brady, 1865) Semicytherura sella (Sars, 1865)
Living Dead Dumping only site only X X
X
X X X X X X X X X X X
433
We distinguish between biocoenosis, thanatocoenosis and taphocoenosis for our analysed associations. The biocoenosis is a community of organisms living together in a given biotope. The thanatocoenosis describes an association of organismic remains (potential fossils, in our case empty shells) found in a given place. This association only contains parts of the former biocoenoses because of selective destruction of specimens/skeletons. Hence, a thanatocoenosis is autochthonous but reflects only parts of the former biocoenosis. The taphocoenosis comprises elements of several biocoenoses, i. e. contains allochthonous and autochthonous or only allochthonous components. Methods for discrimination of these types of associations are discussed in detail for ostracods in Boomer et al., 2003. Selected specimens were documented by scanning electron microscopy and light microscopy. Diversity was measured by Fisher alpha index (Fisher et al., 1943; compare Murray, 1991) and Pielou evenness index (compare Buzas, 1979). An index for the dumping influence was used for incorporating this factor into the data set for a Principal Component Analysis. This index is expressed with higher values for the dumping site shortly
X X X
X
X
X
X
X
X X X X X X X X X X X X X X X
1977). The degree of staining varies strongly for different ostracod taxa. A firm closing of valves can prevent a penetration of stain into the carapace cavity. These problems make the Bengal Rose staining method better suitable for foraminiferans than ostracods (Brouwers et al., 2000). On the other hand, disarticulated valves, broken, abraded or corroded shells and size sorting of individuals from different ontogenetic stages can indicate allochthonous (i.e. transported) faunal components (see Boomer et al., 2003).
Fig. 4. Foraminifera (1–20) and Ostracoda (21–35) from the study area. All these SEM pictures are given as external side views if not otherwise stated. 1–3: Ammotium cassis; 1–2 microsphaeric specimens, samples MUC and 922, 3 — macrosphaeric specimen, sample 418; 4: Astrammina sphaerica, sample 924; 5: Nodulina dentaliniformis, sample 921; 6: Eggerella scabra, sample 917; 7: Subreophax aduncus, fragment, sample 924; 8: Ammoscalaria runiana, sample 922; 9 — 10: Miliammina fusca, Fig. 9 is partly damaged in the apertural area, samples 920 and 921; 11: Cribroelphidium incertum, sample 924; 12: Cribroelphidium williamsoni, last chamber is missing, sample 920; 13: Cribroelphidium gerthi, sample 920; 14: Cribroelphidium excavatum, sample 920; 15 — 16: Cribroelphidium albiumbilicatum, Fig. 15 represents the large and thick form asklundi as described by Lutze (1965), both from sample 924; 17: Ammonia batavus, umbilical view, sample 920; 18 — 19: Ophthalmina kilianensis, apertural and side view, samples 927 and 916; 20: Haynesina germanica, sample 920; 21: Cytheromorpha fuscata, right side of a female, sample 970; 22: Cyprideis torosa f. torosa, left valve of a juvenile, sample 766; 23: Cytherura atra, right valve, sample 915; 24 — 25: Semicytherura sella, left side of a female and a male carapace, samples 924 and 916; 26: Eucythere argus, right side of a female, sample 968; 27: Heterocyprideis sorbyana, female left valve, sample 968; 28: Palmoconcha laevata, right side of a male carapace, sample 916; 29: Hirschmannia viridis, right side of a female carapace, sample 927; 30: Palmoconcha guttata, female left valve, sample 922; 31: Robertsonites tuberculatus, left side of a female carapace, sample 916; 32 — 33: Sarsicytheridea bradii, left side of a female and internal view of a female right valve, samples 418 and 420; 34 — 35: Leptocythere pellucida, right sides of a smooth female and a fossae bearing male, both from sample 916.
434
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Table 3 Total (living + dead) foraminifer abundances in tests per 100 ml sediment (every upper row in bold numbers)
water depth. Sedimentologically, there is no significant difference between the samples from the dumping site and the surroundings (Fig. 3; Bohling, 2005a). Other taxa than ostracods and foraminiferans within the samples are juvenile Lamellibranchiata (e. g. Arctica islandica), Gastropoda and Polychaeta as well as worm tubes. Significant differences within the macro-fauna are not recognizable because of low numbers in these samples of relatively small volumes. Reworked Upper Cretaceous microfossils (mainly foraminiferans) occur sporadically. 4.2. Foraminifera and Ostracoda We found 15 foraminifer and 17 ostracod species. Of these, five foraminifer and five ostracod species occurred dead only (Table 2; Fig. 4). The dominating species in biocoenosis and thanatocoenosis as well as taphocoenosis are clearly the large agglutinated Ammotium cassis within the Foraminifera (Table 3) Table 4 Total (living + dead) ostracod abundances in valves per 100 ml sediment (bold numbers in every first row)
The number of living specimens is given in every lower row (normal numbers) and the total number in every upper row (bold). The column Counted tests indicates the absolute total number of foraminiferan tests of each sample. The samples from within the dumping site area are highlighted with two double lined frames. Full sample numbers (IOW designation) were given with highlighted numbers as used in the present paper.
after the dumping event, lower values afterwards and zero values in other sites. Because of low numbers of counted individuals within most samples, we used species abundance values (tests/valves per 100 ml) instead of dominance (proportion) values for statistical analysis (see Patterson and Fishbein, 1989 and Fatela and Taborda, 2002 for discussion). Statistics were done with the program Data Desk® 6.1. 4. Results 4.1. Environmental factors and other biota The sediment of sampled stations is well sorted fine sand with a low organic content (0.2–0.8%; Table 1). Only exceptions are stations 915 and 927 (the shallowest stations) with dominating medium or coarse sand (Fig. 2). There is a general but weak trend to higher silt contents with increasing
The number of living specimens is given in every second row (normal numbers) and the total number in every first row (bold). The column Counted valves indicates the absolute total number of ostracod valves of each sample. The samples from within the dumping site area are highlighted with two double lined frames. Full sample numbers (IOW designation) were given with highlighted numbers as used in the present paper.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
435
Fig. 5. Abundance of total foraminiferans and ostracods (living + dead) in relation to water depth. The bold regression line indicates the trend for foraminiferans (points), the broken line for ostracods (squares). Open circles or squares show dumping samples. A trend of increasing foraminiferan numbers with greater water depth is recognizable. This trend is driven by Ammotium cassis abundance. The inset shows the time series from the dumping site with lower abundance of foraminiferans after dumping.
and the smooth shelled Sarsicytheridea bradii within the Ostracoda (Table 4). About 28% of total foraminiferan association and 49% of total ostracod association are living specimens. The mean abundance is 83 foraminiferan tests respectively 26 ostracod specimens per 100 cm3 for living associations and 297 foraminiferan tests respectively 129 ostracod valves per 100 cm3 for total associations. With greater water depth the number of foraminiferans in total association increases distinctively (Fig. 5). This is not as clear in living associations and still less for ostracods. The dominating Ammotium cassis drives the abundance trend within foraminiferans with its abundance. The diversity (Fisher alpha index) of total associations is with 0.4 to 3.2 for foraminiferans and 1.0 to 2.5 for ostracods low. There is a weak trend in both taxonomic groups for higher species numbers in shallower water (Fig. 6). The dumping site displays the highest species numbers. Most abundant species show a characteristic depth distribution. The abundant foraminifer species A. cassis and N. dentaliniformis become frequent with increasing water depth. E. scabra prefers the deepest sampled depth interval (Fig. 7). Typical for shallower water is C. albiumbilicatum (Fig. 7). All other foraminiferan taxa do not show depth preferences or are too rare for a distribution analysis. Frequent deeper water ostracod species are S. bradii and P. laevata (Fig. 7). Ostracod species with a shallower water depth distribution are Eucythere argus and Hirschmannia viridis (Fig. 7). C. torosa and C. candida occur within the dumping site only. Analysing the complete faunistic data for a classification of the samples we get a group of deeper water stations (N18.5 m in general) and a second one containing shallower water
stations as well as samples from the dumping site (Fig. 8). Interestingly, most dumping site samples fit into the shallow water group despite their greater water depth. 5. Discussion The abundance of living and dead foraminiferans is much lower in our study area than this one documented by Lutze (1965) from the northern part of the Mecklenburg Bight,
Fig. 6. Diversity (Fisher alpha index and evenness) of foraminiferans (points) and ostracods (squares) in different water depth. Open circles or squares show dumping samples. The bold regression line indicates the weak trend for foraminiferans, the broken line for ostracods. Some samples are missing from this diagram because of too low number of specimens. The insets show the time series for the dumping site with higher species numbers after dumping until March, 2004. The evenness is not remarkable influenced by the dumping event.
