Effects of thermal discharge from Neka power plant (southern Caspian Sea) on macrobenthic diversity and abundance

Author’s Accepted Manuscript Effects of Thermal Discharge from Neka Power Plant (Southern Caspian Sea) on Macrobenthic Diversity and Abundance Ayda Bozorgchenani, Jafar Seyfabadi, Mohammad Reza Shokri www.elsevier.com/locate/jtherbio

PII: DOI: Reference:

S0306-4565(17)30498-9 https://doi.org/10.1016/j.jtherbio.2018.05.002 TB2109

To appear in: Journal of Thermal Biology Received date: 22 November 2017 Revised date: 2 May 2018 Accepted date: 11 May 2018 Cite this article as: Ayda Bozorgchenani, Jafar Seyfabadi and Mohammad Reza Shokri, Effects of Thermal Discharge from Neka Power Plant (Southern Caspian Sea) on Macrobenthic Diversity and Abundance, Journal of Thermal Biology, https://doi.org/10.1016/j.jtherbio.2018.05.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Effects of Thermal Discharge from Neka Power Plant (Southern Caspian Sea) on Macrobenthic Diversity and Abundance Ayda Bozorgchenania1, Jafar Seyfabadia,* Mohammad Reza Shokrib a

Department of Marine Biology, Faculty of Marine Sciences, Tarbiat Modares University, Noor, Mazandaran, Iran.

b

Department of Marine Biology Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran.

[email protected] (A. Bozorgchenani) [email protected] (J. Seyfabadi) [email protected] [email protected] (M.R. Shokri)

*Corresponding author at: Tarbiat Modares University, Noor, Mazandaran, Iran. +98 11 44553102;

Abstract Effects of thermal discharge from Neka power plant on macrobenthic diversity and abundance was studied in the southern coast of the Caspian Sea. Samples were collected with Van Veen grab of 0.0250 m 2 surface area from 7 stations in winter and summer. A total of 42 species were identified that belonged to 22 genera, 18 families, 13 orders, six classes and three phyla. Bivalve with a total abundance of 90% in winter and 86% in summer constituted the most abundant group throughout samplings, the highest abundance of which belonged to the family Cardiidae. Gastropods followed bivalve in total abundance (8%) in summer and polychaetes (7%) in winter. Statistical analysis indicated significantly higher macrobenthos density at the thermal discharge stations that also took separate positions in the cluster analysis. Temperature was an important factor on the amount of organic matter. Chlorophyll and phaeopigment at the thermal discharge stations were lower than the other stations because of the increased turbulence. The CCA test indicated that temperature was the most influential among all the studied physicochemical factors. The Spearman rank correlation coefficient also showed that the majority of macrobenthic groups had a positive correlation with the organic matter (r=0.34, p<0.05). Macrobenthic species were grouped according to their commonalities relative to these three classes using a Bray-Curtis similarity index and similarity profile (SIMPROF) permutation tests analysis (PRIMER 6). Based on the SIMPER analysis, the cockle Hypanis minima and the polychaete Hypaniola kowalewskii with high abundances played the most important role in making differences among the stations, but won’t be taken as the “thermal indicating species”. The PERMANOVA test showed that the combination of season and stations had a significant effect. The density of macrobenthos was higher in the thermal discharge stations, but diversity in these stations reduced in comparison with the other stations.

Keywords: Macrobenthos, Southern Coast of the Caspian Sea, Thermal Discharge, Power Plant 1. Introduction As the largest landlocked water body in the world, the Caspian Sea harbors many benthic and pelagic species (Dumont, 1998; Kostianoy and Kosarev, 2005). The closed nature of this sea has made it susceptible to adverse 1

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impacts as the result of human activities. Various environmental problems of the Caspian Sea have different origins. Power generation is considered as one of the anthropogenic activities. It has been proved that the use of water as cooling or supplying industrial products can have adverse effects. Thermal discharge can locally increase the temperature of the adjoining water and, therefore, can be considered as thermal pollution, which can have different or unpredictable effects on aquatic environment and organisms (Crema and Pagliai, 1980). Quality assessment of ecological changes in the sea can be efficient with the study of sedimentary habitats and benthic fauna, because the highest concentration of pollution load is on the seafloor. The relative importance of heat stress caused by coastal power plant mainly depends on the power plant design, discharge station, ambient temperature, and the characteristics of the study area (Lardicci et al., 1999; Chou et al., 2004). Benthos play important roles in the food chain structure and recycling energy (Andrew and Ann, 1996). As for the biomass, polychaetes, crustaceans and mollusks are more important among the benthic invertebrate communities. Being limited in mobility and escaping, benthic organisms are sensitive to pollution, including the thermal discharge (Bamber and Spencer, 1984). That is why they are used to determine the effect of various pollutants to aquatic communities (Aleem, 1990; Warwick, 1993), and often regarded as bio-indicators, particularly where coastal environments is under anthropogenic threads (Desroy et al., 2003). Most species of benthic communities in the Caspian Sea are considered as endemic (Herman et al., 1999; Platell et al., 2006). In general, water discharge from power-generating plants is roughly 10ºC warmer than receiving waters and in a confined space can have positive, negative and neutral effects (Riera et al., 2011). Different studies in the field of thermal discharges on the benthos communities throughout the world have had various results, including being ineffective in some areas with no conspicuous changes in the diversity, abundance of the dominant species, community structure, and species distribution (Loi and Wilson, 1979; Lardicci et al., 1999). On the other hand, it was found effective in some areas and some genera resistant to thermal stresses were observed at thermal discharge (Bamber and Spencer, 1984). Cheng et al. (2004) also observed decreased macrobenthic diversity near the thermal discharge. Therefore, while in some areas a negative correlation was observed between the increased water temperature and the macrobenthic diversity (Kailasam and Sivakami, 2004), in other areas the highest abundance and diversity was observed near the power plant (Riera et al., 2011). In Iran despite several works on benthic communities, studies on the impact of thermal discharge on macrobenthos are very limited (Mirzajani and Kiabi, 2000; Taheri et al., 2008; Roohi et al., 2010; Nemati et al., 2015). In the present study, we examined the impact of thermal discharge on the macrobenthic communities. 2. Materials and Methods 2.1. Study area Providing 7% of the country's electricity, Neka Power Plant (36° 50' 14" N, 53° 15' 30" E) is one of the largest plants the Middle East and the largest one in northeast of Iran on the southern coast of the Caspian Sea. The main fuel is natural gas, followed by mazut. Water for cooling the plant is supplied from the Caspian Sea and the discharge directly flows back to the sea through two channels, the eastern channel (260 m length and of 11 m width) and the western channel (560 m length and 6 m width). The channel depth is 3.6 meters. The maximum water flow rate per unit of steam is 208000 m3/h-1 and for the combined cycle unit is 40,000 m3/h-1 (Farabi et al., 2009). 2

