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Inner Shelf Environments and Their Impact on the Distribution of Benthic Foraminifera from the Gulf of Mannar, off Kayalpattinam, Southeast Coast of India

Christinal J.*, V. Kumar, S. Selvaraj, T. Gangaimani

Department of Geology, National College (Autonomous), Tiruchirapalli, Tamilnadu - 620001

Abstract: Identification of change in foraminiferal assemblage with respect to environmental modifications will be a positive contribution to know varied marine micro ecosystem. The occurrence of benthic foraminiferal species is controlled to a great extent by physical factors such as depth, temperature, salinity, and dissolved oxygen content of bottom water, character of the bottom sediments, and availability of biological factors such as food supply, presence of symbiotic organisms and predators. In order to observe the impact of inner shelf environments on the distribution of benthic foraminifera, sediment and bottom water samples were collected from the inner shelf off Kayalpattinam, once in four months for a year, at 18 locations with a depth range between 1.76 m and 14.89 m., during the months of May 2016, September 2016 and January 2017 representing summer, pre-monsoon and winter/post monsoon respectively. In the present study, 81 foraminiferal species belonging to 42 genera, 30 families, 16 super families of the 4 sub orders (Textulariina, Miliolina, Lagenina and Rotaliina) have been identified. The spatial and temporal distribution of the foraminiferal fauna has been evaluated and correlated with observed environmental parameters like CaCO3 content, organic matter content, sand-silt-clay ratio of the substrate and temperature, salinity, dissolved oxygen content and pH of bottom water. Higher calcium carbonate content (>26%), organic matter content (0.9 - 1.03%) higher temperature (32.7 -33.3°C), higher salinity (32.6 to 33.3ppt) and dissolved oxygen (5.7 to 6 ml/l) prevailed during summer months are considered to be favourable for higher foraminiferal population in the present study. Depth is also considered as one of the effective factors controlling the population of foraminifera along with the other congenial parameters. The favourable niche for population abundance is found to be silty sand.

Keywords: inner shelf, benthic foraminifera, substrate characters, bottom water characters, spatial and temporal distribution, Kayalpattinam, southeast coast of India

Received February 19, 2021; Revised March 26, 2021; Accepted April 06, 2021

Citation: Christinal J., V. Kumar, S. Selvaraj, T. Gangaimani, Inner Shelf Environments and Their Impact on the Distribution of Benthic Foraminifera from the Gulf of Mannar, off Kayalpattinam, Southeast Coast of India. Applied Ecology and Environmental Sciences, 9 (3). 396-409. January 2021. doi:10.12691/aees-9-3-10

1. Introduction

Foraminifers are unicellular microorganisms widely distributed in marine and brackish water environments [1]. Many studies relating foraminiferal population distribution with factors like nutrition, dissolved oxygen, salinity, temperature and substrate have been carried out. Benthic foraminiferal species grouped by changing depth and latitudinal variation [2]; change in environmental factors have an impact on the morphology of foraminiferal test [3], salinity controlled the distribution of foraminifera [4], sediment type and organic matter content have an impact on living benthic foraminifera[5], oxygen depleted environments lead to diverse aspects of foraminiferal adaptation [6], distribution of brackish water benthic foraminifera can be used to understand bio geography and paleoenvironmental assessment [7], typical paralic sub-environments were characterized by typical foraminiferal species assemblages [8], strong and highly significant relationship of foraminifera assemblages have corelated with elevation and environment [9].

Industrial waste mainly with trace elements, agricultural and domestic waste affected the density and diversity of foraminiferal assemblages [10,11,12], environmental stress by anthropogenic and natural elements can result in test deformation [13]. Distribution of inner shelf benthic foraminifera with respect to the changes in substrate and bottom water characters have been studied from the Bay of Bengal, off Porto Novo [14], from the Palk Bay, off Rameswaram [15,16] and from the Palk strait from off Manamelkudi [17].

Foraminifera adapted to various niches on the sea floor viz., estuaries, salt marshes, marine marginal water bodies etc., are very sensitive to the environmental modifications and pollutional interferences and hence can effectively be used as an indicator for understanding the inner shelf environments of Gulf of Mannar, off Kayalpattinam.

