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Influence of Bottom Water Parameters on the Distribution of Benthic Foraminifera from the Gulf of Mannar, Off Tiruchendur, Southeast Coast of India

R. Vijayan*, V. Kumar, K. Sivakumar, J. Christinal, S. Selvaraj, T. Gangaimani

Department of Geology, National College (Autonomous), (Bharathidasan University), Tiruchirappalli, Tamilnadu - 620001

Abstract: Foraminifera are found in all marine environments, but they are very particular about the congenial environment for their reproduction, diversity and abundance. To understand the influence of bottom water parameters on the distribution of foraminifera from the shallow shelf region of Bay of Bengal, off Tiruchendur, Southeast Coast of Tamil Nadu, sediment and bottom water samples were collected at 27 stations, along three traverses viz. from off Veerapandianpattinam, off Tiruchendur and from off Alandurai, ranging in depths from 1.6m to 18.5m. The samples were collected during three seasons representing, summer (May 2016), pre monsoon (October 2016) and winter (January 2017) and thus the total samples amounted to 81. A total of 105 species of foraminifera have been identified from 47 genera, 32 families, 16 superfamilies and 4suborders. Among these 105 foraminiferal species, five were found to be widespread and abundant viz. Ammonia beccarii, A. tepida, Asterorotalia inflata, Nonioniodes boueanum and Quinqueloculina seminulam. Various bottom water parameters such as temperature, salinity, dissolved oxygen and pH were determined and correlated with the foraminiferal population. Temporally, higher temperature, salinity, dissolved oxygen and pH of bottom water observed during summer (May 2016) were congenial for higher population in the study area. Optimum conditions for the higher population and abundance of foraminifera are: Temperature: > 32.0°C, Dissolved oxygen: >6.0 mg/l, Salinity: >32 ppt and pH>8.1.

Keywords: benthic foraminifera, inner shelf, bottom water characteristics, Gulf of Mannar, off Tiruchendur

Received July 23, 2021; Revised August 29, 2021; Accepted September 09, 2021

Citation: R. Vijayan, V. Kumar, K. Sivakumar, J. Christinal, S. Selvaraj, T. Gangaimani, Influence of Bottom Water Parameters on the Distribution of Benthic Foraminifera from the Gulf of Mannar, Off Tiruchendur, Southeast Coast of India. Applied Ecology and Environmental Sciences, 9 (9). 786-794. January 2021. doi:10.12691/aees-9-9-1

1. Introduction

The shallow marine shelf regions of the east coast of India have provided a congenial environment for thriving of foraminifera. They nurtured with a broad ecological adaptability and their distribution and abundance are influenced by environmental factors such as substrate characteristics, depth and bottom water parameters. The growth and reproduction are constant as long as the environmental factors are favourable but as these depart from optimal values, rate of growth and frequency of reproduction decline. There are many studies relating to foraminifera and their relation to many ecological factors. Foraminifera are considered as environmental indicators owing to their rapid response to various pollution interferences [1,2,3]. Foraminiferal abundance and diversity are controlled by many factors like nutrition, dissolved oxygen conditions, pH, salinity, substrate and temperature [4,5,6,7,8]. High numbers of aberrant tests were attributed to high salinity conditions rather than anthropogenic stresses [9].

Benthic foraminifera are excellent indicators of water quality which influence their distribution and abundance [10]. Numerous studies have been made on the ecology and distribution of recent benthic foraminifera from the southeast and west coasts of India [11,12,13,14,15,16]. Higher temperature, salinity, pH and dissolved oxygen content noticed during April favoured higher reproduction and abundance of foraminiferal population [17]. The present study elucidates the influence of bottom water parameters such as temperature, salinity, dissolved oxygen and pH on the abundance and distribution of the widespread foraminiferal species in the shallow shelf region of Bay of Bengal, off Tiruchendur and adjoining coasts Southeast Coast of Tamil Nadu.

2. Study Area

The area under study is situated in the Gulf of Mannar. It is the region with 130 -275 km width, 160 km length covering an area of about 10,000 sq. km. that lies in between south eastern India and western Sri Lanka. In India, it extends from Rameshwaram to Kanyakumari districts of Tamil Nadu state. It has one of the important bioreserve popularly known as the Gulf of Mannar Biosphere Reserve that was declared as the first marine biosphere reserve of India in 1989.

The area under investigation covers the inner shelf from off the coast of Veerapandianpattinam in the north to from off Alandurai in the south and geographically situated between the latitudes 8o27’- 8o33’ N and longitudes 78o06’-78o14’ E (Figure 1).

The study area practices generally a tropical climate and experiences two types of monsoons namely, Southwest and Northeast. Southwest monsoon which extends from June to September, adds only scanty amount to the annual rainfall. On the other hand, Northeast monsoon, from October to December is often accompanied by cyclones gives ample amount to the annual rainfall. Summer is experienced from March to May while winter from December to February.

