International Research Journal of Environment Sciences________________________________ ISSN 2319–1414Vol. 3(9), 5-13, September (2014) Int. Res. J. Environment Sci. International Science Congress Association 5 Distribution of Benthic Foraminifera off Cuddalore, Bay of Bengal, Southeast Coast of IndiaTabita Symphonia and Senthil Nathan D. Dept. of Earth Sciences, Pondicherry University, Puducherry, INDIA Available online at: www.isca.in, www.isca.me Received 3rd July 2014, revised 2nd August 2014, accepted 18th August 2014 AbstractBenthic foraminifera from both surface and core sediments collected along two transects in the offshore region of Cuddalore were studied in parallel to environmental variables and sediment characteristics. Altogether 95 species belonging to 47 genera and 6 orders were identified. Analysis revealed that species richness is high in the inner shelf while abundance increases seaward. Amphistegina, Quinqueloculina, Operculina and Elphidium are dominant in areas of coarser sediments and strong current activity. The outer shelf assemblage is characterised by muddy sediments rich in Uvigerina, Bulimina and Bolivina. Living specimens were rare though few numbers were found in the near shore region. The temperature, pH, dissolved oxygen and dissolved nitrogen content of the sample locations exhibited minimal changes except salinity. Strong currents, slight variations in the physicochemical parameters, mixing of cytoplasm during the development stages of tests would have resulted in test abnormalities. Four kinds of textures were identified: Sand, slightly sandy mud, slightly muddy sand, muddy sand. Statistical analysis showed that taxonomic richness never exceeded 13 per sample and they are more or less evenly distributed in all the stations. Keywords: Benthic foraminifera, diversity, sediments, physicochemical parameters, statistical analysis, Bay of Bengal, India. IntroductionBenthic foraminifera are single- celled microorganisms found ubiquitously in all the marine habitats. They are easy to collect and have good fossilization potential offering vast scope to study them in detail. They are sensitive to pollution, changes in the sea level, environment and also provide excellent dataset for statistical analysis. In the recent years a world wide application of benthic foraminifera as a bio - monitoring tool to investigate the changes in environmental parameters due to natural calamities and anthropogenic effect has been witnessed. Test abnormalities are noticed in naturally stressed environments exhibiting variations in pH, salinity and other parameters; pollution4 and also due to biological changes during the development stage. The aim of this study is i. to examine the changes in the foraminiferal assemblages and know their distribution pattern both spatially and vertically using a multifaceted (micropaleontological, sedimentological and statistical) approach, ii. to deduce the response of foraminifera to environmental factors such as bathymetry, substrate, salinity, water currents etc. Study Area: The area under investigation spans the continental shelf and the upper slope off Cuddalore where Ponnaiyar and Gadilam Rivers drain in to the Bay of Bengal. The river Ponnaiyar, with an estimated length of 430 km, is one of the largest interstate flowing eastern rivers. It originates from the eastern slope of Nandidurg Hills of Karnataka and flows through Karnataka and Tamil Nadu prior to joining the Bay of Bengal 3 miles north of Cuddalore. It has a catchment area of 16,019 km. It divides further into Ponnaiyar and Gadilam rivers below the Thirukovilur anicut. The river sediments provide an important source of building material. Known for its significance since historic times, this river continues to play an indispensable role even today. People in Karnataka and Tamil