Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China

Marine Pollution Bulletin xxx (2015) xxx–xxx

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Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul

Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China Yan Li Lei a, Tie Gang Li a,⇑, Hongsheng Bi b, Wen Lin Cui c, Wen Peng Song c, Ji Ye Li c, Cheng Chun Li a a Department of Marine Organism Taxonomy & Phylogeny, Key Laboratory of Marine Geology and Environment, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, PR China b Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomon, MD 20688, USA c The Organization of North China Sea Monitoring Center, SOA, PR China

a r t i c l e

i n f o

Article history: Received 5 October 2014 Revised 12 May 2015 Accepted 12 May 2015 Available online xxxx Keywords: Benthic foraminifera Biological response Ecological monitoring Indicator species The Yellow Sea

a b s t r a c t The 2011 oil spill in the Bohai Sea was the largest spill event in China. Nine sediment cores were taken near the spill site and environmental factors including Polycyclic Aromatic Hydrocarbon (PAHs), oils, sulfides, organic carbon were measured 6 months later. Benthic foraminifera were separated into >150 lm (large) and 63–150 lm (small) size fractions for 2-cm depth interval of each sediment core. Statistical analyses suggested that the species composition of living foraminifera was impacted by oils, PAHs and sulfides. Large foraminifera were more sensitive to the oils than the small. Abnormal specimens were positively correlated with oils or PAHs. Small forms, however, tended to have high reproduction and mortality. Pollution-resistant and opportunistic taxa were identified to calculate a Foraminiferal Index of Environmental Impacts (FIEI). The FIEI increased from low to high oil-polluted station and from deep layer to surface sediment reflects the impact of oil pollution in this area. Ó 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).

1. Introduction Oil spills have a wide range of adverse impacts on the marine environment at different temporal scales (Peterson, 2001). They can have dire consequences on the survival of marine flora and fauna including ecological and economically important fish and mammals (Brody et al., 1996; Murphy et al., 1997; Wiens et al., 1996) and affect marine organisms by disrupting reproduction (Andres, 1997; Lamont et al., 2012), development (Gonzalez-Doncel et al., 2008; Incardona et al., 2014), and feeding (Romero et al., 2012). Besides the direct impacts on marine organisms and their habitats, the toxic substances can also affect human health through food webs (Aguilera et al., 2010; Gin et al., 2001; O’Rourke and Connolly, 2003). There is a large body of literature on large oil spills such as the 1978 ‘‘Amoco Cadiz’’ spill in France (Dauvin, 1998; Mille et al., 1998), the 1989 ‘‘Exxon Valdez’’ spill in Alaska (Atlas and Hazen, 2011; Harwell et al., 2010; Payne et al., 2008; Peterson, 2001) and the 2010 ‘‘Deepwater Horizon’’ spill in the Gulf of Mexico (Kurtz, 2013; Lavrova and Kostianoy, 2011). The 2011 ‘‘Penglai’’ oil spill in the Bohai Sea was the worst oil spill in China. There were approximately 723 barrels (115 m3) of

⇑ Corresponding author. E-mail address: [email protected] (T.G. Li).

oil and 2620 barrels (416 m3) of mineral oil-based drilling mud seeping into the Bohai Sea (http://www.soa.gov.cn/) and yet very few studies have examined the potential environmental impact. The Bohai Sea is a half-closed sea and is only connected with the Yellow Sea through the Bohai Strait. The residence water in the Bohai Sea has a mean age of >1.2–3.9 years (Liu et al., 2012). To examine and assess the potential impact of the ‘‘Penglai’’ oil spill on the local marine environment, we investigated the potential of using benthic foraminifera as biotic indicators. Benthic organisms are used extensively as biotic indicators of environment because they generally have limited mobility and cannot avoid adverse environmental changes. Benthic foraminifera are particularly useful for environmental monitoring (Frontalini and Coccioni, 2011; Hallock et al., 2003; Foster et al., 2012). First, they are widely distributed and very diverse. Second, they can preserve historical information in their shells (>500 million years) which can be used to study the marine environments from ancient (Cambrian) to present (Holocene). Therefore, their species composition and chemical elements reflect palaeoenvironment (Spero et al., 1997; Li et al., 2009; Nigam et al., 2009). Third, they are sensitive to changes in marine environments such as water temperature, salinity, pH, water mass, ocean current, marine geographical variables (Murray, 1991, 2006). Furthermore, their shells preserved at different depths in sediment can reflect environmental changes including oil exploitation activities (Denoyelle et al., 2010; Sabean

http://dx.doi.org/10.1016/j.marpolbul.2015.05.020 0025-326X/Ó 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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et al., 2009), which is particularly useful when no baseline data were available. Previous studies showed that foraminifera could serve as biotic indicators to evaluate the impacts of oil spills (Casey et al., 1980; Armynot du Châtelet et al., 2004). Durrieu et al. (2006) and Mojtahid et al. (2006) showed that benthic foraminifera could be used to estimate the pollution from oil drill mud disposal. However, Locklin and Maddocks (1982) found no negative effects of petroleum operations on benthic foraminifera on the southwest Louisiana shelf. The general responses of benthic foraminifera to pollutants include decreased diversity and increased dominance of tolerant or opportunistic species, or alteration of species morphology and reproduction, but different species may show differential response. For example, Morvan et al. (2004) conducted a laboratory culture experiment and observed morphological abnormalities of benthic foraminifera (Ammonia tepida) and a reduction of reproduction rate under oil pollution. But Ernst et al. (2006) found that the mortality of foraminiferal faunas increased in response to the presence of oils in a laboratory microcosm experiment, but some species did increase their density by increasing their reproduction. Although the toxic hydrocarbon components appeared to be responsible for the observed changes in foraminiferal abundance and species composition (Armynot du Châtelet and Debenay, 2010; Mojtahid et al., 2006), species-specific responses to environmental stress induced by oil pollution were evident. Considering the bio-geographical distribution of foraminifera and the different habitat may colonize different foraminiferal community dominated by different species, the foraminiferal responses to the oil pollution should vary among different foraminiferal communities from different geographical regions. When compared to other regions, e.g., the temperate Atlantic regions (e.g. Brunner et al., 2013; Hallock et al., 2003), there is a lack of studies on monitoring and assessing environmental impact of oil spills using benthic foraminifera in the Western Pacific region, Chinese continental shelf in particular (Li et al., 2009; Jian et al., 2000). As offshore drilling increases, there is a growing need to identify suitable indicator species and develop local indices that could be used to assess environmental conditions. While there were a variety of foraminiferal indices have been developed, e.g., diversity indices, Foraminiferal Abnormality Index (FAI, Coccioni et al., 2005) and Foraminiferal Index of Environmental Impact (FIEI, Mojtahid et al., 2006), all indices require baseline information on local foraminiferal fauna and identification of indicator species. But in the Bohai Sea, information on species composition and distribution of recent benthic foraminifera is not available and how they respond to oil spills remains unknown. After the 2011 ‘‘Penglai’’ oil spill in the Bohai Sea, we started to explore the potential of using foraminifera to evaluate the status of oil pollution. The objectives of the present study are to: (1) investigate the horizontal distribution of living foraminiferal fauna and examine vertical distribution using their fossil records; (2) examine how benthic foraminifera respond to oil spill and identify potential indicator species; (3) assess environmental status of the survey area. The ultimate goal is to build a regional index based on indicator species to assess environmental stress and provide background information on local foraminiferal species composition and distribution.