436
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Fig. 7. Total (living + dead) abundance of foraminiferans (points) and ostracods (squares) in different water depth. Open circles or squares show dumping samples. The synthesis diagram in box shows estimation for mean depth position of the halocline based on abundance trends of the selected taxa. Foraminifer species with highest abundances in greater water depths are Ammotium cassis, Nodulina dentaliniformis and Eggerella scabra. E. scabra displays the lowermost depth distribution level. Sarsicytheridea bradii, the most abundant ostracod species within the study area, is much more frequent in greater water depths. Also, Palmoconcha laevata prefers greater water depths. The hyaline foraminifer Cribroelphidium albiumbilicatum is restricted to water depths b 17 m in general. The four samples with higher abundances below 17 m water depth are all from the dumping site. Ostracod species with a shallower water depth distribution are Eucythere argus and Hirschmannia viridis.
where probably the environment is more stable in the deeper water. The foraminiferan fauna encountered in our study corresponds to the Ammotium cassis association in species composition and environmental parameters. This association was defined by Murray (1991) for the Atlantic seaboard of Europe and Africa. It differs from associations documented by Lutze (1965) from the marginal Mecklenburg Bight, the only published study on foraminiferans touching the area before. His dominating species were Cribroelphidium excavatum, Eggerella scabra, Subreophax aduncus and Ammotium cassis. A. cassis was much less dominating than in our study. At the present state of knowledge it is hard to say if this different picture is caused by changing distribution patterns during the last 40 years or simply by differences in settlements in the southern and northern part of the Mecklenburg Bight. However, Lutze (1974) describes a very similar association with clearly dominating A. cassis from water depths between 16 and 20 m in the Kiel Bight. We know from Lutze (1965) that the distribution pattern of foraminiferans in the Baltic Sea is highly variable due to changing environmental situation, especially salinity variation. The lower salinity limit of A.
cassis association is 17 psu (Lutze, 1965; Murray, 1991), close to around 19 psu in deeper water of the Mecklenburg Bight. This ecological boundary situation for A. cassis is reflected in temperature, too. The species tolerates up to 19 °C, but prefers b3 °C (Murray, 1991). An optimal situation is given in winter; however, temperature rises even in bottom water in general to 13 °C in summer, causing a critical range for A. cassis above the halocline. The higher abundance of Ammotium cassis with increasing depth reflects more frequent suitable environmental conditions below the upper limit of the oscillating halocline at about 15 m water depth (Figs. 5 and 7). On the other hand, these changing conditions cause a higher diversity of thanatocoenoses at shallower water depth (Fig. 6), because the dead assemblage preserves a long term view onto associations and allochthonous elements from shallower water additionally. Olsson (1976) describes A. cassis as preferring and dominating the transient water layer, where the halocline oscillates and higher nutrient amounts are available. This explains the higher abundances with increasing water depth in our study. The surface of organic rich sediments in the southern Mecklenburg Bight is often covered with tests of A. cassis, as it was reported for the Kiel Bight area, too (Linke and Lutze, 1993). They are so big and densely spread that it is clearly visible for the naked eye by observing the content of a box corer on board. Biomass production values of up to 5 g m− 2a− 1 are calculated by Wefer & Lutze (1976) for about 20 m water depth in the Kiel Bight. A similar situation is reflected by high numbers of this species within total association in the dumping area before the dumping experiment (Fig. 5: Oct 00). After burying the historical layer with sediment by dumping, the foraminiferan number of the newly established sediment surface is distinctively lower. It takes some time until the old abundance of the total association is reached again — in our case about two and a half years (Fig. 5: Jun 03). Powilleit et al. (in press) found significantly changed macro-benthos communities on our dumping site some weeks after dumping and a completely recovered macro-benthos community 2 years after the dumping experiment took place. This time frame meets our results very well. Beside the problem of recolonialization and
Fig. 8. This dendrogram shows the grouping of samples based on a cluster analysis (complete linkage) using faunistic data (foraminifer and ostracod abundance and diversity). Samples below and above about 18.5 m water depth are placed in two different groups. The dumping site samples (indicated with asterisks) fit into the shallower water group or are outliers. Before calculation, the samples with a very low number of individuals (samples 257 and 682 — both from the dumping site) as well as all taxa occurring in less than three samples were excluded and highly correlated (N 0.9) variables reduced to one variable of each of these pairs.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Fig. 9. Ratio of total (living + dead) foraminifer to ostracod number in different water depth. Open rhombi show dumping site samples. A weak trend to higher ratios with increasing water depth is visible. The ratio falls within the dumping area after dumping in April, 2001 and increases later on.
time consuming production of tests for the thanatocoenosis, we assume long term sediment redeposition on the newly created sea bottom because of initial higher relief energy. Such
437
redeposition is especially for larger foraminiferans as A. cassis a problem, if they are buried. They prefer the sediment surface and occur above the Redox Potential Discontinuity Layer (Linke and Lutze, 1993), but cannot move fast to the surface after burial. Such process may delay the reestablishment of the typical thanatocoenosis additionally. Also, the self-locomotion of large foraminiferans as A. cassis is too slow for a recolonization by active movement and the tests are too heavy for transport by dispersal (Olsson, 1977), hence, the only way to settle the new substrate is by release and transport of embryonic juveniles (compare Wefer and Richter, 1976; Alve, 1999). Wefer (1976) reports two reproduction periods of A. cassis in the Kiel Bight area, one in spring and one in autumn. This reproduction time fixes the pattern as it was presumed by Wefer & Richter (1976) for Cribroelphidium excavatum in a colonization experiment in the Eckernförder Bight, western Baltic Sea. Hess et al. (2005) report a recolonization period for foraminiferans of 6 to 9 months under unstable environmental conditions in a submarine canyon in the Bay of Biscay after turbidite disposition by tempests. Alve (1999) estimates a recolonization period of one to several years for foraminiferan associations if this process is driven by reproduction mainly, what is coincident with our observations. The samples studied by Lutze (1965) from the outer Mecklenburg Bight were used by Rosenfeld (1977) for
Fig. 10. Principal Components Analysis on three abiotic and eleven ostracod variables (species abundances and ostracod diversity). The first factor is relatable to water depth. The second factor correlates with the dumping influence as shown by the high loading of the allochthonous Cyprideis torosa and a higher diversity caused by input of additional (allochthonous) species. Both components explain 57.1% of the cumulative variance. The other factors are much weaker in influence and hard to interpret (see Table 5). The picture is similar to this of foraminiferans, however, water depth and dumping influence are not so easy to distinguish and the grain size has a greater importance (Table 6).
438
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Table 5 Factor loadings of the first six factors of Principal Components Analysis on three abiotic and ostracod variables (species abundances and ostracod diversity)
High loadings are dark (N0.75) or light shaded (N0.5). The first factor is clearly correlatable with water depth, the second one with the dumping event. The other factors are much weaker in influence and hardly to interpret. Compare Fig. 10.
ostracod analyses. He found a similar species spectrum, with other proportions however, and put it to his association 3, typical for the deeper water of basins and furrows in the Baltic
Sea. Rosenfeld's (1977) dominant species were Sarsicytheridea bradii, S. punctillata, Paracyprideis fennica and Neocytherideis crenulata. Both S. punctillata and P. fennica are very rare in our study. P. fennica seems to avoid the transitional water layer (Rosenfeld, 1977), which could explain its scarcity. However, we do not know the cause for the low number of S. punctillata. The picture of ostracod number distribution is different from the one for foraminiferans. They do not show a distinct increase of abundance with water depth (Fig. 5). Arlt et al. (1982) describe a strong decrease from 0 to 20 m water depth with about 72% of ostracods found above 20 m followed by a very weak decreasing trend down to maximal depths in the southern Baltic Sea. Regarding the ratio between foraminifer and ostracod number, we can see a higher value before than immediately after dumping (Fig. 9). This ratio evolves up to normal values with time. We explain this phenomenon with faster recolonization of the new substrate by immigration of the much faster moving ostracods, whereas foraminiferans settle the new substrate mainly by reproduction. A study on shallow water ostracods from a close location at Poel Island (southern Mecklenburg Bight) showed speeds of about 0.1 to 0.6 mm/s for ostracods moving on sediment surface and even not more slowly within the superficial sediment (Borck and Frenzel, 2006). Calculating the time needed for an ostracod crawling a straight line from the periphery to the centre of the largest mound of dumped sediment with a diameter of 28 m,
Fig. 11. Proportion of allochthonous elements within foraminifer plus ostracod total association (living + dead) during time series sampling within the dumping area. The first column shows the mean value with standard deviation for all stations outside the dumping field (sampled in October, 2002) as a reference value. The proportion of allochthonous elements, mostly transported with dumped sediment, decreases after the dumping experiment in April, 2001. In March, 2004 allochthonous elements are not detectable anymore.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440 Table 6 Factor loadings of the first six factors of Principal Components Analysis on three abiotic and foraminiferan variables (species abundances and foraminiferan diversity)
High loadings are dark (N0.75) or light shaded (N0.5). The first factor is correlatable with the dumping event, the second one clearly with water depth. The other factors are much weaker in influence and hardly to interpret.