Figure 1. Location map of the study area

2. Study Area

The study area comprising the southern part of Gulf of Mannar, East coast of India (Figure 1), lies in the geographic coordinates N 838’ to N 840’15” to E 7807’30” to E 7812’30” and forms a part of toposheet numbers 58 L/1 and 58 L/5 of the Survey of India.

The region forms the southern part of the South Indian Granulite terrain (SGT), which is a high-grade metamorphicterrain under granulite facies. The Gulf of Mannar receives riverine input through a number of rivers, of which the Thamirabaraniis the major source, debouches in the study area. As there are few check dams constructed recently in the estuarine portion the sedimentation influx into the shore is reduced considerably. Generally, the area is an undulating topography with general slope towards the east.

The area experiences generally a tropical climate and witnessing two types of monsoons namely, Southwest and Northeast. Southwest monsoon is from June to September, accounts for scanty to moderate rainfall while during Northeast monsoon, from October to December, often accompanied by cyclones andgives ample amount of annual rainfall. The annual average temperature varies from 26.0°C to 37.0°C with an average humidity of ∼65%. Generally, summer is experienced during months March, April and May while winter from December to February.

3. Objective

In order to assess the environmental impact on foraminifera from the inner shelf sediments of Gulf of Mannar, off Kayalpattinam the following objectives are taken up:

• to inventory the foraminifera fauna and their quantitative composition

• to ascertain the inner shelf environmental parameters

• to discover the effect of environmental parameters on the seasonal and spatial variation of benthic foraminiferal fauna.

4. Materials and Methods

4.1. Field Work

The sediment and bottom water samples were collected at 18 stations from the inner shelf sediments of Gulf of Mannar, off Kayalpattinam ranging in depths from 1.76 to 14.89 meters, during the months of May 2016, September 2016 and January 2017 representing summer, pre-monsoon and winter/post monsoon respectively and the total samples amounted to 54. All the sediment samples were collected by taking necessary precautions, making use of Petersen mud grab and an unit volume of 100 ml wet sediment taken from the top layer of each sample was preserved immediately in a 10% neutralized formaldehyde solution for foraminiferal study. At each station, samples of water from the sediment - water interface were collected with the help of a Nansen reversible water sampler and the temperature of the bottom water was noted using built in thermometer. Dissolved oxygen content of each bottom water sample was observed by using portable A113 dissolved oxygen analyser, salinity values by using Kerro salinometer and pH with the aid of H19828 pH meter after making necessary precautions in sampling and standardisation.

4.2. Laboratory Work

For identifying living foraminifera, Walton's [18] rose Bengal staining technique have been used.Foraminiferal tests were then separated from the residue by floatation method using carbon tetrachloride.In the laboratory, sand-silt-clay ratio in the sediment samples was estimated using standard sieving and pipette method of Krumbein and Pettijohn [19]. Textural nomenclature of Trefethen [20] has been used todescribe the sediment types.

Calcium carbonate was determined by following titration method of Piper [21] while Organic matter was estimated by the chromic acid method of Walkley and Black as detailed out by Jackson [22]. Benthic foraminifera tests were picked and mounted using a stereo binocular microscope and their taxa were identified by following the classification of Loeblich and Tappan [23].

5. Results and Discussion

5.1. Foraminifera

In the present study, 81 foraminiferal species belonging to 42 genera, 30 families, 16 super families of the 4 sub orders (Textulariina, Miliolina, Lagenina and Rotaliina) have been identified (Table 1). Among these, nine species belong to Textulariina, 28 belong to Miliolina, eight species belong to Lagenina and the rest 36 species belong to Rotaliina.

5.1.1. Living Foraminifera Population

In the current study, living foraminiferal species were observed in all the 54 samples collected and studied. Spatially, the living population varies from 83 (station 18, September) to 395 (station 8, May) specimens per 100ml. of wet sediment. The maximum living population was noticed in the farthest stations from the shore (stations 8, 9, 10) and the minimum foraminiferal population was found in near shore stations (stations 1 and 18).

Spatially, living foraminiferal population gradually increases from the shore to farthest stations. Seasonally, the living population size is found to be maximum (5392 specimens) in summer (May), minimum (4676 specimens) in pre-monsoon (September) (Figure 2).

5.1.2. Total Foraminiferal Population

In the study area, the total (living + dead) population size ranges from 295 (station 18, September) to 1177 (station 8, May) specimens per 100 ml of wet sediments. Temporally, the total population is found to be maximum (16097 specimens) during summer (May) and minimum (13910 specimens) in pre-monsoon (September) (Figure 3).

