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A field experimental study on recolonization and succession of macrobenthic infauna in defaunated sediment contaminated with petroleum hydrocarbons
Estuarine, Coastal and Shelf Science 68 (2006) 627e634 www.elsevier.com/locate/ecss
A field experimental study on recolonization and succession of macrobenthic infauna in defaunated sediment contaminated with petroleum hydrocarbons L. Lu a,*, R.S.S. Wu b b
a Fisheries and Oceans Canada, West Vancouver Laboratory, 4160 Marine Drive, West Vancouver, B.C. V7V 1N6, Canada Centre for Coastal Pollution and Conservation, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China
Received 23 December 2005; accepted 16 March 2006 Available online 11 May 2006
Abstract A field experiment was carried out in Hong Kong to study the patterns of recolonization and succession of subtidal macrobenthos in defaunated sediment contaminated with petroleum hydrocarbons and to determine the time required for benthic recovery from petroleum contamination. A total of 31 species was found and 83 animals/tray and 14 species/tray on an average were recorded after one month. Initial colonization was dominated by polychaetes in both abundance and species number (accounting for 69.1% and 64.5%, respectively). Abundance of macrobenthos came to a small crest (308 animals/tray) after three months, reached a sharp peak (1257 animals/tray) after six months, and then declined to a steady level. Abundance, species number and diversity in the petroleum-contaminated sediment were significantly lower than those in the control sediment in the early successional stages, indicating deleterious effects of petroleum hydrocarbons on recolonization and succession of macrobenthos. Petroleum hydrocarbons in sediment significantly altered species composition of macrobenthos in recolonization and succession. No significant differences in community parameters and species composition between the petroleum-contaminated and the control communities were found after 11 months, indicating that macrobenthic community had recovered from petroleum contamination. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: contamination; macrobenthos; recolonization; petroleum; soft-sediment; succession
1. Introduction Petroleum hydrocarbons are persistent in sediments. Crude oils have been shown to persist for several years without any sign of degradation (Rudling, 1976). Sanders et al. (1980) found effects of hydrocarbons on biota five years after the spill of No. 2 fuel oil. Persistence of toxic subsurface oil and chronic exposures on beaches had long-term risk and impacts, and continued to affect wildlife 12 years after the Exxon Valdez oil spill (Peterson et al., 2003; Short et al., 2004). It is, therefore, conceivable that petroleum hydrocarbons in
* Corresponding author. E-mail address: [email protected] (L. Lu). 0272-7714/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2006.03.011
sediment may exert harmful effects on macrobenthic recolonization and succession. Krebs and Burns (1978) found high levels of fuel oil (up to 6000 mg/kg) in sediment after a spill, and reported chronic toxicity on the crab Uca pugnax for up to seven years. Poulton et al. (1997) found that the overall macrobenthic diversity decreased during an 18-month study following a crude oil spill (petroleum hydrocarbons in sediment ¼ 80e270 mg/kg), and clearly demonstrated the persistent effect of oil on benthic community. Lenihan (1992) reported a dramatic change in benthic communities along a gradient of petroleum hydrocarbon contamination at McMurdo Station in Antarctica. In the same area, Lenihan et al. (1995) found high mortality of a benthic amphipod (Heterophoxus videns) at a polluted site (total petroleum hydrocarbons ¼ 4500 mg/kg) and a decrease in mortality along
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a decreasing pollution gradient. Gesteira and Dauvin (2000) found a very low colonization of amphipods during the four years after oil spills in Europe. Nance (1991) found that both the abundance and diversity of macrobenthic communities were lowest in petroleum hydrocarbon laden sediment at stations near the discharge site for oil/gas field produced water. The study of Jewett et al. (1996) in Alaska suggested a possible adverse impact of the Exxon Valdez oil spill on the benthic community. Olsgard and Gray (1995) found that contamination of oil-based drill-cuttings in Norway caused reduction in key components of the benthic communities, and the impact persisted several years after cessation of drill-cutting discharges. In an experimental study carried out in Norway, Berge (1990) found a lower density and species number of macrobenthos in defaunated sediment contaminated with crude oil. In contrast, however, the study of Kingston et al. (1995) showed no significant changes in benthic community structure following the wreck of the oil tanker Braer. Despite numerous studies on the effects of oil on benthic communities following accidental oil spills, few experiments on the effects of oil on the recovery of macrofauna have been conducted. Spies et al. (1988) compared the effects of kelp and crude oil in sediments on the colonization of benthic infauna in a subtidal experiment. Stark et al. (2003) studied the effects of oil and heavy metal contamination of sediments on recruitment of Antarctic benthic infauna in a field experiment. The study of Berge (1990) provided a long-term recovery with controls for comparison, and concluded that longer time scales than his 13-month experiment would be needed for the oilcontaminated communities to achieve conditions approaching those of the control. The effects of petroleum hydrocarbons on the recolonization and succession of macrobenthic communities, especially in tropical and sub-tropical regions, are poorly known. The aim of this study is to investigate the patterns of recolonization and succession of macrobenthic infauna in defaunated sediment contaminated with petroleum hydrocarbons, and determine the time required for benthic recovery from petroleum contamination.
2. Materials and methods 2.1. The study site A field experiment was carried out at Kat O (22 300 N, 114 200 E), a relatively un-contaminated site in the northeast of Hong Kong, from April 1996 to March 1997. The site is sheltered and the sea bottom is homogeneous in terms of sediment particle size (coarse-medium sand), organic content (w1.4%) and water depth (0.5 m Chart Datum). Temperature of bottom water at the study site ranged between 16.9 C in February 1997 and 29.3 C in July 1996; salinity between 25.8& in June 1996 and 35.0& in January 1997; and dissolved oxygen between 6.38 mg/L in October 1996 and 8.04 mg/L in February 1997.
2.2. Experimental design Sediment used in the experiment was collected from the subtidal level (0.5 m Chart Datum) of the study site, and air dried under sunlight for one month. Defaunated sediment was sampled and checked under a binocular dissecting microscope before use to make sure that there was no living animal. Defaunated sediment was contaminated with 5000 mg/kg diesel oil (dry wt.). Concentrations in this range have been shown to exert harmful effects on macrobenthos (Krebs and Burns, 1978; Hartwick et al., 1982; Berge, 1990; Nance, 1991; Lenihan et al., 1995). Defaunated sediment contaminated with petroleum hydrocarbons was put in labelled plastic trays (L: 33 cm, W: 25.5 cm, D: 11 cm, surface area: 0.084 m2), and placed randomly on top of the sediment at 0.5 m C.D. of the study site in April 1996. After deployment five trays were retrieved monthly from May to November 1996, and two trays were retrieved in March 1997. During each sampling, five trays of control sediment (without any added contaminants) and five replicate grabs of the surrounding sediment were also taken simultaneously for comparison (Lu and Wu, 2000). 2.3. Treatment of sediment samples Sediment in each tray was washed through a 0.5-mm sieve, and the residues retained on the sieve were preserved in a 10% formalin seawater solution. In the laboratory, benthic animals were sorted under a binocular dissecting microscope, identified to the lowest possible taxonomic levels and counted. 2.4. Data processing Dominant species in each sampling were identified by rankscore analysis (Fager, 1957). The 10 most abundant species were ranked, with the most abundant species receiving the highest numerical rank. Biological Index (BI) for each species was calculated by summing the values of each replicate for each sampling. Species diversity of each sample was calculated using ShannoneWiener’s index (H0 ) (Shannon and Weaver, 1963). Evenness of each sample was calculated using Pielou’s index (J ) (Pielou, 1966). Similarity between benthic samples was calculated, using the BrayeCurtis coefficient (Bray and Curtis, 1957). Data were transformed using fourth root before computing the coefficient. Non-metric multi-dimensional scaling (MDS) was used to investigate differences in community structure (Clarke and Warwick, 2001). Analysis of similarities (ANOSIM) was carried out to test differences in community composition between sample groups. ANOSIM was measured using the global test (R) (Clarke and Warwick, 2001). A oneway ANOVA was used to test differences in benthic parameters (abundance, species number, diversity and evenness) during the study period. A two-tailed t-test was used to test differences in benthic parameters between the petroleum-contaminated and the control sediments in each sampling.