2. Materials and methods 2.1. Study area and background information The Bohai Sea is the innermost gulf of the North Yellow Sea of China with an area 78,000 km2 and high sediment loadings from

river runoff (Fig. 1). There are 16 rivers entering the Bohai Sea including the Yellow River. The average residence time water in the Bohai Sea is 3 years (Liu et al., 2012). Current from the Yellow Sea entered the Bohai Sea from the bay mouth and flowed west towards inner Bay. The dominant circulation pattern is anticlockwise (Chen, 2009). The Bohai Sea has significant hydrocarbon deposits and offshore oil exploration started in 1980s. The ‘‘Penglai’’ field is that biggest oil field in this region, which is 51% owned by the China National Offshore Oil Corporation (CNOOC), and 49% owned by the ConocoPhillips (COPC). The exploration of the ‘‘Penglai’’ Oilfield started in 1999 and the operation started on December 31, 2002. From June to July in 2011, at least two major leaks events occurred in the ‘‘Penglai’’ Oilfield, which became the largest oil spill accident in China. 2.2. Sampling Nine sediment cores with a depth of 22–28 m to the surface were sampled on December 18–19, 2011 in the Bohai Sea (38°100 -39°000 N, 119°300 –120°10E). The locations of the oil spill and sampling sites were shown in Fig. 1. For detecting the impact of oil pollution, the sediments near the oil spill site were intensively sampled. Station 14 was closest to the spill site, followed by St22, St36, St31, St11, St19 and St6. Station 26 was furthest away from the spill site and was considered as a reference site. StA8 was considered as an intermediate station. Sediment samples were taken using a 0.1 m2 Gray–Ohara box corer. At each sampling station, environmental variables (water depth, sediment type, sediment color) and pollution factors including Polycyclic aromatic hydrocarbons (PAHs), oils, sulfides and organic carbon were measured from the surface sediment (Table 1). Sediment grain size analysis was based on Shepard (1954). The measurements for the chemical contaminants of the sediments were based on the Chinese National Standards of GB/T 18668-2002 and GB/T 17378.5-2007. The sampled sediment cores were subsampled using a recently developed Pushing-type Quantitative Layering Sampler with an inner diameter of 6 cm, i.e., 28.26 cm2 sampling surface (Fig. 2). Each core was sliced every 2-cm interval until 12–16 cm depth. The sliced sediment stratums were immediately fixed using 95% ethanol mixed with 1 g/L Rose Bengal such that live and dead specimens could be distinguished. Samples were then stored in a dark, cooling box and transported to the laboratory within 24 h. In the laboratory, each sediment stratum was washed over a 63 lm screen. The residues were dried in the oven below 50 °C for 24 h and weighted and sieved through 63 lm and 150 lm meshes. Benthic foraminifera were picked and counted for two size fractions, >150 lm and 63–150 lm, respectively (Jian et al., 1999). The volumes of sample were consistent with each other, i.e. 56.55 cm3, but the dry weights varied from 31.3 g to 50 g among stations. The foraminiferal specimens were concentrated by an isopycnic separation technique using tetrachloromethane (D = 1.59) and the residues were also examined. 2.3. Classification and analyses Foraminifera were enumerated under a Nikon SSZ1500 stereomicroscope, with continuous zooming to a maximum amplification of 225. Specimens were observed and photographs were taken under the microscope. Foraminifera were identified to species level based on Loeblich and Tappan (1987, 1992, 1994), Hayward et al. (2014) and the relevant regional taxonomic literature (e.g. Wang et al., 1988). To investigate the spatial pattern, total foraminiferal fauna were separated as living, dead and abnormal. Individuals were picked and inventoried, and were separated into

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx





N CHINA



Oils



94 to 146 146 to 158 158 to 239 239 to 419 419 to 487

26



Bohai Sea





 



Yellow Sea











to to to to to







PAHs 24 38 40 45 68

26



38 40 45 68 123



11 36 22



32 36 37 46 55

 

to to to to to

36 37 46 55 66



6

A8



19 11 36 22



14

C

31







B 

31







Organic carbon



0.17 0.26 0.32 0.33 0.39

26

 

to to to to to

0.26 0.32 0.33 0.39 0.67







14



Sulfides 26







19







6

A8



 A 









6

A8



6

A8



19 11 36 22



19 11 36 22



14



14

31



 

D 









E 

31







Fig. 1. Map of 9 sampling stations (A) and distributions of pollution factors (B–E). (A) Sampling sites were shown by black dots and the oil spill site was indicated by the open square. Arrows showing a schematic drawing of the general circulation pattern in the Bohai Sea. (B) Concentration of oils (lg/g); (C) concentration of Polycyclic Aromatic Hydrocarbon (PAH, ng/g); (D) concentration of sulfides (lg/g) and (E) concentration of organic carbon (%).

Table 1 Basic information and pollution parameters in the 9 sampling sites of the Bohai Sea. The samples were taken from the upper 2-cm sediment layer. Sampling sites

Water depth (m)

Sediment color

Sediment type

Distance to oil spill site (km)

St26 StA8 St6 St19 St11 St36 St22 St14 St31

26 28 28 28 28 27 27 24 22

Yellow Yellow brown Yellow Yellow Yellow Yellow brown Yellow Yellow Yellow

Silt clay Clay silt Silt clay Silt clay Silt clay Clay silt Silt clay Silt clay Silt

100.40 35.42 24.14 18.46 13.86 11.92 7.34 6.28 14.08

two size fractions: large foraminifera (>150 lm) and small foraminifera (63–150 lm). Because the small size group mostly included mainly juvenile or larva of large foraminifera and some small unidentified species, therefore only large foraminifera were chosen to investigate the vertical distribution. In general, whole sample was analyzed, but when foraminiferal density was too high, a riffle was used to subset samples with a minimum of 300–1000 individuals of total fauna examined from each sample. For each station, the abundance of total fauna, live fauna and abnormal fauna, species richness (number of species per sample), Margalef index (D), Shannon–Wiener diversity (H0 ) and evenness (J0 ) were calculated. Margalef index (D) was calculated as S  1/ln N, where S is the total number of species and N is the total number of individuals. Shannon–Wiener index (H0 )

was calculated as RPi ln(Pi), where Pi is the proportion of total number of species made up of the ith species. Evenness (J0 ) was calculated as J0 = H0 /ln S. Species made up >15% of the total abundance were considered as dominant species. Foraminiferal bioindicators were selected based on three criteria: highly recognizable morphology, abundant and common in oil contaminated regions, frequent occurrence in various depth layers which allows comparison over time. Based on our preliminary analysis, we selected indicator species to construct the Foraminiferal Index of Environmental Impact (FIEI, Mojtahid et al., 2006) to evaluate the pollution status among stations. FIEI = (Nr + N0)/Ntot  100, where Nr is the total quantity of pollution-resistant taxa, N0 is the number of individuals of opportunistic taxa and Ntot is the total number of individuals in the foraminiferal assemblage. In this study the pollution-resistant taxa were determined among the dominant species whose occurrence was significantly positively correlated to the oils. While those were also frequent or abundant at some oil-polluted stations but were not significantly correlated to oils, were considered as opportunistic taxa. 2.4. Statistical analysis Simple nonparametric Spearman correlation was used to evaluate the relationship between biotic variables (the abundance of total, living and abnormal foraminifera, species richness, diversity indices and evenness) and the pollution parameters (PAHs, oils, sulfides, and organic carbon). These analyses were performed using the Statistical Package for the Social Sciences (SPSS, version 15.0).

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

sampling stations were mostly silt clay, but St36 was clay silt and St31 was silt. The sediment colors were most of yellow but St36 was yellow brown (Table 1). Oils’ concentration was highest at St22, followed by St11, St36, St14, St19, St26, St6, StA8 and St31 (Fig. 1). The PAHs concentration was highest at St31, followed by St22, St14, St19, St6, St36, St26, StA8 and St11 (Fig. 1). Concentration of sulfides was highest at St26, followed by StA8, St22, St36, St19, St11, St6, St14 and St31 (Fig. 1). Organic carbon was highest at St26, followed by StA8, St36, St22, St11, St6, St14, St19 and St31. MDS analysis using the four pollution factors separated the 9 sampling stations into several different groups: the first group comprised St26 and StA8. Other distinct groups included St6-St19-St14, and St36-St22. St31 and St11 were standing alone but in different directions (Fig. 3). 3.2. Horizontal distribution of foraminifera in surface stratum

Fig. 2. Schema diagram of the Pushing-type Quantitative Layering Sampler. 1. Push rod with scales; 2. Stainless steel sampling tube.

Clusters were separated using the Ward method based on the species-abundance data. Canonical Correspondence Analysis (CCA) was performed to test relationships between foraminiferal species distribution and pollution factors, and was analyzed. Data were log (x + 1) transformed to meet the assumptions of normality and homogeneity of variances. To examine the spatial variation of community structure, multidimensional scaling (MDS) ordination using Bray-Curtis similarity matrices was performed in PRIMER v6.1 package (Clarke and Gorley, 2006). Stations-based pollution parameters and species-abundance data of foraminifera (>150 lm) were analyzed separately. To detect how oil-pollution affects living foraminifera, multivariate biota-environment (BIOENV) analysis were performed by examining biotic and abiotic similarity matrices. The significance of biota-environment correlations was test using the routine RELATE (Clarke and Gorley, 2006). The spatial distribution of sampling sites and their pollution parameters were visualized in Surfer (version 8.0, Golden Software Inc., Golden, CO, USA). Small foraminiferal group mainly contains small specimens or juveniles of large foraminifera, due to their small size and difficulty in identification, especially in differentiation of abnormal forms from normal, statistical analyses were mainly based on large foraminiferal group.