we get a figure between 7 and 39 h. The whole recovering process of ostracod assemblage took about two and a half years in our site (Fig. 9: Jun 03), as observed for foraminiferans. Looking on the general distribution of foraminiferans, ostracods and on the values of some abiotic factors with a help of the Principal Component Analysis we recognize water depth (relative position to halocline) and the sediment dumping as the most important factors driving the composition of total associations (Fig. 10, Table 5). The mean discriminating depth between deeper and shallower water species (Fig. 7) indicates a mean water depth of about 17 m for the halocline, what meets the hydrographic data of 10–15 m to 20 m in the Mecklenburg Bight. Allochthonous elements of the microfauna are the best indicators for the dumped sediment (Fig. 11). They cause a higher diversity (species number) in dumping site samples (Fig. 6) as it was observed by Drapala (1993) for turbidites in the deep sea as well. Shallow water and estuarine species as Ammonia batavus, Miliammina fusca, Candona candida, Cyprideis torosa and Leptocythere lacertosa occur as dead specimens and mainly or even exclusively within the dumping area (Table 1). They derive from shallower water closer to the shore or even from the Warnow estuary with significant lower salinity (C. candida and C. torosa f. torosa), in front of which the dumped sediment was taken. Within the succession of the thanatocoenosis from the dumping site a decreasing proportion of such allochthonous elements is visible (Fig. 11). The sample of October, 2003 is an exception, maybe because of sediment reworking within the dumping site. On the other hand, the number of counted specimens is too low for exact and stable data concerning proportions of 10% or less allochthonous elements. This causes a large error range. Patterson & Fishbein (1989) recommend analysing taxa with at least 50% dominance only in 50 specimens counts and with at least 10% dominance only in 300 specimens counts. In March, 2004, two and a half years after sediment dumping, no allochthonous elements are still detectable.
439
6. Conclusions The main factors for the distribution of total foraminifer and ostracod association distributions are water depth, respectively changes of parameters along depth gradient, especially the discontinuity layer of the halocline, and dumping influence in our study. Larger and event-like sediment redeposition can be indicated by microfossils respectively hard parts of meiofaunal organisms. A short time change of the living associations (some weeks to months after deposition event) is probable but within our study not provable because of the large time intervals of sampling and too small sampled sediment volumes shortly after sediment dumping. However, the taphocoenosis recovers more slowly than biocoenosis in composition and abundance values because of a diluting or burial effect of thanatocoenosis by sediment input and conserves allochthonous elements introduced with redeposited sediment, which show the event in our study until two and a half years after sediment dumping. This phenomenon may be used to detect the impact of anthropogenic sediment dumping as well as large scale natural sediment redeposition by storm events, turbidites, earthquakes or tsunamis. A quantitatively and qualitatively changed microfauna with allochthonous elements should be visible in fossil sediments, too, if the redeposited sediment volume is big enough. Acknowledgements We thank the crew of Research vessel ‘Professor Albrecht Penck' for supporting the sampling. The samples were taken during cruises for the project DYNAS (Dynamics of Natural and Anthropogenic Sedimentation), funded by the German Ministry of Education and Research (Grant No. 03F0280A). Gerhard Graf, Martin Powilleit (University of Rostock), David Horne (Queen Mary, University of London) and Robin Edwards (Trinity College, Dublin) gave us valuable comments on our manuscript. The first author was supported by a sponsorship of the German Federal Environmental Foundation (DBU). References Alve, E., 1999. Colonization of new habitats by benthic foraminifera: a review. Earth-Science Reviews 46, 167–185. Arlt, G., Müller, B., Warnack, K.-H., 1982. On the distribution of Meiofauna in the Baltic Sea. Internationale Revue der gesamten Hydrobiologie 67 (1), 97–111. Bohling, B., 2005a. Monitoring auf der Probeklappstelle - Sedimentologie. In: Harff, J. (Ed.), Projekt DYNAS II- Dynamik natürlicher und anthropogener Sedimentation - Vorhaben: Sedimentationsprozesse in der Mecklenburger Bucht, Phase 2 - Abschlußbericht (Meilenstein 10). IOW, Warnemünde, pp. 59–66. http://www.io-warnemuende.de/projects/dynas/. Bohling, B., 2005b. Estimating the risk for erosion of surface sediments in the Mecklenburg Bight (south-western Baltic Sea). Baltica 18 (1), 3–12. Boomer, I., Horne, D.J., Slipper, I.J., 2003. The use of ostracods in palaeoenvironmental studies, or what can you do with an ostracod shell? In: Park, L.E., Smith, A.J. (Eds.), Bridging the gap: trends in the ostracod biological and geological sciences. The Paleontological Society Papers, vol. 9, pp. 153–179. Borck, D., Frenzel, P., 2006. Micro-habitats of brackish water ostracods from Poel Island, southern Baltic Sea coast. Senckenbergiana maritima 36 (2), 99–107. Brouwers, E.M., Cronin, T.M., Horne, D.J., Lord, A.R., 2000. Recent shallow marine ostracods from high latitudes: implications for late Pliocene and Quaternary palaeoclimatology. Boreas 29, 127–143.
440
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Buzas, M.A., 1979. The measurement of species diversity. Foraminiferal Ecology and Paleoecology. SEPM Short Course, vol. 6, pp. 3–10. Drapala, V., 1993. The use of ostracods in detecting fine grained turbidites in deep sea cores. In: Jones, P., McKenzie, K. (Eds.), Ostracoda in the Earth and Life Sciences. Balkema, Rotterdam, pp. 559–568. Fatela, F., Taborda, R., 2002. Confidence limits of species proportions in microfossil assemblages. Marine Micropaleontology 45 (2), 169–174. Fisher, R.A., Corbet, S.A., Williams, C.B., 1943. The relation between the number of species and the number of individuals in a random sample of animal population. Journal of Animal Ecology 12, 42–58. Frenzel, P., Henkel, D., Siccha, M., Tschendel, L., 2005a. Do ostracod associations reflect macrophyte communities? A case study from the brackish water of the southern Baltic Sea coast. Aquatic Sciences 67, 142–155. Frenzel, P., Tech, T., Bartholdy, J., 2005b. Checklist and annotated bibliography of Recent Foraminiferida from the German Baltic Sea coast. In: Tyszka, J., Oliwkiewicz-Miklasińska, M., Gedl, P., Kaminski, M.A. (Eds.), Methods and Applications in Micropalaeontology. Studia Geologica Polonica, vol. 124, pp. 67–86. Gorsline, D.S., 1979. Shelf-sediment dynamics and solid-waste disposal. In: Palmer, H.D., Gross, M.G. (Eds.), Ocean Dumping and Marine Pollution. Dowden, Hutchinson & Ross, Stroudsburg, pp. 9–16. Harff, J. (Ed.), 2003. Projekt DYNAS - Dynamik natürlicher und anthropogener Sedimentation - Vorhaben: Sedimentationsprozesse in der Mecklenburger Bucht - Abschlußbericht (Meilenstein 6). IOW, Warnemünde.135 pp. http:// www.io-warnemuende.de/projects/dynas/. HELCOM, 1992. HELCOM Recommendations 13/1: Disposal of dredged spoilsadopted 6 February 1992, having regard to Article 9, Paragraph 2 of the Helsinki Convention. Helsinki. 25 pp. http://www.helcom.fi/stc/files/ Guidelines/guide_rec13_1.pdf. Hess, S., Jorissen, F.J., Venet, V., Abu-Zied, R., 2005. Benthic foraminiferal recovery after recent turbidite deposition in Cap Breton Canyon, Bay of Biscay. Journal of Foraminiferal Research 35 (2), 114–129. Klie, W., 1938. Ostracoda, Muschelkrebse. In: Dahl, M., Bischoff, H. (Eds.), Die Tierwelt Deutschlands und der angrenzenden Meeresteile nach ihren Merkmalen und nach ihrer Lebensweise, vol. 34(3). Gustav Fischer, Jena, p. 230. Koch, M., 1994. Situation der Baggergutverbringung im Bereich der Wasser-und Schiffahrtsdirektion Ost. Mitteilungen der Bundesanstalt für Gewässerkunde Nr. 6: Unterbringung von belastetem Baggergut im aquatischen Milieu, pp. 7–12. Koblenz. Lass, H.U., Margaard, L., 1996. Wasserstandsschwankungen und Seegang, In: Rheinheimer, G. (Ed.), Meereskunde der Ostsee, 2nd edition. Springer, Berlin, pp. 68–74. Linke, P., Lutze, G.F., 1993. Microhabitat preferences of benthic foraminifera — a static concept or a dynamic adaptation to optimize food acquisition? Marine Micropaleontology 20, 215–234.