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Evenness (J ) data were arcsin square root transformed prior to ANOVA in an attempt to normalize data (Zar, 1999).
5
629
H'
0.9
J
0.8
3. Results 3.1. Abundance and species number Initial colonization occurred quickly in the petroleumcontaminated sediment. After the first month of the experiment a total of 31 species was found, with an average of 83 animals/tray and 14 species/tray recorded. In terms of species and abundance the initial community was dominated by polychaetes (20 species, accounting for 64.5% of total number of species; 58 animals/tray, accounting for 69.1%). Gastropods were also abundant (14 animals/tray, accounting for 16.3%). Total abundance of the macrobenthic community increased gradually to a small crest (308 animals/tray) after three months, reached a sharp peak (1257 animals/tray) after six months, followed by a sharp decline and then stabilized (Fig. 1). The small crest was mainly attributed to the high abundance of Capitella capitata. The highest peak of abundance was mainly attributed to the establishment of the bivalves Spondervilia sp. and Musculus mirandus and the gastropod Gastropoda sp.3. Mortality of these three species caused the sharp decline in abundance. Species number increased gradually, peaked (49 species/tray) after six months and then leveled off (Fig. 1). Changes in abundance and species number over the succession were highly significant (one-way ANOVA, p < 0.0001). 3.2. Species diversity
Abundance
2000
60
Species number 1500 40
1000 20
500
0 Apr 96
Species number / tray
Abundance (animals / tray)
Species diversity (H0 ) and evenness (J ) showed a similar pattern during the experiment (Fig. 2). Both indices increased and peaked after seven months, i.e., in November 1996. Low values of both indices were recorded in July and October conforming to the patterns of abundance. Changes of the two indices with succession were highly significant (one-way ANOVA, p < 0.01).
0
May
Jun
Jul
Aug
Sep
Oct
Nov 96
Mar 97
Fig. 1. Mean abundance and species number of macrobenthic community in the defaunated sediment contaminated with petroleum hydrocarbons during the study period (mean SE).
0.7 0.6
3
0.5 0.4
2
0.3
Evenness (J)
Diversity (H')
4
0.2
1
0.1 0.0
0 Apr 96
May
Jun
Jul
Aug
Sep
Oct
Nov 96
Mar 97
Fig. 2. Mean values of species diversity (H0 ) and evenness (J ) of macrobenthic community in the defaunated sediment contaminated with petroleum hydrocarbons during the study period (mean SE).
3.3. Species composition A total of 141 species, including 59 species of polychaetes, 27 species of gastropods, 25 species of bivalves, six species of decapods, four species of amphipods, three species each of turbellarians and nemerteans, two species each of actinians, sipunculids, and isopods, and one species each of scaphopod, cumacean, insect, phoronid, echinoid, ophiuroid, brachiopod, and amphioxus was recorded during the experimental period. The polychaete Platynereis bicanaliculata, the Gastropod Euplica sp. and the crab Portunus argentatus were recorded only in the first month. The top five dominant species in the petroleum-contaminated sediment in each month, as identified by the Biological Index (BI), are shown in Table 1. The dominant species and their ranks changed every month with succession. The small polychaetes Capitella capitata and Pionosyllis sp. were most abundant in the first four months. Changes in abundance of the 12 most dominant species in the petroleum-contaminated sediment were compared with those in the control sediment during the study period (Fig. 3). Different species showed different successional patterns and peaked in different months. Five species, i.e., the polychaete C. capitata, the bivalves Spondervilia sp. and Musculus mirandus, and the gastropods Gastropoda sp.1 and sp.3, appeared to be opportunistic species in the petroleumcontaminated sediments. Spondervilia sp., the most abundant species recorded in the experiment, reached a peak (579 animals/grab) in October 1996 and then declined sharply. MDS ordination of replicate samples clearly demonstrated the changes in community structure over the experimental period (Fig. 4). The points move from the right to the left with decreasing distances between groups, showing the increasing similarity of the community structure over time of succession. 3.4. Comparison with the control community The abundance of macrobenthic infauna in the petroleumcontaminated sediment was significantly lower than that in the control sediment in May, July, September and November 1996. Species number was significantly lower in the petroleum-contaminated sediment for the first seven months.
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Table 1 The top five dominant species in petroleum-contaminated sediment and control sediment during the study period Petroleum-contaminated sediment Species
Control sediment Cumulative % by no.
Species
% by no.
Cumulative % by no.
30.7 19.4 16.1 10.6 6.9
30.7 50.1 66.2 76.8 83.7
May 1996 Chironomidae sp. Gastropoda sp.1 Spio filicornis Corophium sp. Pionosyllis sp.
40.0 19.4 7.9 6.0 5.0
40.0 59.4 67.3 73.3 78.3
June 1996 Capitella capitata Pionosyllis sp. Caulleriella bioculata Musculus mirandus Clypeomorus sp.
37.7 22.3 6.1 3.0 2.1
37.7 60.0 66.1 69.1 71.2
June 1996 Pionosyllis sp. Musculus mirandus Capitella capitata Prionospio malmgreni Caulleriella bioculata
21.4 7.9 6.9 6.0 5.1
21.4 29.3 36.2 42.2 47.3
July 1996 Capitella capitata Pionosyllis sp. Prionospio malmgreni Musculus mirandus Caulleriella bioculata
65.0 7.7 4.3 3.9 3.1
65.0 72.7 77.0 80.9 84.0
July 1996 Caulleriella bioculata Pionosyllis sp. Musculus mirandus Prionospio malmgreni Bivalvia sp.1
18.3 14.8 14.4 10.0 3.9
18.3 33.1 47.5 57.5 61.4
August 1996 Capitella capitata Pionosyllis sp. Gastropoda sp.3 Prionospio malmgreni Neanthes caudata
46.4 12.3 5.3 4.7 2.5
46.4 58.7 64.0 68.7 71.2
August 1996 Pionosyllis sp. Caulleriella bioculata Prionospio malmgreni Poecilochaetus serpens Branchiostoma belcheri
17.3 11.4 6.5 4.4 4.2
17.3 28.7 35.2 39.6 43.8
September 1996 Clypeomorus sp. Capitella capitata Prionospio malmgreni Linopherus hirsuta Pionosyllis sp.
21.6 12.0 9.5 3.9 3.8
21.6 33.6 43.1 47.0 50.8
September 1996 Aonides oxycephala Prionospio malmgreni Psammobia radiata Spondervilia sp. Capitella capitata
15.9 13.5 3.6 3.5 2.9
15.9 29.4 33.0 36.5 39.4
October 1996 Spondervilia sp. Musculus mirandus Gastropoda sp.3 Clypeomorus sp. Prionospio malmgreni
46.0 14.9 10.3 7.2 2.4
46.0 60.9 71.2 78.4 70.8
October 1996 Spondervilia sp. Gastropoda sp.3 Clypeomorus sp. Aonides oxycephala Musculus mirandus
38.3 12.0 10.1 5.8 4.0
38.3 40.3 50.4 56.2 60.2
November 1996 Aonides oxycephala Linopherus hirsuta Epicodakia delicatula Clypeomorus sp. Prionospio malmgreni
15.2 11.0 10.8 6.2 5.6
15.2 26.2 37.0 43.2 48.8
November 1996 Clypeomorus sp. Aonides oxycephala Spondervilia sp. Prionospio malmgreni Paguridae sp.