3.2.1. Large group Both the abundances of total fauna and living fauna were lowest at St31: 150 and 72 individuals 10 cm2 respectively. High abundance of total and living foraminifera occurred at stations 11, 36 and 22 where concentrations of oil-pollutant were high and were close to the oil spill site (Table 2; Fig. 1). The highest abundance of total fauna was observed at St11 (488 individuals 10 cm2) and the maximum living abundance was at St22 (238 individuals 10 cm2). The percentage of living fauna ranged from 34.4% to 60.1% but there was no clear relationship with oil pollutants. High densities of living fauna sometimes occurred at stations with moderate pollution (e.g. St11, St36 and St22). Noteworthily, various morphological abnormal forms were observed including malformation in chambers, test with warts, diminution in the last chamber, color darken with dwarfism etc. (Plates 1 and 2). The percentage of abnormal specimens was higher at polluted stations (e.g. St36, St22 and St31). The highest amount of deformed specimens occurred at St22, up to 31%. In contrast, at St26, the reference station, the proportion of abnormal specimens was only 4.6% (Table 2). Species richness was highest at St26 with a value of 28, and lowest at St14 with a value of 18. Margalef index (D) and Shannon–Wiener index (H0 ) were both highest at St6 (4.59 and 2.57, respectively), but their lowest values were observed at St22 (=3.12) and St26 (=1.88), respectively. Community evenness (J0 ) ranged from 0.97 (St22) to 0.89 (St14). 3.2.2. Small group Similar to large foraminifera, the abundances of the total fauna and living fauna in this group were lowest at St31, 1935 vs. 45 individuals 10 cm2, respectively, and were highest at St11, 6791 and

3. Results 3.1. Environmental factors The oil spill site was at the inside of the entrance from the Yellow Sea to the Bohai Bay (Fig. 1). The sediment types of

Fig. 3. Multidimensional scaling (MDS) ordination for pollution factors using Euclidean distance among 9 sampling sites. To perform the MDS analysis, data were log (x + 1) transformed and Spearman rank correlations were calculated.

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx Table 2 Foraminiferal community parameters at the 9 sampling sites in the surface sediment layer, 0–2 cm. St26

StA8

St6

St19

St11

St36

St22

St14

St31

>150 lm fraction Total abundance (inds. 10 cm2) Living abundance (inds. 10 cm2) Abnormal abundance (inds. 10 cm2) Living ratio (%) Abnormal ratio (%) Species richness (S) Margalef index (D) Shannon–Wiener index (H0 ) Evenness (J0 ) Specimens examined

451 181 21 40.2 4.6 28 4.42 1.88 0.57 1278

224 103 34 45.7 15.1 24 4.25 2.26 0.71 636

231 88 50 38.0 21.6 26 4.59 2.57 0.79 657

320 110 75 34.4 23.4 26 4.33 2.42 0.74 457

488 221 89 45.2 18.3 21 3.23 2.41 0.79 361

456 172 124 37.7 27.3 23 3.59 2.41 0.77 687

439 238 136 54.2 31.0 20 3.12 2.50 0.84 318

191 115 46 60.1 24.1 18 3.24 2.02 0.70 544

150 72 41 48.2 27.2 22 4.19 2.26 0.73 430

63–150 lm fraction Total abundance (inds. 10 cm2) Living abundance (inds. 10 cm2) Living ratio (%) Species number (S) Margalef index (D) Shannon–Wiener index (H0 ) Evenness (J0 ) Specimens examined

2931 181 6.2 16 1.88 1.59 0.57 259

2716 113 4.2 14 1.64 1.70 0.64 121

2808 181 6.5 18 2.14 1.85 0.64 124

3916 566 13.9 17 1.93 1.37 0.48 173

6791 815 12.0 12 1.25 1.63 0.66 76

4255 113 2.7 20 2.27 1.37 0.46 188

2716 91 3.3 22 2.66 1.72 0.56 241

2275 79 3.5 18 2.20 1.36 0.47 201

1935 45 2.3 16 1.98 1.43 0.52 171

815 individuals 10 cm2 respectively. Comparing to the large foraminifera, the total abundances of small fauna were remarkably higher. It is noteworthy that living abundance was not that high, the ratio varied from 2.3% to 13.9% among stations, markedly lower than the living ratio of large fauna (Table 2). Species richness, Margalef diversity index (D) and Shannon– Wiener index (H0 ) were all lowest at St11 with a value of 12, 2.61 and 2.47, respectively, and were all highest at St22, with a value of 22, 4.76 and 3.05, respectively. But the three parameters were all lower than large size group. Community evenness (J0 ) among the nine stations was similar. 3.3. Species composition of foraminifera in surface layer and below surface A total of >100 foraminiferal species was identified from surface and below surface samples, and 53 species were observed in the surface layer (0–2 cm). Surface samples were different from below surface samples, e.g., some species did not occur in below surface samples and some species increased their abundance. The species compositions of large and small groups were similar in the surface layer (0–2 cm, Tables A1 and A2). Calcareous foraminifera made up 80–90% of the total fauna, and agglutinated tests made up 10–20%. Rotaliida species were predominant, followed by Textulariida and Miliolida. Astrorhizida and Lagenida were relatively rare. 3.3.1. Large group A total of 41 species representing 27 genera and five orders (Astrorhizida, Textulariida, Miliolida, Lagenida and Rotaliida) were identified in surface layers (Table A1). The common species included Ammoglobigerina globigeriniformis, Cribrononion incertum, Buccella frigida, Elphidium macellum, Cribroelphidium magellanicum, Quinqueloculina ungeriana, Cribrononion asiaticum, Verneuilinulla advena, A. tepida, Ammonia inflata, Rotalidium annectens, Rotalinoides compressiusculus, Ammonia pauciloculatus, Ammonia ketienziensis, Elphidium advenum. These species were also observed in samples below surface (Table A1). Among them, A. globigeriniformis, C. incertum, B. frigida, E. macellum and C. magellanicum were most frequent. Species composition showed distinct variation among surveyed stations. C. magellanicum accounted for up to 50% of total foraminiferal abundance at St26 but rapidly decreased to 17–30% at the stations near the spill site. A. globigeriniformis and B.

frigida were dominant at St26, making up 13% and 10% of total abundance, respectively. Several species appeared to be oil-philic: B. frigida showed a large increase in its abundance near the oil spill site, making up to 19% at heavily polluted site (St14). C. incertum was only 5% of total abundance at St26, and increased to 11–26% of total abundance near the oil spill site. Species including E. macellum, Q. ungeriana, C. asiaticum, V. advena, A. tepida, R. annectens, R. compressiusculus were frequently observed at all stations and they usually accounted for 1–7% of total abundance (Fig. 4). 3.3.2. Small group A total of 37 species representing 27 genera within four orders (Textulariida, Miliolida, Lagenida and Rotaliida) was identified from sediment samples at different depths. C. magellanicum was predominant species at the surface layer and it made up on average 62% (ranged from 53% to 71%) of total abundance in small foraminiferal group. V. advena was the second abundant species at the surface layer, accounting for on average 6% (ranged from 1% to 14%) of total abundance in small foraminiferal group. Species such as A. globigeriniformis, C. incertum, B. frigida and C. asiaticum were often observed at all stations but with relatively low abundance in this size spectrum (Fig. 4). 3.4. Linkage between foraminiferal community and pollution factors In >150 lm fraction, simple nonparametric Spearman correlation analysis results showed several community parameters were significantly correlated to the oils. Living abundance and abnormal abundance were positively correlated to oils (p < 0.05). In addition, the percentage of abnormal individuals was also positively correlated to PAHs (p < 0.05). Margalef index (D) negatively correlated to oils. In contrast, no parameter of 63–150 lm fraction was significantly correlated to oils, except that the total and living abundance of small foraminifera were negatively correlated to PAHs (Table 3). The BIOENV analysis results suggested that the composition/distribution of living foraminiferal species was related to the combination of PAHs, oils and sulfides (R = 0.490; p = 0.019). Note that oils were included in all correlations. The foraminiferal biotic variables were significantly correlated to several different combinations of pollution factors (Table 4). MDS analysis was performed using the station based abundance of total foraminifera and large living foraminifera separately to

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Plate 1. Microphotographs of dominant and common species of benthic foraminifera in the Bohai Sea, showing normal specimens and abnormal individuals (indicated by arrows). Scale bars = 200 lm. 1. Ammoglobigerina globigeriniformis (Park and Jones, 1865) showing normal (a–d) and abnormal (e and f) specimens. 2. Verneuilinulla advena (Cushman, 1922) showing normal (a and b) and abnormal (c) specimens. 3. Quinqueloculina ungeriana (d’Orbigny, 1846) showing normal (a–c) and abnormal (d) specimens. 4. Cribrononion asiaticum (Polski, 1959) showing normal (a–c) and abnormal (d and e) specimens. 5. Cribrononion incertum (Williamson, 1858) showing normal (a–c) and abnormal (d–f) specimens. 6. Elphidium macellum (Fichtel and Moll, 1798) showing normal (a–c) and abnormal (d and e) specimens.

examine the spatial patterns of the total and living foraminiferal assemblages among stations (Fig. 5). Both St31 and St14 were separated from other stations. Stations near the spill site (St19, St11, St22 and St36) were clustered together. St26 and StA8 were grouped together in Fig. 5A, but separated in Fig. 5B. Results reflected the status of oil impact, but the total abundance was consistent with the pollution factors (Fig. 3).