Nadu states rely upon this water resources for drinking water, industrial and agricultural purposes. The Gadilam River covers a distance of 112 km as it streams through Villupuram and Cuddalore districts of Tamil Nadu and eventually drains into the Bay near Cuddalore. It has a drainage area of 900 km and is bounded by Ponnaiyar and Vellar basins. The climate in this region is subtropical with a maximum mean temperature of 26 °C. The average annual rainfall received is around 1040 mm. The Cuddalore shelf is narrow and has an average width of 79 km. It is concave shaped with a gentle gradient up to 3000 m of water depth. Two submarine canyons with steeply sloping, V- shaped walls are identified with their heads situated between 36 and 54 m depth10. Material and Methods Sample collection: The collection of substrate sediment samples were carried out on a cruise in June 2012. Sediments were collected using van Veen grab sampler in two transects (figure 1) from different water depths ranging between ~ 10 and ~ 450 m. However, the sediments from beyond 100 m of water depth (transect –I) could not be retrieved owing to strong currents during the onset of SW monsoon. 50 g of sediment was International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(9), 5-13, September (2014) Int. Res. J. Environment Sci. International Science Congress Association 6 scraped from the top surface of the sediment and preserved in already cleansed vials containing Rose – Bengal solution (� 70% of ethanol and 2 g of stain /l)11 for a fortnight12. Rose – Bengal solution is used to stain the living specimens and only brightly coloured foraminifera are counted as alive13. Physicochemical parameters like depth, temperature, pH, salinity, dissolved oxygen and dissolved nitrogen content were measured on board ‘ROV - Sagar Paschimi’ using SCUBA Submersible Fluorometer (table 1). A short core was also collected using gravity corer from water depth of ~ 12.5 during a cruise on ‘ORV – Sagar Manjusha’ in February 2013. The top 5 cm of the core was sliced into 1-cm-thick samples, and 2-cm-thick layers were obtained from the remaining portion. Subsamples from every 5 cm interval were used for granulometric analyses. Figure-1 Study area showing sample locations Table-1 Coordinates and physicochemical parameters of the study area Sample Id Latitude N Longitude E Depth (m) T (°C) pH Salinity (psu) DO (mg/l) DN (ml/l) SP-1 11.771452 79.826236 11 27.05 8.63 35.61 6.53 8.53 SP-2 11.772075 79.939649 32 27.26 8.77 35.71 6.62 8.62 SP-3 11.770849 79.951955 58 27.41 8.75 36.08 6.70 8.71 SP-4 11.771093 79.958250 74 27.91 8.80 37.29 6.76 8.77 SP-5 11.770603 79.969360 106 27.91 8.81 38.98 6.98 9.01 SP-6 11.771099 79.977993 139 27.84 8.82 39.83 7.22 9.28 SP-7 11.772358 79.999795 252 28.15 8.80 43.39 8.15 10.30 SP-8 11.773137 80.035980 411 28.35 8.81 43.09 8.68 10.95 SP-9 11.734540 79.817194 9 27.99 8.73 36.21 6.53 8.51 SP-10 11.734767 79.833419 15 28.06 8.95 36.64 6.56 8.54 SP-11 11.734709 79.884370 26 28.35 8.85 37.39 6.58 8.56 SP-12 11.732830 79.975230 75 28.62 8.84 38.41 6.78 8.79 SP-13 11.733510 79.984649 119 27.92 8.84 39.40 7.11 9.15 SP-14 11.733705 79.992583 161 28.15 8.82 41.16 7.60 9.71 SP-15 11.734279 80.024614 282 27.99 8.81 41.91 8.29 10.48 SP-16 11.736374 80.039914 404 27.95 8.80 41.52 8.73 11.01 SM-2 11.747205 79.832283 12.5 - - - - - Note: SP refers to surface samples and SM stands for core sample. International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(9), 5-13, September (2014) Int. Res. J. Environment Sci. International Science Congress Association 7 Sample processing: Sediments: The collected sediment samples were first air dried and then oven dried at 40°C overnight. 