Small scale morphodynamics of shoreface-connected ridges and their impact on benthic macrofauna

    Small scale morphodynamics of shoreface-connected ridges and their impact on benthic macrofauna Edith Markert, Ingrid Kr¨oncke, Adam Kubicki PII: DOI: Reference:

S1385-1101(15)00015-5 doi: 10.1016/j.seares.2015.02.001 SEARES 1337

To appear in:

Journal of Sea Research

Received date: Revised date: Accepted date:

28 August 2014 30 January 2015 7 February 2015

Please cite this article as: Markert, Edith, Kr¨oncke, Ingrid, Kubicki, Adam, Small scale morphodynamics of shoreface-connected ridges and their impact on benthic macrofauna, Journal of Sea Research (2015), doi: 10.1016/j.seares.2015.02.001

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Small scale morphodynamics of shoreface-connected ridges and

T

their impact on benthic macrofauna

RI P

Edith Markert, Ingrid Kröncke, Adam Kubicki

SC

Senckenberg am Meer, Department of Marine Research, Südstrand 40, D-26382, Wilhelmshaven

MA NU

* Corresponding author. E-mail address: [email protected]

Keywords

macrofauna, morphodynamics, hydroacoustics, habitat mapping, sediment transport,

PT

ED

southern North Sea

Abstract

CE

The first interdisciplinary analysis (biological and sedimentological) of macrofauna communities influenced by long-term morphodynamics of shoreface-connected ridges in the

AC

German Bight on small scale is presented in this study. The study area covering 4 km2 was located off the island of Spiekeroog, in an area known as a Tellina fabula community. Sediment samples taken at 27 sample sites were coupled with side-scan sonar data to draw a precise sediment map of the area, as well as with high-resolution multi-beam bathymetry data to understand the morphodynamics changes of the seabed between 2003 and 2010. The macrofauna data acquired at the same 27 sites were analysed for community structure using non-metric multidimensional scaling, the ANOSIM and PERMANOVA test. Correlations between biological and environmental variables were examined with the BIOENV procedure. The study revealed a shore-parallel sediment zonation with clear and sharp borders induced by local morphodynamics, which together with specific local bathymetry affected the formation of three different macrofauna affinity groups. One group was located on the shoreface and in the troughs (dominant species: Scoloplos armiger, Lanice conchilega, Notomastus latericeus), one on the landward flanks of the ridges (dominant species: Aonides paucibranchiata, Goniadella bobretzkii), and one on the ridge crests (dominant species: 1

ACCEPTED MANUSCRIPT Ophelia spp. juv., Spio goniocephala). The spatial distribution of the affinity groups, their taxa number and abundance of species was dependent on surface sediment pattern resulting from local hydrodynamics, which in turn is known to influence the food availability. A seaward steepening of ridges took place and was an effect of erosion up to 0.34 m on landward flanks

T

in and accumulation up to 0.29 m on seaward flanks in seven years. The studied shoreface-

RI P

connected ridges migrated seawards with a pace of 5 m/year for the large ridge and 20 m/year for the small ridge. Elongated mud-pockets were common in the deepest parts of the troughs, but seemed to be unstable in time. The identified general seaward migration of

MA NU

migrate with the morphodynamics of the ridges.

SC

shoreface-connected ridges seemed to be slow enough for the macrofauna communities to

1. Introduction

Elongated rhythmic bedforms (typical spacing of several kilometres) called shorefaceconnected ridges are shoreline-oblique linear features typically associated with a gently sloping sandy shelf substrate, experiencing recurrent severe storm events at water depths of

ED

5-30 m (Duane et al., 1972; Vis-Star et al., 2009). In general, the length of the crests of shoreface-connected ridges may exceed 30 km, their width 1 km, and their height exceeds

PT

6 m (Swift et al., 1978; Antia, 1996; van de Meene and van Rijn, 2000; Schwab et al., 2000). Shoreface-connected ridges are active under present hydrodynamic conditions (van de Meene et al., 1996) being structured by different factors like tides or storms. Son et al. (2012)

CE

presented worldwide examples with similar and dissimilar sedimentary features, which emphasize various controlling mechanisms for different shoreface-connected ridges, but in

AC

general numerical models suggest that ridges tend to migrate in the direction of the dominant tidal current with 1-10 m/yr (Calvete et al., 2001; de Swart et al., 2008). Shoreface-connected ridges have been studied intensively along the east coast of the United States of America (e.g. Duane et al., 1972; Swift et al., 1978; Swift and Field, 1981a, b), Argentine (Swift et al., 1978), Brazil (Figueiredo et al., 1982), on the central Dutch coast (e.g. van de Meene and van Rijn, 2000), the Flemish Banks (Trentesaux et al., 1994), as well as along the German coast of the southern North Sea (Antia, 1996), but their migration was never confirmed by high-resolution bathymetry data. The ridges observed in the German Bight off the East Frisian Islands form a westward opening angle of 10-17° with the shoreline (Fig. 1). The coastal morphodynamics is ruled in this area by tidal, wind- and wave-driven hydrodynamics, sediment transport and bed elevation, which cause morphology changes depending on the sediment properties such as grain size, porosity and shear stress (Zeiler et al., 2008, Kösters and Winter, 2014). Along 2

ACCEPTED MANUSCRIPT the German coast of the North Sea, storms from north-westerly and westerly directions are able to induce water levels of up to five meters above mean sea level (Zeiler et al., 2008). The tides in this area are semi-diurnal and the mean tidal range is 2.6 m. Tidal current velocities measured during calm weather conditions range between 0.3 m/s and 0.6 m/s. The

PT

ED

MA NU

SC

RI P

T

dominance of an eastward directed flood current is well documented (Antia et al, 1995).

AC

CE

Fig. 1. Study area north of Spiekeroog (Germany, North Sea).

The study area located ca. 3.5 km north of the island of Spiekeroog (Fig. 1) covered an area of 4 km2, which included two generations of shoreface-connected ridges at water depths of 920 m below chart datum (Normal Null). Previous surface sediment studies based on grab sampling showed that these ridges were composed mainly of sandy fraction with coarser grains on the landward flanks and in the troughs, and finer fraction on the steeper seaward flanks (Antia, 1993; Son et al., 2012). No macrofauna studies had been carried out in this area in the past. The benthic macrofauna plays a vital role for the nutrition cycle, detrital decomposition and as a food source for higher trophic levels, and additionally, the macrofauna species are sensitive indicators for changes in the marine environment (e.g. Kröncke and Reiss, 2010). In this context, many studies in the last years focused on the macrofauna of the North Sea 3

ACCEPTED MANUSCRIPT on a large spatial scale (e.g. Dyer et al., 1983; Salzwedel et al., 1985; Künitzer et al., 1992; Rachor and Nehmer, 2003; Kröncke et al., 2013), and on small spatial scale (e.g. Brown et al., 2002; Weber et al., 2004; Kröncke et al., 2011). On the latter scale the distribution of macrofauna communities is known to be correlated strongly with the sediment composition

T

(e.g. Salzwedel et al., 1985; Künitzer et al., 1992; Rachor and Nehmer, 2003). The

RI P

hydrodynamic energy influences the sedimentation and re-suspension of the sediment particles (e.g. Rhoads, 1974; Rhoads and Boyer, 1982; Snelgrove and Butman, 1994), as well as the food availability, and organic enrichment of the sediment (e.g. Gray, 1974;