Figure 2. Living foraminifera population

Figure 3. Total foraminifera population

5.2. Substrate Characters

5.2.1. Sand-Sily-Clay Ratio

The correlation between texture of sediment and foraminiferal population was understood from several studies. The most favorable accommodative substrate for the foraminiferal abundance is silty sand [16,24,25,26,27,28]. Elakkiya and Manivannan [29] after their study on recent benthic foraminifera from off the coast of Arkattuthurai (near Nagapattinam), south east coast of India concluded that the important ecological factors that controls the distribution of foraminifera are organic matter content, calcium carbonate content and nature of the substrate. Kurbjeweit et. al [30] described the positive relation of benthic foraminiferal abundance with oxygen content, pore volume, carbon content and chloroplastic pigment equivalents of the sediment while distributional patterns related to sand fraction, dissolved oxygen, calcium carbonate and organic carbon content of the sediment of the Arabian sea.

Table 1. Taxonomy Chart of 81 Benthic Foraminiferal Species from the study Area

Table 2. Sediment types of varied stations, off Kayalpattinam

Figure 4. Relative abundance of Sand -Silt -Clay ( May 2016)

Figure 5. Relative abundance of Sand-Silt-Clay (September 2016)

Figure 6. Relative abundance of Sand-Silt-Clay (January 2017)

In the present study, among the twelve possible sediment types of Trefethen’s [20] textural nomenclature, the sediments taken from the study area fell only in two sediment types viz. sand and silty sand (Table 2). The foraminiferal population is relatively very poor in stations 1, 2, 16, 17 and 18 where the substrate is sandy and the population is more in stations 3-15 where the substrate is siltysand in all the three seasons (Figure 2). In general, larger foraminiferal populations are associated with low energy area and comparatively deeper part of the collection while the population is less in samples near the high-energy environment (near shore stations). The data related to sand silt clay percentages of all the samples collected are in relative abundance chart (Figure 4, Figure 5 and Figure 6). Thus, it is evident that the silty sand substrate offers a favourable condition for the foraminiferal abundance of the area.

5.2.2. Calcium Carbonate

The variation in calcium carbonate content of the sediments had a bearing on the abundance of foraminifera and showed a positive relation [25,29,30,31,32]. The calcium carbonate content, in the deeper segment of the traverse, coinciding with the alignment of coral reefs, is found to be higher that favours higher population [33]. Post et.al [34] exhibited the relationship between benthic foraminifera and whole micro biotic community with changes in environment and found that benthic foraminifera showed much stronger correlation to calcium carbonate content rather than other micro biotic community. The higher calcium carbonate content in beach sands of Kovalam favors maximum distribution of foraminifera [35]. Temporally, the mean values CaCO3 content was higher during May (summer) and spatially along the deeper part of all the collections which was positively correlated with foraminiferal population [27]. Temporally, higher percentage of CaCO3 prevailed during April was one of the congenial factors for higher population during that period [36].

In the present study the percentage of calcium carbonate content is generally moderate ranging from 17.9% (station 18, September) to 26.6% (station 8, May). Pearl and chunk beds are the main source for the higher CaCO3 content of sediments in stations 7-12. Relatively, the calcium carbonate content was found to be higher in stations 8, 9 and 10 in all the seasons and positively correlated with higher population. Lower values are recorded in station 1 followed by 18. Seasonally, higher percentage of calcium carbonate observed during May (Table 3) and was one of the controlling factors for the seasonal abundance of population in that period. In general, calcium carbonate content is considered to be the main influencing factor for abundance of living population in the study area (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12).

Table 3. CaCo3 content range of varied stations, off Kayalpattinam

Figure 7. Distribution of Environmental parameter (May-2016)

Figure 8. Living foraminifera distribution in May-2016

Figure 9.Distribution of Environmental parameters September-2016

Figure 10. Living foraminifera distribution in September -2016

Figure 11. Distribution of Environmental parameters January - 2017

Figure 12. Living foraminifera distribution in January -2017

5.2.3. Organic Matter

High sedimentation, greater input, slow decay and humid condition may be considered to be the reason for the high values of organic matter [32]. Organic matter content is not an effective factor that controls the population abundance, but along with other parameters like CaCO3 content, depth and water parameters like salinity, dissolved oxygen content and temperature plays an important role [27]. The organic matter content was found higher and favoured higher foraminiferal population, when the other parameters were congenial [29,30,36,37]. Eric Armynot et. al [5] confirmed that foraminifera density is low and species richness is high in sediments with a low organic matter content (<2%) and foraminifera density is high and species richness at an intermediate value in sediments with very high organic matter content. Martins et.al [38] revealed that opportunistic species populate in areas where the substrate is composed of fine-grained sediments enriched in organic matter. The lower organic matter content in sandy sediments and higher organic matter content in the fine sediments are observed in inner shelf sediments [27,36].