3.5. Identifying of foraminiferal bioindicators To identify species could be used to evaluate the impact of oil pollution, a dendogram of the occurrence of different species was constructed for large foraminifera (Fig. 6). The species were separated into two distinct clades (25% similarity level). Clade 1 contained 28 taxa which rarely occurred, or if they did occur, their

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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7

Plate 2. Continue. 7. Cribroelphidium magellanicum (Heron-Allen and Earland, 1932) showing normal (a and b) and abnormal (c–f) specimens. 8. Buccella frigida (Cushman, 1922) showing normal (a–c) and abnormal (d–f) specimens. 9. Ammonia inflata (Seguenza, 1862) showing normal (a–c) and abnormal (d–f) specimens. 10. Ammonia tepida (Cushman, 1926) showing normal (a and b) and abnormal (c–e) specimens. 11. Rotalidium annectens (Parker et Jones, 1865) with normal (a–c) and abnormal (d and e) specimens. 12. Rotalinoides compressiusculus (Brady, 1884) with normal (a–c) and abnormal (d and e) specimens.

abundance tended to be low. Clade 2 had 13 common species with high occurring frequency and high abundance (Fig. 6; Table A1). The relationships among the distributions of large foraminiferal species were summarized by CCA (Fig. 7). Species was numbered and was consistent with Fig. 6. Many species distributed along the oils axis, indicating strong influence by oils. In addition, several species distributed along the axis of PAHs or sulfide or organic carbon, suggesting a close relationship to the corresponding environmental factor.

Based on Spearman correlations, cluster analysis and the CCA along with the spatial and vertical distribution, 4 resistant and 3 opportunistic species were selected as bioindicators. The total and/or living abundance of B. frigida, E. macellum, C. asiaticum, V. advena were positively correlated to oils (Table 5), which were considered as pollution resistant taxa. The following three species of A. globigeriniformis, C. incertum and Q. ungeriana were regarded as opportunistic taxa because although they increased their abundance at stations with high concentration of oils, no significant

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

3.6. Foraminiferal Index of Environmental Impact (FIEI) in sediment layers

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

A

St26 StA8 St6

St19 St11 St36 St22 St14 St31

A. globigeriniformis B. frigida C. magellanicum C. asiaticum A. tepida R. annectens A. pauciloculatus E. advenum

C. incertum E. macellum Q. ungeriana V. advena A. inflata R. compressiusculus A. ketienziensis Others

100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0%

B

In order to comparing pollution status among stations and between the present and the past times in the Bohai Sea, the FIEI using selected bioindicators were calculated in surface sediment layers and also in sediment depths (Table 6). In the surface layer, the FIEI based on living fauna was lowest at St26 (=33.59) and highest St31 (=88.73). The FIEI based on living fauna was also high at St11 (=72.44), and ranged from 40 to 60 at other stations. The FIEI value based on total foraminifera was also lowest at St26 (=38.65). The FIEI based on total fauna was relatively high at St14 and St31 (64.51 and 66.74, respectively) and ranged from 40 to 60 at other stations. The high values of FIEI at stations near the spill site (St14 and St31) were consistent with high abundance of pollution-resistant or opportunist species and low abundance of sensitive species (Tables 6 and A1). The depth-specific FIEI values (Table 6; Fig. 9) suggested that FIEI increased from deep layer to surface layer. The FIEI values in the deepest stratums, 14–16 cm, were lowest, under 40. Then the FIEI values slightly increased in upper stratums, varying between 40 and 60 from 8 to 14 cm depth. The great increase of FIEI was observed at 6–8 cm depth, 60 at St31. The FIEI values were similar at 2–6 cm depth but with a slight increase. In the surface 0– 2 cm layers the FIEI values at most stations reached to the maximum (Table 6). 4. Discussion 4.1. Sediment environments among stations

St26 StA8 St6

St19 St11 St36 St22 St14 St31

Fig. 4. Percent composition of common foraminiferal species in >150 lm fraction (A) and in 63–150 lm fraction (B) at the 9 stations in the surface sediment, 0–2 cm. Note that data were based on total foraminiferal fauna.

correlations could be detected (Table 5). The spatial distribution of the selected bioindicators in surface layer of 0–2 cm was shown in Fig. 8. Their total and living abundance had a similar tendency of variations in the surface layer. In addition, the abundance of foraminiferal indicator species tended to decrease with depth (Fig. 9).

As one of the largest energy consumers and rapidly increasing demand, offshore drilling is becoming an important source for fossil fuel. In China, the Bohai Sea is the most important oil production area since 1980s and the local marine environment is heavily impacted by oil pollution (Hu et al., 2013, 2011; Qin et al., 2011). By nature, the Bohai Sea is a half-closed sea with limited water exchange with the Yellow Sea. The general circulation pattern is characterized by an east–westwards, north–southwards, anticlockwise currents from bay mouth to the inner (Chen, 2009). To properly understand the results, it is important to fit the observed biological changes in physical environment. In the present study, the overall concentrations of pollutants in sediment samples were not so high with the highest PAHs

Table 3 Correlations (Spearman’s r values) between foraminiferal community parameters and environmental factors. Data were based on the data after log (x + 1) transformed from each sample of the 9 sediments taken from 0 to 2 cm surface layer. Because the same data were used in several analyses (pollution parameters), the a-level was reduced from 0.05 to 0.025. p-values (in the lower line parentheses) beneath 0.025 are marked in double asterisks. PAHs

Oils

Sulfides

Organic carbon

>150 lm fraction Total abundance Living abundance Abnormal abundance Living ratio (%) Abnormal ratio (%) Species richness (S) Margalef index (D) Shannon–Wiener index (H0 ) Evenness (J0 )

0.600(0.088) 0.267(0.488) 0.150(0.700) 0.383(0.308) 0.817(0.007)⁄⁄ 0.360(0.342) 0.200(0.606) 0.300(0.433) 0.000(1.000)

0.683(0.042)⁄ 0.883(0.002)⁄⁄ 0.800(0.010)⁄⁄ 0.067(0.865) 0.300(0.433) 0.502(0.168) .700(0.036)⁄ 0.067(0.865) 0.667(0.050)

0.500(0.170) 0.500(0.170) 0.083(0.831) 0.233(0.546) 0.433(0.244) 0.435(0.242) 0.217(0.576) 0.317(0.406) 0.100(0.798)

0.519(0.152) 0.527(0.145) 0.142(0.715) 0.050(0.898) 0.485(0.185) 0.248(0.520) 0.092(0.814) 0.075(0.847) 0.033(0.932)

63–150 lm fraction Total abundance Living specimens Living ratio (%) Species richness (S) Margalef index (D) Shannon–Wiener index (H0 ) Evenness (J0 )

0.686(0.041)⁄ 0.720(0.029)⁄ 0.517(0.154) 0.571(0.108) 0.683(0.042)⁄ 0.233(0.546) 0.583(0.099)

0.477(0.194) 0.226(0.559) 0.083(0.831) 0.420(0.260) 0.350(0.356) 0.050(0.898) 0.150(0.700)

0.343(0.366) 0.351(0.354) 0.150(0.700) 0.025(0.949) 0.167(0.668) 0.283(0.460) 0.233(0.546)

0.311(0.415) 0.227(0.557) 0.025(0.949) 0.059(0.880) 0.142(0.715) 0.301(0.431) 0.276(0.472)

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx Table 4 Summary of results from biota-environment (BIOENV) analysis showing the best matches of pollution factors with spatial distribution of living foraminiferal species in >150 lm fraction at 9 sampling sites. The a-level was ranked to 0.05. p-values beneath 0.05 were considered as significant and are marked in asterisks. Rank

R

Environmental variables

p

1 2 3 4 5 6 7 8 9 10

0.490 0.469 0.423 0.416 0.408 0.385 0.373 0.370 0.364 0.310

PAHs, Oils, Sulfide PAHs, Oils Oils Oils, Sulfide PAHs, Oils, Sulfide, Organic Carbon PAHs, Sulfide PAHs, Oils, Organic Carbon PAHs Oils, Organic Carbon Oils, Sulfide, Organic Carbon