10.8 10.5 10.5 8.0 6.6
10.8 21.3 31.8 39.8 46.4
March 1997 Pionosyllis sp. Aonides oxycephala Prionospio malmgreni Clypeomorus sp. Epicodakia delicatula
27.7 10.6 8.5 6.5 6.5
27.7 38.3 46.8 53.3 59.8
March 1997 Pionosyllis sp. Dexaminidae sp. Aonides oxycephala Epicodakia delicatula Capitella capitata
30.4 13.2 12.7 5.0 3.6
30.4 43.6 56.3 61.3 64.9
May 1996 Capitella capitata Pionosyllis sp. Gastropoda sp.1 Chironomidae sp. Spio filicornis
% by no.
Species diversity (H0 ) and evenness (J ) were significantly lower in the petroleum-contaminated sediment in Junee August 1996 (Fig. 5). Overall, no significant differences in community parameters were found between the petroleumcontaminated and the control sediments after 11 months. The top five dominant species following initial colonization in the petroleum-contaminated sediment were quite different
from those in the control sediment (Table 1). The insect Chironomidae sp. was the most dominant species in the control sediment, while the polychaete Capitella capitata, which was found in low abundance in the control sediment (Fig. 3), predominated in the petroleum-contaminated sediment. The most dominant species were different in the petroleum-contaminated and the control sediments for the first
Petroleum Control
50
25
0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 96 97
50 0 Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Musculus mirandus 300 Petroleum Control 200
100
0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 96 97
175 150
Petroleum Control
125 100 75 50 25 0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 97 96
Epicodakia delicatula 60
Petroleum Control
40
20
0
Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Pionosyllis sp. 200
Petroleum Control
150 100 50 0 Apr 96
May Jun
Jul
Aug Sep
Abundance (animals / tray)
100
Abundance (animals / tray)
150
Abundance (animals / tray)
Abundance (animals / tray) Abundance (animals / tray)
Petroleum Control
75 50 25 0
Apr May Jun
Jul
Aug Sep Oct Nov Mar 96 97
Spondervilia sp.
Petroleum Control
Abundance (animals / tray)
200
631
Caulleriella bioculata 100
Capitella capitata 250
Clypeomorus sp.
Abundance (animals / tray)
Abundance (animals / tray)
Gastropoda sp.1 75
Abundance (animals / tray)
Abundance (animals / tray)
Abundance (animals / tray)
Abundance (animals / tray)
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Oct
Nov Mar 96 97
900
Petroleum Control
600
300
0 Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Gastropoda sp.3 200
Petroleum Control
150 100 50 0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 96 97
Linopherus hirsuta 65 60 55 50 45 40 35 30 25 20 15 10 5 0
Petroleum Control
Apr May Jun 96
Jul
Aug Sep Oct Nov Mar 96 97
Aonides oxycephala 100
Petroleum Control
75 50 25 0 Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Prionospio malmgreni 75
Petroleum Control
50
25
0 Apr May Jun 96
Jul
Aug Sep Oct Nov Mar 96 97
Fig. 3. Mean abundance of 12 dominant species in the petroleum-contaminated sediment and those species in the control sediment during the study period (mean SE).
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632
1 5 5 55 77 8 7 7 6 6 66 6
1
5
8 7
2
3 3 33 3 4 44 2 4 4
1 1
2
2 2
1
Fig. 4. MDS ordination of macrobenthic samples (stress ¼ 0.11), showing changes in community structure of macrobenthos in the defaunated sediment contaminated with petroleum hydrocarbons during the study period (1 ¼ May 1996, 2 ¼ June 1996, 3 ¼ July 1996, 4 ¼ August 1996, 5 ¼ September 1996, 6 ¼ October 1996, 7 ¼ November 1996, 8 ¼ March 1997).
five months. The abundance of some dominant species, e.g. C. capitata, Caulleriella bioculata, Musculus mirandus and Linopherus hirsuta, generally showed different patterns in the petroleum-contaminated and the control sediments. Other species, e.g. Spondervilia sp., Gastropoda sp.3, Clypeomorus sp. and Pionosyllis sp., exhibited similar patterns in both sediments. The abundance of C. capitata was much higher in the petroleum-contaminated sediment than in the control sediment from June to August 1996, while the abundance of C. bioculata was much lower in the petroleumcontaminated sediment in July and August 1996. Aonides oxycephala in the petroleum-contaminated sediment appeared two months later during succession and its abundance was significantly lower before November 1996. Results of one-way ANOSIM test for macrobenthic samples between the petroleum-contaminated and the control communities are shown in Fig. 6. Global R decreased generally during the experiment and no significant difference in community composition was found in March 1997. 4. Discussion Petroleum hydrocarbons are known to be toxic to benthos. Inhibition of settlement of barnacle larvae by crude oil was observed in the intertidal zone of a Norwegian fjord (Nelson, 1981). Nelson (1982) suggested that the most serious potential impact of an oil spillage is the disruption of settlement and growth among juveniles in rocky intertidal communities. Poulton et al. (1997) reported a decrease in overall macrobenthic diversity after a spill of crude oil. Lu (2005) found strongly negative correlations between community parameters
(abundance, species number and diversity) of macrobenthos and the concentrations of total petroleum hydrocarbons in sediments of Singapore waters. Petroleum hydrocarbons may also modify the physical properties of sediment, thereby, influencing recolonization of macrobenthos (Berge, 1990). Organic enrichment of sediment by petroleum hydrocarbons may enhance the development of macrobenthic infauna due to an increase in food supply upon degradation. In Norway, Berge et al. (1987) found that 33% of the originally added crude oil (18 000 mg/kg dry wt.) remained in the sediment after 13 months of exposure, and results of oil biodegradation resembled the effects of eutrophication. Concentration of petroleum hydrocarbons in contaminated sediments decreased from 682 mg/kg to 244 mg/kg (dry wt.) after 20 days of field exposure and stabilized afterwards at the same study site in Hong Kong (Lam and Zhang, unpublished data). An organic enrichment effect (high individual abundance of a few species) was recorded at a site close to the source of oil contamination in the North Sea (Kingston, 1992). Jewett et al. (1999) recorded higher abundance of most families at oiled sites in Prince William Sound, Alaska, USA, 16 months after the Exxon Valdez oil spill. Spies et al. (1988) found that the responses of macrofauna to crude oil in sediments were similar to those expected from other sources of organic matter (e.g. kelp) in a field experiment. In this study, initial colonization and subsequent succession of macrobenthic community were retarded in sediments contaminated with petroleum hydrocarbons, resulting in significant reductions in abundance and species number, as well as changes in species composition and community structure. The polychaete Capitella capitata is well known as a ubiquitous opportunistic species and an initial colonizer of disturbed marine sediment (Grassle and Grassle, 1974; McCall, 1977; Pearson and Rosenberg, 1978; Zajac and Whitlatch, 1982a,b; Whitlatch and Zajac, 1985; Diaz-Castaneda et al., 1989). In the present study, this species was only recorded in low abundance in the control sediments in the early months of colonization. Capitella capitata was, however, most abundant and, therefore, predominated during the first four months in the petroleum-contaminated sediments, showing the typical characteristics of an opportunistic species during succession. The result clearly indicates that C. capitata is more tolerant than other species to petroleum hydrocarbons and/or hydrogen sulfide in sediment. Organic enrichment caused by petroleum hydrocarbons may also enhance the development of this species after degradation of hydrocarbons because of an increase in organic food supply. Opportunists are often poor competitors (McCall, 1977) and are replaced by other species at a later stage after they have prepared the sediment, making it more suitable for other species to settle upon (Pearson and Rosenberg, 1978; Arntz and Rumohr, 1982). In this study, the dominance of Capitella capitata ended after severe mortality and subsequent replacement by molluscs, e.g., Clypeomorus sp. and Spondervilia sp. The sharp decline of the C. capitata population may result from interspecific competition, intraspecific depletion of
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Species number
Abundance
Control
Control Petroleum 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0
4
M ar 97
96
6 N
ov
ct 9
96
Evenness Control Petroleum
Control Petroleum
0.9
***
** **
O
96
Se p
Au g
96
96
Ju l
ay
Ju n
96
**
Species diversity
5
***
**
*** * ** ***
M
ov N
M ar 97
6
96
O
Se p
96
6
Au g
l9
96
Ju
Ju n
M ay
96
*
**
Petroleum
Species / tray
*
**
ct 9
1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0
96
Animals / tray
633
**
0.8
**
**
0.7 0.6
J/ tray
H'/ tray
3 2
0.5 0.4 0.3 0.2
1
0.1 0
M ar 97
N
ov
96
96 ct
96 O
96 g
Se p
l9
6 Au
Ju
n
96
96 ay
Ju
N
M
ov
ct O
M ar 97
96
96
96 p
96 Se
g Au
Ju
Ju
l9
96 n
96 ay M
6
0.0
Fig. 5. Comparison of mean values in abundance, number of species, species diversity and evenness between the petroleum-contaminated and the control communities during the study period (mean SE). Asterisks denote significant difference as identified by t-tests (*p < 0.05, **p < 0.01, ***p < 0.001).