SC

Snelgrove and Butman, 1994; Kröncke and Bergfeld, 2003; Kröncke, 2006). Thus, stronger currents and turbulences inhibit the deposition of organic material and result in deposition of

MA NU

coarse sediments (Pearson and Rosenberg, 1978; Rhoards and Boyer, 1982), while muddy sediments occur under calmer hydrodynamic conditions. Govaere et al. (1980) observed a close relation between tidal velocity and direction, the residual currents and the macrofauna distribution. They found that the community structure and its distribution remained stable as long as the currents and the amount of suspended organic material did not change. Morphodynamic processes are important factors for the colonization of habitats by

ED

macrofauna (Newell et al., 1998, Olafsson et al., 1994). Weber et al. (2004) studied smallscale (scales of metres) morphological structures in the Southern Bight of the North Sea in

PT

areas of shoreface-connected ridges, where they found a higher abundance of the macrofauna in the troughs than on the crests. They found that differences in morphological

CE

features matched with differences in the macrofauna communities. Baptist et al. (2006) have been monitoring macrofauna on shoreface-connected ridge off Netherlands for 2 years. They could find differences in communities due to seasonality and sediment composition, but they

AC

had no information on seabed changes of the ridges. For this study we combined hydroacoustic methods for relief and sediment mapping to describe morphodynamics of the shoreface-connected ridges offshore the island of Spiekeroog in the past seven years in combination with macrofauna community studies. With the combined approach of the ground-truthing and hydroacoustic methods we intend to study i) long-term dynamics and the sediment composition of the shoreface-connected ridges, ii) the small-scale spatial distribution of macrofauna communities and iii) to compare sediment and macrofaunal patterns in respect to seabed dynamics in time.

4

ACCEPTED MANUSCRIPT 2. Materials and methods 2.1. Seafloor morphology and surficial sediment sampling The sediment mapping in the area was approached twice. In March 2010 during relatively

T

calm condition the entire area was scanned using the Benthos SIS-1624 side-scan sonar

RI P

operating at 382 kHz frequency with along- and across-track resolution of better than 0.1 m. The side-scan sonar was set to collect backscatter data from 200-metre swath. In September 2010 weather conditions allowed covering only a fragment of the pre-designed area and

SC

therefore the sediment map from March 2010 was used as a primary source of sediment

AC

CE

PT

ED

MA NU

pattern (Fig. 2).

Fig. 2. Data sets collected in the area a) sonograph of March 2010; b) sonograph of September 2010; c) sampling sites SPRJ shown over sediment map, the histograms represent examples of grain-size distributions characteristic for different sediment zones; d) bathymetry of March 2010 shown over the sediment map and naming convention used in this study.

The backscatter intensity of the sonographs was calibrated by grab samples analysed earlier (Son et al., 2012) as well as by newly taken ones. The latter were taken using a 0.1 m² Van Veen type grab-sampler at 27 sampling sites. Sampling took place along two parallel cross5

ACCEPTED MANUSCRIPT shore transects, and in addition three sites were selected to investigate the deepest part of a trough (Fig. 2). At each site three grabs were taken, of which two were used for studies of benthic macrofauna and one for sedimentological study. The sediment was analysed in a laboratory after desalting and dividing the volumes into gravel, sand and mud fractions

T

(according to Wentworth, 1922). Gravel fractions were sieved mechanically, whereas sand

RI P

and mud were analysed separately by a MacroGranometer settling tube (Brezina, 1979) and a SediGraph III system, respectively. The results were plotted at quarter-phi intervals (where

SC

phi = −log2 diameter in mm) and allowed classification of patchiness on the sonograms. During the campaign in September 2010 bathymetry has been mapped using the Reson

MA NU

SeaBat 8125 multi-beam echo-sounder operating at 455 kHz interfaced with a Magellan Aquarius 5002 Long Range Kinematic Global Navigation Satellite System. This configuration allows bathymetry mapping with vertical and lateral accuracies of better than 0.05 m (Ernstsen et al., 2006). Swath of the echo-sounder equalled to ca. three times the depth, what resulted in narrower view in respect to the side-scan sonar. A measuring grid with spacing of 180 m was applied, which meant obtaining a full side-scan sonar mosaics and a

ED

partial multi-beam echo-sounder bathymetry. The seafloor in the investigated area had been scanned twice previously in 2003 and 2007 using the same method (Son et al., 2012). Thus

PT

for each of two transects of macrofauna sampling sites of 2010 three bathymetry profiles were plotted for comparison of relief changes in time.

CE

2.2. Macrofauna sample treatment Samples taken in March 2010 for macrofaunal analyses were sieved on-board over 1 mm mesh size, and the retained material was fixed with 4% buffered formaldehyde. Samples of

AC

coarse sediments were decanted before sieving. In the laboratory the samples were stained with Rose Bengal and the organisms were identified on the lowest possible taxonomic level. The statistical analysis was carried out by using the PRIMER v6 (Plymouth Marine Laboratory) software (Clarke and Gorley, 2006). Diversity was analysed according to Shannon and Weaver (1949) and Pielou (1969). For multivariate analyses the data were fourth root transformed and the Bray-Curtis similarity coefficient (Bray and Curtis, 1957) was calculated. Hierarchical clustering based on group average linking was carried out for testing the similarity among the taxa. Ordination was done by non-metric multidimensional scaling (nMDS) (Shepard, 1962; Kruskal, 1964). The ANOSIM randomisation test and the PERMANOVA routine were used for testing for significant differences between the affinity groups (Clarke and Green, 1988; Anderson et al. 2008). The SIMPER analysis was utilised for detecting the characteristic species per affinity group (Clarke and Warwick, 2001). 6

ACCEPTED MANUSCRIPT Correlations between biological and environmental variables (depth, porosity, shells, gravel, sand and mud) were examined with the BIOENV procedure, for analysing if the found affinity groups are (or are not) correlated with the 6 investigated abiotic factors. Therefore, the resemblance matrix of macrofauna abundance was compared with the resemblance matrix

T

of normalized abiotic variables. Additionally, to examine correlations between species

RI P

abundance and corresponding environmental and sedimentological data, Spearman’s rank correlation coefficients were calculated for the 15 characteristic species and the 6 abiotic variables. The classification of the different feeding types of the different species in the

SC

communities was done according to literature (e.g. Fauchald and Jumars, 1979; Lincoln, 1979; Eleftheriou and Basford, 1989; Hayward and Ryland, 1990; Hartmann-Schröder,

MA NU

1996).