Lutze, G.F., 1964. Zum Färben rezenter Foraminiferen. Meyniana 14, 43–47. Lutze, G.F., 1965. Zur Foraminiferen-Fauna in der Ostsee. Meyniana 15, 75–142. Lutze, G.F., 1974. Foraminiferen der Kieler Bucht (Westliche Ostsee): 1. ’Hausgartengebiet“ des Sonderforschungsbereiches 95 der Universität Kiel. Meyniana 26, 9–22. Lutze, G.F., Altenbach, A., 1991. Technik und Signifikanz der Lebendfärbung benthischer Foraminiferen mit Bengalrot. Geologisches Jahrbuch A128, 251–265. Matthäus, W., 1996. Temperatur, Salzgehalt und Dichte, In: Rheinheimer, G. (Ed.), Meereskunde der Ostsee, 2nd edition. Springer, Berlin, pp. 75–81. Murray, J.W.,1991. Ecology and Palaeoecology of Benthic Foraminifera. Longman Scientific & Technical, John Wiley & Sons Essex, New York, 379 pp. Netzband, A., 2002. Internationale Entwicklungen im Umgang mit Baggergut. HANSA- Schiffahrt- Schiffbau – Hafen 139 (10), 56–61. Niedermeyer, R.-O., Werner, F., Janke, W., 1995. Die heutige Ostsee und ihre südwestliche Küste. In: Duphorn, K., Kliewe, H., Niedermeyer, R.-O., Janke, W., Werner, F. (Eds.), Die deutsche Ostseeküste. Sammlung Geologischer Führer, 88. Gebr. Borntraeger, Berlin, pp. 51–90. Olsson, I., 1976. Distribution and ecology of the foraminiferan Ammotium cassis (Parker) in some Swedish Estuaries. Zoon 4, 137–147. Olsson, I., 1977. Wall structure of the foraminifer Ammotium cassis (Parker) and its ecological significance. Zoon 5, 11–14. Patterson, R.T., Fishbein, E., 1989. Re-examination of the statistical methods used to determine the number of point counts needed for micropaleontological quantitative research. Journal of Paleontology 63, 245–248. Powilleit, M., Kleine, J., Leuchs, H., 2006. Impacts of experimental dredged material disposal on a shallow, sublittoral macrofauna community in Mecklenburg Bay (western Baltic Sea). Marine Pollution Bulletin 52 (4), 386–396. Rosenfeld, A., 1977. Die rezenten Ostracoden-Arten in der Ostsee. Meyniana 29, 11–49. Uffenorde, H., 1972. Ökologie und jahreszeitliche Verteilung rezenter benthonischer Ostracoden des Limski-Kanals bei Rovinj (nördliche Adria). Göttinger Arb. Geol. Paläont. 13, 121. Wefer, G., 1976. Environmental effects on growth rates of benthic foraminifera (shallow water, Baltic Sea). Ist International Symposium on Benthonic Foraminifera of Continental Margins. Part A. Ecology and Biology. Maritime Sediments Special Publication, vol. 1, pp. 39–50. Wefer, G., Lutze, G.F., 1976. Benthic foraminifera biomass production in the Western Baltic. Kieler Meeresforschungen, Sonderheft 3, 76–82. Wefer, G., Richter, W., 1976. Colonization of artificial substrates by foraminifera. Kieler Meeresforschungen, Sonderheft 3, 72–75.
Contents lists available at ScienceDirect
Journal of Marine Systems j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j m a r s y s
Environmental impact assessment of sediment dumping in the southern Baltic Sea using meiofaunal indicators Peter Frenzel a,⁎, Corinna Borrmann a, Beate Lauenburg a, Björn Bohling b, Jan Bartholdy c a b c
Meeresbiologie, Institut für Biowissenschaften, Universität Rostock, Albert-Einstein-Str. 3, 18051 Rostock, Germany Christian-Albrechts-Universität zu Kiel, Institut für Geowissenschaften, AG Sedimentologie, Küsten-und Schelfgeologie, Otto-Hahn-Platz 1, 24118 Kiel, Germany Bredereicher Str. 17, 16798 Fürstenberg, Germany
a r t i c l e
i n f o
Article history: Received 7 April 2006 Received in revised form 8 January 2007 Accepted 9 January 2007 Available online 24 April 2008 Keywords: Foraminifera (Protista) Ostracoda (Crustacea) Environmental micropalaeontology Brackish water Halocline oscillation Germany Mecklenburg-Vorpommern Mecklenburg Bight 54.2°N 11.9°E
a b s t r a c t An experimental sediment dumping was carried out in the southern part of the Mecklenburg Bight in June 2001. Foraminiferans and ostracods from superficial sandy sediment were studied in a time series from before dumping until March 2004 in order to assess changes in associations and recolonization patterns of both groups. Additionally, an area sampling covering the dumping site and its surroundings from 15.5 to 20.7 m water depth made it possible to compare associations inside and outside the dumping area as well as the water depth dependent distribution of foraminiferans and ostracods. Salinity values vary within the high alpha-mesohaline and low polyhaline range. The dominating species are Ammotium cassis (Foraminifera) and Sarsicytheridea bradii (Ostracoda). The diversity is low (Fisher alpha index from 0.4 to 3.2 for foraminiferans and 1.0 to 2.5 for ostracods), but higher within the dumping site samples. These higher values are explainable by input of allochthonous tests and valves representing additional species. After the sediment dumping it took two and a half years to reestablish the total foraminiferan association and the total foraminifer/ostracod ratio within the dumping site. Total foraminiferan abundance increases remarkably with water depth (mean 83 tests in 100 ml) driven by higher nutrient availability and more suitable salinity and temperature values within the zone of the oscillating halocline. The distribution of shallow water species such as Cribroelphidium excavatum, Eucythere argus and Hirschmannia viridis, within the transient water layer A. cassis, Nodulina dentaliniformis, S. bradii and Palmoconcha laevata and below Eggerella scabra indicate the depth position of the halocline. Water depth and sediment dumping influence are the main driving factors for the distribution of foraminifer and ostracod associations within the study area. However, a significant sedimentological difference between samples inside and outside the dumping area is not recognizable. © 2008 Elsevier B.V. All rights reserved.
1. Introduction A frequently discussed anthropogenic impact on the marine environment is the dumping of dredged material. International conventions on the protection of the sea demand
⁎ Corresponding author. Present address: Institute of Geosciences, University of Jena, Burgweg 11, 07749 Jena, Germany. Tel.: +49 3641 948619; fax: +49 3641 948622. E-mail addresses: [email protected] (P. Frenzel), [email protected] (C. Borrmann), [email protected] (B. Lauenburg), [email protected] (B. Bohling), [email protected] (J. Bartholdy). 0924-7963/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jmarsys.2007.01.016
minimizing of environmental damage by dumping dredged material (e. g. HELCOM Recommendations 13/1 for the Baltic Sea, compare HELCOM, 1992). In the German Baltic Sea coastal area annually about 2.0 up to 2.5 million m3 dredged material is generated (Netzband, 2002). The majority of this material is not contaminated (Koch, 1994). The dumping of these uncontaminated sediments can cause environmental problems only in terms of the volume of deposits laid down on the sea floor, in the additional turbidity of the coastal waters near the discharge point, and in the possible establishment of unstable deposits on the sea floor (Gorsline, 1979). From the biological point of view especially the burial of benthic organisms is a
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
crucial effect of the dumping procedure. This study deals with the impact of sediment dumping in a south-western Baltic Sea site on two meiofaunal groups (Foraminifera and Ostracoda). They are classical microfossils in paleontology as well and possess easily preservable hard parts. In a previous study (Bohling, 2005a) it was not possible to detect unambiguous effects of a test dumping on the sedimentology around a dumping field in this selected study area. Thus the question arises, whether the meiofauna/”microfossils” may serve as a possible indicator for dumping effects or even large scale natural sediment displacements. Unfortunately, our knowledge about the foraminiferans and ostracods of the Mecklenburg Bight is rather limited. It is based on general occurrence of foraminiferans in the Mecklenburg Bight and its coast (Frenzel et al., 2005b) and on general remarks (Klie, 1938) and data about shallow water forms (Frenzel et al., 2005a) for the ostracods. The detailed and substantial studies by Rosenfeld (1977) on ostracods and Lutze (1965) on foraminiferans touch the Mecklenburg Bight in the northernmost part only. Hence, a baseline study of the distribution patterns of both meiofaunal groups in the area around the dumping site also had to be carried out.