food resources or accumulation of toxic substances (Grassle and Grassle, 1974; McCall, 1977). The study of Berge (1990), in Norway, indicated that longer periods (beyond his 13-month experiment) would be needed for macrobenthic communities in sediment contaminated with 4520 mg/kg (wet wt.) of crude oil to achieve conditions approaching those of controls. Olsgard and Gray (1995) found that benthic fauna was still affected several years after the
**
1.00
Global R
0.75
** **
**
**
**
**
0.50
cessation of oil-based drill-cutting discharges. In the present experiment, however, complete recovery was found in the petroleum-contaminated sediments after 11 months, as indicated by abundance, species number, diversity and evenness, as well as community composition. A macrobenthic community in equilibrium was also reached after 11 months in the present study, as indicated by successional patterns of benthic parameters. Nevertheless, recolonization can be scale-dependent (Thrush et al., 1996), and the recovery rate of macrobenthic infauna may be quite different in an event of real diesel spill. It should be noted that the persistence and toxicity of oil in marine sediments may rely on factors such as the time and degree of mixing, the hydrodynamic conditions, the porosity of the sediments, the geochemical conditions in the pore water, the turbulence by faunal and physical processes, and the presence of oil-degrading bacteria.
0.25
Acknowledgments ar 97 M
96 ov N
O
ct
96
96 Se p
96 g Au
l9 6 Ju
96 n Ju
M
ay
96
0.00
Fig. 6. Results of one-way ANOSIM test for macrobenthic samples between the petroleum-contaminated and the control communities during the study period (**p < 0.01).
This study was supported by a research grant (No. 9040187) from the Research Grants Council, Hong Kong SAR, China. The authors would like to thank the Agriculture and Fisheries Department of the Hong Kong SAR for their technical support in this project.
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References Arntz, W.E., Rumohr, H., 1982. An experimental study of macrobenthic colonization and succession, and the importance of seasonal variation in temperate latitude. Journal of Experimental Marine Biology and Ecology 64, 17e45. Berge, J.A., 1990. Macrofauna recolonization of subtidal sediments. Experimental studies on defaunated sediment contaminated with crude oil in two Norwegian fjords with unequal eutrophication status. I. Community response. Marine Ecology Progress Series 66, 103e116. Berge, J.A., Lichtenthaler, R.G., Oreld, F., 1987. Hydrocarbon depuration and abiotic changes in artificially oil contaminated sediment in the subtidal. Estuarine, Coastal and Shelf Science 24, 567e583. Bray, J.R., Curtis, J.T., 1957. An ordination of upland forest community of Southern Wisconsin. Ecological Monograph 27, 325e349. Clarke, K.B., Warwick, R.M., 2001. Changes in marine communities: an approach to statistical analysis and interpretation, second ed. PRIMER-E, Plymouth, UK, 177 pp. Diaz-Castaneda, V., Richard, A., Frontier, S., 1989. Preliminary results on colonization, recovery and succession in a polluted area of the south North Sea (Dunkerque’s Harbour, France). In: Ros, J.D. (Ed.), Topics in Marine Biology. Scientia Marina 53, 705e716. Fager, E.W., 1957. Determination and analysis of recurrent groups. Ecology 38, 586e595. Gesteira, J.L.G., Dauvin, J.C., 2000. Amphipods are good bioindicators of the impact of oil spills on soft-bottom macrobenthic communities. Marine Pollution Bulletin 40, 1017e1027. Grassle, J.F., Grassle, J.P., 1974. Opportunistic life histories and genetic systems in marine benthic polychaetes. Journal of Marine Research 32, 253e284. Hartwick, E.B., Wu, R.S.S., Parker, D.B., 1982. Effects of a crude oil and an oil dispersant (Corexit 9527) on population of the littleneck clam (Protothaca staminea). Marine Environmental Research 6, 291e306. Jewett, S.C., Dean, T.A., Laur, D.R., 1996. Effects of the Exxon Valdez oil spill on benthic invertebrates in an oxygen-deficient embayment in Prince William Sound, Alaska. In: Rice, S.D., Spies, R.B., Wolfe, D.A., Wright, B.A. (Eds.), Proceedings of the Exxon Valdez Oil Spill Symposium. American Fisheries Society, Bethesda, MD, pp. 440e447. Jewett, S.C., Dean, T.A., Smith, R.O., Blanchard, A., 1999. Exxon Valdez oil spill: impacts and recovery in the soft-bottom benthic community in and adjacent to eelgrass beds. Marine Ecology Progress Series 185, 59e83. Kingston, P.F., 1992. Impact of offshore oil production installations on the benthos of the North Sea. ICES Journal of Marine Science 49, 45e53. Kingston, P.F., Dixon, I.M.T., Hamilton, S., Moore, D.C., 1995. The impact of the Braer oil spill on the macrobenthic infauna of the sediments off the Shetland Islands. Marine Pollution Bulletin 30, 445e459. Krebs, C.T., Burns, K.A., 1978. Long-term effects of an oil spill on populations of the salt-marsh crab Uca pugnax. Journal of the Fisheries Research Board of Canada 35, 648e649. Lenihan, H.S., 1992. Benthic marine pollution around McMurdo Station, Antarctica: a summary of findings. Marine Pollution Bulletin 25, 318e323. Lenihan, H.S., Kiest, K.A., Conlan, K.E., Slattery, P.N., Konar, B.H., Oliver, J.S., 1995. Patterns of survival and behaviour in Antarctic benthic invertebrates exposed to contaminated sediment: field and laboratory bioassay experiments. Journal of Experimental Marine Biology and Ecology 192, 233e255. Lu, L., 2005. Relationship between soft-bottom macrobenthic communities and environmental variables in Singaporean waters. Marine Pollution Bulletin 51, 1034e1040.