3. Results

3.1. Bathymetry and sediments in 2010 and previous years In the period of six months between March and September 2010 most of the bathymetry

ED

changes were calculated within the measuring device accuracy of 0.05 m (Table 1). Low summer morphodynamics in the area were confirmed also in a planimetric view of collected

PT

sonograms. Although the mosaic from September 2010 was greatly affected by sea-state conditions, it was possible to match patchiness corresponding to March 2010 series with high

CE

confidence (Fig. 2a and b). In the investigated area a cross-shore zonation of sediment types was observed (Fig. 2c). The small shore-connected ridge in the south (see Fig. 2d) was

AC

composed of a variety of sediment types ranging from fine to coarse sand with a low percentage of coarser sediment fraction (< phi 3). The shoreface of the island of Spiekeroog was covered by fine sand (phi 2-3), exceeding 90% of the sample weight down to the trough, where a linear deposit ca. 30-metres wide containing mud (> phi 4) was taken in the upper 5 cm of the sample SPRJ02. The lower landward side of the inner shoreface-connected ridge was composed of medium to coarse sand (< phi 1) with traces of coarser sediment particles and small diameter pebbles visible on sonograms. The upper part of the landward flank was composed of medium sand (phi 1-2) reaching the crest line. The seaward flank of the inner ridge was covered by fine to medium sand (phi 1-3) down to the trough line, where muddy layer was registered in a form of belt yet again. The landward flank of the outer ridge similarly to the inner ridge was divided at the half height into lower coarse-sand dominated sediment with coarser fractions including pebbles (
ACCEPTED MANUSCRIPT

RI P

SC

2003-2010 IX +0.52 -0.15 +0.28 -0.04 -0.09 -0.03 -0.21 -0.25 +0.04 +0.29 -0.07 -0.10 -0.18 +0.10 +0.06 -0.04 -0.06 -0.34 -0.23 +0.44 -0.49 -0.28 +0.78 -1.72

MA NU

ED

2010 III2010 IX (-0.01) (-0.04) (+0.05) (-0.11) (+0.06) (+0.04) (+0.01) (-0.02) (-0.08) (+0.04) (-0.03) (-0.01) (-0.01) (-0.02) (-0.08) (-0.02) (+0.01) (0.00) (+0.01) (-0.15) (-0.14) (-0.24) (+0.01) (-0.12)

PT

20072010 III (+0.32) (-0.12) (+0.15) (-0.04) (-0.03) (-0.09) (-0.12) (-0.16) (-0.01) (+0.03) (0.00) (-0.10) (-0.07) (-0.02) (+0.12) (-0.15) (-0.16) (-0.11) (-0.02) (-0.05) (-0.26) (-0.03) (+0.04) (-0.52)

CE

SPRJ04 SPRJ05 SPRJ06 SPRJ07 SPRJ08 SPRJ09 SPRJ10 SPRJ11 SPRJ12 SPRJ13 SPRJ14 SPRJ15 SPRJ16 SPRJ17 SPRJ18 SPRJ19 SPRJ20 SPRJ21 SPRJ22 SPRJ23 SPRJ24 SPRJ25 SPRJ26 SPRJ27

20032007 (+0.21) (+0.01) (+0.08) (+0.11) (-0.12) (+0.02) (-0.10) (-0.07) (+0.13) (+0.22) (-0.04) (+0.01) (-0.10) (+0.14) (+0.02) (+0.13) (+0.09) (-0.23) (-0.22) (+0.64) (-0.09) (-0.01) (+0.73) (-1.08)

T

Table 1. Bathymetry changes calculated based on four investigations at sampling stations between 2003 and September 2010.

Bathymetry in the area has been investigated three times during the time-span of seven

AC

years. A series of cross-shore transects carried out in 2003, 2007 and September 2010 were plotted for comparison along two transects of macrobenthos sites (Fig. 3) in order to study the long-term morphodynamics of the habitats. In both transects the shape of the shoreface topped with the small shoreface-connected ridge was visible as well as the shape of the inner ridge limited by troughs. The cross-sections showed an asymmetry of the inner ridge with the seaward flank steeper (0.7°) than the landward flank (0.4°). This feature was shallower on the western transect. The trend however, suggested further steepening of the seaward flank due to erosion of the landward flank (reaching 0.34 m at site SPRJ21, Fig. 3, Table 1) and accumulation on the opposite flank (0.29 m at SPRJ13) coupled with relatively stable length of the ridge. The deepest part of the trough was surprisingly fixed in seven years time at the eastern cross-section, whereas nearly 600 m westwards, at the second cross-section both troughs migrated northwards by 35 m (Fig. 3). The outer large ridge was investigated only up to the middle of landward flank in 2003 and 2007, so we lacked comparable material for the full relief cross-section of this ridge. Available data show that the 9

ACCEPTED MANUSCRIPT erosion took place on this section of the landward flank up to 0.18 m in seven years at site SPRJ16. The largest change of bathymetry on the other hand occurred on the upper shoreface of the island of Spiekeroog, which was associated with a migration of the small ridge. Over 0.5 m of sediment accumulated at sites SPRJ04 and SPRJ26 in seven years

T

time and at the same time at site SPRJ27 a 1.7-metre erosion took place (Fig. 3, Table 1).

RI P

There was another elongated bedform of smaller size attached to the shoreface at about 15 m water depth in September 2010. It was sampled twice at sites SPRJ06 and SPRJ23. In the time-frame of seven years the accumulation was observed at these sites of 0.28 m and

CE

PT

ED

MA NU

SC

0.44 m, respectively.

Fig. 3. a) Bathymetry change in centimetres between 2003 and 2010; b) western (I) and

AC

eastern (II) bathymetry transects in 2003, 2007 and 2010 crossing sampling sites of September 2010.

3.2. Macrofauna in 2010 A total of 11576 organisms were identified corresponding to 118 taxa. The most dominant taxa was the annelids (47%), being followed by crustaceans (27%), molluscs (16%) and echinoderms (3%). Non-metric multidimensional scaling (nMDS) and the ANOSIM test (Global R Value 0.89; significance level of sample statistic 0.1%) revealed 3 significant affinity groups and one outlier (site SPRJ13) (Fig. 4). Additionally, the PERMANOVA analysis revealed significant differences between the 3 clusters formed by affinity group 1, 2 and 3 (PERMANOVA main test, df= 3, F= 7.7685, p= 0.001, p(Monte Carlo)= 0.001, for data of 10

ACCEPTED MANUSCRIPT pairwise test see Table 2). Because of these results and the results of the cluster analysis,

MA NU

SC

RI P

T

the affinity group 4 (site SPRJ13) was handled as an outlier.

Fig. 4. Classification (cluster; A) and ordination (nMDS; B) diagrams based on macrofauna

PT

ED

abundance data, including clusters at 40% of similarity (circles).

CE

Table 2. Results of the PEREMANOVA pairwise test of the macrofauna affinity groups and their statistically significant differences (p< 0.05). p

p(MC)

1, 2

AC

Affinity groups t

2.8988

0.001

0.001

2, 3

3.641

0.001

0.001

2, 4

1.8178

0.077

0.012

1, 3

2.8426

0.002

0.002

1, 4

2.0737

0.165

0.024

3, 4

1.4747

0.128

0.095

11

ACCEPTED MANUSCRIPT To test the relationship between the affinity group composition and environmental variables, the BIOENV procedure was employed on a species assemblage similarity matrix adjusted for 27 sites. The results are presented in Table 3. The extent to which the two pattern match, reflects the degree to which the abiotic data explains the biotic pattern (rho= 1 (similar)- 0

T

(dissimilar)). For the environmental matrix, the water depth revealed the best association with

RI P

the macrofauna distribution (rho= 0.308), although the correlation factors calculated with BIOENV (p= 0.002) revealed a weak correlation. It was followed by porosity (rho= 0.276) and sand (0.21). For the environmental variables mud (rho= 0.171), shells (rho= 0.138) and

SC

gravel (rho=0.07) a low correlation was calculated (Table 3). The results of the Spearman’s rank correlations showed significant correlations of various characteristic taxa of the found

MA NU

affinity groups with the sediment composition and water depth (Fig. 5).