Seasonally, the mean values organic matter content was higher during May (summer) and spatially, in stations collected in the deeper part of every collection was positively correlated with foraminiferal population [27]. Though, organic matter content has no specific relationship with foraminiferal population, with its optimum amount (0.70 - 0.93%) along with other parameters plays an important role [36].

Hess and Jorissen [39] concluded that the distribution pattern of living benthic foraminifera in the Cap Breton canyon, Bay of Biscay, depend on organic matter content and oxygen concentration in the sedimentary column.

In the present study, the percentage of organic matter content is generally low ranging from 0.535% (station 1, September) to 1.234% (station 4, May) and directly proportional to the sediment fines. Active freshwater influx, turbidity of the coast because of monsoonal weather attributed to lesser sediment fines and the resultant lower organic matter content during September. Higher calcareous dust subsequently sediment fines accounts for higher organic matter along greater depths. Spatially, the organic matter content was found to be more between stations 5 to 14 in all the seasons. Lowest values are recorded in station 1 followed by 18, where the substrate is always sandy (Table 4). Organic matter content was relatively higher in stations 5, 6, 7, 11 and 12 as the clay percentage was comparatively higher than other stations (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12). Seasonally, organic matter 0.9 to 1.03 % in the sediments observed during May (summer) are suggested for an abundance of living foraminiferal population in the present study.

Table 4. Organic matter content range of varied stations,off Kayalpattinam

5.3. Bottom Water Characteristics

5.3.1. Salinity

Many studies revealed that salinity play a vital role in the diversity and abundance of foraminiferal population. An increase or decrease in salinity values was found to influence abundance of certain species and complete absence of others. The salinity shows positive correlation with foraminiferal population [27,40,41]. Lei et.al [42] found out that foraminiferal abundance and species richness have a positive relation to salinity. Benthic species undergone partial deformation after short term exposure to low salinity, can regain the form, still holding impressions of the hyposaline conditions [43]. Kasilingam et.al [28] concluded that the general trend in modern shallow water foraminiferal assemblage is increasing spatial diversity with increasing salinity gradients and environmental stability. Scott et.al [44] revealed that the low diversity and high abundance of foraminifera species in the Nemuro Bay wetland areas of Japan where salinity values were low. Hayward et.al [45] concluded that with increasing salinity there is an increase in calcareous forams and decrease in agglutinated forams for the brackish foraminifera of New Zealand. Yanko et. al [46] confirmed that low salinity or high heavy metal contamination results in the predominance of deformed living foraminiferal species. Moghaddasi et.al [47] after their study of benthic foraminiferal abundance and distribution in the Northern Oman Sea (Iranian side) continental shelf sediments explained the dominance of suborder ROTALIINA in the northern region and LAGENINA in the stations with higher depth. Important environmental factors controlling distribution of species were found to be water depth, salinity and substrate. Jean-Perre Debanay [48] observed that, in the hypersaline Araruama Lagoon of Brazil, morphological abnormalities were attributed to variations in salinity conditions rather than anthropogenic impact and was responsible for the predominance of Ammonia tepida in the more affected northern part of the area.

In the study area, salinity variation is very meagre between stations of a season and hence have a limited influence on foraminiferal population. Temporally, salinity values show considerable variation which is ascertained by the average salinity values of different seasons; higher values during May (32.95ppt) followed by January (31.68ppt) while the minimum is observed during September (30.3 ppt) (Figure 13). Higher salinity values (32.6 to 33.3ppt) observed during May is mainly due to the scanty flow of fresh water from the river and higher evaporation rate and are positively correlated with the foraminiferal population, while the minimum during September is mainly caused by the bay depression and higher input of fresh water through rivers (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12).