The coastal tract, belongs to the study area is geologically dominated by recent sediments comprising red soil, coastal sand, river alluvium, laterite, red teri, shell limestone, calcareous sandstone and patches of garnet and ilmenite sand. (Source: District survey report, Dept. of Geology and Mining, Govt. of Tamil Nadu).

3. Objective

In order to appraise the influence of bottom water parameters on the distribution of foraminifera from the inner shelf sediment of Gulf of Mannar, off Tiruchendur the following objectives were addressed: i. to ascertain the composition and to discover the distribution of living and total (living + dead) population of the fauna, ii. to correlate foraminiferal population distribution with observed environmental parameters and iii. to decipher the influence of bottom water parameters on distribution of foraminiferal species.

Figure 1. Location map of the area

4. Materials and Methods

4.1. Field Work

For the present study, sediment and bottom water samples were collected at 27 stations, along three traverses viz. from off Veerapandianpattinam, off Tiruchendur and from off Alandurai, ranging in depths from 1.6m to 18.5m. The samples were collected during the months of May 2016, October 2016 and January 2017 representing summer, pre monsoon and winter and thus the collection amounted to a total of 81.

The sediment samples were collected taking necessary precautions using Van Veen grab. A unit volume of 50 ml. wet sediment was taken from each sample and was preserved in a 10 % solution of neutralized formaldehyde for foraminiferal study. Small quantity of sodium carbonate was added to the samples to maintain the alkaline condition and all the samples were indexed. Respective depths of the water column above the sampling sites were also recorded.

Samples of water from the sediment water interface were collected using a Nansen reversible water sampler. Temperature of the bottom water was recorded from the built-in thermometer for all the samples collected. Dissolved oxygen content of the bottom water was measured by using dissolved oxygen analyser (Make: Hanna model A113), immediately after the collection. Salinity is a measure of total salt content of water and measured using portable salinometer (Make: ATC 23907). The values of pH of the water sample were observed by a pH meter (Make: Hanna, Model 101E) after making necessary precautions in sampling and standardization.

4.2. Laboratory Work

For the study of living foraminifera Walton's [18] staining technique with rose Bengal has been used. The foraminiferal tests were separated by floatation method using carbon tetrachloride [19]. The faunal specimens thus obtained were picked and mounted using a stereo binocular microscope and different genera and species were identified by following the classification proposed by Loeblich and Tappan [20]. The living and dead population were counted separately for all the samples collected.

5. Results and Discussion

5.1. Foraminifera

The qualitative analysis of the sediment samples from the area led to the recognition of 105 benthic species of foraminifera belong to 42 genera, 28 families, 15 super families and 4 orders. All the 105 benthic foraminiferal species identified in the study area are found both as living and dead. Among these 105 foraminiferal species, five were considered as widespread and abundant viz. Ammonia beccarii, A. tepida, Asterorotalia inflata, Nonioniodes boueanum and Quinqueloculina seminulam, as they were found in all the 81 samples as living and the living foraminiferal number for a season is greater 210 specimens per 50 ml of wet sediment.

5.1.1. Living Foraminiferal Number

Living foraminiferal number (LFN) per 50 ml of wet sediment varies from 71 (Station A1, October) to 401 (Station A9, May) (Figure 2). LFN is more in samples collected from off Veerapandianpattinam than the other two areas. Spatially, maximum LFN is noticed in stations V9, T9 and A9 (farthest stations from the shore) and is very less in stations V1, T1 and A1 (near shore stations). In general, the LFN is gradually increasing from the shore station to the farthest station of each traverse. Seasonally, the LFN is found to be minimum (5202) in October and is maximum (5966) in May.

Figure 2. Living Foraminiferal Number (per 50 ml. of wet sediments)

Figure 3. Total (Live + Dead) Foraminiferal Number (per 50 ml of wet sediment)

5.1.2. Total Foraminiferal Number

Total foraminiferal number (TFN) per 50 ml. of wet sediment varies from 323 (Station A1, October) to 1330 (Station T9, May) (Figure 3). Spatially, maximum TFN is noticed in stations V9, T9 and A9 (farthest stations from the shore) and is very less in stations V1, T1 and A1 (near shore stations). In general the TFN is gradually increasing from the shore station to the farthest station of each traverse. Seasonally, the TFN is found to be is minimum in October (17701) and is maximum in May (21552).

5.2. Bottom Water Parameters

5.2.1. Temperature

The relative abundance of both the living and dead calcareous benthic foraminifera is negatively correlated with depth and positively correlated with temperature [21]. 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 show a decrease in shell size with decreasing temperature [22]. Temperature was seen to be positively correlated with population size. Collections during May recorded a high mean temperature and favoured a higher population [23]. Temperature was found to be the significant stress factor than salinity and critical temperature thresholds were observed at 30 and 35°C. [24].