Table 3. Results of the BIOENV analysis with the 4th root transformed macrofauna abundances and 6 normalized abiotic variables. Correlation (rho)

p

Depth

0.308

0.002

Shells Gravel

PT AC

Mud

0.276

0.002

0.21

0.013

0.171

0.032

0.138

0.052

0.07

0.198

CE

Porosity Sand

ED

Environmental variables

12

MA NU

SC

RI P

T

ACCEPTED MANUSCRIPT

ED

Fig. 5. Spearman’s rank correlation factors calculated for 15 macrofauna species and 6 abiotic factors a) depth, b) porosity, c) shells, d) gravel, e) sand, and f) mud. Species names: Abr alb= Abra alba, Aon pau= Aonides paucibranchiata, Bat ele= Bathyporeia elegans, Cap

PT

min= Capitella minima, Eum san= Eumida sanguinea, Gon bob= Goniadella bobretzkii, Har gla= Harmothoe glabra, Lan con= Lanice conchilega, Not lat= Notomastus latericeus, Oph

CE

spec. juv.= Ophiura spec. juv., Pis rem= Pisione remota, Sco arm= Scoloplos armiger, Spi

AC

gon= Spio goniocephala, Tel fab= Tellina fabula, Tra for= Travisia forbesii.

The affinity group 1 (Fig. 4) consisted predominantly of polychaetes such as Aoinides paucibranchiata, Goniadella bobretzkii and Pisione remota. All sites of this group were located on the landward flanks of the large ridges, where coarse sand and gravel dominated (Fig. 6, ). A total of 22 taxa/ 0.1 m2 and 1640 ind./ m2 were found in this group. In opposition, Shannon Index (1.58) and evenness (0.51) were low (Table 4). Characteristic species according the SIMPER analysis were the polychaetes Aonides paucibranchiata, Goniadella bobretzkii, Pisione remota and Lanice conchilega (Table 4). The dominant feeding type was interface feeding (71%) followed by predators among all groups (23%) (Table 4). Apart from the depth, correlations (Fig. 5) between the abundance of the polychaete Aonides

13

ACCEPTED MANUSCRIPT paucibranchiata (group 1), the content of shells (0.66) and gravel (0.64) were calculated,

ED

MA NU

SC

RI P

T

while it was negatively correlated with sand content (-0.58).

PT

Fig. 6. The distribution of the affinity groups 1(), 2 (), 3() and 4() superimposed on the

AC

CE

sediment and bathymetry map in a) planimetric view and b) in 3D view.

14

ACCEPTED MANUSCRIPT

RI P

T

Table 4. Benthic macrofauna affinity groups characterization, being shown the stations indentification, the mean taxa numbers (Taxa/ 0,1 m2), mean abundance (N/ m2), mean Shannon Index (H’(loge)/ m2), mean evenness (J’/ m2), percentage of the different feeding types and sediment types. Additionally, a list of the 15 most characteristic species (according SIMPER) and its feeding behaviour (in brackets) are represented, being provided their mean abundance per m2, in each group. Abbreviation of the feeding types: SSD= subsurface deposit feeder, IF= interface feeder, SD= surface deposit feeder, P= predator, SL= sand licker. Cluster

1 ()

Stations SPRJ

9, 10, 15, 1-8, 14, 17, 22, 23, 11, 12, 18, 19, 13

J’/ m

2

H’(loge)/ m

2

24, 25

22

31,14

1640

2914

0.51

0.66

1.58

Sediment

coarse sand

4 ()

20, 26, 27

SC

N/ m

2

16, 21

3 ()

MA NU

Taxa/0,1 m

2

2 ()

2.28

22

19

642

220

0.71

0.88

2.18

2.59

fine sand to medium medium sand fine

sand

sand, mud

to fine sand

medium sand

55.78

40.33

46.16

28.48

31.66

46.16

1.76

7.73

0.79

7.69

22.59

7.96

4.71

0

0

0

9.34

0

Scoloplos armiger (SSD)

40

625

43

35

Lanice conchilega (IF)

177

597

8

5

Notomastus latericeus (SSD)

18

567

2

0

Abra alba (SD)

26

164

5

5

Harmothoe glabra (P)

47

112

1

0

Eumida sanguinea (P)

2

105

0

0

Capitella minima (SSD)

4

66

1

5

Tellina fabula (IF)

0

22

0

5

Aonides paucibranchiata (IF)

873

7

5

5

Goniadella bobretzkii (P)

234

15

21

0

Pisione remota (P)

51

3

3

0

Ophelia spec. juv. (SSD)

6

4

189

0

Travisia forbesi (SSD)

0

0

39

0

Spio goniocephala (IF)

0

1

115

15

Bathyporeia elegans (SL)

0

0

43

0

Feeding types [%] 4.60

IF

71.04

ED

SSD

SD

SL 2

PT

P

to

AC

feeding type

CE

Dominant Taxa [N/ m ] and

15

ACCEPTED MANUSCRIPT

Group 2 included 14 sites (Fig. 4) and was located on the fine sand area covering the seaward flanks and in the troughs, but some samples were also present on coarse sand (Fig

T

6, ). This group was characterized by the highest taxa number (31/ 0.1 m 2) and abundance

RI P

(2914/ m2) as well as high evenness (0.66) and high Shannon Index (2.28) (Table 4). Characteristic species according the SIMPER analysis were the polychaetes Scoloplos armiger, Lanice conchilega, Notomastus latericeus, Harmothoe glabra, Eumida sanguinea,

SC

Capitella minima and the bivalve Abra alba (Table 4). More than 50% of the dominant species in group 2 were subsurface deposit feeders (56%) whereas 29% were interface

MA NU

feeders (Table 4), species that may switch between surface deposit feeding and suspension feeding. Positive significant correlations between mud content and abundance of polychaetes Harmothoe glabra (0.51), Lanice conchilega (0.49), Scoloplos armiger (0.54), Notomastus latericeus (0.57), Eumida sanguinea (0.62) and the bivalve Abra alba (0.61), dominant taxa of group 2, were found (Fig. 5). Also, positively correlations between depth and the species Notomastus latericeus (0.55), Eumida sanguinea (0.46) and Abra alba (0.71)

ED

and negatively correlations between sand and Harmothoe glabra (-0.42), Lanice conchilega (-0.42) and Abra alba (-0.58) were found.