2.2. Sampling and laboratory procedures 2.2.1. Sampling Sampling was conducted to compare the benthic community features near the thermal discharge and the zones not influenced by the thermal discharge. Macroinvertebrates along with sediment samples were collected twice in the summer (Aug, 2015) and winter (Feb, 2015) from seven stations, which included one station near the eastern thermal discharge channel (IE) and one station near the western discharge channel (IW), plus two control stations out of the boundary of the thermal discharge influence to the east (CE) and west (CW), approximately 1 km from the thermal sources, respectively. Three additional stations, viz. C1 (about 90 m eastward), C2, (about 200 m westward), and C3 (approximately 250 m south of C1 station) were designated to determine the temperature gradient (Fig. 1). Therefore, totally seven stations were sampled during each sampling, all of them from 5 m depths and all samplings were conducted in three replications, using a Van Veen grab of 0.0225 m2. About 150 g of wet sediments samples were taken for determination of the total organic matter content, and another 150 g for particle size distribution, sedimentary pigments, including photosynthetic (chlorophyll-a) and non-photosynthetic pigments (phaeopigments) from each station. For the sedimentary pigments, the top 1cm layer of the undisturbed sediment was taken using a cutoff 60 cm3 syringe and about 5 g of it was placed in each centrifuge tube. All samples for sedimentary pigments were frozen until further analysis. Sediment samples containing macroinvertebrates was also immediately placed in separate zip-lock plastic bags labeled and fixed in 4% formalin. The samples were then stained with Rose Bengal (1 g L -1) in order to mark the living organisms in the sample and then transferred to laboratory. All sediments samples were conducted in three replications. Several environmental variables were measured to assess their relationship with community parameters of macroinvertebrates, including water temperatures (°C) and dissolved oxygen (DO, mg/l) measured with OxyGuard® (Handy Gamma model), salinity (PSU) with a handy refractometer (Milwaukee®: MR100ATC model), and acidity (pH) measured with MARTINI® (pH 56 model) sets, respectively. In addition, the accurate geographical positions were recorded using a hand-held GPS (Garmin, error < 3 meters) (Table 1). 2.2.2. Laboratory procedures Sediment samples were washed through a 0.5 mm sieve and the retained macroinvertebrates were preserved in 4% formalin. The macroinvertebrate individuals were enumerated and identified to the lowest possible taxonomic level. For identification, we used mainly the available taxonomical literatures (Birstein and Romanova, 1968; Stock et al., 1998). For the sedimentary pigments, the centrifuge tubes were stored in the dark at -20°C prior to pigment extraction and were measured by extracting the fat soluble pigments into acetone and measuring the optical density of the acetone extract using a spectrophotometer before and after acidification (Gambi and Dappiano, 2004). For the organic matter content and grain size, the sediment samples were dried at 70°C for 24h and separately analyzed for organic matter by the ignition method (Gambi and Dappiano, 2004). The grain size of sediments was classified into seven fractions: >2 mm, 1–2 mm, 0.5–1 mm, 0.25–0.5 mm, 0.125–0.25 mm, 0.063–0.25 mm and <63 mm. 2.3. Statistical analyses 3

Prior to analysis, biotic and abiotic data were tested for normality (P-value ≥ 0.05) by using Shapiro–Wilk test. The one-way ANOVA (SPSS ver. 20) was applied to evaluate the significant differences of mean abundance and diversity among stations. The density of each species was calculated from the mean estimated density of the three replicates in each station. The significant differences in total density and species richness of macroinvertebrates, amount of total organic matter (TOM %), sedimentary chlorophyll-a and phaeopigment over time between the impact and control sites were tested by one-way ANOVA in SPSS. PERMANOVA testing was used to show the effects of station and season on the macrobenthic community. The data of ecological indices were normalized and homogenized by using Shapiro-Wilk normality test (P-value ≥ 0.05). The three common ecological indices were calculated by the PRIMER software (ver. 6.1.6: Clarke and Gorley, 2006): the Margalef index of species richness: (

(1) (Margalef, 1973)

the Shannon index of species diversity: ( 2015)

)

(2) (Shannon and Weaver,

and the Pielou index of evenness: (

)

(3) (Pielou,

1969) where in all cases S= total number of species, is the proportion (n/N) of individuals of one particular species found (n) divided by the total number of individuals found (N). To determine the relationships between benthos densities with distance from the thermal discharge, multivariate analysis such as cluster analysis was used. Similarity between samples was carried out by PRIMER clustering software. To reduce the effect of dominant species, data were the square-root transformed prior to analysis and the similarity among stations was calculated by Bray Curtis index. To identify environmental variables that influence the abundance, biodiversity and population structure of the macroinvertebrate, we used the Canonical Correspondence Analysis (CCA) in CANOCO 5 software (Microcomputer Power, Inc., USA). Also, Spearman rank correlation coefficient was used to correlate benthic parameters to environmental variables. A Bray-Curtis similarity index was used to group (cluster) the different macrobenthic species, according to their commonalities in all three locations (impact; gradient; and control) to provide an integrated assessment of all interactions between macrobenthos and the various locations. The clusters were determined using group averaging calculations. Similarity profile (SIMPROF) permutation tests were used to test for significant differences in the hierarchical cluster structure. The SIMPER routine in PRIMER (version 6.1.6) was used to determine which species contributed most to the dissimilarity (or similarity) of the macroinvertebrate assemblages during sampling periods. 3. Results A total of 42 macrobenthic species were identified that belonged to 22 genera, 18 families, 13 orders, six classes and three phyla (Table 2). 4