431
Table 1 Abiotic factors for the studied samples
2. Study area The Baltic Sea has an estuarine circulation pattern with water body stratification. The bottom water shows higher salinity with general lower and less variable temperature and an upper water body with lower salinity and more variable temperature conditions (Matthäus, 1996). The stratification may cause oxygen deficiency during longer periods of lacking water intrusion from the North Sea. A tidal influence is not remarkable in the inner Baltic Sea (Lass and Margaard, 1996). The Mecklenburg Bight is situated in the south-western Baltic Sea. The study area lies in the southern part of the Mecklenburg Bight, north of Bad Doberan in north-eastern Germany (Fig. 1). All samples derive from water depths from 15 to 21 m. The depth level of the layer of discontinuity (halocline) is here 10–15 m to about 20 m oscillating over the year (personal communication H. U. Lass, Institute of Baltic Sea Research Warnemünde). Salinity shows about 12–14 psu in the surface water and 19–21 psu in the deeper water (Niedermeyer et al., 1995). The mean water temperature varies between 3 °C in winter and 17 °C in summer within the upper water layer and is about 13 °C in deeper water in summer (personal communication H. U. Lass). Near-bottom
The samples from within the dumping site area are highlighted with two double lined frames. Full sample numbers (IOW designation) were given with highlighted numbers as used in the present paper.
water temperatures and salinities at the dumping site varied between 9.1 to 14.2 °C and 13.5 to 18.8 PSU respectively at the sampling occasions between June, 2000 and July, 2003 (Powilleit et al., 2006). The sediment at the sea floor of the study area is well sorted fine sand (Bohling, 2005b). Only the south-western and south-eastern edge of the sampled area is covered with medium to coarse sand. The sediment type distribution in the Mecklenburg Bight can be considered as stable (Bohling, 2005b). The macrofauna of the disposal site area prior to the dumping in June, 2001 could be characterised as a well-established soft bottom community typically found in the western Baltic Sea with the dominant bivalve species Arctica islandica, Macoma balthica, the cumacean Diastylis rathkei, and the polychaete Nephtys hombergii (Powilleit et al., 2006). 3. Material and methods
Fig. 1. The Mecklenburg Bight in the southern Baltic Sea and grid of sampled stations with isobaths (October, 2002). The black framed square in the overview indicates the study area.
An experimental dumping of sediment was executed in the study area within the DYNAS project (compare Harff, 2003) in April, 2001. The used sediment derives from a close to shore site in front of the Warnow estuary about 12 km to the west. Several distinct sediment mounds with diameters of
432
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Fig. 2. Plots of sedimentological parameters against water depth with trend lines. Dumping site samples are indicated by hollow circles. The mean grain size of the sandy sediment decreases with increasing water depth, showing a lower variance in grain size distribution and higher silt proportions which causes higher organic contents (TOC) and higher water contents of the sediment.
up to 28 m and heights of up to 1.5 m were created by the experimental dumping. The dumping site was observed during the next 3 years in intervals of some months for documenting impact on macrofauna and sedimentology as well as recolonialization of the site (Bohling, 2005a; Powilleit et al., 2006). Five sediment samples were used for the present study. The material derives from the uppermost 1–2 cm sediment and was freeze-dried immediately after winning. Because of other studies the volume left for meiofaunal analysis varies around only 30 cm3. An area sampling (twelve samples) was done on October 14, 2002, one and a half years after dumping. Only one station lies within the dumping field, all the others group in a grid around (Fig. 1). The used sampling device was a box core sampler as in the time series. Again, 1–2 cm superficial sediment were taken, but fixed immediately in 70% ethanol with Bengal Rose stain following Lutze (1964) in order to identify living specimens in the lab. Each sample contained about 70 cm3 to 100 cm3 sediment volume. Because of the sandy sediment character, we concentrated foraminiferan tests and ostracods by repeated (five times) flotation of dried sediment in water. The floating material was given on a 200 µm and 63 µm sieve and afterwards dried in an oven at 60 °C. Measured sediment parameters were mean grain size, sorting (Trask) and sand and silt content (all measured by sieving) as well as water content and total organic carbon by loss on ignition method. Foraminiferans and ostracods from both sample series (time and area sampling) were picked completely from the 200 µm size fraction. The smaller fraction and the flotation
residues were spot checked for larger quantities of shells, what was not the case. We distinguished between living and dead foraminiferans on the base of stained tests (compare Lutze and Altenbach, 1991). Well preserved tests, i.e. complete and not corroded or abraded, with a stained lumen in one or more chambers were regarded as living individuals. Agglutinated tests had to be wetted before examining the chamber lumen under the microscope. Here, stained residues of pseudopodia and catched detritus around the aperture often indicated activity during sampling. Living ostracods were counted if stained and well preserved carapaces with soft body were present (compare Uffenorde, 1972 and Rosenfeld,
Fig. 3. Dendrogram of a cluster analysis (complete linkage) on sediment parameters (mean grain size, silt content, sorting, water content, TOC). The dumping site (asterisk) lies within the main group of samples, whereas samples with coarse grain size and low TOC values are grouped outside.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440 Table 2 Living and dead Foraminifera and Ostracoda from the study area Taxon
Species
Foraminifera Ammonia batavus Hofker, 1951 Ammoscalaria runiana (Heron-Allen and Earland, 1916) Ammotium cassis (Parker, 1870) Astrammina sphaerica (Heron-Allen and Earland, 1932) Cribroelphidium albiumbilicatum (Weiss, 1954) Cribroelphidium excavatum (Terquem, 1875) Cribroelphidium gerthi (Van Voorthuysen, 1957) Cribroelphidium incertum (Williamson, 1858) Cribroelphidium williamsoni (Haynes, 1973) Eggerella scabra (Williamson, 1858) Haynesina germanica (Ehrenberg, 1840) Miliammina fusca (Brady, 1870) Nodulina dentaliniformis (Brady, 1881) Ophthalmina kilianensis Rhumbler, 1936 Subreophax aduncus (Brady, 1882) Ostracoda Candona candida (O. F. Müller, 1776) Cyprideis torosa (Jones, 1850) f. littoralis Cyprideis torosa (Jones, 1850) f. torosa Cytheropteron latissimum (Norman, 1865) Cytherura atra (Sars, 1865) Eucythere argus (Sars, 1865) Hirschmannia viridis (O. F. Müller, 1785) Leptocythere baltica (Klie, 1929) Leptocythere pellucida (Baird, 1850) Leptocythere psammophila (Guillaume, 1976) Neocytherideis crenulata (Klie, 1929) Palmoconcha guttata (Norman, 1865) Palmoconcha laevata (Norman, 1865) Paracyprideis fennica (Hirschmann, 1909) Robertsonites tuberculatus (Sars, 1865) Sarsicytheridea bradii (Norman, 1865) Sarsicytheridea punctillata (Brady, 1865) Semicytherura sella (Sars, 1865)
Living Dead Dumping only site only X X
X
X X X X X X X X X X X
433
We distinguish between biocoenosis, thanatocoenosis and taphocoenosis for our analysed associations. The biocoenosis is a community of organisms living together in a given biotope. The thanatocoenosis describes an association of organismic remains (potential fossils, in our case empty shells) found in a given place. This association only contains parts of the former biocoenoses because of selective destruction of specimens/skeletons. Hence, a thanatocoenosis is autochthonous but reflects only parts of the former biocoenosis. The taphocoenosis comprises elements of several biocoenoses, i. e. contains allochthonous and autochthonous or only allochthonous components. Methods for discrimination of these types of associations are discussed in detail for ostracods in Boomer et al., 2003. Selected specimens were documented by scanning electron microscopy and light microscopy. Diversity was measured by Fisher alpha index (Fisher et al., 1943; compare Murray, 1991) and Pielou evenness index (compare Buzas, 1979). An index for the dumping influence was used for incorporating this factor into the data set for a Principal Component Analysis. This index is expressed with higher values for the dumping site shortly
X X X
X
X
X
X
X
X X X X X X X X X X X X X X X
1977). The degree of staining varies strongly for different ostracod taxa. A firm closing of valves can prevent a penetration of stain into the carapace cavity. These problems make the Bengal Rose staining method better suitable for foraminiferans than ostracods (Brouwers et al., 2000). On the other hand, disarticulated valves, broken, abraded or corroded shells and size sorting of individuals from different ontogenetic stages can indicate allochthonous (i.e. transported) faunal components (see Boomer et al., 2003).
Fig. 4. Foraminifera (1–20) and Ostracoda (21–35) from the study area. All these SEM pictures are given as external side views if not otherwise stated. 1–3: Ammotium cassis; 1–2 microsphaeric specimens, samples MUC and 922, 3 — macrosphaeric specimen, sample 418; 4: Astrammina sphaerica, sample 924; 5: Nodulina dentaliniformis, sample 921; 6: Eggerella scabra, sample 917; 7: Subreophax aduncus, fragment, sample 924; 8: Ammoscalaria runiana, sample 922; 9 — 10: Miliammina fusca, Fig. 9 is partly damaged in the apertural area, samples 920 and 921; 11: Cribroelphidium incertum, sample 924; 12: Cribroelphidium williamsoni, last chamber is missing, sample 920; 13: Cribroelphidium gerthi, sample 920; 14: Cribroelphidium excavatum, sample 920; 15 — 16: Cribroelphidium albiumbilicatum, Fig. 15 represents the large and thick form asklundi as described by Lutze (1965), both from sample 924; 17: Ammonia batavus, umbilical view, sample 920; 18 — 19: Ophthalmina kilianensis, apertural and side view, samples 927 and 916; 20: Haynesina germanica, sample 920; 21: Cytheromorpha fuscata, right side of a female, sample 970; 22: Cyprideis torosa f. torosa, left valve of a juvenile, sample 766; 23: Cytherura atra, right valve, sample 915; 24 — 25: Semicytherura sella, left side of a female and a male carapace, samples 924 and 916; 26: Eucythere argus, right side of a female, sample 968; 27: Heterocyprideis sorbyana, female left valve, sample 968; 28: Palmoconcha laevata, right side of a male carapace, sample 916; 29: Hirschmannia viridis, right side of a female carapace, sample 927; 30: Palmoconcha guttata, female left valve, sample 922; 31: Robertsonites tuberculatus, left side of a female carapace, sample 916; 32 — 33: Sarsicytheridea bradii, left side of a female and internal view of a female right valve, samples 418 and 420; 34 — 35: Leptocythere pellucida, right sides of a smooth female and a fossae bearing male, both from sample 916.