PT

The affinity group 3 (Fig. 4) was found on fine to medium sand in the shallowest water depth of the study area on top of the ridges (Fig. 6, ). The most characteristic species found in

CE

this group were Ophelia spp., Spio goniocephala and Travisia forbesi. For this group a mean abundance of 642 ind./ m2, Shannon Index of 2.18 and evenness of 0.71 were found (Table 4). More than 50% of the dominant species in group 3 were subsurface deposit feeders

AC

(40%) and 32% were interface feeders (Table 4). The abundance of the polychaete Spio goniocephala was negatively correlated with mud content (-0.58), but positively correlated with sand content (0.63), like the sand licking amphipod Bathyporeia elegans (0.6) (Fig. 5). One site (SPRJ13) did not belong to any of the 3 found affinity groups, but according to the cluster analysis and the PERMANOVA test it showed some similarity to affinity group 3. Site SPRJ13 was located on fine to medium sand in the seaward side of the inner ridge (Fig. 6, 2

2

). A low taxa number (19/ 0.1 m ) and abundance (220/ m ) was found, but also a high

evenness (0.88) and Shannon Index (2.59). This gives a good reason to exclude this site out of affinity group 3. Low abundances for example for the species Scoloplos armiger and Spio goniocephala were found. Other characteristic species for group 3, like juvenile Ophelia, Bathyporeia elegans and Travisia forbesi did not occur. Here subsurface deposit feeders and interface feeders dominated, each with 46% (Table 4). The abundance of the polychaete 16

ACCEPTED MANUSCRIPT Scoloplos armiger was negatively correlated with sand content (-0.31), but positively correlated with mud content (0.54) (Fig. 5). Similar to group 3, the abundance of Spio

T

goniocephala was positively correlated with sand content (0.63).

RI P

4. Discussion

4.1. Small scale variability in sediment composition of shoreface-connected ridges

SC

The cross-shore zonation of the sandy sediment covering shoreface-connected ridges is quite well documented in the literature, but in this study the sediment pattern was shown for

MA NU

the first time in respect to the high-resolution bathymetry. Son et al. (2012) suggested that the coarse sediment overlays the troughs, but their study was made using point sampling based on a 250-metre grid. Hydroacoustic backscatter data collected in this study showed accurately that the trough’s bottom forms a strict border between fine sand of the shoreface and medium to coarse sand on the landward flank of the ridges. This remarkable feature may have a physical explanation, yet none of the existing numerical models was able to

ED

reproduce such a set-up. Coarser fractions observed on the landward flank and finer on the seaward one are suspected to be the product of long-term sediment sorting triggered by

PT

energy gradients of currents overflowing the ridge (Trowbridge, 1995; Calvete et al., 2001; de Swart et al. 2008; Vis-Star et al., 2009). Assuming such a process, it is unclear how the

CE

troughs filled in with pockets of semi-consolidated mud deposits similar in texture to fluid mud (e.g. Schrottke et al., 2006). Such pockets were observed on sonograms not only in March 2010, but also during rough-weather conditions in September 2010 (Fig. 2). Such mud layer

AC

was also encountered by Son et al. (2012) at two sites on the landward trough sampled in 2005. They suggested that this fine sediment is a product of sorting of the local Pleistocene deposit, but did not speculate on its longevity. We have found no explanation for unexpected stability of the mud layer at ca. 20 m water depth. In general, a decreasing current velocity could result in higher mud content in the troughs (Snelgrove and Butman, 1994). The troughs are expected to be sheltered from tidal and wave current action, but one needs to take into account that the slopes flanking the troughs are gentler than 1 degree. It is therefore probable that tidal action remobilizes the mud daily, but there exist a constant delivery of this fraction from tidal flats via tidal inlets. The amounts of mud might be however, so insignificant that the mud is traceable in the only morphological sediment trap in the area.

4.2. Small scale variability of associated affinity groups 17

ACCEPTED MANUSCRIPT In general, the southern and western area of the German Bight, North Sea is known to be a part of the Tellina fabula community (Salzwedel, 1985; Rachor and Nehmer, 2003). In our area of investigation we found several affinity groups in this Tellina fabula community.

T

The affinity groups identified on small spatial scale are similar to communities in other

RI P

regions in the North Sea performed on large spatial scale (e.g. Dyer et al., 1983; Eleftheriou and Basford, 1989; Künitzer et al., 1992; Rachor and Nehmer, 2003; Kröncke et al., 2011). Although, we did not find a strong correlation between the benthic affinity groups and abiotic

SC

variabilities, we found high correlations of several characteristic species of the corresponding affinity groups with particular abiotic factors. In this study, we found a high heterogeneity in

MA NU

sediment composition and macrofauna composition on small spatial scale due to differences in hydrodynamics, which correspond with autecological preferences of the macrofauna species.

The organisms found in the coarser sand areas on the landward side of the ridge are known to have a preference for coarse and gravely sediments, such as the group 1, species Aonides paucibranchiata and Goniadella bobretzkii (Hartmann-Schröder, 1996). A similar

ED

affinity group was found by Markert et al. (2013) in sorted bedforms near the Sylt Island ca. 120 km north of the study area and the found species are known to be common in coarse

PT

sediment coastal areas near the West Frisian Islands (Salzwedel, 1985; Rachor and Nehmer, 2003). Since, the deposition of organic material is controlled by hydrodynamic

CE

energy, coarse sediments retain little organic material as a food source (Pearson and Rosenberg, 1978; Kröncke, 2006) and macrofauna species must be nutritionally adapted to this high hydrodynamics. Therefore, in our study few taxa of feeding types like interface

AC

feeder and predators were common in coarse sediments in high abundances, what causes the low diversity.

In general, a relationship between communities and hydrodynamically mediated sediment composition, and food availability is well understood (e.g. Gray, 1974; Pearson and Rosenberg, 1978; Snelgrove and Butmann, 1994; Kröncke and Bergfeld, 2003). We therefore assumed a similar relationship in this small scale study. Species, such as the interface feeding polychaete Lanice conchilega, preferring finer sediments, occurred mainly on the shoreface and seaward flank (group 2, 597 ind./ m2) of the inner ridge. There, high abundances of subsurface deposit feeders and interface feeders occurred due to higher sedimentation rates of organic material under lower hydrodynamics. In general, high abundances of Lanice conchilega are known to influence the diversity in benthic communities caused by higher sedimentation rates due to changes in hydrodynamics (Rabaut et al., 2007; 18

ACCEPTED MANUSCRIPT van Hoey et al., 2008; Callaway et al., 2010). Co-occurring species benefit from environmental changes (van Hoey et al., 2008), such as the polychaetes Spiophanes bombyx (Rabaut et al., 2007) and Eumida sanguinea, as well as bivalves such as Abra alba (Callaway et al., 2010; Rabaut et al., 2007). Some of these species were also present in high

T

abundances in the group 2 in our study. We found also high abundances of Notomastus

RI P

latericeus, although the polychaete is known to be negatively affected by high abundances of Lanice conchilega (Callaway et al., 2010). In general, a medium diversity was found. The dominant species in group 2 are also found in the Tellina fabula community (e.g. Salzwedel

SC

et al., 1985; Rachor and Nehmer, 2003) in homogeneously fine to medium sands north of Norderney (Dörjes, 1976; Kröncke and Reiss, 2010; Kröncke et al., 2013). This affinity group

MA NU

was the most similar to the known large scale community of Tellina fabula. The extended communities on coarse-grained landward flanks (group 1) and fine-grained seaward flanks of the ridges (group 2) in our study area presented high mean abundances. Dörjes (1976) explained the taxa maxima at the seaward slopes of shoreface-connected ridges near the island of Norderney by a high sediment stability and food availability due to

ED

the longitudinal current parallel to the coast.