3.1. Changes in abundance Bivalve constituted the most abundant group throughout samplings. Majority of the identified genera in winter were cockles, Hypanis (36.7%) and Abra (13.8%), followed by the invasive mussel, Mytilaster (11.9%), zebra mussel, Dreissena (11%), the snail, Pseudamnicola (10%), and lagoon cockle, Cerastoderma (8.1%) (Fig. 2a). Majority of the identified genera in summer were Hypanis (32%), followed by Mytilaster (14.8%), bristle worm, Hypaniola (11.9%), Cerastoderma (10.1%), Dreissena (7.3%), and mud worm, Streblospio (5.8%) (Fig. 2b). 3.2. Macrobenthos density The highest density of bivalves, ostracods and gastropods was observed in the discharge stations (IE, IW and C3) (Fig. 3). One-way ANOVA showed significant differences for bivalves (df=6, F=11.75, P=0.00), gastropods (df=6, F=4.91, P=0.00), olighochaetes (df=6, F=5.13, P=0.00) in macrofaunal community among the seven stations in winter, while there were no significant differences for malacostraca (df=6, F=1.17, P=0.36), ostracods (df=6, F=1.20, P=0.35), and polychaetes (df=6, F=0.86, P=0.53). Duncan post-hoc test showed increase in some macrobenthic density with increasing temperature, which was significantly higher at thermal discharge stations than the control ones (Fig. 3). The maximum number of bivalves was found in discharge and C3 stations in summer (Fig. 4). One-way ANOVA showed significant differences for bivalves (df=6, F=71.87, P=0.00), gastropods (df=6, F=9.66, P=0.00) and polychaetes (df=6, F=5.88, P=0.00) in macrofaunal community among the seven stations in summer, while there were no significant differences for malacostracans (df=6, F=2.60, P=0.05), ostracods (df=6, F=0.29, P=0.93) and oligochaetes (df=6, F=1.29, P=0.31). Duncan post-hoc test showed increase in the macrobenthic density with increasing temperature, which was significantly higher at thermal discharge stations (Fig. 4). Distribution of the grain size (percent of sand, silt, clay), showed the highest amount of silt in the control stations in winter and the highest amount of sand in the control stations in summer (Fig. 5). The maximum amounts of sand in winter and summer were 49.2% in IE station and 54.2 % in CE station, respectively; the maximum amounts of clay in winter and summer were 80.3% and 35.2% in IW station, respectively; the maximum amount of silt in winter and summer were 51.4% in CW station and 54% in CE station, respectively. Among the stations, the highest and the lowest percent of organic matter were found in the IW and C2 stations, respectively (Fig. 6). Seasonal comparison showed the highest level of the organic matter in summer (Fig. 7). Chlorophyll and phaeopigment at thermal discharge stations were lower than the other stations. In winter and summer, lowest chlorophyll levels were observed at IW and IE stations, respectively (Fig. 8). 3.3. Changes in ecological indices The Shannon-Wiener diversity index was inversely related to temperature, as its mean value (±SE) in the control stations was significantly higher than the impacted ones (F=6.66, p≥0.05); the highest and lowest diversity values were observed in stations CW (2.61±0.03) and C2 (2.04±0.03), respectively. In summer, the highest and lowest diversity values were observed in stations CW (2.39±0.04) and IE (2.08±0.01), respectively (Fig. 9). The Pielou's evenness increased (F=3.97, p≥0.05) from the thermal discharge stations to the control 5

ones, the highest (0.84±0.01) and the lowest (0.59±0.00) values of which were, respectively, observed in CW and C1 stations in winter (Fig. 9). The species richness of each site (impact or control) was the sum of the number of species recorded for that site. The Margalef index of species richness showed no significant difference between the impacted and control stations (p≥0.05), the highest mean value of which (4.35±0.04) was recorded in CW station in winter (Fig. 9). 3.4. Changes in environmental variables The mean (±SE) of the eight registered environmental variables in each sampling period and the total mean are given in Fig. 10. The mean (±SE) water temperature at various stations during summer and winter is given in Table 1. Stations were divided based on temperature to three categories of 12, 13, 15°C (a mean value of 3°C more than ambient seawater) in winter and three categories of 28, 29, 33°C (a mean value of 5°C more than ambient seawater) in summer (Fig 11 and 12). 3.5. Impact of environmental factors on the macroinvertebrate in the analysis of CCA The CCA analysis by CANOCO showed that gastropods, bivalves, ostracods, and olighochaetes were almost in a similar orientation, while crustaceans and polychaetes were in a different orientation (Fig. 13a). Crustaceans had a positive correlation with the dissolved oxygen (r=0.67, p<0.01). Stations with high dissolved oxygen level (CW in winter) showed higher species diversity, while higher temperature had a negative impact on species diversity (r= -0.01, p<0.05) (Table 6). Among the environmental variables, salinity and temperature were positively correlated, but a negative correlation existed between dissolved oxygen and temperature. The organic matter had a positive correlation with the majority of macrobenthic groups, viz. gastropods (r=0.30, p<0.05), bivalves (r=0.34, p<0.05), polychaetes (r=0.18, p<0.05), and ostracods (r=0.36, p<0.05) (Fig. 13a). The organic matter had a positive correlation with the thermal discharge stations, while chlorophyll and phaeopigment showed negative correlations. Stations IW in winter and CE in summer had positive correlations with clay and sand, respectively. The abundance of some species, such as L. bacuana, and S. graciloides, increased at stations in winter as the result of increased dissolved oxygen (Fig. 14). The CCA test indicated that temperature was the most influential of all the studied environmental variables. The highest abundance of polychaetes was observed at the thermal discharge stations (Fig. 13b). 3.6. PERMANOVA and SIMPER analyses PERMANOVA test showed that stations and seasons both had significant effects on the macrobenthic groups (Table 3). The SIMPER analysis showed the greatest dissimilarity between the impacted and control stations in summer (59.5%) and in winter (54.8%), which was mainly contributed by bivalves and polychaetes (Table 5). H. minima considered as an indicator species at the thermal discharge. Comparison of the thermal discharge stations in two seasons revealed that H. minima and H. kowalewskii had the high abundance that also played the most important role in separating the stations, but cannot be introduced as “thermal indicating species”. 4. Discussion Although development of industrial activities in coastal areas brings about great advantages, it can also adversely affect marine habitats and ecosystems. Macrobenthos play an important role in the food chain 6