5.3.2. Temperature

Temperature is an important parameter that governs the growth and reproduction of foraminifera in coastal areas [43,49]. Kurtarkar et.al [50] discovered that out of all specimens fed with the same amount of food, both the growth was more rapid and the reproduction was more frequent in specimens kept in comparatively warmer water. Temporally, the temperature variation exhibited an effect on both living and total population and was seen to be positively correlated with population size [40]. Kurtarkar et. al [51] suggested that the foraminiferal response to temperature variation is species-specific; the shell size of several benthic foraminifera increased with decreasing temperature but a few other benthic foraminifera shows a decrease in shell size with decreasing temperature.

Subba Rao et.al [52] after observing the distribution pattern and population density of foraminiferal species from shelf sediments of Visakhapatnam concluded that these were influenced by bottom water temperature and currents, rather than sediment attributes and water salinity.

In the study area, spatially, no appreciable variation in temperature is noticed but there is a considerable variation between seasons. Temporally, mean temperature is relatively higher (32.95°C) during summer followed by January (31.17°C). The minimum temperature is observed during September (30.84°C) (Figure 13). In general, increasing temperature is positively correlated with population of foraminifera (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12).

5.3.3. Dissolved Oxygen

The dissolved oxygen concentration is higher compared to other stations due to the dense and extensive patches of benthic algae in the shallow environment [34]. The abundance of population of foraminifera is positively correlated with an increase of dissolved oxygen content [30,40]. Dissolved oxygen has repeatedly been shown to be a limiting factor for benthic foraminifera [53] and to have an influence on morphology in terms of shell and pore size [54]. Some low oxygen benthic foraminifera have been observed to migrate to habitats with low oxygen conditions [55,56,57,58,59]. Rasheed and Ragothaman [14] stated that dissolved oxygen is one of the factors contributing to the abundance of living population in the Bay of Bengal, off Porto Novo. In benthic foraminifera, species with smaller shells, larger pores and higher pore densities have been linked with low oxygen [31,60,61]. Ramanathan [62] stated that dissolved oxygen was one of the factors favouring the growth of foraminifera.

Figure 13. Seasonal variations of Salinity and Temperature

Figure 14. Seasonal variations of pH and Dissolved Oxygen

In the current study, distribution of dissolved oxygen shows a clear seasonal variation and no appreciable spatial variation. Temporally, maximum mean volume (6.6 ml/l) is observed in September and followed by January. The seasonal average of dissolved oxygen content is May 5.81 ml/l, Sep 6.61 ml/l, and January 6.02 ml/l (Figure 14). Higher dissolved oxygen content observed during September may be due to lower temperature and salinity values. Warm water holds less dissolved oxygen than cold water because the molecules are moving faster than in cold water thereby allow oxygen to escape from the water (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12). Dissolved oxygen content (5.7 to 6 ml/l) existed during summer months are considered to be favourable along with other congenial factors for higher foraminiferal population in the present study.

5.3.4. pH (Hydrogen Ion Concentration)

The reduced pH is commonly connected with low abundance and diversity of foraminifera [63]. Low fluctuation in pH values maintained the alkaline medium within the limit of faunal indulgence [13]. The values of pH did not vary much during different seasons and between stations, in the inner shelf environments [40,64]. Kurtarker et.al [43] noted that the dissolution of calcareous tests also take place in alkaline seawater than that was noted before. Influx of fresh water during rainy season can decrease salinity that can directly result in a low pH, altogether causing dissolution of foraminiferal tests [65]. If dissolution of calcareous tests is high, it can cause predominance of non-calcareous agglutinated forms than calcareous forms [66].

Saraswat R. et. al. [67] after the experimental study of salinity induced pH confirmed that a pH below 7.5 can severely disrupt the calcite secretion and reproduction ability of benthic foraminifera. An experimental study to understand influence of increased atmospheric CO2 that may happen in the near future revealed that high CO2 can end up in ocean acidification declining foraminiferal survival rate and calcification [68]. The reduced pH is generally associated with low abundance and diversity of foraminifera [69].

In the present study, the pH values of the bottom waters show only a negligible variation both spatially and temporally (Figure 14). Hence its impact on the distribution of foraminifera is not for any accurate determination (Figure 7, Figure 8, Figure 9, Figure 10, Figure 11 and Figure 12).