Similar to Weber et al. (2004), we found higher abundances of the macrofauna species on

PT

top of the sand ridges (group 3) in comparison to the troughs (group 2). The higher mud content in the troughs indicated differences in food availability for some feeding types, such

CE

as surface-deposit feeders. Here we found more subsurface deposit and interface feeding species. Beside the low abundances of macrofauna in the troughs (group 2), the presence of Capitella minima (subsurface deposit feeder) and Tellina fabula (interface feeder) appeared

AC

to be restricted to the muddier parts of our study area. The low abundances of macrofauna species on top of the ridges (group 3) indicated an area withhigh exposition to hydrodynamics. In other high-energy locations namely the inlet regions in the Wadden Sea (Reiss and Kröncke, 2001; Nehmer and Kröncke, 2003) or the shallow parts of the Dogger Bank (Wieking and Kröncke, 2005; Kröncke, 2011) macrofauna species number and abundance were also found to be low in relation to low food availability. High velocity tidal and ocean currents result in erosion processes, and formation of unstable sandy sediments preferred by interface-feeding polychaetes, such as Magelona johnstoni, Spio martinensis, Scoloplos squamata as well as crustaceans of the genus Bathyporeia (Reiss and Kröncke, 2001). However, in this study a high abundance and mean diversity of the sand-inhabiting subsurface deposit or interface feeding polychaetes Ophelia spp. juv., Travisia forbesi and Spio goniocephala (Hartmann-Schröder, 1996) was found in group 3. 19

ACCEPTED MANUSCRIPT

4.3. Sediment dynamics morphodynamics

and

response

of

macrofauna

communities

to

T

Constant erosion of landward flanks of the large ridges as well as accumulation of the

RI P

seaward flanks of the inner ridge observed in the past seven years supported the notion of sediment sorting across the ridges (Trowbridge, 1995). It is noteworthy however, that between 2003 and 2007, Son et al. (2012) observed that the changes in bathymetry were so

SC

residual that it was not possible to describe this morphological trend. Only the implementation of bathymetry 2010 data allowed tracing steepening of seaward flanks and

MA NU

seaward movement of the large ridges postulated by numerical models (e.g. de Swart et al. 2008). It seems therefore that seven years time is the shortest period necessary for in-situ monitoring of ridges of these dimensions in order to establish their morphodynamics using high-accuracy methods. The migration pace calculated to 5 meters per year in seaward direction seems to be in agreement with numerical modelling predictions of Calvete et al. (2001). The small ridge on the other hand migrated four times faster. A comparison of its

ED

crest alignment between 2003 and 2010 yielded a difference of over 130 meters, which suggests an average speed of nearly 20 meters per year with the flood current. Even such

PT

velocity is however, ten times smaller than ones calculated for bedforms of similar height investigated in nearby tidal channels (Kubicki and Bartholomä, 2011). This suggests that the morphodynamics of both generations of shoreface-connected ridges are triggered chiefly by

CE

periodic high-energy storm events. The shoreface plain, over which the small ridge was migrating, appeared to be stable in time. The plain was covered by the affinity group 2, which

AC

contained tube-worms Lanice conchilega. Dense aggregations of these organisms (several thousands of individuals per m2 are common in the North Sea) can stabilize surface sediments due to their feature of attaching sand to the inner thin organic layer (van Hoey et al. 2008; Callaway et al, 2010). Individuals of L. conchilega are short living (usually less than 2 years- Rhoads and Boyer, 1982), but populations can survive for several years (van Hoey et al. 2008). It is therefore possible that the shoreface plain in the study area was stable in time due to hydrodynamic equilibrium, which was greatly supported by L. conchilega community acting as sediment reinforcement. Since the affinity groups found in our study are typical for coarse sand sediments (group 1 on landward flanks of the ridges) and for fine to coarse sand (group 2, seaward flanks) with high abundances of common North Sea macrofauna species, the macrofauna communities seem to be able to follow the slow and continuous migration of the characteristic shorefaceconnected ridges feature over years and reveal no disturbance or succession. 20

ACCEPTED MANUSCRIPT

5. Summary

T

This is the first study worldwide, where high-precision bathymetry and long-enough

RI P

monitoring revealed true values of migration of shoreface-connected ridges. A seaward steepening of ridges took place and was an effect of erosion up to 0.34 m on landward flanks in and accumulation up to 0.29 m on seaward flanks in seven years. The studied shoreface-

SC

connected ridges migrated seawards with a pace of 5 m/year for the inner ridge and 20 m/year for the small ridge. The seabed dynamics can be therefore called low and allows forming stable benthic communities. For the first time in German Wadden Sea a high-

MA NU

resolution sediment mapping was used to reveal that the shore-parallel sediment zonation of the investigated shoreface-connected ridges off the island of Spiekeroog had distinctive borders induced by local long-term morphodynamics. Discovered elongated mud-pockets were common in the deepest parts of the troughs, but seemed to be unstable in time. Such abiotic features allowed forming three different benthos affinity groups in the area of ridges.

ED

One group of Scoloplos armiger, Lanice conchilega and Notomastus latericeus was located on the shoreface and in the troughs, one of Aonides paucibranchiata and Goniadella bobretzkii on the landward flanks of the ridges, and one of Ophelia spp. juv. and Spio

PT

goniocephala on top of the ridges. The pattern of sediments and macrofauna groups were congruent. The spatial distribution of these macrofauna affinity groups was undoubtedly

CE

dependent on sediment pattern and local water depths. The first affinity group containing Lanice conchilega acting

as sediment

reinforcement is likely co-responsible for

AC

morphological stability of the shoreface off the Spiekeroog Island.

Acknowledgements

The biological part of this study was funded by the Lower Saxony Ministry for Environment and Climate Protection and the Lower Saxony Ministry for Science and Culture within the project “Scientific monitoring concepts for the German Bight (WIMO)”. The geological part of the research was carried out within the framework of the BMBF (Federal Ministry of Education and Research) project AufMod (03KIS088). The authors thank Captain Karl Baumann and the crew of RV ”Senckenberg” for support during the measuring campaigns. We are also thankful to Arnulf Möller for collection and post-processing of bathymetry data, to Corinna Schollenberger and Astrid Raschke for carrying out sediment analyses and to Denise Marx, Angela Schmidt and Annette Steudle for sorting macrofauna samples. Last but

21

ACCEPTED MANUSCRIPT not least, we sincerely thank the editor and the anonymous reviewers for their helpful comments and improvements of the manuscript.

RI P

T

References

Anderson, M. J., Gorley, R. N., Clarke, K. R., 2008. PERMANOVA+ for PRIMER: Guide to

SC

Software and Statistical Methods. PRIMER-E, Plymouth.

Antia, E. E., 1993. Surficial grain-size statistical parameters of a North Sea shorefaceconnected ridge: patterns and process implication. Geo-Mar Lett 13: 172-181.

MA NU

Antia, E. E., Flemming, B. W., Wefer, G., 1995. Calm-weather spring and neap tidal current characteristics on a shoreface-connected ridge complex in the German Bight (southern North Sea). Geo-Mar Lett 15: 30-36.