structure, the transfer of energy, and considered as a representative of the total production index in the aquatic environment (Owen, 1974). The structure of macrobenthic communities plays a key role in the dynamics of nutrition, metabolic processes and the carbon cycle (Schwinghamer, 1981). Their importance as the main food for fishes and other large predators has long been recognized. The various degree of resistance of macrobenthos to pollution has made them among the best organisms in determining the quality of the aquatic environment (Wallen, 2002). 4.1. Density and abundance of macrobenthic Bivalvian mollusks with a total abundance of 90% in winter and 86% in summer maintained their dominance in both sampling seasons, followed by gastropods and polychaetes (Fig. 2). This indicates that density of macrobenthos have relatively reduced during the summer sampling, which is consistent with an earlier study (Arieli et al., 2011), while in contrast with another one in which the highest density are reported in summer (Tweedley et al., 2012). In general, there was a relative increase in the density of the more thermal-tolerating species from the thermal discharge stations to the control stations, which was significant for H. minima and H. kowalewskii in both seasons (p ≤ 0.05). This finding is consistent with a similar study in the Canary Islands where the highest density of macrobenthic was observed in areas near power plant turbines (Riera et al., 2011. Therefore, the higher temperature regime may be one of the factors influencing the density of macrobenthos. High temperature regime can alter the normal physiological functions of aquatic fauna and thereby affecting the population density. Discharge stations exhibited the highest density of macrobenthos in comparison with the control stations, and this density was higher in winter than in the summer. Thermal discharge affects the natural seasonal changes in temperature which may have serious ramifications on macrobenthic communities, especially during summer months when the natural water temperature can go above 30 °C. The development of gonads in many bivalves in temperate regions occurs when the water temperature reaches 10 -14 °C and reach sexual maturity in AugustSeptember. Spawning in bivalves are stimulated by increased temperature and thermal shock ( Bachelet, 1980; Tweedley et al., 2012). Another reason for the reduction of macrobenthic density during summer could be attributed to the feeding activities of benthivore fishes as well as the effects of fishery activities that disturb macrobenthic communities, for which several studies have been conducted in the area (Farabi et al., 2009; Nemati et al., 2015). The macrobenthic individuals in their various life cycles can be considered as a food item for many fishes. In summer, when the water is warmer, the fishes show more feeding activity. It seems that decrease of water temperature in the winter causes reduced feeding activity and, hence, increased macroinvertebrates community. 4.2. Impact of sediment factor in the different stations Diversity and density of benthic fauna have close relationship with the type of sediment. Macrobenthos density in the coarser sediment particles (sand) was higher than in the clay. The highest density of macrobenthos was found at eastern thermal discharge station (IE) in summer that had the highest percent of sand and silt (Fig. 5b), which was in correspondence with another study (Mohammed, 1995). Literally heterogeneous stations with silty and sandy beds and average amount of organic matter are suitable site for life, reproduction and feeding of macrobenthic organisms as noticed by their abundance. The density was influenced mainly by the silt-clay 7

content. These results suggest that the macrobenthic community outside power plants were influenced mainly by the sediment characters. The sediment with less homogenized particles and higher quantity of fine-grained particles tends to have higher habitat diversity. Thus, more macrobenthos will inhabit there. The total organic matter, the amount of which is associated with other environmental parameters, can change the density and diversity of macrobenthos (Pearson and Rosenberg, 1978). High temperature was found to be an important factor in increasing the amount of organic matter at thermal discharge stations and it was higher in the summer than the in winter, which could be related to the increased primary production (Birstein and Romanova, 1968; Cheng et al., 2004; Pourjomeh et al., 2014). Muddy substrate is suitable for the deposit feeding organisms that burrow into the sediment (Nybakken, 1993). In the present study, there was a positive relationship between the clayey bed and abundance of Nereis, particularly the IW station that had the highest amount of clay. On the other hand, the abundance of crustaceans in the clayey beds decreased. Researchers believe that high organic matter increase the frequency of tolerant species of polychaetes and decrease the frequency of such sensitive macrobenthic organisms as mollusks and crustaceans (Muxika et al., 2005; Sarkar et al., 2005; Carvalho et al., 2006). C1 and C2 stations had the highest amount of silt in summer that also showed the decreased abundance of bivalves and crustaceans, which was in correspondence with an earlier study (Lu, 2005). The highest abundance of bivalves was observed in stations having grains coarser than clay because the filtering is easier in this seabed (Figs. 3, 4, and 5). The sediment chlorophyll content, as the indicator of primary production, can reveal macrobenthic trophic status. There was a correlation between the increased concentrations of chlorophyll with the logarithmic wet weight of macrobenthos (r=0.27, p<0.05). Chlorophyll and phaeopigment in IE and IW stations were lower than the other stations (Fig. 8), which could be attributed to the increased turbidity and reduced light penetration (Smith et al., 2000). Deposit feeding polychaetes were dominant in station C2 that had less turbulence, finer grained sediment, and the highest chlorophyll content, while filter feeders were dominant in the stations that had sandy substrate and less chlorophyll, which were in correspondence with the earlier studies (Graca et al., 2004; Beaty et al., 2006 ; Principe, 2008). In general, the effect of environmental variables on the structure of community differs from one station to another. 4.3. Ecological indices Various factors such as the grain size of sediments, turbulence, and temperature influence the benthic community to a great extent (Mclusky and Elliot, 2004). The Shannon-Wiener diversity index has a great potential to show the presence or absence of stressors in the environment (Karydis and Tsirtsis, 1996). The highest mean (±SE) of the species diversity was obtained in Cw station (2.61±0.03) in winter, while the highest density of macrobenthos was observed in the stations having the highest average temperature of 15 °C in winter and 33 °C in summer (Fig. 9). This indicated that the temperature had a positive correlation with the macrobenthic abundance, but a negative correlation with diversity (r = 0.37, p < 0.05, r = -0.01, p < 0.05, respectively) (Table 6), which had also been indicated in an earlier study (Cheng et al., 2004). In southeast coast of India, a negative correlation between the water temperature and the macrobenthic diversity was observed (Kailasam and Sivakami, 2004). The lowest species diversity was also reported from the discharge stations where increased turbulence, thermal stress and the other environmental instability were observed (Desroy et al., 8