Lu, L., Wu, R.S.S., 2000. An experimental study on recolonization and succession of marine macrobenthos in defaunated sediment. Marine Biology 136, 291e302. McCall, P.L., 1977. Community patterns and adaptive strategies of the infaunal benthos of Long Island Sound. Journal of Marine Research 35, 221e266. Nance, J.M., 1991. Effects of oil/gas field produced water on the macrobenthic community in a small gradient estuary. Hydrobiologia 220, 189e204. Nelson, W.G., 1981. Inhibition of barnacle settlement by Ekofisk crude oil. Marine Ecology Progress Series 5, 41e43. Nelson, W.G., 1982. Experimental studies of oil pollution on the rocky intertidal community of a Norwegian fjord. Journal of Experimental Marine Biology and Ecology 65, 121e138. Olsgard, F., Gray, J.S., 1995. A comprehensive analysis of the effects of offshore oil and gas exploration and production on the benthic communities of the Norwegian continental shelf. Marine Ecology Progress Series 122, 277e306. Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanography and Marine Biology: An Annual Review 16, 229e311. Peterson, C.H., Rice, S.D., Short, J.W., Esler, D., Bodkin, J.L., Ballachey, B.E., Irons, D.B., 2003. Long-tern ecosystem response to the Exxon Valdez oil spill. Science (Washington DC) 302, 2082e2086. Pielou, E.C., 1966. Shannon’s formula as a measure of species diversity: its use and misuse. American Naturalist 100, 463e465. Poulton, B.C., Finger, S.E., Humphrey, S.A., 1997. Effects of a crude oil spill on the benthic invertebrate community in the Gasconade River, Missouri. Archives of Environmental Contamination and Toxicology 33, 268e276. Rudling, L., 1976. Oil Pollution in the Baltic Sea. A Chemical Analytical Search for Monitoring Methods, SNV PM 783. National Swedish Environmental Protection Board, pp. 1e80. Sanders, H.L., Grassle, J.F., Hampson, G.R., Morse, L.S., Garner-Price, S., Jones, C.C., 1980. Anatomy of an oil spill long-term effects from the grounding of the barge Florida off West Falmouth, Massachusetts, USA. Journal of Marine Research 38, 265e380. Shannon, C.E., Weaver, W., 1963. The Mathematical Theory of Communication. University of Illinois Press, Urbana, Illinois, 125 pp. Short, J.W., Lindeberg, M.R., Harris, P.M., Maselko, J.P., Pella, J.J., Rice, S.D., 2004. Estimate of oil persisting on the beaches of Prince William Sound 12 years after the Exxon Valdez oil spill. Environmental Science and Technology 38, 19e25. Spies, R.B., Hardin, D.D., Toal, J.P., 1988. Organic enrichment or toxicity? A comparison of the effects of kelp and crude oil in sediments on the colonization and growth of benthic infauna. Journal of Experimental Marine Biology and Ecology 124, 261e282. Stark, J.S., Snape, I., Riddle, M.J., 2003. The effects of petroleum hydrocarbon and heavy metal contamination of marine sediments on recruitment of Antarctic soft-sediment assemblages: a field experimental investigation. Journal of Experimental Marine Biology and Ecology 283, 21e50. Thrush, S.F., Whitlatch, R.B., Pridmore, R.D., Hewitt, J.E., Cummings, V.J., Wilkinson, M.R., 1996. Scale-dependent recolonization: the role of sediment stability in a dynamic sandflat habitat. Ecology 77, 2472e2487. Whitlatch, R.B., Zajac, R.N., 1985. Biotic interaction among estuarine infaunal opportunistic species. Marine Ecology Progress Series 21, 299e311. Zajac, R.N., Whitlatch, R.B., 1982a. Responses of estuarine infauna to disturbance. I. Spatial and temporal variation of initial recolonization. Marine Ecology Progress Series 10, 1e14. Zajac, R.N., Whitlatch, R.B., 1982b. Responses of estuarine infauna to disturbance. II. Spatial and temporal variation of succession. Marine Ecology Progress Series 10, 15e27. Zar, J.H., 1999. Biostatistical Analysis, fourth ed. Prentice-Hall, Upper Saddle River, New Jersey, 123 pp.
A field experimental study on recolonization and succession of macrobenthic infauna in defaunated sediment contaminated with petroleum hydrocarbons L. Lu a,*, R.S.S. Wu b b
a Fisheries and Oceans Canada, West Vancouver Laboratory, 4160 Marine Drive, West Vancouver, B.C. V7V 1N6, Canada Centre for Coastal Pollution and Conservation, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon, Hong Kong SAR, China
Received 23 December 2005; accepted 16 March 2006 Available online 11 May 2006
Abstract A field experiment was carried out in Hong Kong to study the patterns of recolonization and succession of subtidal macrobenthos in defaunated sediment contaminated with petroleum hydrocarbons and to determine the time required for benthic recovery from petroleum contamination. A total of 31 species was found and 83 animals/tray and 14 species/tray on an average were recorded after one month. Initial colonization was dominated by polychaetes in both abundance and species number (accounting for 69.1% and 64.5%, respectively). Abundance of macrobenthos came to a small crest (308 animals/tray) after three months, reached a sharp peak (1257 animals/tray) after six months, and then declined to a steady level. Abundance, species number and diversity in the petroleum-contaminated sediment were significantly lower than those in the control sediment in the early successional stages, indicating deleterious effects of petroleum hydrocarbons on recolonization and succession of macrobenthos. Petroleum hydrocarbons in sediment significantly altered species composition of macrobenthos in recolonization and succession. No significant differences in community parameters and species composition between the petroleum-contaminated and the control communities were found after 11 months, indicating that macrobenthic community had recovered from petroleum contamination. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: contamination; macrobenthos; recolonization; petroleum; soft-sediment; succession
1. Introduction Petroleum hydrocarbons are persistent in sediments. Crude oils have been shown to persist for several years without any sign of degradation (Rudling, 1976). Sanders et al. (1980) found effects of hydrocarbons on biota five years after the spill of No. 2 fuel oil. Persistence of toxic subsurface oil and chronic exposures on beaches had long-term risk and impacts, and continued to affect wildlife 12 years after the Exxon Valdez oil spill (Peterson et al., 2003; Short et al., 2004). It is, therefore, conceivable that petroleum hydrocarbons in
* Corresponding author. E-mail address: [email protected] (L. Lu). 0272-7714/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.ecss.2006.03.011
sediment may exert harmful effects on macrobenthic recolonization and succession. Krebs and Burns (1978) found high levels of fuel oil (up to 6000 mg/kg) in sediment after a spill, and reported chronic toxicity on the crab Uca pugnax for up to seven years. Poulton et al. (1997) found that the overall macrobenthic diversity decreased during an 18-month study following a crude oil spill (petroleum hydrocarbons in sediment ¼ 80e270 mg/kg), and clearly demonstrated the persistent effect of oil on benthic community. Lenihan (1992) reported a dramatic change in benthic communities along a gradient of petroleum hydrocarbon contamination at McMurdo Station in Antarctica. In the same area, Lenihan et al. (1995) found high mortality of a benthic amphipod (Heterophoxus videns) at a polluted site (total petroleum hydrocarbons ¼ 4500 mg/kg) and a decrease in mortality along
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a decreasing pollution gradient. Gesteira and Dauvin (2000) found a very low colonization of amphipods during the four years after oil spills in Europe. Nance (1991) found that both the abundance and diversity of macrobenthic communities were lowest in petroleum hydrocarbon laden sediment at stations near the discharge site for oil/gas field produced water. The study of Jewett et al. (1996) in Alaska suggested a possible adverse impact of the Exxon Valdez oil spill on the benthic community. Olsgard and Gray (1995) found that contamination of oil-based drill-cuttings in Norway caused reduction in key components of the benthic communities, and the impact persisted several years after cessation of drill-cutting discharges. In an experimental study carried out in Norway, Berge (1990) found a lower density and species number of macrobenthos in defaunated sediment contaminated with crude oil. In contrast, however, the study of Kingston et al. (1995) showed no significant changes in benthic community structure following the wreck of the oil tanker Braer. Despite numerous studies on the effects of oil on benthic communities following accidental oil spills, few experiments on the effects of oil on the recovery of macrofauna have been conducted. Spies et al. (1988) compared the effects of kelp and crude oil in sediments on the colonization of benthic infauna in a subtidal experiment. Stark et al. (2003) studied the effects of oil and heavy metal contamination of sediments on recruitment of Antarctic benthic infauna in a field experiment. The study of Berge (1990) provided a long-term recovery with controls for comparison, and concluded that longer time scales than his 13-month experiment would be needed for the oilcontaminated communities to achieve conditions approaching those of the control. The effects of petroleum hydrocarbons on the recolonization and succession of macrobenthic communities, especially in tropical and sub-tropical regions, are poorly known. The aim of this study is to investigate the patterns of recolonization and succession of macrobenthic infauna in defaunated sediment contaminated with petroleum hydrocarbons, and determine the time required for benthic recovery from petroleum contamination.