Antia, E., 1996. Patterns of Tidal Flow Asymmetry on Shoreface-Connected Ridge

ED

Topography off Spiekeroog Island, German Bight. Ger J Hydrogr 48: 97-107. Baptist, M. J., van Dalfsen, J., Weber, A., Passchier, S., van Heteren, S., 2006. The distribution of macrozoobenthos in the Southern North Sea in relation to meso-scale

PT

bedforms. Estuar Coast Shelf S 68: 538-546. Bray, J. R., Curtis, J. T., 1957. An ordination of the upland forest communities of southern

CE

Wisconsin. Ecol Monogr 27: 325–349. Brezina, J., 1979. Particle size and settling rate distribution of sand-sized materials. PARTEC

AC

79, 2nd European Symposium on Particle Characterisation, Nürnberg. 21 pp. Brown, C. J., Cooper, K. M., Meadows, W. J., Limpenny, D. S., Rees, H. L., 2002. Smallscale Mapping of Sea-bed Assemblages in the Eastern English Channel Using Sidescan Sonar and Remote Sampling Techniques. Estuar Coast Shelf S 54: 263-278. Callaway, R., Desroy, N., Dubois, S. F., Fournier, J., Frost, M., Godet, L., Hendrick, V. J., Rabaut, M., 2010. Ephemeral Bio-engineers or Reef-building Polychaetes: How Stable are Aggregations of the Tube Worm Lanice conchilega (Pallas, 1766)? Integrative and Comparative Biology, Oxford University Press 50(2): 237-250. Calvete, D., Falques, A., de Swart, H. E., Walgreen, M., 2001. Modelling the formation of shoreface-connected sand ridges on storm-dominated inner shelves. J Fluid Mech 441: 169193. Clarke, K. R., Gorley, R.N., 2006. PRIMER v6: User Manual/Tutorial. PRIMER-E, Plymouth. 22

ACCEPTED MANUSCRIPT Clarke, K. R., Green, R. H., 1988. Statistical design and analysis for a “biological effects” study. Mar Ecol Prog Ser 46: 213-226. Clarke, K. R., Warwick, R. M., 2001. Change in marine communities: an approach to

T

statistical analysis and interpretation, 2nd edition. PRIMER-E, Plymouth.

RI P

de Swart, H. E., Walgreen, M., Calvete, D., Vis-Star, N. C., 2008, Nonlinear modeling of shoreface-connected ridges; Impact of grain sorting and interventions, Coast Eng 55: 642656.

SC

Dörjes, J., 1976. Primärgefüge, Bioturbation und Makrofauna als Indikatoren des Sandversatzes im Seegebiet vor Norderney (Nordsee). Senckenberg Marit 8: 171-188.

MA NU

Duane, D. B., Field, M. J., Meisenburger, E. P., Swift, D. J. P., Jeffress Williams, S., 1972. Linear shoals on the Atlantic inner continental shelf: Florida to Long Island. In: Swift, D. J. P., Duane, D. B., Pikley, O. H. (Eds.), Shelf Sediment Transport: Process and Pattern. Dowden, Hutchinson and Ross, Stroudsburg, PA, 447-498.

Dyer, M. F., Fry, W. G., Fry, P. D., Cranmer, G. J., 1983. Benthic regions within the North

ED

Sea. J Mar Biol Ass U K 63: 683-693.

PT

Eleftheriou, A., Basford, D. J., 1989. The macrobenthic infauna of the offshore northern North Sea. J Mar Biol Ass UK 69(1): 123-143.

CE

Ernstsen, B. V., Noormets, R., Hebbeln, D., Bartholomä, A., Flemming, B. W., 2006. Precision of high-resolution multibeam echo sounding coupled with high-accuracy positioning

AC

in a shallow water coastal environment. Geo-Mar Lett 26: 141-149. Fauchald, K.; Jumars, P. A., 1979. The diet of worms: a study of polychaete feeding guilds, in: Barnes, M. (Ed.), 1979. Oceanogr Mar Biol Ann Rev 17: pp. 193-284. Figueiredo, A. G. J., Sanders, J. E., Swift, D. J. P., 1982. Storm-graded layers on inner continental shelves: examples from southern Brazil and the Atlantic coast of the central United States. Sediment Geol 31: 171-190. Govaere, J. C. R., van Damme, D., Heip, C., De Coninck, L. A. P., 1980. Benthic communities in the Southern Bight of the North Sea and their use in ecological monitoring. Helgoländer Meeresun. 33: 507-521. Gray, J. S., 1974. Animal-sediment relationships. Oceanogr Mar Biol: Ann. Rev. 12: 223-261. Hartmann- Schröder, G., 1996. Teil 58. Annelida, Borstenwürmer, Polychaeta. 2. neubearb. Auflage. In: Dahl, F. (Begr.), Schuhmann, H. (Hrsg.). Die Tierwelt Deutschlands und der 23

ACCEPTED MANUSCRIPT angrenzenden Meeresteile nach ihren Merkmalen und nach ihrer Lebensweise. Jena, Stuttgart, Zoologisches Museum Berlin. 648 p. Hayward, P. J., Ryland, J. S., 1990. The marine fauna of the British Isles and north-west

T

Europe. Vol. 1: Introduction and Protozoans to Arthropods. Clarendon Press: Oxford, 1-627

RI P

pp.

Kösters, F., Winter, C., 2014. Exploring German Bight coastal morphodynamics based on modelled bed shear stress. Geo-Mar Lett 34: 21-36.

SC

Kröncke, I. 2006. Structure and function of macrofaunal communities influences by hydrodynamically controlled food availability in the Wadden Sea, the open North Sea, and

MA NU

the Deep-sea. A synopsis. Senckenberg Marit 36: 123-164.

KRÖNCKE, I. 2011. CHANGES IN DOGGER BANK MACROFAUNA COMMUNITIES IN THE 20TH CENTURY CAUSED BY FISHING AND CLIMATE. ESTUAR COAST SHELF S 94 (3): 234-245.

Kröncke, I., Bergfeld, C., 2003. North Sea Benthos: a Review. Senckenberg Marit 33: 205-

ED

268.

Kröncke, I., Reiss, H., 2010. Influence of macrofauna long-term natural variability on benthic

PT

indices used in ecological quality assessment. Mar Pollut Bull 60: 58-68. Kröncke, I., Reiss, H., Eggleton, J. D., Aldridge, J., Bergman, M. J. N., Cochrane, S.,

CE

Craeymeersch, J. A., Degraer, S., Desroy, N., Dewarumez, J.-M., Duineveld, G. C. A., Essink, K., Hillewaert, H., Lavaleye, M. S. S., Moll, A., Nehring, S., Newellm, R., Oug, E.,

AC

Pohlmann, T., Rachor, E., Robertson, M., Rumohr, H., Schratzberger, M., Smith, R., Vanden Berghe E., van Dalfsen, J., van Hoey, G., Vincx, M., Willems, W., Rees, H. L., 2011. Changes in North Sea macrofauna communities and species distribution between 1986 and 2000. Estuar Coast Shelf S 94: 1-15. Kröncke, I., Reiss, H., Dippner, J. W., 2013. Effects of cold winters and regime shifts on macrofauna communities in shallow coastal regions. Estuar Coast Shelf S 119: 79-90. Kruskal, J. B., 1964. Nonmetric multidimensional scaling: a numerical method. Psychometrika 29: 115–129. Kubicki, A., Bartholomä, A., 2011. Sediment dynamics in the Jade tidal channel prior to port construction, southeastern North Sea. J Coast Res SI 64: 771-775. Künitzer, A., Basford, D., Craeymeersch, J. A., Dewarumez, J. M., Dörjes, J., Duineveld, G. C. A., Eleftheriou, A., Heip, C., Herman, P., Kingston, P., Niermann, U., Rachor, E., H. 24

ACCEPTED MANUSCRIPT Rumohr, H., de Wilde, P. A. J., 1992. The benthic infauna of the North Sea: species distribution and assemblages. ICES J Mar Sci 49: 127-143. Lincoln, R. J., 1979. British marine Amphipoda: Gammaridea. 658pp., London (British

T

Museum for Natural History).