2003; Jayaraj et al., 2007). In our study, the interaction between environmental factors showed that temperature had a negative correlation with the dissolved oxygen (r = -0.6, p < 0.05). This is due to the increase in the metabolic rate as the result of increase in temperature that enhances biochemical reactions that, in turn, decreases the dissolved oxygen and species diversity (Kraufvelin and Salovius, 2004). Decreased dissolved oxygen can, in turn, reduce reproduction rate that can negatively affect the macrobenthic community structure (Sarkar et al., 2005; Yokoyama et al., 2007). High temperature of the thermal discharge station in summer has been considered as a factor in reducing competition and increasing the density of macrobenthos due to increases in phytoplanktonic biomass (Sarkar et al., 2005). In a brackish water system, such as the Caspian Sea, two main environmental variables (salinity and oxygen supply) affect the composition of the benthic community and species abundance (Rönnberg and Bonsdorff, 2004). The salinity acts as a natural stressor affecting benthic diversity in a similar way as human impact. In our study, oxygen decreases in the thermal stations, because of the sensitivity of this factor to temperature changes, while salinity variations were very slight. Density variations were in agreement with the temperature changes. The highest mean of the species evenness (0.845 ± 0.016) was obtained in Cw station that was related to its optimal conditions in this station, including type of substrate, amount of total organic matter and its low turbulence (Fig. 9). Indeed, low water turbulence was an important factor in increasing the amount of organic matter that could eventually change the ecological indices like evenness, which is in correspondence with earlier studies (Cheng et al., 2004; Wang et al., 2009). Although species richness of the macrobenthos didn’t statistically show any particular trend during the two sampling seasons (F=0.27, p=0.62) in winter, (F=4.14, p=0.09) in summer, a higher value (4.356±0.042) was observed in Cw station in winter. Another reason for this reduction is that thermally polluted sediment may be unable to support sessile invertebrates and will have a negative impact on macroinvertebrates using the habitat for shelter, food, nesting and juvenile settlement. Overall, sessile benthic organisms have been reported as particularly susceptible to thermal discharge, and an increase of a few degrees centigrade can threaten their survival (Laws, 1993; Logue et al., 1995). On the other hand, decrease in species richness might be attributed to the influence of fishery on the temporal patterns of species composition. There are various evidences that fisheries have impacted the environment, but the extent and duration of the impact depend on local conditions (Churchill., 1989; Hiddink et al., 2006; He and Winger, 2010). Indirect effects on the seabed are related to the stress imposed on the benthos, including short term postfishing mortality or damage on the organisms, and long-term changes to the benthos community. In this regard, a general decrease in diversity can be predicted as long-lived slow-growing species are removed or killed by human activities. The removal of the macrobenthos also has variable effects. In shallow areas where the damage is intermittent, recolonisation soon occurs. However, where the macrobenthos is substantially removed and recovery is not permitted, the change is permanent. For instance, the immediate decrease in species richness might in part be attributed to recruitment processes, which is in turn influenced by increase in water temperature (Alipoor et al., 2011). The trawl nets reduce density and species richness of macroinvertebrates. Trawl affects the environment in both direct and indirect ways. Direct effects include scraping and ploughing of the substrate, sediment resuspension, destruction of benthos, and dumping of processing waste. Indirect effects include postfishing mortality and long-term trawl-induced changes to the benthos. However, these trawl sediment clouds can also contribute to the total suspended sediment load and modelled sediment resuspension by trawling. This suspended sediment reduces light levels on the substrate, and when the sediment eventually settles out, the benthos can be smothered. (Smith et al., 2000; De Biasi, 2004; Hixon and Tissot, 2007; Shephard et al., 2010). 9

The density of macrobenthos was higher in the thermal discharge stations, but the number of species was reduced. The lower species richness in the thermal discharge stations can be attributed to the interaction of environmental variables, such as high temperatures, the high percent of sand and silt, the low percent of clay and the high amount of chlorophyll. It could also be attributed to the increase of stress-tolerant species, as the polychaete (H. kowalewskii,) and the bivalve (H. minima) in this study. The increased organic matter had maximum role in the reduced ecological indices of macrobenthos in this study. 4.4. Ordination and relation with the abiotic environmental variables The CCA test indicated temperature as the most influential factor that had a negative correlation with abundance of crustaceans and a positive correlation with dissolved oxygen (r=-0.59, p<0.05; r= 0.67, p<0.05, respectively). Decrease in temperature was associated with increased dissolved oxygen and the appearance of crustaceans, such as amphipods, when moving away from the thermal discharge stations. Being sensitive to heat, amphipods were not observed in the thermal discharge stations. Temperature and its interaction with other environmental factors were associated with the presence or absence of some macrobenthic groups/species that could or couldn’t tolerate the changes (Fig. 13a). Therefore, increase in temperature was associated with reduced species diversity in the thermal discharge stations, which was consistent with the findings of Jegadeesan and Ayyakkanna (1992). Polychaetes (H. kowalewskii, H. invalida) had the highest macrobenthic abundance in the thermal discharge stations (Fig. 14), which can, therefore, be considered as the resistant group to thermal discharge. This is in correspondence with the findings of Bamber and Spenser (1984) who observed polychaetes and olighochaetes in the discharge station of a power plant. Among the environmental variables, the total organic matter, as a food source for benthic organisms, had a great influence on the macrobenthic community, majority of which showed a positive correlation (r=0.34, p<0.05). The highest amount of organic matter was found in the station Iw that had the highest percentage of clay (Fig. 6). Since the fine grain has higher surface to volume ratio, its ability to ion-adsorption is higher. The PERMANOVA test showed that the environmental factors and biological variables were related to the changing seasons. Comparing the results of the CCA and PERMANOVA tests revealed that the high temperature at discharge stations caused the difference in macrobenthic density. The interaction of these two factors was obvious upon using the PERMANOVA. As a matter of fact, temperature is the main reason for these differences and this result also revealed in the interaction between season and station. 4.5. Indicator species (Cluster and SIMPROF analysis) Based on SIMPROF output results in PRIMER 6, the average significant similarity of one cluster grouping with another was 61%. SIMPROF addresses multivariate structure among samples, showing that there is clear structure associated with differences among season. Clustering of the variables (species) with SIMPROF identifies groups of species through the stations. Temperature is characterized by a dramatic decline in diversity and increase in abundances at the thermal discharge stations. Based on the Bray-Curtis similarity matrix, the cluster analysis of the macrobenthic density of the six delineated groups showed that two types of indicators species, including the polychaetes (H. kowalewskii,) and the bivalve (H. minima), had the highest abundance in groups 1 and 2 (Iw, IE and C3 stations) near the thermal discharge stations, followed by the groups 3 and 4 (C1 and C2 stations) in the lower area of the thermal discharge, and the groups 5 and 6 (CE and CW stations) 10