0.019⁄⁄ 0.040⁄⁄ 0.006⁄⁄ 0.021⁄⁄ 0.082 0.051 0.108 0.106 0.097 0.111

9

industrial discharges. Therefore oils and PAHs were low at St26 station but sulfides and organic carbon were high. In the present study, the impact was relatively clear at broad scale. Oil contaminates were high at the stations near the spill site (St36, St22 and St14), and current could bring oil contaminates diffused to the surrounding stations such as St6, St19, StA8 and St31. Another important factor is sediment type (Mojtahid et al., 2006). For example, the silty sediment type at St31 has strong impact on water exchange and degradation of oil containments. Although St14 was nearest to the spill site, statistical analysis based on environmental factors and foraminiferal abundance suggested St31 was the most severely affected site. The measurements on pollution factors among sampling sites indicated that St22, St11 and St14 were heavily impacted by oils, but PAHs representing biological accumulation at St31 and St22 were highest. To understand the observed patterns, it requires detail information on near bottom currents and biological processes related to oil degradation. 4.2. Horizontal and vertical distribution of foraminiferal communities

Fig. 5. Multidimensional scaling (MDS) ordination on abundance of total foraminiferal fauna (A), and abundance of living foraminiferal fauna (B) in >150 lm fraction using Euclidean distance among 9 sampling sites. To perform the MDS analysis, data were log (x + 1) transformed and Spearman rank correlations were calculated.

concentration of 123 ng/g, lower than the commonly referred effects range-low (ERL) concentration of 4022 ng/g (Long et al., 1995), but comparable to the value reported by Denoyelle et al. (2010) with sediment PAHs concentrations up to 160 g/kg close to the discharge point of oil polluted drill mud. The relative low concentrations of pollutants could be attributed to fact that sampling occurred 6 months after the spill and pollutants might be degraded or transported away by near bottom currents. In this study, the concentrations of oils tended to be high at stations near the spill site except St31. Although sediment type in St31 was silt, which might not retain oils contaminants very well, the concentration of PAHs, representing bioaccumulation of hydrocarbon was still high at St31. Meanwhile, in the contaminant based cluster analysis St31 was separated from other stations, indicating its different environment characteristics. St26 was selected as the reference site because it was the farthest from the oil spill site, but this station was located near coast, which often received

To our best knowledge, we are not aware that any studies have investigated the relationship between benthic foraminifera and oil pollution in the Bohai Sea. The present study not only investigated the potential of using foraminifera to evaluate the environmental impact of oil spill, but also provide knowledge on species composition and potential indicator species which will provide baseline information for future studies. Studies have found that the abundance of benthic foraminifera was less than 200 individuals per 10 cm2 in >150 lm fraction in areas with oil drilling. For example, in Angola, northwestern of Africa, the abundance ranged from 20 to 200 individuals per 10 cm2 in sediments affected by oily cutting discharge (Jorissen et al., 2009). Another study in the outer continental shelf off Congo of central Africa found the abundance was <170 individuals per 10 cm2 at a station impacted by oily drill cutting disposal on the sea floor environment (Mojtahid et al., 2006). Additionally, a seasonal study carried out at a 550 m deep station in the Bay of Biscay in northwest of Atlantic showed the benthic foraminiferal abundance was from 35 to 200 individuals per 10 cm2 at a 550 m deep station, and from 25 to 90 individuals per 10 cm2 at a 1000 m deep two open slope stations (Fontanier et al., 2003, 2006). In the present study the abundance of total fauna was ranged from 150 to 488 individuals per 10cm2, living abundance varied from 72 to 238 individuals per 10 cm2 in >150 lm fraction. Overall, the density benthic foraminifera in the Bohai Sea appeared to be higher when compared to other regions. The species composition and abundance showed a distinct uneven distribution as a result of oil spill. The lowest abundances of total fauna and living fauna, for both large and small foraminiferal assemblages, occurred at St31 (Table 2), suggesting heavy impact from oil-pollution in the study area. St26 appeared to be in the best condition based on community parameters of large foraminiferal group, e.g., highest species richness and Margalef index. Furthermore, St26 also had the least proportion of abnormal individuals which indicated less environmental stress. Next to St26, diversity parameters at St6 and at St19 were higher than other sites. Additionally, the lowest species richness was observed at St14, and the highest percentage of abnormal specimens was observed at St22, suggesting potential environmental stress at these stations. The overall community structure was also consistent with environmental conditions. The results from MDS analysis on the abundance of individual species were consistent with the environmental conditions at different stations. Meanwhile, other community parameters including the total, living, abnormal fauna, Margalef index (D) were all related to either oils or PAHs. Our results confirmed that oil pollution have impact most benthic

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Fig. 6. Cluster analysis on Bray–Curtis similarity matrices by Ward method for foraminiferal species, based on the abundance of individual species of total fauna in >150 lm fraction. Note that species were separated into two distinct clades.

foraminiferal species and can further affect community parameters and species composition. The deposition of foraminifera in sediments could also provide historical information and allows a comparison between the present and the past time to examine the impact of oil pollution. In the present study, we utilized the vertical distribution of foraminifera to select the bioindicator species, which offers an opportunity to examine potential changes at individual stations. Our results revealed that the community structure was different at different sediment layer, with a general trend of increasing proportion of arenaceous types and a reduction of hyaline forms from the bottom to the top layers. Using selected bioindicators of the foraminifera in each sediment depth, we established a local FIEI index which could be used to investigate the historical changes in environmental conditions, oil pollution in particular, in the Bohai Sea.

4.3. Responses of benthic foraminifera to oil pollutant Different foraminiferal species may show differential response to oil pollution. Specifically, large foraminifera were more sensitive to the oils than the small foraminifera. For large foraminifera, their abundance, abnormality and Margalef index were negatively affected by oils. In contrast, small foraminifera did not show significant response to oils. This result was consistent with the study conducted on continental margin off Africa by Jorissen et al. (2009), which also showed that large-sized foraminiferal taxa appeared more sensitive than small in sediments impacted by oily cuttings discharged during oil exploration. In the same study, they also found that both species number and Shannon–Wiener index were high at the distant station and decreased with increasing distance from the disposal site (Jorissen et al., 2009).

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Fig. 7. Canonical Correspondence Analysis (CCA): plot of relationships between foraminiferal species (in Arabic numbered) and pollution factors (PAHs, Oils, Sulfide and Organic carbon). Data were based on total foraminiferal species in >150 lm fraction and were transformed by log (x + 1). Each number of the species was concordant with that in Fig. 6. The species names in the figure were numbered as follows: 1, Ammoglobigerina globigeriniformis; 2, Cribrononion incertum; 3, Buccella frigida; 4, Elphidium macellum; 5, Cribroelphidium magellanicum; 6, Protelphidium sp1; 7, Polskiammina asiatica; 8, Quinqueloculina ungeriana; 9, Quinqueloculina bellatula; 10, Cribrononion asiaticum; 11, Verneuilinulla advena; 12, Ammonia tepida; 13, Pseudoeponides japonicas; 14, Ammonia inflate; 15, Rotalidium annectens; 16, Rotalinoides compressiusculus; 17, Ammonia falsobeccarii; 18, Ammobaculites formosensis; 19, Nonionoides cf. grateloupii; 20, Fissurina lucida; 21, Fissurina cf. marginata; 22, Lagenammina asymmetrica; 23, Psammosphaera fusca; 25, Ammonia pauciloculatus; 26, Textularia foliacea; 27, Lagena spicata; 28, Amphicoryna proxima; 29, Nouria textulariformis; 31, Quinqueloculina polygona; 35, Textularia oceanica; 36, Spiroloculina bohaiensis; 37, Lagena hispidula; 38, Nodosaria communis; 39, Siphogenerina raphanus; 40, Rosalina globularis; 47, Ammonia sp.; 56, Spiroloculina planulata; 77, Ammonia ketienziensis; 78, Gyroidella planata; 80, Protelphidium sp2; 89, Elphidium advenum.