RI P

Markert, E., Holler, P., Kröncke, I., Batholomae, A., 2013. Benthic habitat mapping of sorted bedforms using hydroacoustic and ground-truthing methods in a coastal area of the German Bight/ North Sea. Estuar Coast Shelf S 129: 94-104.

SC

Nehmer, P., Kröncke, I., 2003. Macrofaunal Communities in the Wichter Ee, a Channel System in the East Frisian Wadden Sea. Senckenberg Marit 32: 1-10.

MA NU

Newell, R. C., Seiderer, L. J., Hitchcock, D. R., 1998. The impact of dredging works in coastal waters: A review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed. Oceanogr Mar Biol: Ann Rev 36: 127-178. Olafsson, E. B., Peterson, C. H., Ambrose Jr, W. G., 1994. Does recruitment limitation structure populations and communities of macro-invertebrates in marine soft sediments: The

ED

relative significance of pre- and post-settlement processes. Oceanogr Mar Biol: Ann Rev 32: 65-109.

PT

Pearson, T. H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanogr Mar Biol: Ann Rev 16: 229-

CE

311.

Pielou, E., 1969. An introduction into mathematical ecology.- New York, London, 286 S.

AC

Rabaut, M., Guilini, K., van Hoey, G., Vincx, M., Degraer, S., 2007. A bio-engineered softbottom environment: The impact of Lanice conchilega on the benthic species-specific densities and community structure. Estuar Coast Shelf S 75: 525-536. Rachor, E., Nehmer, P., 2003. Erfassung und Bewertung ökologisch wertvoller Lebensräume in der Nordsee. 1-175. Reiss, H., Kröncke, H., 2001. Spatial and Temporal Distribution of Macrofauna in the Otzumer Balje (East Frisian Wadden Sea Germany). Senckenberg Marit 31: 283-298. Rhoads, D. C., 1974. Organism-sediment relations on the muddy sea floor. Oceanogr Mar Biol: Ann Rev 12: 263-300. Rhoads, D. C., Boyer, L. F., 1982. The effects of marine benthos on physical properties of sediments. A successional perspective. In: McCall, P.L., Tevesz, M.J.S. (Eds) Animalsediment relations: the biogenic alteration of sediments, New York: 3-52. 25

ACCEPTED MANUSCRIPT Salzwedel, H., Rachor, E., Gerdes, D., 1985. Benthic makrofauna communities in the German Bight. Veröff. Inst. Meeresforsch. Bremerh. 20: 199-267. Schrottke, K., Becker, M., Bartholomä, A., Flemming, B. W., Hebbeln, D., 2006: Fluid mud

RI P

parametric sub-bottom profiler. Geo-Mar Lett 26(3): 185-198.

T

dynamics in the Weser estuary turbidity zone tracked by high-resolution side-scan sonar and

Schwab W. C., Thieler E. R., Allen J. R., Foster D. S., Swift B. A., Denny J. F., 2000. Influence of inner-continental shelf geologic framework on the evolution and behavior of the

SC

barrier-island system between Fire Island Inlet and Shinnecock Inlet, Long Island, New York. J Coast Res 16(2): 408–422.

MA NU

Shannon, C., Weaver, W., 1949: The mathematical theory of communication. Chicago, 117 S.

Shepard, R. N., 1962. The analysis of proximities: multidimensional scaling with an unknown distance function. Psychometrika, 27: 219-246.

Snelgrove, P. V. R., Butman, C. A., 1994. Animal-sediment relationship revisited: cause

ED

versus effect. Oceanogr Mar Biol: Ann Rev 32: 111-117. Son, C. S., Flemming, B. W., Bartholomä, A., Chun, S. S., 2012. Long-term changes in

PT

morphology and textural sediment characteristics in response to energy variation on shoreface-connected ridges off the East Frisian barrier-island coast, southern North Sea. J

CE

Sediment Res 82: 385-399.

Swift D. J. P., Parker G., Lanfredi N. W., Perillo G., Figge K., 1978. Shoreface-

AC

connectedSand Ridges on American and European shelves: A comparison. Estuar Coast Mar Sci 7: 257–273.

Swift, D. J. P., Field, M. E., 1981a. Evolution of a classic sand ridge field: Maryland sector, North American inner shelf. Sedimentology 28: 461-482. Swift, D. J. P., Field, M. E., 1981b. Storm-built sand ridges on the Maryland inner shelf: a preliminary report. Geo-Mar Lett 1: 33-37. Trentesaux, A., Stolk, A., Tessier, B., Chamley, H., 1994. Surficial sedimentology of the Middelkerke Bank (southern North Sea). Mar Geol 121: 43-55. Trowbridge, J. H., 1995. A mechanism for the formation and maintenance of shore-oblique sand ridges on storm-dominated shelves. J Geophys Res 100 (C8), 16071-16086.

26

ACCEPTED MANUSCRIPT van de Meene, J. W. H., Boersma, J. R., Terwindt, J. H. J., 1996. Sedimentary structures of combined flow deposits from the shoreface-connected ridges along the central Dutch coast. Mar Geol 131: 151-175.

T

van de Meene, J. W. H., van Rijn, L. C., 2000. The shoreface-connected ridges along the

RI P

central Dutch coast- part 1: field observations. Continental Shelf Res 20: 2295-2323. van Hoey, G., Guilini, K., Rabaut, M., Vincx, M., Degraer, S., 2008. Ecological implications of

ecosystems. Mar Biol 154: 1009-1019.

SC

the presence of the tube-building polychaete Lanice conchilega on soft-bottom benthic

Vis-Star, N. C., de Swart, H. E., Calvete, D., 2009. Effect of wave–bedform feedbacks on the

MA NU

formation of, and grain sorting over shoreface-connected sand ridges. Ocean Dynam 59: 731-749.

Weber, A., van Dalfsen, J., Passchier, S., van der Spek, A., van Heteren, S., 2004. Ecomorphodynamics of the North Sea seafloor and macrobenthos zonation. Marine Sandwave and River Dune Dynamics (MARID2004): 308-313.

ED

Wentworth C. K., 1922. A scale of grade and class terms for clastic sediments. J Geol 30(5): 377-392.

PT

Wieking, G., Kröncke, I., 2005. Is benthic trophic structure affectes by food quality? The Dogger Bank example. Mar Biol 146: 387-400.

CE

Zeiler, M., Schwarzer, K., Ricklefs, K., 2008. Seabed Morphology and Sediment Dynamics.

AC

Die Küste 74: 31-44.

27

ACCEPTED MANUSCRIPT Highlights

T

An interdisciplinary analysis of macrofauna communities on shoreface-connected ridges is

RI P

presented.

SC

We used hydroacoustic methods in combination with macrofauna community studies.

MA NU

The results showed a shore-parallel sediment zonation induced by morphodynamics. Morphodynamics and bathymetry affected the formation of three different macrofauna affinity groups.

The slow migration of the shoreface-connected ridges allows the macrofauna communities to

AC

CE

PT

ED

migrate too.

28