(SIMPROF test, P < 0.05; Figs. 15 and 12). The macrobenthic community structures in the two seasons also showed similar patterns. Based on the SIMPER analysis, the bivalve, H. minima, which also had the most important role in the distinction between the thermal discharge stations and the other stations, can be considered as an indicator species. Spawning of this mollusk may take place continually or triggered by environmental factors such as day length. The probability of spawning depends markedly on the temperature. Members of Hypanis inhabit in a wide range of salinity and are sensitive to hyper accumulation of organic matter (Yuryshynets, 2001). Furthermore, comparison of the stations showed the highest abundance of the polychaete H. kowalewskii in summer that also played the most important role in making the difference. This might be attributed to the tolerability of this species to various environmental variables, such as temperature, salinity, and the sediment grain size. Members of the family Ampharetidae are generally small and inconspicuous and have been little studied. This species is one of few polychaete species able to inhabit freshwater, tolerating a wide range of salinity, temperature, and depth. It lives within a muddy tube with a mucous-like substance and a preference for mud, gravel, and silt deposits (Sporka, 1998; Filinova et al., 2008; Norf et al., 2010). Spawning occurs from late May to early September. Offspring are brooded for about 2 weeks before they leave the parental dwelling tube and enter the water column (Norf et al., 2010), which can additionally increase reproductive success by reducing larval mortality during early planktonic life stages (McHugh, 1993; Schroeder and Hermans, 1975). The reproductive traits of this species might explain the high expansion of H. kowalewskii in the thermal discharge stations.

5. Conclusion We demonstrated that the heat budget at seasons must be taken into account to quantify properly the effects of thermal pollution on marine habitats. Our results indicated that the density of macrobenthos was higher in the thermal discharge stations, but the diversity in these stations was relatively lower. Therefore, the higher temperature may be one of the factors influencing the density of some benthic organisms, including the thermaltolerant species. Bivalve constituted the most abundant group throughout samplings, 90% in winter and 86% in summer. Temperature was an important factor on the amount of organic matter. Chlorophyll and phaeopigment at the thermal discharge stations were lower than the other stations because of the increased turbulence. Acknowledgment This work was completed in partial fulfillment of the masters of Marine Biology degree at University of Tarbiat Modares (TMU, Noor, Iran), Faculty of Marine Science. We are grateful to Dr. Nemat Mahmoudi, Saeed Ebrahimnezhad, Sareh Nabavi for helps in the field and laboratory works. Competing interests: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Appendix A

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Appendix B

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Pourjomeh, F., Hakim Elahi, M., Rezai, H., Amini, N., 2014. The distribution and abundance of macrobenthic invertebrates in the Hormozgan Province the Persian Gulf. Journal of the Persian Gulf 5 (15), 25-32. Principe, R.E., 2008. Taxonomic and size structures of aquatic macroinvertebrate assemblages in different habitats of tropical streams, Costa Rica. Zoological Studies 47 (5), 525-534. Riera, R., Núñez, J., Martín, D., 2011. Effects of thermal pollution on the soft bottoms surrounding a power station in the Canary Islands (NE Atlantic Ocean). Oceanology 51 (6), 1040-1046. Rönnberg, C., Bonsdorff, E., 2004. Baltic Sea eutrophication: Area-specific ecological consequences. Hydrobiologia 514, 227–241. Roohi, A., Kideys, A.E., Sajjadi, A., Hashemian, A., Pourgholam, R., Fazli, H., Eker-Develi, E., 2010. Changes in biodiversity of phytoplankton, zooplankton, fishes and macrobenthos in the Southern Caspian Sea after the invasion of the ctenophore Mnemiopsis leidyi. Biological Invasions 12 (7), 2343-2361. Sarkar, S.K., Bhattacharya, A., Giri, S., Bhattacharya, B., Sarkar, D., Nayak, D.C., Chattopadhaya, A.K., 2005. Spatiotemporal variation in benthic polychaetes (annelida) and relationships with environmental variables in a tropical estuary. Wetland Ecology and Management 13, 55-67. Schroeder, P.C., Hermans, C.O., 1975. Annelids: Polychaeta. In reproduction of marine invertebrates. Annelids and Echiurans, New York: Academic Press 3, 1-213. Schwinghamer, P., 1981. Characteristic size distributions of integral benthic communities. Canadian Journal of Fisheries and Aquatic Sciences 38 (10), 1255-1263. Shannon, C.E., Weaver, W., 2015. The mathematical theory of communication. University of Illinois press. Shephard, S., Brophy, D., Reid, D.G., 2010. Can bottom trawling indirectly diminish carrying capacity in a marine ecosystem? Marine Biology 157, 2375–2381. Smith, C.J., Papadopoulou, K.N., Diliberto, S., 2000. Impact of otter trawling on an eastern Mediterranean commercial trawl fishing ground. ICES Journal of Marine Science 57 (5), 1340-1351. Sporka, F., 1998. The typology of floodplain water bodies of the Middle Danube (Slovakia) on the basis of the superficial polychaete and oligochaete fauna. Hydrobiologia 386 (1), 55-62. Stock, J., Mirzajani, A., Vonk, R., Naderi, S., Kiabi B., 1998. Limnic and brackishwater Amphipoda (Crustacea) form Iran. Beauforita Insttute for Systematics and Population Biology (Zoological Museum) Universtty of Amsterdam 48, 173-233. Taheri, M., Seyfabadi, J., Abtahi, B., Foshtomi, M.Y., 2008. Population changes and reproduction of an alien spionid polychaete, Streblospio gynobranchiata, in shallow waters of the south Caspian Sea. JMBA2 Biodiversity Records, Published on-line, 1-5.

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Ayda Bozorgchenani is a M.Sc. in marine biology with research interests in benthic ecology at the department of Marine Biology, Faculty of Marine Sciences, Tarbiat Modares University, Noor, Mazandaran, Iran. Her particular research interests include: effects of thermal discharge on macroinvertebrate communities and sediment characteristics in the Southern Caspian Sea, factors affecting macroinvertebrate richness and diversity, relationship between type bottom macrobenthic communities and environmental variables.

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Dr. Jafar Seyfabadi is the head of the department of Marine Biology, Faculty of Marine Sciences, Tarbiat Modares University, Noor, Mazandaran, Iran. His research interests: marine invertebrate, 2. marine biology, 3. marine fishculture.

Dr. Mohammad Reza Shokri is a marine biologist with research and teaching interests in coral reef ecology at the department of Marine Biology Faculty of Life Sciences and Biotechnology, Shahid Beheshti University, Tehran, Iran. His interests in coral reef ecology, reef fish ecology, marine conservation, and marine environmental management. His particular research interests include testing the surrogacy value of biotic and abiotic features of marine ecosystems, selecting and designing marine protected areas, coral reef molecular ecology, reef fish ecology, and the management and conservation of marine biodiversity.