434
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Table 3 Total (living + dead) foraminifer abundances in tests per 100 ml sediment (every upper row in bold numbers)
water depth. Sedimentologically, there is no significant difference between the samples from the dumping site and the surroundings (Fig. 3; Bohling, 2005a). Other taxa than ostracods and foraminiferans within the samples are juvenile Lamellibranchiata (e. g. Arctica islandica), Gastropoda and Polychaeta as well as worm tubes. Significant differences within the macro-fauna are not recognizable because of low numbers in these samples of relatively small volumes. Reworked Upper Cretaceous microfossils (mainly foraminiferans) occur sporadically. 4.2. Foraminifera and Ostracoda We found 15 foraminifer and 17 ostracod species. Of these, five foraminifer and five ostracod species occurred dead only (Table 2; Fig. 4). The dominating species in biocoenosis and thanatocoenosis as well as taphocoenosis are clearly the large agglutinated Ammotium cassis within the Foraminifera (Table 3) Table 4 Total (living + dead) ostracod abundances in valves per 100 ml sediment (bold numbers in every first row)
The number of living specimens is given in every lower row (normal numbers) and the total number in every upper row (bold). The column Counted tests indicates the absolute total number of foraminiferan tests of each sample. The samples from within the dumping site area are highlighted with two double lined frames. Full sample numbers (IOW designation) were given with highlighted numbers as used in the present paper.
after the dumping event, lower values afterwards and zero values in other sites. Because of low numbers of counted individuals within most samples, we used species abundance values (tests/valves per 100 ml) instead of dominance (proportion) values for statistical analysis (see Patterson and Fishbein, 1989 and Fatela and Taborda, 2002 for discussion). Statistics were done with the program Data Desk® 6.1. 4. Results 4.1. Environmental factors and other biota The sediment of sampled stations is well sorted fine sand with a low organic content (0.2–0.8%; Table 1). Only exceptions are stations 915 and 927 (the shallowest stations) with dominating medium or coarse sand (Fig. 2). There is a general but weak trend to higher silt contents with increasing
The number of living specimens is given in every second row (normal numbers) and the total number in every first row (bold). The column Counted valves indicates the absolute total number of ostracod valves of each sample. The samples from within the dumping site area are highlighted with two double lined frames. Full sample numbers (IOW designation) were given with highlighted numbers as used in the present paper.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
435
Fig. 5. Abundance of total foraminiferans and ostracods (living + dead) in relation to water depth. The bold regression line indicates the trend for foraminiferans (points), the broken line for ostracods (squares). Open circles or squares show dumping samples. A trend of increasing foraminiferan numbers with greater water depth is recognizable. This trend is driven by Ammotium cassis abundance. The inset shows the time series from the dumping site with lower abundance of foraminiferans after dumping.
and the smooth shelled Sarsicytheridea bradii within the Ostracoda (Table 4). About 28% of total foraminiferan association and 49% of total ostracod association are living specimens. The mean abundance is 83 foraminiferan tests respectively 26 ostracod specimens per 100 cm3 for living associations and 297 foraminiferan tests respectively 129 ostracod valves per 100 cm3 for total associations. With greater water depth the number of foraminiferans in total association increases distinctively (Fig. 5). This is not as clear in living associations and still less for ostracods. The dominating Ammotium cassis drives the abundance trend within foraminiferans with its abundance. The diversity (Fisher alpha index) of total associations is with 0.4 to 3.2 for foraminiferans and 1.0 to 2.5 for ostracods low. There is a weak trend in both taxonomic groups for higher species numbers in shallower water (Fig. 6). The dumping site displays the highest species numbers. Most abundant species show a characteristic depth distribution. The abundant foraminifer species A. cassis and N. dentaliniformis become frequent with increasing water depth. E. scabra prefers the deepest sampled depth interval (Fig. 7). Typical for shallower water is C. albiumbilicatum (Fig. 7). All other foraminiferan taxa do not show depth preferences or are too rare for a distribution analysis. Frequent deeper water ostracod species are S. bradii and P. laevata (Fig. 7). Ostracod species with a shallower water depth distribution are Eucythere argus and Hirschmannia viridis (Fig. 7). C. torosa and C. candida occur within the dumping site only. Analysing the complete faunistic data for a classification of the samples we get a group of deeper water stations (N18.5 m in general) and a second one containing shallower water
stations as well as samples from the dumping site (Fig. 8). Interestingly, most dumping site samples fit into the shallow water group despite their greater water depth. 5. Discussion The abundance of living and dead foraminiferans is much lower in our study area than this one documented by Lutze (1965) from the northern part of the Mecklenburg Bight,
Fig. 6. Diversity (Fisher alpha index and evenness) of foraminiferans (points) and ostracods (squares) in different water depth. Open circles or squares show dumping samples. The bold regression line indicates the weak trend for foraminiferans, the broken line for ostracods. Some samples are missing from this diagram because of too low number of specimens. The insets show the time series for the dumping site with higher species numbers after dumping until March, 2004. The evenness is not remarkable influenced by the dumping event.
436
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Fig. 7. Total (living + dead) abundance of foraminiferans (points) and ostracods (squares) in different water depth. Open circles or squares show dumping samples. The synthesis diagram in box shows estimation for mean depth position of the halocline based on abundance trends of the selected taxa. Foraminifer species with highest abundances in greater water depths are Ammotium cassis, Nodulina dentaliniformis and Eggerella scabra. E. scabra displays the lowermost depth distribution level. Sarsicytheridea bradii, the most abundant ostracod species within the study area, is much more frequent in greater water depths. Also, Palmoconcha laevata prefers greater water depths. The hyaline foraminifer Cribroelphidium albiumbilicatum is restricted to water depths b 17 m in general. The four samples with higher abundances below 17 m water depth are all from the dumping site. Ostracod species with a shallower water depth distribution are Eucythere argus and Hirschmannia viridis.
where probably the environment is more stable in the deeper water. The foraminiferan fauna encountered in our study corresponds to the Ammotium cassis association in species composition and environmental parameters. This association was defined by Murray (1991) for the Atlantic seaboard of Europe and Africa. It differs from associations documented by Lutze (1965) from the marginal Mecklenburg Bight, the only published study on foraminiferans touching the area before. His dominating species were Cribroelphidium excavatum, Eggerella scabra, Subreophax aduncus and Ammotium cassis. A. cassis was much less dominating than in our study. At the present state of knowledge it is hard to say if this different picture is caused by changing distribution patterns during the last 40 years or simply by differences in settlements in the southern and northern part of the Mecklenburg Bight. However, Lutze (1974) describes a very similar association with clearly dominating A. cassis from water depths between 16 and 20 m in the Kiel Bight. We know from Lutze (1965) that the distribution pattern of foraminiferans in the Baltic Sea is highly variable due to changing environmental situation, especially salinity variation. The lower salinity limit of A.
cassis association is 17 psu (Lutze, 1965; Murray, 1991), close to around 19 psu in deeper water of the Mecklenburg Bight. This ecological boundary situation for A. cassis is reflected in temperature, too. The species tolerates up to 19 °C, but prefers b3 °C (Murray, 1991). An optimal situation is given in winter; however, temperature rises even in bottom water in general to 13 °C in summer, causing a critical range for A. cassis above the halocline. The higher abundance of Ammotium cassis with increasing depth reflects more frequent suitable environmental conditions below the upper limit of the oscillating halocline at about 15 m water depth (Figs. 5 and 7). On the other hand, these changing conditions cause a higher diversity of thanatocoenoses at shallower water depth (Fig. 6), because the dead assemblage preserves a long term view onto associations and allochthonous elements from shallower water additionally. Olsson (1976) describes A. cassis as preferring and dominating the transient water layer, where the halocline oscillates and higher nutrient amounts are available. This explains the higher abundances with increasing water depth in our study. The surface of organic rich sediments in the southern Mecklenburg Bight is often covered with tests of A. cassis, as it was reported for the Kiel Bight area, too (Linke and Lutze, 1993). They are so big and densely spread that it is clearly visible for the naked eye by observing the content of a box corer on board. Biomass production values of up to 5 g m− 2a− 1 are calculated by Wefer & Lutze (1976) for about 20 m water depth in the Kiel Bight. A similar situation is reflected by high numbers of this species within total association in the dumping area before the dumping experiment (Fig. 5: Oct 00). After burying the historical layer with sediment by dumping, the foraminiferan number of the newly established sediment surface is distinctively lower. It takes some time until the old abundance of the total association is reached again — in our case about two and a half years (Fig. 5: Jun 03). Powilleit et al. (in press) found significantly changed macro-benthos communities on our dumping site some weeks after dumping and a completely recovered macro-benthos community 2 years after the dumping experiment took place. This time frame meets our results very well. Beside the problem of recolonialization and
Fig. 8. This dendrogram shows the grouping of samples based on a cluster analysis (complete linkage) using faunistic data (foraminifer and ostracod abundance and diversity). Samples below and above about 18.5 m water depth are placed in two different groups. The dumping site samples (indicated with asterisks) fit into the shallower water group or are outliers. Before calculation, the samples with a very low number of individuals (samples 257 and 682 — both from the dumping site) as well as all taxa occurring in less than three samples were excluded and highly correlated (N 0.9) variables reduced to one variable of each of these pairs.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Fig. 9. Ratio of total (living + dead) foraminifer to ostracod number in different water depth. Open rhombi show dumping site samples. A weak trend to higher ratios with increasing water depth is visible. The ratio falls within the dumping area after dumping in April, 2001 and increases later on.