In the present study the abundance of small foraminifera was about one order of magnitude higher than the large one, but the living ratio was about one order of magnitude lower than that the large group (Table 2). It suggests that benthic foraminifera may enhance their production to compensate their high mortality in this area, and therefore small foraminifera responded to oil-pollution by high production and high mortality. This result was consistent with a laboratorial mesocosm study conducted in an intertidal mudflat (Bay of Bourgneuf, France) where benthic foraminifera exposed to oil-polluted seawater showed a dual

response to oil-induced pollution (Ernst et al., 2006). The foraminiferal density in some oil-treated mesocosms strongly increased by enhancing their production, on the other hand, they may experience elevated mortality. In the present study, large volume of deformed foraminiferal specimens was observed in the samples, surface 0–2 cm layer in particular. The percentage of deformed individuals increased as concentration of oil pollutants increased (Table 2). Statistical analysis results showed that the abnormal specimens significantly increased as oils concentration increased, meanwhile, the abnormal ratio were significantly positively correlated with PAHs (Table 3). In other studies, Foraminiferal Abnormality Index (FAI), an index of percentage of abnormal specimens within the sample (Coccioni et al., 2005) has been used to evaluate the stress of environment from pollution contaminates (Armynot du Châtelet and Debenay, 2010). A laboratorial culture experiment documented that benthic foraminifera (A. tepida) responded to oil pollution by morphological abnormalities, cellular modification and a low rate of production (Morvan et al., 2004). Several studies (e.g. Vénec-Peyré, 1981; Yanko et al., 1992; Morvan et al., 2004) also observed very low foraminiferal abundance as well as morphological abnormalities. Our results were consistent with previous studies and demonstrated that both the abundance of abnormal individuals and abnormal ratio were significantly correlated with oils, and PAHs, respectively (Table 3). Considering that the natural background for the abnormality value is around 1–2%, values that we observed are high (4.6–31.0%) and indicate that foraminiferal assemblages were affected by environmental stress, at a different extent, in all sampled stations (Frontalini and Coccioni, 2011; Morvan et al., 2004). The composition and faunal distribution of benthic foraminifera in the Bohai Sea have not been studied in detail before. However, different foraminiferal species showed different advantages in assessing pollution status and several bioindicators were documented in different pollution environments. The foraminiferal community was dominated by opportunistic species including Haynesina germanica, A. tepida and Cribroelphidium gunteri in heavy metal polluted sediments at the Goro lagoon in Italy (Luciani, 2007). In an African open marine slope affected by disposal of oil drill cuttings, the common foraminiferal taxa included Chilostomella oolina and small-sized bolivinids and buliminids. Sensitive species included Uvigerina peregrina, Cancris auriculus and Cribrostomoides subglobosus (Jorissen et al., 2009). Unlike Italian and African sediments, the Bohai Sea is located in shallow continental shelf in the north temperate zone. Therefore the foraminiferal assemblages in this region were characterized by cold temperate and shallow water species dominating and were very different with the above studies. In addition, study conducted in an Italian Bagnoli Bay, which was heavily affected by industrial

Table 5 Spearman’s correlation between foraminiferal bioindicators and pollution factors. Data were based on total and living foraminiferal abundances in >150 lm fraction and were log (x + 1) transformed. Species

Abundance

PAHs

Oils

Sulfide

Organic carbon

Ammoglobigerina globigeriniformis

Total Living Total Living Total Living Total Living Total Living Total Living Total Living

0.517(0.154) 0.500(0.170) 417(0.265) 0.383(0.308) 0.367(0.332) 0.008(0.983) 0.100(0.798) 0.267(0.488) 0.250(0.516) 0.050(0.898) 0.267(0.488) 0.067(0.865) 0.126(0.748) 0.077(0.845)

0.567(0.112) 0.633(0.067) 0.850(0.004)⁄⁄ 0.533(0.139) 0.800(0.010)⁄⁄ 0.866(0.003)⁄⁄ 0.633(0.067) 0.417(0.265) 0.683(0.042)⁄ 0.717(0.030)⁄ 0.350(0.356) 0.033(0.932) 0.678(0.045)⁄⁄ 0.928(0.000)⁄⁄

0.650(0.058) 0.533(0.139) 0.483(0.187) 0.233(0.546) 0.617(0.077) 0.227(0.557) 0.317(0.406) 0.567(0.112) 0.567(0.112) 0.283(0.460) 0.200(0.606) 0.167(0.668) 0.209(0.589) 0.162(0.678)

0.778(0.014)⁄ 0.561(0.116) 0.410(0.273) 0.301(0.431) 0.594(0.092) 0.072(0.854) 0.276(0.472) 0.427(0.252) 0.678(0.045)⁄ 0.477(0.194) 0.033(0.932) 0.351(0.354) 0.118(0.763) 0.205(0.596)

Buccella frigida Cribrononion asiaticum Cribrononion incertum Elphidium macellum Quinqueloculina ungeriana Verneuilinulla advena

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Abundance (ind. 10cm-2) 90 Ammoglobigerina globigeriniformis

pollution tolerant and opportunistic taxa. This result is consistent with Mojtahid et al. (2006) in which they observed the lowest benthic foraminiferal density at sites within the immediate vicinity of oil-polluted, but high density at sites within the intermediate vicinity and then decreased. Alve (1995) pointed out the characteristic features of foraminiferal assemblages in oil-polluted region that proximal areas included decreased diversity and increased dominance of tolerant or opportunistic species compared to distant areas. In the present study, the pollutant resistant species and opportunistic species were identified through cluster analysis and CCA. Cluster analysis grouped common and dominant species among stations and CCA identified species affected the most by oil pollution. Among the dominant species, the sensitive taxon, C. magellanicum, showed a distinct decline from the reference site (St26) to heavily polluted stations. The pollution resistant taxa B. frigida, E. macellum, C. asiaticum, V. advena increased their abundance from the low to the high oil-polluted stations. Several opportunistic species including A. globigeriniformis, C. incertum and Q. ungeriana were also abundant at oil spill region but there were not statistical significant correlations with oils (Table 5). Information at species level provides critical information in understanding the spatial variation in community parameters, and furthermore the pollution tolerant and opportunistic taxa were selected to build FIEI index.

Living Total

45 0 70

Buccella frigida St26 StA8 St6 St19 St11 St36 St22 St14 St31

35 0 40

Cribrononion asiaticum St26 StA8 St6 St19 St11 St36 St22 St14 St31

20 0 60

Cribrononion incertum St26 StA8 St6 St19 St11 St36 St22 St14 St31

30 0 30

Elphidium macellum St26 StA8 St6 St19 St11 St36 St22 St14 St31

15 00 36

Quinqueloculina St26 StA8 St6 St19 St11 St36 St22 St14 St31 ungeriana

18 14 00

4.4. Using foraminiferal indices to assess the oil pollution There were several foraminiferal indices including FIEI (Mojtahid et al., 2006), Foraminiferal Abnormality Index (AI, Coccioni et al., 2005) and Foraminifera in Reef Assessment and Monitoring Index (FI, Hallock et al., 2003). Since oil pollution often has severe biotoxicity and bioaccumulation and exerted comprehensive impacts on marine organisms and ecosystem, it is difficult to assess pollution status among stations if only using single chemical value. Therefore many studies attempted to selected suitable bioindicators to evaluate the pollution status of environments. The FIEI index is often region-specific because the index is based on the relative abundance of the selected indicator species, i.e., pollution-tolerant and opportunistic taxa. According to Mojtahid et al. (2006) and Denoyelle et al. (2010), the pollution-resistant taxa and opportunistic taxa were identified based on their spatial patterns. FIEI index was therefore corresponded to the accumulated percentage of opportunistic and stress-tolerant taxa. By using the cumulative percentage of pollution-tolerant and opportunistic taxa, the FIEI can also reflect pollution stress at an elevated level. Denoyelle et al. (2010) showed

Verneuilinulla St26 StA8 St6 advena St19 St11 St36 St22 St14 St31

7 0 St26 StA8 St6 St19 St11 St36 St22 St14 St31 Fig. 8. Spatial distribution of the abundance (individuals 10 cm2) of bioindicators at 9 stations.

discharge documented several pollution tolerant benthic foraminiferal species, among them E. macellum is capable of tolerating the presence of PAHs (Bergamin et al., 2003). In the present study, the abundance of both total fauna and living fauna were high at stations with intermediate concentration of oil pollutants (e.g. St11 and St22) but relatively low at the reference site (St26), indicating an oil-philic property of benthic foraminifera. High abundance could be attributed to the increase of

Ammoglobigerina globigeriniformis

Elphidium Quinqueloculina Verneuilinulla macellum advena ungeriana

Cribrononion incertum

Cribrononion asiaticum

Buccella frigida

0-2 cm

Sediment depth

2-4 cm 4-6 cm 6-8 cm 8-10 cm 10-12 cm 12-14 cm 14-16 cm 00

2550 25

0

30

0

10

0

30

0

75

0

20

0

5

10

Mean abundance (ind. 10cm-2) Fig. 9. Vertical distribution of foraminiferal indicator species (Ammoglobigerina globigeriniformis, Buccella frigida, Cribrononion asiaticum, Cribrononion incertum, Elphidium macellum, Quinqueloculina ungeriana, Verneuilinulla advena) in each sediment depth. Data were based on the average value of species abundances across 9 stations within the same sediment depth interval.