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Fig. 1. Detailed map of the sampling site in the area of Neka Power Plant. IE= Eastern impacted station, IW= Western impacted station, C1= First eastern control station, CE= Second eastern control station, C2 = First western control station, CW = Second western control station, C3=Thermal broadcast station.

Fig. 2. Pie chart of the identified genera in winter (a) and summer (b)

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Fig. 3. Mean (logarithmic) density (ind.m–2 ± SE) of macrobenthic groups along the thermal gradient in winter. IE = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station.

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Fig. 4. Mean (logarithmic) density (ind.m–2 ± SE) of macrobenthic groups along the thermal gradient in winter. I E = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station.

Fig. 5. Grain size analysis (average %) of sediments in winter (a) and summer (b). I E = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station.

Fig. 6. The mean percentage of organic matter in the station. IE = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station. 23

Fig. 7. Changes of organic matter in two season

Fig. 8. Total pigment contents (1-2 cm sediment layers) at seven stations in winter (a) and summer (b). I E = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station. 24

Fig. 9. Mean of macrobenthos Shannon diversity index (a), evenness (b), and species richness (c) among the thermal gradient. IE = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station. S1 = Sampling in winter, S2 = Sampling in summer.

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Fig. 10. The mean values of eight registered environmental variables among sampling periods in winter (a) and summer (b). I E = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station, Ts = surface temperature, Td = deep temperature, pHs = surface acidity, pHd = deep acidity, DOs = surface dissolved oxygen, DOd = deep dissolved oxygen, S S = surface salinity, SD = deep salinity.

Fig. 11. Changes in density based on temperature in winter (a) and summer (b).

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Fig. 12. Similarity dendrogram of the Neka Power Plant based on 42 macrobenthic species in winter (a) and summer (b). I E = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station.

Fig. 13. The CCA results of the correlations between macrobenthic groups and (a) water variables, and (b) sediment variables. Ts = surface temperature, Td = deep temperature, pHs = surface acidity, pHd = deep acidity, DOs = surface dissolved oxygen, DOd = deep dissolved oxygen, SS = surface salinity, SD = deep salinity. IE = Eastern impacted station, IW = Western impacted station, C1 = First 27

eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station, S1 = Sampling in winter, S2 = Sampling in summer.

Fig. 14. The CCA diagram showing the 42 macrobenthic species and environmental variables vectors in sampling periods. The vector lines represent the relationship of significant environmental variables to the ordination axes and their length is proportional to their relative significance. Ts = surface temperature, Td = deep temperature, pHs = surface acidity, pHd = deep acidity, DOs = surface dissolved oxygen, DOd = deep dissolved oxygen, S S = surface salinity, SD = deep salinity.

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Fig. 15. A cluster analysis of the different macrobenthos species according to their similarity in the three location based parameters temperature (impact; gradiant; and control). The clusters were based on a Bray-Curtis similarity index and were determined using group averaging calculations. Similarity profile (SIMPROF) permutation tests were used to test for significant differences in the hierarchical cluster structure . The macrobenthos species abbreviations are provided in Table 4.

Table 1 The geographical positions and temperature of the stations. IE = Eastern impacted station, IW = Western impacted station, C1 = First eastern control station, CE = Second eastern control station, C2 = First western control station, CW = Second western control station, C3 = Thermal broadcast station. Station

IE IW C1 CE C2 CW C3

Coordinates

Winter temperatures (°C)

Summer temperatures (°C)

14.59

33.49

15.21

33.59

13.41

26.52

12.43

28.48

13.61

28.66

12.20

28.39

14.17

32.19

N 36° 50.860' E 53° 15.370' N 36° 50.961' E 53° 14.834' N 36° 50.855' E 53° 15.437' N 36° 51.109' E 53° 15.931' N 36° 50.956' E 53° 14.777' N 36° 50.754' E 53° 14.211' N 36° 50.995' E 53° 15.043'

Table 2 Macrobenthic organisms found in the sediments adjacent to Neka Power Plant, southern Caspian Sea, Iran. Class

Order

Family

Cardidae Bivalvia

Veneroida

Dreissenidae

Gastropoda

Mytiloida

Semelidae Mytilidae

Hygrophila

Planorbidae

Species Cerastoderma Lamarcki (Reeve, 1845) Didacna baeri (Grimm, 1877) Didacna longipes (Grimm, 1877) Hypanis vitrea (Eichwald, 1829) Hypanis caspia (Eichwald, 1829) Hypanis plicata (Eichwald, 1829) Hypanis albida (Logvinenko & Starobogatov, 1967) Hypanis minima (Logvinenko & Starobogatov, 1967) Dreissena polymorpha polymorpha (Pallas, 1771) Dreissena polymorpha andrusovi (Brusinain andrusov, 1897) Dreissena elata (Andrusov, 1897) Abra ovate (Philippi, 1836) Mytilaster lineatus (Gmelin, 1791) Anisus kolesnikovi (Logvinenko & Starobogatov, 1966) Anisus eichwaldi (Cless. & Dyb. 1888)

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Class

Order

Family

Species

Littorinimorpha Cycloneritimorpha

Lithogliphydae Neritidae

Terebellida

Ampharetidae

Spionida

Spionidae

Pyrgohydrobia cylindrical (Logvinenko & Starobogatov, 1968) Pyrgohydrobia turrita (Logvinenko & Starobogatov, 1968) Pyrgohydrobia dubia (Logvinenko & Starobogatov, 1968) Pyrgohydrobia oviformis (Logvinenko & Starobogatov, 1968) Pyrgohydrobia gemmate (Kolesnikov, 1947) Pyrgohydrobia convexa (Logvinenko & Starobogatov, 1966) Pyrgula lencoranica (Logvinenko & Starobogatov, 1968) Pyrgulaconus (Eichwald, 1838) Pseudamnicola brusiniana (Clessin & Dybowski, 1876) Theodoxus pallasi (Lindholm, 1924) Hypaniola kowalewskii (Grimm, 1927) Hypania invalida (Grube, 1927) Streblospio gynobranchiata (Rice & Levin, 1998)

Phyllodocida

Nereidae

Nereis diversicolor (Muller, 1776)