time consuming production of tests for the thanatocoenosis, we assume long term sediment redeposition on the newly created sea bottom because of initial higher relief energy. Such
437
redeposition is especially for larger foraminiferans as A. cassis a problem, if they are buried. They prefer the sediment surface and occur above the Redox Potential Discontinuity Layer (Linke and Lutze, 1993), but cannot move fast to the surface after burial. Such process may delay the reestablishment of the typical thanatocoenosis additionally. Also, the self-locomotion of large foraminiferans as A. cassis is too slow for a recolonization by active movement and the tests are too heavy for transport by dispersal (Olsson, 1977), hence, the only way to settle the new substrate is by release and transport of embryonic juveniles (compare Wefer and Richter, 1976; Alve, 1999). Wefer (1976) reports two reproduction periods of A. cassis in the Kiel Bight area, one in spring and one in autumn. This reproduction time fixes the pattern as it was presumed by Wefer & Richter (1976) for Cribroelphidium excavatum in a colonization experiment in the Eckernförder Bight, western Baltic Sea. Hess et al. (2005) report a recolonization period for foraminiferans of 6 to 9 months under unstable environmental conditions in a submarine canyon in the Bay of Biscay after turbidite disposition by tempests. Alve (1999) estimates a recolonization period of one to several years for foraminiferan associations if this process is driven by reproduction mainly, what is coincident with our observations. The samples studied by Lutze (1965) from the outer Mecklenburg Bight were used by Rosenfeld (1977) for
Fig. 10. Principal Components Analysis on three abiotic and eleven ostracod variables (species abundances and ostracod diversity). The first factor is relatable to water depth. The second factor correlates with the dumping influence as shown by the high loading of the allochthonous Cyprideis torosa and a higher diversity caused by input of additional (allochthonous) species. Both components explain 57.1% of the cumulative variance. The other factors are much weaker in influence and hard to interpret (see Table 5). The picture is similar to this of foraminiferans, however, water depth and dumping influence are not so easy to distinguish and the grain size has a greater importance (Table 6).
438
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Table 5 Factor loadings of the first six factors of Principal Components Analysis on three abiotic and ostracod variables (species abundances and ostracod diversity)
High loadings are dark (N0.75) or light shaded (N0.5). The first factor is clearly correlatable with water depth, the second one with the dumping event. The other factors are much weaker in influence and hardly to interpret. Compare Fig. 10.
ostracod analyses. He found a similar species spectrum, with other proportions however, and put it to his association 3, typical for the deeper water of basins and furrows in the Baltic
Sea. Rosenfeld's (1977) dominant species were Sarsicytheridea bradii, S. punctillata, Paracyprideis fennica and Neocytherideis crenulata. Both S. punctillata and P. fennica are very rare in our study. P. fennica seems to avoid the transitional water layer (Rosenfeld, 1977), which could explain its scarcity. However, we do not know the cause for the low number of S. punctillata. The picture of ostracod number distribution is different from the one for foraminiferans. They do not show a distinct increase of abundance with water depth (Fig. 5). Arlt et al. (1982) describe a strong decrease from 0 to 20 m water depth with about 72% of ostracods found above 20 m followed by a very weak decreasing trend down to maximal depths in the southern Baltic Sea. Regarding the ratio between foraminifer and ostracod number, we can see a higher value before than immediately after dumping (Fig. 9). This ratio evolves up to normal values with time. We explain this phenomenon with faster recolonization of the new substrate by immigration of the much faster moving ostracods, whereas foraminiferans settle the new substrate mainly by reproduction. A study on shallow water ostracods from a close location at Poel Island (southern Mecklenburg Bight) showed speeds of about 0.1 to 0.6 mm/s for ostracods moving on sediment surface and even not more slowly within the superficial sediment (Borck and Frenzel, 2006). Calculating the time needed for an ostracod crawling a straight line from the periphery to the centre of the largest mound of dumped sediment with a diameter of 28 m,
Fig. 11. Proportion of allochthonous elements within foraminifer plus ostracod total association (living + dead) during time series sampling within the dumping area. The first column shows the mean value with standard deviation for all stations outside the dumping field (sampled in October, 2002) as a reference value. The proportion of allochthonous elements, mostly transported with dumped sediment, decreases after the dumping experiment in April, 2001. In March, 2004 allochthonous elements are not detectable anymore.
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440 Table 6 Factor loadings of the first six factors of Principal Components Analysis on three abiotic and foraminiferan variables (species abundances and foraminiferan diversity)
High loadings are dark (N0.75) or light shaded (N0.5). The first factor is correlatable with the dumping event, the second one clearly with water depth. The other factors are much weaker in influence and hardly to interpret.
we get a figure between 7 and 39 h. The whole recovering process of ostracod assemblage took about two and a half years in our site (Fig. 9: Jun 03), as observed for foraminiferans. Looking on the general distribution of foraminiferans, ostracods and on the values of some abiotic factors with a help of the Principal Component Analysis we recognize water depth (relative position to halocline) and the sediment dumping as the most important factors driving the composition of total associations (Fig. 10, Table 5). The mean discriminating depth between deeper and shallower water species (Fig. 7) indicates a mean water depth of about 17 m for the halocline, what meets the hydrographic data of 10–15 m to 20 m in the Mecklenburg Bight. Allochthonous elements of the microfauna are the best indicators for the dumped sediment (Fig. 11). They cause a higher diversity (species number) in dumping site samples (Fig. 6) as it was observed by Drapala (1993) for turbidites in the deep sea as well. Shallow water and estuarine species as Ammonia batavus, Miliammina fusca, Candona candida, Cyprideis torosa and Leptocythere lacertosa occur as dead specimens and mainly or even exclusively within the dumping area (Table 1). They derive from shallower water closer to the shore or even from the Warnow estuary with significant lower salinity (C. candida and C. torosa f. torosa), in front of which the dumped sediment was taken. Within the succession of the thanatocoenosis from the dumping site a decreasing proportion of such allochthonous elements is visible (Fig. 11). The sample of October, 2003 is an exception, maybe because of sediment reworking within the dumping site. On the other hand, the number of counted specimens is too low for exact and stable data concerning proportions of 10% or less allochthonous elements. This causes a large error range. Patterson & Fishbein (1989) recommend analysing taxa with at least 50% dominance only in 50 specimens counts and with at least 10% dominance only in 300 specimens counts. In March, 2004, two and a half years after sediment dumping, no allochthonous elements are still detectable.