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Table 6 Foraminiferal Impact of Environmental Index (FIEI) values in sediment depths based on the abundance of foraminiferal bioindicators in >150 lm size fraction. The Bioindicators included the following resistant taxa: Buccella frigida, Elphidium macellum, Cribrononion asiaticum, Verneuilinulla advena, and the following opportunistic taxa: Ammoglobigerina globigeriniformis, Cribrononion incertum, Quinqueloculina ungeriana. Note that 40 < FIEI was considered no polluted, 60 < FIEI < 80 was moderately polluted, FIEI > 80 was severely polluted. Sediment depths (cm)

Abundance of indicators

St26

StA8

St6

St19

St11

St36

St22

St14

St31

0–2

Total individuals Living individuals Total individuals Total individuals Total individuals Total individuals Total individuals Total individuals Total individuals

38.65 33.59 21.04 28.64 26.79 27.27 27.21 – –

58.65 64.83 49.14 44.13 45.08 – – – –

50.99 60.08 41.79 41.50 42.34 37.09 38.82 38.33 33.76

47.26 60.90 – – – – 27.98 34.17 32.93

49.17 72.44 35.56 37.37 41.90 42.01 38.35 29.27 –

52.84 64.61 44.59 41.94 46.06 37.61 – – –

53.46 57.14 48.88 47.84 43.32 35.74 45.03 – –

64.51 60.19 – – – – 42.76 43.49 –

66.74 88.73 57.67 64.81 59.85 – – – –

St26

StA8

St6

St19

St11

St36

St22

St14

St31

that the FIEI index was effective in assessing oil-pollution. However, constructing an FIEI index requires a detailed background investigation of local fauna and selection of foraminifera as indicator species. In the present study, the study sites reflected different levels of pollution and the spatial extent, both horizontally and vertically, of the samples provide adequate background information for the selection of indicator species. Denoyelle et al. (2010) suggested that an FIEI value within 40–50 indicated a low degree of environmental stress, and a value above 60 indicated a strong environmental impact of oil pollution. In the present study, based on the horizontal and vertical distribution of benthic foraminifera, we classified the pollution status in Bohai Sea using the selected indicators into four categories: FIEI < 40 means unpolluted; 40 < FIEI < 60 means lightly polluted; 60 < FIEI < 80 means moderately polluted; FIEI > 80 means severely polluted. Although the classification based on FIEI is somewhat arbitrary, the pollution status is consistent with the observed pollutant concentrations and other community parameters including density, diversity and species composition of the total and living fauna and abnormal specimens. Based on our FIEI calculation result (Table 6), St26 could be considered unpolluted (FIEI < 40), the following 6 stations including St6, St19, St11, St22, St36 and StA8 were lightly polluted (40 < FIEI < 60); St14 were moderately polluted (FIEI > 60). St31 could be considered moderately to severely polluted (FIEI > 60 based on total foraminifera, or FIEI > 80 based on living fauna). The most significant advantage using foraminifera as bioindicators is that this organism reflects sediment dynamics. They also records environmental information of ambient water and deposition in respective stratums, providing a dynamic archive of the local environmental changes. Engle (2000) suggested that the ideal bioindicator would not only quantify the present environmental status in ecosystems but also document the effects of anthropogenic and natural stressors on the organisms over time (Hallock et al., 2003). In the study area, sediment deposition rate was reported about 0.2–0.4 cm/a (Li et al., 2002, 2003). If we assume that every 3-cm sediment corresponds to 10 year’s deposition, the FIEI index reflected environmental conditions at each sediment depth (Fig. 10). The FIEI appeared to decrease from surface strata to deep layer. The oil exploration in the Bohai Sea started in late 1960s, corresponding to the deposition 14–16 cm depth, where the FIEI values in sediments at 14–16 cm was within 30–40. But oil drilling started in the 1980s, corresponding to 10-cm sediment depth, where FIEI was within 40–50. The largest increase of FIEI occurred at the 8–10 cm depth at most stations, but afterwards the values remained stable. In the surface layer most stations evidently had the highest FIEI values, and at some stations was as high as 70. Although this was only a rough assessment, the FIEI index provided us a general picture of environmental changing expressed by foraminifera in space and time. However,

80 70 Foraminiferal Impact of Environmental Index

2–4 4–6 6–8 8–10 10–12 12–14 14–16

60 50 40 30 20 10 0 0-2cm

2-4cm

4-6cm

6-8cm

8-10cm 10-12cm 12-14cm 14-16cm

Fig. 10. Values of the Foraminiferal Impact of Environmental Index (FIEI) in sediment depths based on resistant and opportunistic bioindicators of foraminifera at the 9 stations sampled in the Bohai Sea in 2011.

like any other indices, it is not an easy task to construct a region-specific FIEI index, because it requires background information on species composition and changes in abundance and it also needs to adjusted and verified over time to reflect local foraminiferal fauna.

5. Conclusion The present study demonstrates the potential of utilizing benthic foraminifera to evaluate environmental changes using samples collected near the 2011 oil spill site in the Bohai Sea. Based on the horizontal and vertical distribution of foraminifera, large size group (>150 lm) were more sensitive to oil pollutants than the small size group (63–150 lm fraction). The abundances of total fauna, living fauna and abnormal specimens were all significantly positively correlated to oils, suggesting the presence of oil-philic foraminiferal community in the Bohai Sea, but with decreased diversity. The variation in species composition of living foraminifera could attribute to a combination of oils, PAHs and sulfides. However, small foraminifera appeared to respond to oil pollution differently, with an enhanced production and high mortality. The proportion of abnormal specimens tended to be more abundant at high oil-polluted sites, and it was significantly correlated with PAHs, indicating a negative effect of oil spill on foraminiferal community. In the present study, benthic foraminiferal species showed differential response to oil pollution, and therefore they could be used as bioindicators. Four species including B. frigida, E. macellum, C. asiaticum and V. advena were pollution resistant taxa. Three species

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

of A. globigeriniformis, C. incertum and Q. ungeriana were regarded as opportunistic taxa. The FIEI index constructed from pollution tolerant and opportunistic was a straightforward tool to evaluate the oil pollution status. At the reference site, i.e., no pollution (St. 26), the FIEI was <40; At the slightly polluted sites (St6, St19, St11, St22, St36 and StA8), the FIEI ranged from 40 to 60; At the moderately polluted site (St14) the FIEI ranged from 60 to 80; At the severely polluted site, FIEI could be >80 (St31). The vertical profile of FIEI also provided a general picture of oil drilling related environment stress in the study area with low FIEI in deep layer and high FIEI near surface (10 cm to surface layer), corresponding oil drilling activities started in this area in the 1980s.

foundations of GZH201100202; GASI-03-01-03-01, XDA11030201; DOMEP (MEA)-01-01-E, No. 201303. Special thanks are due to Dr. Zhimin Jian (Tongji University, China) for many supports and instructions to the first author in foraminiferal research. We thank the Editor-in-chief Prof. Charles Sheppard and anonymous referees for helpful comments on the manuscript. We acknowledge Ms. Xuejiao Wang, Ms. Mengmeng Zheng, Ms. Lina Cao and Mr. Shuaishuai Dong in sample treatments (Department of Marine Organism Taxonomy & Phylogeny, Institute of Oceanology, Chinese Academy of Sciences).

Appendix A Acknowledgments See Tables A1 and A2. This work received financial support from the National Science Foundation of China Nos. 41176132; 41476043; 41006021 and

Table A1 The occurrence of the foraminiferal taxa of >150 lm fraction in different sediment strata with respective abundance (individuals 10 cm2) at the 9 sampling sites in the Bohai Sea. Note that size was measured on 5–10 randomly selected individuals for each species. Both test length and width were measured for each individual. Mean values were presented here. Species

Size (lm)

Distribution in sediment strata

St26

StA8

St6

St19

St11

St36

St22

St14

St31

Astrorhizida Lagenammina asymmetrica Psammosphaera fusca

662  304 485  348

0–2 cm 0–16 cm

– 0.4

– –

– 1.8

1.4 1.4

– 2.8

– 3.5

– –

– 0.4

– 0.7

Textulariida Ammobaculites formosensis Ammoglobigerina globigeriniformis Nouria textulariformis Polskiammina asiatica Textularia foliacea Textularia oceanica Verneuilinulla advena

498  131 397  339 356  242 365  310 1132  513 459  286 317  146

0–8, 10–12 cm 0–16 cm 0–2 cm 0–14 cm 0–2, 4–8, 10–12 cm 0–2, 8–12, 14–16 cm 0–12 cm