–

–

Cumacea

Pseudocumatidae

Mesogastropoda

Pyrgulidae

Hydrobiidae

Polychaeta Olighochaeta*

Malacostraca

Amphipoda

Pontogammaridae Pontogammaridae

Malacostraca

Amphipoda

Ostracoda

Podocopida

*Olighochaetaidentified at the Class level – = unidentified

Pontoporeiidae Leptocytheridae Loxoconchidae Cytheridae

– Pterocuma pectinata (Swinsky, 1893) Stenocuma gracilis (G.O.Sars, 1894) Stenocuma graciloides (G.O.Sars, 1894) Niphargoides robustoides (G.O.Sars, 1894) Niphargoides compressu (G.O.Sars, 1894) Niphargoides macrurus (G.O.Sars, 1894) Niphargoides similis (G.O.Sars, 1894) Niphargoides carausui (Derzhavin & Pjatakova, 1962) Pontoporeia affinis microphthalma (Grimm, 1880) Leptocythere longa (Negadaev, 1995) Leptocythere bacuana (Livental, 1938) Loxoconcha lipida (Stepanaitys, 1964) Cyprideis littoralis (Brady, 1938)

Table 3 Results of a mixed model PERMANOVA testing for the effects of station and season on the macrobenthic community in the Neka Power Plant, southern Caspian Sea, Iran. Source Season Station Season×Station Residual Total

df

1 3 3 6 13

SS 1787.8 2633.8 1340.4 1235.1 7340.3

MS

30

1787.8 877.94 446.79 205.86

F

8.6845 4.2648 2.1704

P

0.0012 0.0101 0.0587

Table4 The six macrobenthos species groupings that was determined from the Cluster, SIMPROF analyses shown in Fig. 15. The macrobenthos species abbreviations are provided for reference to Figs.15. Group

Group 1

Group 2

Taxa

Pyrgula conus

2.09

Polychaete

Hypaniola kowalewskii

414.59

Bivalve

Hypanis plicata

4314.31

Bivalve

Hypanis minima

4423.81

Bivalve

Dreissena polymorpha

1839.35

Bivalve

Hypanis vitrea

2361.33

Bivalve

Hypanis caspia

713.95

Gastropod

Pyrgohydrobia turrita

452.57

Gastropod

Pseudamnicola brusiniana

482.69

Bivalve

Abra ovata

678.07

Bivalve

Mytilaster lineatus

932.90

Bivalve

Hypanis albida

206.11

Streblospio gynobranchiata

213.45

Oligochaete

183.07

Ostracode

Cyprideis littoralis

67.83

Gastropod

Anisus kolesnikovi

48.97

Ostracode

Leptocythere longa

37.45

Gastropod

Pyrgohydrobia oviformis

45.30

Gastropod

Anisus eichwaldi

66.52

Gastropod

Pyrgohydrobia gemmata

58.40

Bivalve

Dreissena polymorpha andrusovi

80.14

Bivalve

Didacna baeri

62.85

Bivalve

Hypania invalida

13.35

Bivalve

Dreissena elata

10.73

Oligochaete

Group 4

Density (ind/m2)

Gastropod

Polychaete

Group 3

species

31

Group 5

Polychaete

Nereis diversicolor

6.023

Gastropod

Theodoxus pallasi

4.19

Gastropod

Pyrgohydrobia.convexa

4.97

Cumacea

Pterocuma pectinata

4.97

Cumacea

Stenocuma gracilis

3.92

Amphipod

Pontoporeia mikrophthalma Grimm

33.52

Ostracode

Leptocythere bacuana

Bivalve

Group 6

Didacna longipes

20.16

Gastropod

Pyrgula lencoranica

12.04

Gastropod

Pyrgohydrobia dubia

34.30

Amphipod

Niphargoides macrurus

8.11

Amphipod

Niphargoides similis

6.28

Cumacea

Stenocuma graciloides

1.57

Amphipod

Niphargoides carausui

3.92

Niphargoides compressus

6.02

Niphargoides robustoides

5.76

Pyrgohydrobia.cylindrical

4.97

Loxoconcha lepida

10.47

Amphipod Amphipod Amphipod

Gastropod Ostracode

12.04

Table 5 Summary of results of SIMPER (similarity percent) in PRIMER showing the species that most contributed to the difference in macrobenthic assemblage among sampling periods (S1 and S2 are first and second sampling) I E = impacted station, C1 = First control station (gradient), CE = Second control station (abundance data is square root-transformed before SIMPER analysis). SIMPER comparisons

most contributed species

IS1 vs. C1S1

H. minima (Bivalvia), average dissimilarity= 7.12 out of 46.09 total average, more in I0S1 (16.59) versus C1S1 (4.86)

IS1 vs. CES1

H.minima (Bivalvia), average dissimilarity= 7.92 out of 54.81 total average, more in I0S1 (16.59) versus CES1 (4.28) 32

IS2 vs. C1S1

H. minima (Bivalvia), average dissimilarity=6.43 out of 46.88 total average, more in I0S2 (14.80) versus C1S1 (4.86)

IS2 vs. CES1

H.minima (Bivalvia), average dissimilarity= 7.24 out of 56.51 total average, more in I0S2 (14.80) versus CES1 (4.28)

IS1 vs. IS2 IS2 vs. CES2

H.kowalewskii (Polychaeta), average dissimilarity= 2.76 out of 21.41 total Average, more in I0S2 (6.27) versus I0S1 (0.00) H. minima (Bivalvia), average dissimilarity=9.11 out of 59.48 total average, more in I0S2 (14.80) versus CES2 (2.16)

Table 6 Pairwise spearman rank correlations between environmental variables and benthic parameters. Do = Dissolved oxygen, Chl-a = Chlorophyll-a, Tom = Total organic matter. Environmental variables

Abundance

H'

Temperature

0.37

-0.01

pH

0.27

0.44

Do

0.33

-0.33

Salinity

-0.34

0.00

Sand

-0.01

0.30

Silt

-0.19

-0.02

Clay

0.02

-0.24

33

Chl-a

-0.64*

0.10

Tom

0.34

0.14

*. Correlation is significant at the 0.05 level (2-tailed).

Highlights  Density of macrobenthos is higher in the thermal discharge stations, but diversity in these stations reduce in comparison to the other stations and bivalve constituted the most abundant group throughout samplings.  Temperature is an important factor on the amount of organic matter that it was the most influential among all the studied physicochemical factors and the majority of macrobenthic groups have a positive correlation with the organic matter.  The index of evenness increased when moving away from the thermal discharge stations.  The density of bivalves is higher in stations with particles size greater than clay.  Chlorophyll and phaeopigment at the thermal discharge stations are lower than the other stations because of the increased turbulence.

34