2. Materials and methods 2.1. The study site A field experiment was carried out at Kat O (22 300 N, 114 200 E), a relatively un-contaminated site in the northeast of Hong Kong, from April 1996 to March 1997. The site is sheltered and the sea bottom is homogeneous in terms of sediment particle size (coarse-medium sand), organic content (w1.4%) and water depth (0.5 m Chart Datum). Temperature of bottom water at the study site ranged between 16.9 C in February 1997 and 29.3 C in July 1996; salinity between 25.8& in June 1996 and 35.0& in January 1997; and dissolved oxygen between 6.38 mg/L in October 1996 and 8.04 mg/L in February 1997.
2.2. Experimental design Sediment used in the experiment was collected from the subtidal level (0.5 m Chart Datum) of the study site, and air dried under sunlight for one month. Defaunated sediment was sampled and checked under a binocular dissecting microscope before use to make sure that there was no living animal. Defaunated sediment was contaminated with 5000 mg/kg diesel oil (dry wt.). Concentrations in this range have been shown to exert harmful effects on macrobenthos (Krebs and Burns, 1978; Hartwick et al., 1982; Berge, 1990; Nance, 1991; Lenihan et al., 1995). Defaunated sediment contaminated with petroleum hydrocarbons was put in labelled plastic trays (L: 33 cm, W: 25.5 cm, D: 11 cm, surface area: 0.084 m2), and placed randomly on top of the sediment at 0.5 m C.D. of the study site in April 1996. After deployment five trays were retrieved monthly from May to November 1996, and two trays were retrieved in March 1997. During each sampling, five trays of control sediment (without any added contaminants) and five replicate grabs of the surrounding sediment were also taken simultaneously for comparison (Lu and Wu, 2000). 2.3. Treatment of sediment samples Sediment in each tray was washed through a 0.5-mm sieve, and the residues retained on the sieve were preserved in a 10% formalin seawater solution. In the laboratory, benthic animals were sorted under a binocular dissecting microscope, identified to the lowest possible taxonomic levels and counted. 2.4. Data processing Dominant species in each sampling were identified by rankscore analysis (Fager, 1957). The 10 most abundant species were ranked, with the most abundant species receiving the highest numerical rank. Biological Index (BI) for each species was calculated by summing the values of each replicate for each sampling. Species diversity of each sample was calculated using ShannoneWiener’s index (H0 ) (Shannon and Weaver, 1963). Evenness of each sample was calculated using Pielou’s index (J ) (Pielou, 1966). Similarity between benthic samples was calculated, using the BrayeCurtis coefficient (Bray and Curtis, 1957). Data were transformed using fourth root before computing the coefficient. Non-metric multi-dimensional scaling (MDS) was used to investigate differences in community structure (Clarke and Warwick, 2001). Analysis of similarities (ANOSIM) was carried out to test differences in community composition between sample groups. ANOSIM was measured using the global test (R) (Clarke and Warwick, 2001). A oneway ANOVA was used to test differences in benthic parameters (abundance, species number, diversity and evenness) during the study period. A two-tailed t-test was used to test differences in benthic parameters between the petroleum-contaminated and the control sediments in each sampling.
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Evenness (J ) data were arcsin square root transformed prior to ANOVA in an attempt to normalize data (Zar, 1999).
5
629
H'
0.9
J
0.8
3. Results 3.1. Abundance and species number Initial colonization occurred quickly in the petroleumcontaminated sediment. After the first month of the experiment a total of 31 species was found, with an average of 83 animals/tray and 14 species/tray recorded. In terms of species and abundance the initial community was dominated by polychaetes (20 species, accounting for 64.5% of total number of species; 58 animals/tray, accounting for 69.1%). Gastropods were also abundant (14 animals/tray, accounting for 16.3%). Total abundance of the macrobenthic community increased gradually to a small crest (308 animals/tray) after three months, reached a sharp peak (1257 animals/tray) after six months, followed by a sharp decline and then stabilized (Fig. 1). The small crest was mainly attributed to the high abundance of Capitella capitata. The highest peak of abundance was mainly attributed to the establishment of the bivalves Spondervilia sp. and Musculus mirandus and the gastropod Gastropoda sp.3. Mortality of these three species caused the sharp decline in abundance. Species number increased gradually, peaked (49 species/tray) after six months and then leveled off (Fig. 1). Changes in abundance and species number over the succession were highly significant (one-way ANOVA, p < 0.0001). 3.2. Species diversity
Abundance
2000
60
Species number 1500 40
1000 20
500
0 Apr 96
Species number / tray
Abundance (animals / tray)
Species diversity (H0 ) and evenness (J ) showed a similar pattern during the experiment (Fig. 2). Both indices increased and peaked after seven months, i.e., in November 1996. Low values of both indices were recorded in July and October conforming to the patterns of abundance. Changes of the two indices with succession were highly significant (one-way ANOVA, p < 0.01).
0
May
Jun
Jul
Aug
Sep
Oct
Nov 96
Mar 97
Fig. 1. Mean abundance and species number of macrobenthic community in the defaunated sediment contaminated with petroleum hydrocarbons during the study period (mean SE).
0.7 0.6
3
0.5 0.4
2
0.3
Evenness (J)
Diversity (H')
4
0.2
1
0.1 0.0
0 Apr 96
May
Jun
Jul
Aug
Sep
Oct
Nov 96
Mar 97
Fig. 2. Mean values of species diversity (H0 ) and evenness (J ) of macrobenthic community in the defaunated sediment contaminated with petroleum hydrocarbons during the study period (mean SE).
3.3. Species composition A total of 141 species, including 59 species of polychaetes, 27 species of gastropods, 25 species of bivalves, six species of decapods, four species of amphipods, three species each of turbellarians and nemerteans, two species each of actinians, sipunculids, and isopods, and one species each of scaphopod, cumacean, insect, phoronid, echinoid, ophiuroid, brachiopod, and amphioxus was recorded during the experimental period. The polychaete Platynereis bicanaliculata, the Gastropod Euplica sp. and the crab Portunus argentatus were recorded only in the first month. The top five dominant species in the petroleum-contaminated sediment in each month, as identified by the Biological Index (BI), are shown in Table 1. The dominant species and their ranks changed every month with succession. The small polychaetes Capitella capitata and Pionosyllis sp. were most abundant in the first four months. Changes in abundance of the 12 most dominant species in the petroleum-contaminated sediment were compared with those in the control sediment during the study period (Fig. 3). Different species showed different successional patterns and peaked in different months. Five species, i.e., the polychaete C. capitata, the bivalves Spondervilia sp. and Musculus mirandus, and the gastropods Gastropoda sp.1 and sp.3, appeared to be opportunistic species in the petroleumcontaminated sediments. Spondervilia sp., the most abundant species recorded in the experiment, reached a peak (579 animals/grab) in October 1996 and then declined sharply. MDS ordination of replicate samples clearly demonstrated the changes in community structure over the experimental period (Fig. 4). The points move from the right to the left with decreasing distances between groups, showing the increasing similarity of the community structure over time of succession. 3.4. Comparison with the control community The abundance of macrobenthic infauna in the petroleumcontaminated sediment was significantly lower than that in the control sediment in May, July, September and November 1996. Species number was significantly lower in the petroleum-contaminated sediment for the first seven months.