5.3.5. Depth

Water depth is an important factor in determining the foraminiferal distribution. The abundance and diversity of foraminifera are directly associated with changes in depth [36]. It may be ascribed that increasing in depth changes the nature of substratum to more finer sand and turbidity maintain favourable conditions [70]. The relative abundance of benthic foraminifera is positively correlated with depth [71]. Moghaddasi et.al [47] contemplate water depth as a preferable factor in controlling the foraminiferal distribution, in their detailed study on continental shelf sediments along with factors like salinity and substrate type. They proposed that suborder Lagenina shows an increase in abundance towards stations with greater depth in the continental shelf sediments of Northern Oman Sea.

Living specimens have linked with depth distribution in certain foraminifera (Uvigerina peregrina) to macro fauna -influenced microhabitat such as zones containing biotic structures [72,73]. Martins et.al [38] emphasized that in the continental shelf of Campos basin, living foraminiferal composition varies with respect to bathymetry along with sediment characteristics andorganic matter supply. Denne et.al [74], from an investigation in the North-western Gulf ofMexico, demonstrated that the depth distribution of benthic foraminifera is strongly correlated with the limits of water masses. Kumar et.al [27,64] observed that the foraminiferal population shows an increase with respect to depth.

In the study between living and dead foraminiferal assemblages done on Aveiro Continental Shelf of Portugal, it was confirmed that with an increase in depth, dead species shows an increase in diversity with limited changes in heterogeneity while living ones exhibits a decrease in diversity with an increase in heterogeneity [75]. The deep-sea foraminifera are adapted to limited or no supply of food materials for long periods [76]. Stations near to the shore, (< 1m depth) in the Pak bay, contain negligible living populationKumar et.al [77].

Figure 15. Seasonal variations of Depth(m)

In study area, the depth ranges between 1.76 m and 14.89 m (Figure 15). Sediment fines like silt and clay content and organic matter percentage of the substrate is directly proportional to the depth. Pearl and chunk beds are associated with depths above 10 m and account for higher CaCO3. It may be concluded that the depth is generally considered to be important if the other variables are directly associated with changes in depth.

5.4. Summary and Conclusion

Impact of inner shelf environments on the distribution of Benthic foraminifera from the Gulf of Mannar, off Kayalpattinamreveals the following:

Sediment and bottom water samples were collected from 18 stations ranging in depth between 1.76 and 14.89 meters for the months of May 2016, September 2016 and January 2017 representing Summer, Pre-monsoon and winter/post monsoon respectively. In the present study, 81 foraminifera species belonging to 42 genera have been identified and among them are 10 are arenaceous agglutinated, 24 calcareous imperforate and the rest 47 are calcareous perforate.

The fauna is found in living condition in all the 54 samples collected and studied. The living and the total (living+dead) population size are found to be higher in summer (May).Spatially, the population size is more in stations collected along deeper part of the traverse (stations 8-10) during the all seasons.

Sediment parameters like organic matter content, calcium carbonate content and sediment fines show a considerable variation both temporally and spatially. Depth is considered to be important with respect to the distribution of sediment parameters.Bottom water parameters like temperature, salinity, dissolved oxygen content and pH showed negligible variations among stations of a season but showed a distinct variation between seasons. Calcium carbonate content is considered to be the main influencing factor for abundance of living population both spatially and seasonally. Higher calcium carbonate content (>26%) and organic matter content (0.9 - 1.03%) along with other congenial parameters favours higher foraminiferal population in the present study area. Higher temperature (32.7 -33.3°C), higher salinity (32.6 to 33.3 ppt) and dissolved oxygen (5.7 to 6 ml/l) prevailed during summer months are considered to be favourable for higher foraminiferal population in the present study. Depth is also considered as one of the effective factors controlling the population of foraminifera along with the other congenial parameters.

Acknowledgements

The authors are very much thankful to Mr. R. Raghunathan, Secretary, National College (Autonomous), Dr. R. Sundararaman, Principal, National College (Autonomous), Tiruchirappalli for providing the lab and other infra structural facilities. The first author is grateful to Mr. R. Balaji, Secretary & Correspondent, SBIOA Educational Trust, Mr. R. Ganapathy Subramaniyan, Correspondent, SBIOA Schools, Tiruchirapalli and Mrs. Shakudala Sundaram, Principal, SBIOA Senior Secondary School, Trichirapalli-07 for giving permission to pursue the research.

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