100 gm of weighed subsample is placed in a stack of ASTM sieves (2.0 mm = 1 (phi), 1.0 mm = 0 , 0.5 mm = 1 , 0.25 mm = 2 , 0.125 mm = 3 and 0.63 mm = 4 ) and shaken for ten minutes. The grain size fractions are weighed for grain size distribution. The raw weight of each fraction is expressed as its weight percentage. Udden – Wentworth scale for grain size analysis is used to know the gravel, sand and mud content for each sample 14. However, textural class is assigned based on the mud content after Reineck & Siefert 15, and Pejrup16, modified by Fleming17. Foraminiferal analysis: At the lab, samples were wet sieved through 63and 125 m sieves. Around 300 individuals were picked from � 125 m fraction, mounted and identified from each sample. Altogether 8168 benthic foraminifera were recognised from the surface and core sediments. Diversity indices were calculated using the PAleontological STatistics (PAST) software, Version 2.1718: i. Taxonomic richness (S); S is the number of taxa per sample, ii. Dominance (D) is the percentage of the most common species and iii. Shannon Diversity Index (H) is determined from the total count of individuals (n) and the number of individuals (n) present in each taxon using the equation H(S) = ((n /n) In (n/n) 1, 19. iv. Evenness [E] is quantified as the degree of evenness in distribution of species20. v. Margalef’s richness index [(S-1) / ln (n)], (f) Equitability [J] and (g) Fisher- index [S = *ln (1 + n/ )] is the relationship between the species count and the sum of individuals in an assemblage 21, 22. Results and Discussion Grain size distribution: The surficial sediments in the Cuddalore shelf are predominantly characterised by sand. High amount of sand in this region is correlated with the occurrence of high wave energy conditions which caused the winnowing of fine sediments22, due to erosion23 and presence of submarine canyons10. The coarser sediments are composed of gravel, mollusc shells and fragments of bryozoan colonies while carapaces and valves of ostracoda are found in medium sized fraction. In Transect - I, samples from shallow depths ( 75m) exhibit more content of sand (&#x-3.3;女 92%). Mud percentage is below 10 in all the sites. In the second transect, amount of sand is found to decrease gradually with depth but with a sudden decline at 282 m (~ 9%). Less than 20% of mud is found in all the sites except slightly higher quantity at 15 m (~ 39%) and more of mud in 282 m (~92%). Core sediments, showed an overall sandy mud pattern. However, high mud content is witnessed between 20 -25 cm depth (table 2). Physicochemical parameters: In all the sampling stations, temperature varied between 27 – 29°C, dissolved oxygen and nitrogen content varied between 6.5 – 9 mg/l and 8.5 – 11 ml/l respectively. Salinity in northern part of the study area (35- 43 psu) differed slightly compared to that of the southern side (36 -41 psu). The above parameters are observed to steadily increase with increasing depth. pH values were well within the normal range of seawater (7.5 – 8.84) except in two sites, SP- 10 &11 showing 8.95 and 8.85 (table 1). Table-2 Textural class based on mud content after Reineck and Siefert (1980), and Pejrup (1988), modified (Fleming, 2000) Sample Id Sand % Mud % Textural Class SP-1 92.09 7.91 Slightly muddy sand SP-2 95.46 4.55 Sand SP-4 94.25 5.75 Slightly muddy sand SP-9 93.8 6.19 Slightly muddy sand SP-10 61.60 38.405 Muddy sand SP-11 85.94 14.06 Slightly muddy sand SP-13 85.55 14.45 Slightly muddy sand SP-14 80.14 19.84 Slightly muddy sand SP-15 8.31 91.69 Slightly sandy mud SM-2-1 83.02 25.27 Muddy sand SM-2-2 64.51 35.47 Muddy sand SM-2-3 57.37 42.59 Muddy sand SM-2-4 38.45 57.05 Sandy mud SM-2-5 32.57 67.42 Sandy mud SM-2-6 37.94 62.05 Sandy mud SM-2-7 39 61.48 Sandy mud International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(9), 5-13, September (2014) Int. Res. J. Environment Sci. International Science Congress Association 8 Foraminiferal analysis: 95 