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Table 1 The top five dominant species in petroleum-contaminated sediment and control sediment during the study period Petroleum-contaminated sediment Species
Control sediment Cumulative % by no.
Species
% by no.
Cumulative % by no.
30.7 19.4 16.1 10.6 6.9
30.7 50.1 66.2 76.8 83.7
May 1996 Chironomidae sp. Gastropoda sp.1 Spio filicornis Corophium sp. Pionosyllis sp.
40.0 19.4 7.9 6.0 5.0
40.0 59.4 67.3 73.3 78.3
June 1996 Capitella capitata Pionosyllis sp. Caulleriella bioculata Musculus mirandus Clypeomorus sp.
37.7 22.3 6.1 3.0 2.1
37.7 60.0 66.1 69.1 71.2
June 1996 Pionosyllis sp. Musculus mirandus Capitella capitata Prionospio malmgreni Caulleriella bioculata
21.4 7.9 6.9 6.0 5.1
21.4 29.3 36.2 42.2 47.3
July 1996 Capitella capitata Pionosyllis sp. Prionospio malmgreni Musculus mirandus Caulleriella bioculata
65.0 7.7 4.3 3.9 3.1
65.0 72.7 77.0 80.9 84.0
July 1996 Caulleriella bioculata Pionosyllis sp. Musculus mirandus Prionospio malmgreni Bivalvia sp.1
18.3 14.8 14.4 10.0 3.9
18.3 33.1 47.5 57.5 61.4
August 1996 Capitella capitata Pionosyllis sp. Gastropoda sp.3 Prionospio malmgreni Neanthes caudata
46.4 12.3 5.3 4.7 2.5
46.4 58.7 64.0 68.7 71.2
August 1996 Pionosyllis sp. Caulleriella bioculata Prionospio malmgreni Poecilochaetus serpens Branchiostoma belcheri
17.3 11.4 6.5 4.4 4.2
17.3 28.7 35.2 39.6 43.8
September 1996 Clypeomorus sp. Capitella capitata Prionospio malmgreni Linopherus hirsuta Pionosyllis sp.
21.6 12.0 9.5 3.9 3.8
21.6 33.6 43.1 47.0 50.8
September 1996 Aonides oxycephala Prionospio malmgreni Psammobia radiata Spondervilia sp. Capitella capitata
15.9 13.5 3.6 3.5 2.9
15.9 29.4 33.0 36.5 39.4
October 1996 Spondervilia sp. Musculus mirandus Gastropoda sp.3 Clypeomorus sp. Prionospio malmgreni
46.0 14.9 10.3 7.2 2.4
46.0 60.9 71.2 78.4 70.8
October 1996 Spondervilia sp. Gastropoda sp.3 Clypeomorus sp. Aonides oxycephala Musculus mirandus
38.3 12.0 10.1 5.8 4.0
38.3 40.3 50.4 56.2 60.2
November 1996 Aonides oxycephala Linopherus hirsuta Epicodakia delicatula Clypeomorus sp. Prionospio malmgreni
15.2 11.0 10.8 6.2 5.6
15.2 26.2 37.0 43.2 48.8
November 1996 Clypeomorus sp. Aonides oxycephala Spondervilia sp. Prionospio malmgreni Paguridae sp.
10.8 10.5 10.5 8.0 6.6
10.8 21.3 31.8 39.8 46.4
March 1997 Pionosyllis sp. Aonides oxycephala Prionospio malmgreni Clypeomorus sp. Epicodakia delicatula
27.7 10.6 8.5 6.5 6.5
27.7 38.3 46.8 53.3 59.8
March 1997 Pionosyllis sp. Dexaminidae sp. Aonides oxycephala Epicodakia delicatula Capitella capitata
30.4 13.2 12.7 5.0 3.6
30.4 43.6 56.3 61.3 64.9
May 1996 Capitella capitata Pionosyllis sp. Gastropoda sp.1 Chironomidae sp. Spio filicornis
% by no.
Species diversity (H0 ) and evenness (J ) were significantly lower in the petroleum-contaminated sediment in Junee August 1996 (Fig. 5). Overall, no significant differences in community parameters were found between the petroleumcontaminated and the control sediments after 11 months. The top five dominant species following initial colonization in the petroleum-contaminated sediment were quite different
from those in the control sediment (Table 1). The insect Chironomidae sp. was the most dominant species in the control sediment, while the polychaete Capitella capitata, which was found in low abundance in the control sediment (Fig. 3), predominated in the petroleum-contaminated sediment. The most dominant species were different in the petroleum-contaminated and the control sediments for the first
Petroleum Control
50
25
0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 96 97
50 0 Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Musculus mirandus 300 Petroleum Control 200
100
0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 96 97
175 150
Petroleum Control
125 100 75 50 25 0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 97 96
Epicodakia delicatula 60
Petroleum Control
40
20
0
Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Pionosyllis sp. 200
Petroleum Control
150 100 50 0 Apr 96
May Jun
Jul
Aug Sep
Abundance (animals / tray)
100
Abundance (animals / tray)
150
Abundance (animals / tray)
Abundance (animals / tray) Abundance (animals / tray)
Petroleum Control
75 50 25 0
Apr May Jun
Jul
Aug Sep Oct Nov Mar 96 97
Spondervilia sp.
Petroleum Control
Abundance (animals / tray)
200
631
Caulleriella bioculata 100
Capitella capitata 250
Clypeomorus sp.
Abundance (animals / tray)
Abundance (animals / tray)
Gastropoda sp.1 75
Abundance (animals / tray)
Abundance (animals / tray)
Abundance (animals / tray)
Abundance (animals / tray)
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Oct
Nov Mar 96 97
900
Petroleum Control
600
300
0 Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Gastropoda sp.3 200
Petroleum Control
150 100 50 0 Apr May Jun Jul Aug Sep Oct Nov Mar 96 96 97
Linopherus hirsuta 65 60 55 50 45 40 35 30 25 20 15 10 5 0
Petroleum Control
Apr May Jun 96
Jul
Aug Sep Oct Nov Mar 96 97
Aonides oxycephala 100
Petroleum Control
75 50 25 0 Apr May Jun 96
Jul Aug Sep Oct Nov Mar 96 97
Prionospio malmgreni 75
Petroleum Control
50
25
0 Apr May Jun 96
Jul
Aug Sep Oct Nov Mar 96 97
Fig. 3. Mean abundance of 12 dominant species in the petroleum-contaminated sediment and those species in the control sediment during the study period (mean SE).