2.1 58.0 0.7 – 2.5 – 1.8

– 37.1 – – – – 5.3

1.4 15.2 – – 0.4 – 4.6

2.8 29.7 – 1.4 – – 7.1

2.8 53.8 – – – – 7.1

0.7 76.4 – – – – 12.7

– 43.9 – – – – 8.5

– 34.0 – 0.4 – – 3.5

0.4 22.6 – – – – 2.1

Miliolida Quinqueloculina bellatula Quinqueloculina polygona Quinqueloculina ungeriana Spiroloculina bohaiensis Spiroloculina planulata

378  215 620  423 763  599 960  776 800  520

0–4, 6–12, 14–16 cm 0–2, 6–8, 8–10 cm 0–14 cm 0–2, 2–4 cm 0–4, 10–12 cm

1.8 0.4 8.8 – –

1.4 – 5.7 0.4 –

– – 19.5 – 0.4

0.7 – 14.2 – 1.4

– – 31.1 – 1.4

– – 4.2 – 2.8

1.4 – 24.1 1.4 1.4

– – – 0.4 –

1.8 – 5.3 2.5 0.7

Lagenida Amphicoryna proxima Fissurina cf. marginata Fissurina lucida Lagena hispidula Lagena spicata Nodosaria communis

1100  290 273  207 139  97 203  163 280  174 549  174

0–2, 6–8 cm 0–4, 6–10 cm 0–2, 12–14 m 0–2, 2–4, 4–6 cm 0–10, 12–14 cm 0–2, 4–6, 14–16 cm

0.4 1.8 – – 1.1 –

– – – – 0.4 –

– 0.7 – – – –

– 1.4 0.7 – – –

– 2.8 – – 1.4 –

– – – – 1.4 –

– – – – – –

– – – – – 0.4

– – – 0.4 – –

Rotaliida Ammonia falsobeccarii Ammonia inflata Ammonia ketienziensis Ammonia pauciloculatus Ammonia sp. Ammonia tepida Buccella frigida Cribroelphidium magellanicum Cribrononion asiaticum Cribrononion incertum Elphidium advenum Elphidium macellum Gyroidella planata Nonionoides cf. grateloupii Protelphidium sp.1 Protelphidium sp.2 Pseudoeponides japonicus Rosalina globularis Rotalidium annectens Rotalinoides compressiusculus Siphogenerina raphanus

418  365 262  235 275  262 250  220 250  225 311  289 295  264 247  213 269  227 340  262 430  390 470  430 260  230 246  168 249  214 370  335 239  222 262  239 510  457 362  335 610  192

0–16 cm 0–2, 4–16 cm 0–16 cm 0–16 cm 0–2, 4–8, 14–16 cm 0–16 cm 0–16 cm 0–16 cm 0–16 cm 0–16 cm 0–16 cm 0–16 cm 0–2, 8–10 cm 0–4, 8–10, 12–14 cm 0–2, 4–6 cm 0–2 cm 0–12 cm 0–2, 4–6 cm 0–16 cm 0–16 cm 0–2 cm

– 0.4 0.4 8.1 – 6.4 44.6 224 12.0 21.6 1.4 27.9 11.7 0.4 0.4 – – – 4.2 5.3 –

0.4 0.4 0.4 4.2 0.4 1.8 38.6 58.7 11.0 23.7 0.4 10.6 6.4 – 0.7 – – 0.4 8.5 7.1 –

2.8 5.0 – 0.7 – 7.8 27.2 56.9 7.1 26.2 1.4 18.7 7.1 0.7 0.7 7.4 7.4 – 4.6 3.9 –

2.8 10.6 – – – 9.2 47.4 97.6 11.3 33.3 1.4 9.9 11.3 1.4 0.7 – – – 4.2 9.9 –

2.8 14.2 – – – 14.2 62.3 132 19.8 55.2 1.4 21.2 12.7 – 7.1 – – – 17.0 25.5 –

2.8 7.1 – 6.4 – 7.8 55.9 109 31.8 51.6 1.4 24.1 19.8 – – 2.8 0.7 – 14.2 16.3 –

– 9.9 – 11.3 – 8.5 56.6 97.6 29.7 49.5 1.4 28.3 19.8 – – 4.2 – – 15.6 18.4 –

– – – 1.8 – 4.2 36.4 50.9 7.8 28.3 – 13.4 – – 0.4 – – – 5.3 1.1 0.4

0.7 – – 2.8 – 4.2 18.7 26.2 3.5 40.0 0.4 9.2 1.8 – 0.4 – – – – 4.2 –

Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020

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Y.L. Lei et al. / Marine Pollution Bulletin xxx (2015) xxx–xxx

Table A2 The occurrence of the foraminiferal taxa of 63–150 lm fraction in sediment strata with respective abundance (individuals 10 cm2) at the 9 sampling sites in the Bohai Sea. Note that size was measured on 5–10 randomly selected individuals for each species. Both test length and width were measured for each individual. Mean values were presented here. Species

Size (lm)

St26

StA8

St6

St19

St11

St36

St22

St14

St31

Textulariida Ammoglobigerina globigeriniformis Ammoscalaria pseudospiralis Cribrostomoides jeffreysii Polskiammina asiatica Textularia oceanica Verneuilinulla advena

210  180 215  140 120  100 95  90 245  205 270  125

101.9 – – – 11.3 418.8

113.2 – – – – 271.6

181.1 45.3 90.5 – – 316.9

203.7 – 22.6 – – 226.4

271.6 90.5 – – – 271.6

135.8 22.6 45.3 – – 271.6

90.5 22.6 22.6 11.3 – 113.2

45.3 – – – – 22.6

11.3 11.3 – – – 11.3

Miliolida Quinqueloculina bellatula Quinqueloculina ungeriana

360  165 260  180

– –

– –

22.6 45.3

– –

– 181.1

– –

– 11.3

– –

11.3 –

140  100

– –

22.6 –

– –

22.6 –

– –

– –

– –

– 11.3

11.3 –

165  125 210  180 190  160 220  210 200  195 170  160 200  170 280  160 290  130 200  195 170  145 205  180 215  175 180  155 225  190 330  280 90  80 175  160 160  120 200  95 125  120 155  130 200  125 200  180 180  140 200  180 125  145

– – – – 22.6 271.6 – 45.3 34.0 – 22.6 1675 45.3 79.2 67.9 – – – – 79.2 11.3 – – 34.0 – 11.3 –

– 22.6 – 67.9 22.6 181.1 – – – 90.5 – 1517 90.5 67.9 67.9 – – 22.6 – – – – – 158.5 – – –

– – 45.3 – – 113.2 – 22.6 – 90.5 – 1494 – 90.5 – – 22.6 22.6 – 113.2 45.3 – – 22.6 – 22.6 –

– – 22.6 22.6 22.6 226.4 – – – 271.6 22.6 2626 – 22.6 22.6 – – – 22.6 – – – – 113.2 – 22.6 22.6

– – – 271.6 – 452.7 – 90.5 – 362.2 – 3893 – – 181.1 – – – 90.5 – – – – 633.8 – – –

– 22.6 – 67.9 45.3 158.5 45.3 22.6 22.6 158.5 – 2988 – 22.6 22.6 – – – – 45.3 22.6 22.6 22.6 90.5 – – –

34.0 – 22.6 22.6 – 147.1 11.3 – – 181.1 – 1652 22.6 67.9 56.6 – – 11.3 – 34.0 45.3 – – 90.5 34.0 – 11.3

– – – 11.3 22.6 135.8 – – 22.6 45.3 – 1607 22.6 56.6 34.0 – – – – 56.6 56.6 11.3 – 79.2 22.6 11.3 –

– – – – 90.5 237.7 – – 22.6 56.6 – 1234 – 90.5 – 11.3 – – – 11.3 45.3 – – 67.9 – – 11.3

Lagenida Fissurina cf. marginata Lagena substriata Rotaliida Ammonia beccarii Ammonia falsobeccarii Ammonia inflata Ammonia ketienziensis Ammonia pauciloculatus Ammonia sp. Ammonia tepida Bolivina robusta Bolivina striatula Buccella frigida Bulimina marginata Cribroelphidium magellanicum Cribrononion asiaticum Cribrononion incertum Elphidium advenum Elphidium macellum Globocassidulina subglobosa Gyroidella planata Gyroidina orbicularis Hopkinsina atlantica Murrayinella globosa Natlandia secasensis Nonionella stella Protelphidium sp.2 Pseudoeponides japonicus Rotalidium annectens Rotalinoides compressiusculus

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Please cite this article in press as: Lei, Y.L., et al. Responses of benthic foraminifera to the 2011 oil spill in the Bohai Sea, PR China. Mar. Pollut. Bull. (2015), http://dx.doi.org/10.1016/j.marpolbul.2015.05.020