439
6. Conclusions The main factors for the distribution of total foraminifer and ostracod association distributions are water depth, respectively changes of parameters along depth gradient, especially the discontinuity layer of the halocline, and dumping influence in our study. Larger and event-like sediment redeposition can be indicated by microfossils respectively hard parts of meiofaunal organisms. A short time change of the living associations (some weeks to months after deposition event) is probable but within our study not provable because of the large time intervals of sampling and too small sampled sediment volumes shortly after sediment dumping. However, the taphocoenosis recovers more slowly than biocoenosis in composition and abundance values because of a diluting or burial effect of thanatocoenosis by sediment input and conserves allochthonous elements introduced with redeposited sediment, which show the event in our study until two and a half years after sediment dumping. This phenomenon may be used to detect the impact of anthropogenic sediment dumping as well as large scale natural sediment redeposition by storm events, turbidites, earthquakes or tsunamis. A quantitatively and qualitatively changed microfauna with allochthonous elements should be visible in fossil sediments, too, if the redeposited sediment volume is big enough. Acknowledgements We thank the crew of Research vessel ‘Professor Albrecht Penck' for supporting the sampling. The samples were taken during cruises for the project DYNAS (Dynamics of Natural and Anthropogenic Sedimentation), funded by the German Ministry of Education and Research (Grant No. 03F0280A). Gerhard Graf, Martin Powilleit (University of Rostock), David Horne (Queen Mary, University of London) and Robin Edwards (Trinity College, Dublin) gave us valuable comments on our manuscript. The first author was supported by a sponsorship of the German Federal Environmental Foundation (DBU). References Alve, E., 1999. Colonization of new habitats by benthic foraminifera: a review. Earth-Science Reviews 46, 167–185. Arlt, G., Müller, B., Warnack, K.-H., 1982. On the distribution of Meiofauna in the Baltic Sea. Internationale Revue der gesamten Hydrobiologie 67 (1), 97–111. Bohling, B., 2005a. Monitoring auf der Probeklappstelle - Sedimentologie. In: Harff, J. (Ed.), Projekt DYNAS II- Dynamik natürlicher und anthropogener Sedimentation - Vorhaben: Sedimentationsprozesse in der Mecklenburger Bucht, Phase 2 - Abschlußbericht (Meilenstein 10). IOW, Warnemünde, pp. 59–66. http://www.io-warnemuende.de/projects/dynas/. Bohling, B., 2005b. Estimating the risk for erosion of surface sediments in the Mecklenburg Bight (south-western Baltic Sea). Baltica 18 (1), 3–12. Boomer, I., Horne, D.J., Slipper, I.J., 2003. The use of ostracods in palaeoenvironmental studies, or what can you do with an ostracod shell? In: Park, L.E., Smith, A.J. (Eds.), Bridging the gap: trends in the ostracod biological and geological sciences. The Paleontological Society Papers, vol. 9, pp. 153–179. Borck, D., Frenzel, P., 2006. Micro-habitats of brackish water ostracods from Poel Island, southern Baltic Sea coast. Senckenbergiana maritima 36 (2), 99–107. Brouwers, E.M., Cronin, T.M., Horne, D.J., Lord, A.R., 2000. Recent shallow marine ostracods from high latitudes: implications for late Pliocene and Quaternary palaeoclimatology. Boreas 29, 127–143.
440
P. Frenzel et al. / Journal of Marine Systems 75 (2009) 430–440
Buzas, M.A., 1979. The measurement of species diversity. Foraminiferal Ecology and Paleoecology. SEPM Short Course, vol. 6, pp. 3–10. Drapala, V., 1993. The use of ostracods in detecting fine grained turbidites in deep sea cores. In: Jones, P., McKenzie, K. (Eds.), Ostracoda in the Earth and Life Sciences. Balkema, Rotterdam, pp. 559–568. Fatela, F., Taborda, R., 2002. Confidence limits of species proportions in microfossil assemblages. Marine Micropaleontology 45 (2), 169–174. Fisher, R.A., Corbet, S.A., Williams, C.B., 1943. The relation between the number of species and the number of individuals in a random sample of animal population. Journal of Animal Ecology 12, 42–58. Frenzel, P., Henkel, D., Siccha, M., Tschendel, L., 2005a. Do ostracod associations reflect macrophyte communities? A case study from the brackish water of the southern Baltic Sea coast. Aquatic Sciences 67, 142–155. Frenzel, P., Tech, T., Bartholdy, J., 2005b. Checklist and annotated bibliography of Recent Foraminiferida from the German Baltic Sea coast. In: Tyszka, J., Oliwkiewicz-Miklasińska, M., Gedl, P., Kaminski, M.A. (Eds.), Methods and Applications in Micropalaeontology. Studia Geologica Polonica, vol. 124, pp. 67–86. Gorsline, D.S., 1979. Shelf-sediment dynamics and solid-waste disposal. In: Palmer, H.D., Gross, M.G. (Eds.), Ocean Dumping and Marine Pollution. Dowden, Hutchinson & Ross, Stroudsburg, pp. 9–16. Harff, J. (Ed.), 2003. Projekt DYNAS - Dynamik natürlicher und anthropogener Sedimentation - Vorhaben: Sedimentationsprozesse in der Mecklenburger Bucht - Abschlußbericht (Meilenstein 6). IOW, Warnemünde.135 pp. http:// www.io-warnemuende.de/projects/dynas/. HELCOM, 1992. HELCOM Recommendations 13/1: Disposal of dredged spoilsadopted 6 February 1992, having regard to Article 9, Paragraph 2 of the Helsinki Convention. Helsinki. 25 pp. http://www.helcom.fi/stc/files/ Guidelines/guide_rec13_1.pdf. Hess, S., Jorissen, F.J., Venet, V., Abu-Zied, R., 2005. Benthic foraminiferal recovery after recent turbidite deposition in Cap Breton Canyon, Bay of Biscay. Journal of Foraminiferal Research 35 (2), 114–129. Klie, W., 1938. Ostracoda, Muschelkrebse. In: Dahl, M., Bischoff, H. (Eds.), Die Tierwelt Deutschlands und der angrenzenden Meeresteile nach ihren Merkmalen und nach ihrer Lebensweise, vol. 34(3). Gustav Fischer, Jena, p. 230. Koch, M., 1994. Situation der Baggergutverbringung im Bereich der Wasser-und Schiffahrtsdirektion Ost. Mitteilungen der Bundesanstalt für Gewässerkunde Nr. 6: Unterbringung von belastetem Baggergut im aquatischen Milieu, pp. 7–12. Koblenz. Lass, H.U., Margaard, L., 1996. Wasserstandsschwankungen und Seegang, In: Rheinheimer, G. (Ed.), Meereskunde der Ostsee, 2nd edition. Springer, Berlin, pp. 68–74. Linke, P., Lutze, G.F., 1993. Microhabitat preferences of benthic foraminifera — a static concept or a dynamic adaptation to optimize food acquisition? Marine Micropaleontology 20, 215–234.
Lutze, G.F., 1964. Zum Färben rezenter Foraminiferen. Meyniana 14, 43–47. Lutze, G.F., 1965. Zur Foraminiferen-Fauna in der Ostsee. Meyniana 15, 75–142. Lutze, G.F., 1974. Foraminiferen der Kieler Bucht (Westliche Ostsee): 1. ’Hausgartengebiet“ des Sonderforschungsbereiches 95 der Universität Kiel. Meyniana 26, 9–22. Lutze, G.F., Altenbach, A., 1991. Technik und Signifikanz der Lebendfärbung benthischer Foraminiferen mit Bengalrot. Geologisches Jahrbuch A128, 251–265. Matthäus, W., 1996. Temperatur, Salzgehalt und Dichte, In: Rheinheimer, G. (Ed.), Meereskunde der Ostsee, 2nd edition. Springer, Berlin, pp. 75–81. Murray, J.W.,1991. Ecology and Palaeoecology of Benthic Foraminifera. Longman Scientific & Technical, John Wiley & Sons Essex, New York, 379 pp. Netzband, A., 2002. Internationale Entwicklungen im Umgang mit Baggergut. HANSA- Schiffahrt- Schiffbau – Hafen 139 (10), 56–61. Niedermeyer, R.-O., Werner, F., Janke, W., 1995. Die heutige Ostsee und ihre südwestliche Küste. In: Duphorn, K., Kliewe, H., Niedermeyer, R.-O., Janke, W., Werner, F. (Eds.), Die deutsche Ostseeküste. Sammlung Geologischer Führer, 88. Gebr. Borntraeger, Berlin, pp. 51–90. Olsson, I., 1976. Distribution and ecology of the foraminiferan Ammotium cassis (Parker) in some Swedish Estuaries. Zoon 4, 137–147. Olsson, I., 1977. Wall structure of the foraminifer Ammotium cassis (Parker) and its ecological significance. Zoon 5, 11–14. Patterson, R.T., Fishbein, E., 1989. Re-examination of the statistical methods used to determine the number of point counts needed for micropaleontological quantitative research. Journal of Paleontology 63, 245–248. Powilleit, M., Kleine, J., Leuchs, H., 2006. Impacts of experimental dredged material disposal on a shallow, sublittoral macrofauna community in Mecklenburg Bay (western Baltic Sea). Marine Pollution Bulletin 52 (4), 386–396. Rosenfeld, A., 1977. Die rezenten Ostracoden-Arten in der Ostsee. Meyniana 29, 11–49. Uffenorde, H., 1972. Ökologie und jahreszeitliche Verteilung rezenter benthonischer Ostracoden des Limski-Kanals bei Rovinj (nördliche Adria). Göttinger Arb. Geol. Paläont. 13, 121. Wefer, G., 1976. Environmental effects on growth rates of benthic foraminifera (shallow water, Baltic Sea). Ist International Symposium on Benthonic Foraminifera of Continental Margins. Part A. Ecology and Biology. Maritime Sediments Special Publication, vol. 1, pp. 39–50. Wefer, G., Lutze, G.F., 1976. Benthic foraminifera biomass production in the Western Baltic. Kieler Meeresforschungen, Sonderheft 3, 76–82. Wefer, G., Richter, W., 1976. Colonization of artificial substrates by foraminifera. Kieler Meeresforschungen, Sonderheft 3, 72–75.