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632
1 5 5 55 77 8 7 7 6 6 66 6
1
5
8 7
2
3 3 33 3 4 44 2 4 4
1 1
2
2 2
1
Fig. 4. MDS ordination of macrobenthic samples (stress ¼ 0.11), showing changes in community structure of macrobenthos in the defaunated sediment contaminated with petroleum hydrocarbons during the study period (1 ¼ May 1996, 2 ¼ June 1996, 3 ¼ July 1996, 4 ¼ August 1996, 5 ¼ September 1996, 6 ¼ October 1996, 7 ¼ November 1996, 8 ¼ March 1997).
five months. The abundance of some dominant species, e.g. C. capitata, Caulleriella bioculata, Musculus mirandus and Linopherus hirsuta, generally showed different patterns in the petroleum-contaminated and the control sediments. Other species, e.g. Spondervilia sp., Gastropoda sp.3, Clypeomorus sp. and Pionosyllis sp., exhibited similar patterns in both sediments. The abundance of C. capitata was much higher in the petroleum-contaminated sediment than in the control sediment from June to August 1996, while the abundance of C. bioculata was much lower in the petroleumcontaminated sediment in July and August 1996. Aonides oxycephala in the petroleum-contaminated sediment appeared two months later during succession and its abundance was significantly lower before November 1996. Results of one-way ANOSIM test for macrobenthic samples between the petroleum-contaminated and the control communities are shown in Fig. 6. Global R decreased generally during the experiment and no significant difference in community composition was found in March 1997. 4. Discussion Petroleum hydrocarbons are known to be toxic to benthos. Inhibition of settlement of barnacle larvae by crude oil was observed in the intertidal zone of a Norwegian fjord (Nelson, 1981). Nelson (1982) suggested that the most serious potential impact of an oil spillage is the disruption of settlement and growth among juveniles in rocky intertidal communities. Poulton et al. (1997) reported a decrease in overall macrobenthic diversity after a spill of crude oil. Lu (2005) found strongly negative correlations between community parameters
(abundance, species number and diversity) of macrobenthos and the concentrations of total petroleum hydrocarbons in sediments of Singapore waters. Petroleum hydrocarbons may also modify the physical properties of sediment, thereby, influencing recolonization of macrobenthos (Berge, 1990). Organic enrichment of sediment by petroleum hydrocarbons may enhance the development of macrobenthic infauna due to an increase in food supply upon degradation. In Norway, Berge et al. (1987) found that 33% of the originally added crude oil (18 000 mg/kg dry wt.) remained in the sediment after 13 months of exposure, and results of oil biodegradation resembled the effects of eutrophication. Concentration of petroleum hydrocarbons in contaminated sediments decreased from 682 mg/kg to 244 mg/kg (dry wt.) after 20 days of field exposure and stabilized afterwards at the same study site in Hong Kong (Lam and Zhang, unpublished data). An organic enrichment effect (high individual abundance of a few species) was recorded at a site close to the source of oil contamination in the North Sea (Kingston, 1992). Jewett et al. (1999) recorded higher abundance of most families at oiled sites in Prince William Sound, Alaska, USA, 16 months after the Exxon Valdez oil spill. Spies et al. (1988) found that the responses of macrofauna to crude oil in sediments were similar to those expected from other sources of organic matter (e.g. kelp) in a field experiment. In this study, initial colonization and subsequent succession of macrobenthic community were retarded in sediments contaminated with petroleum hydrocarbons, resulting in significant reductions in abundance and species number, as well as changes in species composition and community structure. The polychaete Capitella capitata is well known as a ubiquitous opportunistic species and an initial colonizer of disturbed marine sediment (Grassle and Grassle, 1974; McCall, 1977; Pearson and Rosenberg, 1978; Zajac and Whitlatch, 1982a,b; Whitlatch and Zajac, 1985; Diaz-Castaneda et al., 1989). In the present study, this species was only recorded in low abundance in the control sediments in the early months of colonization. Capitella capitata was, however, most abundant and, therefore, predominated during the first four months in the petroleum-contaminated sediments, showing the typical characteristics of an opportunistic species during succession. The result clearly indicates that C. capitata is more tolerant than other species to petroleum hydrocarbons and/or hydrogen sulfide in sediment. Organic enrichment caused by petroleum hydrocarbons may also enhance the development of this species after degradation of hydrocarbons because of an increase in organic food supply. Opportunists are often poor competitors (McCall, 1977) and are replaced by other species at a later stage after they have prepared the sediment, making it more suitable for other species to settle upon (Pearson and Rosenberg, 1978; Arntz and Rumohr, 1982). In this study, the dominance of Capitella capitata ended after severe mortality and subsequent replacement by molluscs, e.g., Clypeomorus sp. and Spondervilia sp. The sharp decline of the C. capitata population may result from interspecific competition, intraspecific depletion of
L. Lu, R.S.S. Wu / Estuarine, Coastal and Shelf Science 68 (2006) 627e634
Species number
Abundance
Control
Control Petroleum 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0
4
M ar 97
96
6 N
ov
ct 9
96
Evenness Control Petroleum
Control Petroleum
0.9
***
** **
O
96
Se p
Au g
96
96
Ju l
ay
Ju n
96
**
Species diversity
5
***
**
*** * ** ***
M
ov N
M ar 97
6
96
O
Se p
96
6
Au g
l9
96
Ju
Ju n
M ay
96
*
**
Petroleum
Species / tray
*
**
ct 9
1700 1600 1500 1400 1300 1200 1100 1000 900 800 700 600 500 400 300 200 100 0
96
Animals / tray
633
**
0.8
**
**
0.7 0.6
J/ tray
H'/ tray
3 2
0.5 0.4 0.3 0.2
1
0.1 0
M ar 97
N
ov
96
96 ct
96 O
96 g
Se p
l9
6 Au
Ju
n
96
96 ay
Ju
N
M
ov
ct O
M ar 97
96
96
96 p
96 Se
g Au
Ju
Ju
l9
96 n
96 ay M
6
0.0
Fig. 5. Comparison of mean values in abundance, number of species, species diversity and evenness between the petroleum-contaminated and the control communities during the study period (mean SE). Asterisks denote significant difference as identified by t-tests (*p < 0.05, **p < 0.01, ***p < 0.001).
food resources or accumulation of toxic substances (Grassle and Grassle, 1974; McCall, 1977). The study of Berge (1990), in Norway, indicated that longer periods (beyond his 13-month experiment) would be needed for macrobenthic communities in sediment contaminated with 4520 mg/kg (wet wt.) of crude oil to achieve conditions approaching those of controls. Olsgard and Gray (1995) found that benthic fauna was still affected several years after the
**
1.00
Global R
0.75
** **
**
**
**
**
0.50
cessation of oil-based drill-cutting discharges. In the present experiment, however, complete recovery was found in the petroleum-contaminated sediments after 11 months, as indicated by abundance, species number, diversity and evenness, as well as community composition. A macrobenthic community in equilibrium was also reached after 11 months in the present study, as indicated by successional patterns of benthic parameters. Nevertheless, recolonization can be scale-dependent (Thrush et al., 1996), and the recovery rate of macrobenthic infauna may be quite different in an event of real diesel spill. It should be noted that the persistence and toxicity of oil in marine sediments may rely on factors such as the time and degree of mixing, the hydrodynamic conditions, the porosity of the sediments, the geochemical conditions in the pore water, the turbulence by faunal and physical processes, and the presence of oil-degrading bacteria.
0.25
Acknowledgments ar 97 M
96 ov N
O
ct
96
96 Se p
96 g Au
l9 6 Ju
96 n Ju
M
ay
96
0.00
Fig. 6. Results of one-way ANOSIM test for macrobenthic samples between the petroleum-contaminated and the control communities during the study period (**p < 0.01).
This study was supported by a research grant (No. 9040187) from the Research Grants Council, Hong Kong SAR, China. The authors would like to thank the Agriculture and Fisheries Department of the Hong Kong SAR for their technical support in this project.
634
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