species have been identified out of which 59 were hyaline, perforate forms; 28 calcareous, imperforate forms, and 8 agglutinated forms. The recognised species are enlisted in table 3. Surface samples: The total (living + dead) assemblage in the Cuddalore shelf sediments were dominated by Amphistegina (30%). Miliolids comprised (25%) of the foraminiferal population in the first transect and (20%) in the second. Species diversity is higher in the near shore and inner shelf than in the deeper substrate sediments. Cibicides wuellerstorfi, Lobatula(22%) and Quinqueloculina spp. (21%) were found in sandy sediments and in areas of active currents. Higher species dominance found beyond 100 m of water depths is attributed to the availability of more nutrients and organic content. Uvigerina spp., Bulimina marginata and Bolivina spathulatawere found in � 250 m of water depth (SP -16) characterised by higher mud content and lower current velocity. This assemblage indicates the presence of hypoxic - anoxic microhabitat in the sediments contrary to the well oxygenated conditions of the overlying water column. Very few living species were encountered in the samples such as Amphistegina radiata, Ammonia papillosa and Elphidium spp. The lesser number is probably owing to the higher current velocity25. Shannon Index (H) values are � 1.5 in sites with above 80 % of sand. In stations with slightly higher mud content, these values are less. Higher number of dominance in sample no. SP -16 shows low diversity values and represented by very few species. The Margalef’s Index shows � 2 values for three sites SP-1, 14 and 15 (figure 2). More relict specimens stained with ferric ion and broken tests were observed in water depth 50 m. The assemblage includes Triloculina trigonula, Triloculina insignis, Rotalia annectens and Quinqueloculina agglutinans etc. in the order of increasing abundance. Presence of relict forms denotes low rate of deposition in the area of interest. Core samples: Nonion, Ammonia, Elphidium, Cibicides and Triloculina are the dominant genera with more than 5% abundance in all the samples. Nonion elongatum, Nonion fabum, Nonion scaphum, Nonionella labradorica, Nonionella turgida, Nonionella grateloupi, Nonionella stella contributed to nearly half (45.3%) of the entire benthic population. Living foraminiferal assemblage are composed of Nonion, Elphidium and Spiroloculina. They are found in more numbers in the top three centimetres and decreased in the rest of the core.The down - core increase in mud content are correlated with the decrease in diversity and equitability values. Taxonomic Richness (S) ranges between 9 and 10 in the entire core. Shannon diversity values (H) are 2 and equitability values (J) are 0.82 (figure 2). Deformed tests constituted only 6.43% of the entire population picked from the samples. Nonion fabumand Nonion elongatum (~ 60%) are the major contributors while Elphidium advenum, Elphidium crispum, Elphidium discoidalemade up nearly 20 % of the total deformed population. SEM images of few deformed species are shown in figure 1. The types of deformation observed include twisted or distorted shape, protuberances of the final chamber, overdeveloped chambers of the last whorl, reduction in size of the last chamber, twin and quadruplet forms. Developmental accidents26, sharing of the same reproduction cyst, current action, change in pH, and salinity etc.3 could be few factors that are responsible for twin and quadruplet formation in benthic foraminifera. It is also noted that high numbers of deformed tests occur only under polluted conditions. However, less percentage of deformed forms suggest that these test abnormalities may be due to environmental and biological changes. Overall, the distribution pattern in the study area reveals that the environment is more or less stable with only slight changes in the physicochemical parameters. Living foraminiferal assemblage majorly comprised of calcareous forms in the surface sediments and hyaline forms in the core. Core sediments witnessed higher numbers of deformed foraminifera than the surface sediments. 101214SP-1 SP - 2 SP - 4 SP - 9 SP - 10 SP - 11 SP - 13 SP - 14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM - 2 - 3 SM - 2 - 4 SM - 2 - 5 SM - 2 - 6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - 2 - 10 SM - 2 - 11 SM - 2 - 12 SM - 2 - 13 SM - 2 - 14 SM - 2 - 15 SM-2-16 SM - 2 - 17 SM - 2 - 18 SM-2-19 SM - 2 - 20 SM - 2 - 21 Taxonomic Richness (S) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(9), 5-13, September (2014) Int. Res. J. Environment Sci. International Science Congress Association 9 0.20.40.60.81.2SP-1 SP - 2 SP - 4 SP - 9 SP - 10 SP - 11 SP-13 SP - 14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM - 2 - 3 SM - 2 - 4 SM - 2 - 5 SM - 2 - 6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - 2 - 10 SM - 2 - 11 SM - 2 - 12 SM - 2 - 13 SM - 2 - 14 SM - 2 - 15 SM - 2 - 16 SM - 2 - 17 SM - 2 - 18 SM - 2 - 19 SM - 2 - 20 SM - 2 - 21 Dominance (D) 0.51.52.5 SP - 1 SP - 2 SP - 4 SP - 9 SP - 10 SP - 11 SP - 13 SP - 14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM - 2 - 3 SM - 2 - 4 SM - 2 - 5 SM-2-6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - 2 - 10 SM - 2 - 11 SM - 2 - 12 SM - 2 - 13 SM - 2 - 14 SM - 2 - 15 SM - 2 - 16 SM-2-17 SM - 2 - 18 SM - 2 - 19 SM - 2 - 20 SM - 2 - 21 Shannon Index (H) 0.20.40.60.81.2 SP - 1 SP - 2 SP-4 SP - 9 SP - 10 SP - 11 SP - 13 SP - 14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM-2-3 SM - 2 - 4 SM - 2 - 5 SM - 2 - 6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - 2 - 10 SM - 2 - 11 SM - 2 - 12 SM - 2 - 13 SM - 2 - 14 SM - 2 - 15 SM - 2 - 16 SM - 2 - 17 SM - 2 - 18 SM - 2 - 19 SM - 2 - 20 SM - 2 - 21 Evenness (E) International Research Journal of Environment Sciences______________________________________________ ISSN 2319–1414 Vol. 3(9), 5-13, September (2014) Int. Res. J. Environment Sci. International Science Congress Association 10 Figure-2 Statistical parameters based on the relative abundances of benthic foraminifera Conclusion In the present study, 95 species of benthic foraminifera have been identified from 30 sediment samples. The foraminiferal assemblage show an increase in species diversity in the inner continental shelf. Amphistegina, Quinqueloculina, Cibicides andTriloculina are the dominant genera. Epifaunal forms are abundant in coarse grained, high energy environment. The outer shelf – upper slope assemblage exhibits low species diversity, higher abundance of Uvigerina peregrina, Bulimina marginataand Bolivina spathulata. Nonion is the most abundant genera in the core sediments. Relatively fewer tests showing 0.51.52.5 SP - 1 SP - 2 SP - 4 SP - 9 SP - 10 SP - 11 SP - 13 SP-14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM - 2 - 3 SM - 2 - 4 SM - 2 - 5 SM - 2 - 6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - … SM - … SM - … SM - … SM - … SM - … SM - … SM - … SM - … SM - … SM - … SM - … Margalef 0.20.40.60.8 SP - 1 SP - 2 SP - 4 SP - 9 SP - 10 SP - 11 SP - 13 SP - 14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM - 2 - 3 SM - 2 - 4 SM-2-5 SM - 2 - 6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - 2 - 10 SM - 2 - 11 SM - 2 - 12 SM - 2 - 13 SM - 2 - 14 SM - 2 - 15 SM - 2 - 16 SM - 2 - 17 SM - 2 - 18 SM - 2 - 19 SM - 2 - 20 SM - 2 - 21 Equitability (J) 0.51.52.53.5 SP - 1 SP - 2 SP - 4 SP - 9 SP - 10 SP - 11 SP - 13 SP - 14 SP - 15 SP - 16 SM - 2 - 1 SM - 2 - 2 SM - 2 - 3 SM - 2 - 4 SM-2-5 SM - 2 - 6 SM - 2 - 7 SM - 2 - 8 SM - 2 - 9 SM - 2 - 10 SM - 2 - 11 SM - 2 - 12 SM - 2 - 13 SM - 2 - 14 SM - 2 - 15 SM - 2 - 16 SM - 2 - 17 SM - 2 - 18 SM - 2 - 19 SM - 2 - 20 SM - 2 - 21 Fisher