In the present shelf region, temperature varies between 32.2°C and 32.6°C at different depths during May, 30.3°C and 30.9°C during October and between 29.8°C and 30.1°C during January (Figure 4a - 4f). Spatially, there was no appreciable variation of temperature between stations of a collection and hence it had no specific effect on LFN.

Figure 4 a-f. Distribution of water parameters and the corresponding LFN

Figure 5. Seasonal Variation of Water parameters in Correlation with LFN

There is a marked seasonal variation, which can be noticed by the mean temperature values being higher during May (32.4°C) and minimum during January (30.0°C) (Figure 5). Hence, collections during summer (May) recorded a higher population. Increasing temperature was seen to be positively correlated with population size.

5.2.2. Salinity

Musco et al. [25] concluded after their study in the intertidal zone of the Yellow zone that foraminiferal abundance and species richness have a positive relation to salinity. Sreenivasalu et al. [26] through their study in the Beypore estuary reconfirmed this and also suggested that salinity lower than normal value causes a reduction in the test size of foraminiferal species.

Each benthic foraminiferal species has specific limits of tolerance to salinity for their survival, growth and reproduction, supported by other environmental factors [27,28]. Higher salinities are considered to be favourable for the growth and abundance of living foraminiferal population [23,24].

In the present study, the bottom water salinity value ranges between 32.1 ‰ and 32.4 ‰ during May, 29.1 ‰ and 29.6 ‰ during October and 29.7‰ and 30.0 ‰ during January (Figure 4a - 4f). The salinity values do not exhibit conspicuous variations among the stations of a season; but temporally they exhibit appreciable variation. During summer (May) mean salinity value is higher (32.4 ‰) and minimum (30.0 ‰) during winter (January) (Figure 5). The relatively lower values recorded during October may be attributed to heavy inflow of freshwater into the sea during this part of the season. The LFN had a positive relationship with salinity values and seasonally, summer accounts for higher LFN.

5.2.3. Dissolved Oxygen

A number of studies have suggested that bottom water dissolved oxygen concentration is a key factor controlling the distribution of benthic foraminifera [29,30,31,32]. Dissolved oxygen has been considered as one of the parameters influencing the standing crop of foraminifera [17,23,33]. The species abundance is mainly controlled by the bottom water dissolved oxygen content of the region [34]. Dissolved oxygen content (5.7 to 6 mg/l) existed during summer months are considered to be favourable along with other congenial factors for higher foraminiferal population [24].

In the current work, the dissolved oxygen content ranges between 6.2 (mg/l) and 6.5 (mg/l) during May, 5.2 (mg/l) and 5.5 (mg/l) during October and 5.8 (mg/l) and 6.0 (mg/l) during January (Figure 4a - 4f). But there is considerable variation in DO is observed between seasons, which can be observed from the mean values, maximum (6.3 mg/l) during May followed in January (5.9 mg/l) and is minimum (5.4 mg/l) during October (Figure 5). Though spatially, it has no influence over LFN, its impact on LFN is considerable temporally. In general, dissolved oxygen content of bottom water has a positive relationship with LFN. Higher dissolved oxygen content prevailed during summer season (May) accounts for higher LFN in the present study.

5.2.4. pH

The hydrogen ion concentration of approximately less than 7 is expected to adversely affect the production of calcareous tests [35]. The reduced pH is generally associated with low abundance and diversity of foraminifera [36,37]. The water has maintained alkalinity during all the three seasons, well within the limits of the tolerance of the fauna.

Saraswat et al. [38] 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.

In the present area, the pH values oscillate between 8.1 and 8.3 in May, 7.9 and 8.1 in October and 8.1 and 8.2 during January (Figure 4a-4f).Seasonally the mean values varied between 8.0 (October) and 8.2 (May) (Figure 5). The pH values of the bottom water show only a negligible variation both spatially and seasonally and hence its control over LFN is negligible.

5.2.5. Depth

Water depth is an important factor in determining the foraminiferal distribution. The other ecological variables which determine the abundance and diversity of foraminifera are directly associated with changes in depth [23,24,34]. It may be ascribed that increasing in depth changes the nature of substratum to more finer sand and turbidity maintain favourable conditions for the abundance of population [38].

Benthic foraminifera showed much stronger correlation to environmental gradients like water depth, percent carbonate mud, percent gravel, organic carbon flux, temperature and salinity rather than microbiotic community [39]. Rethikala et al. [17] observed that the foraminiferal population shows an increase with respect to depth. The response of foraminifera to phyto- detritus found to be varied with the depth at which the species were found in ocean. Thus, the depth had a great influence on foraminiferal responses to food and plays an important role in the changes in diversity and abundance of foraminifera observed during various seasons and in different geographical regions.

In the present study area comprising 27 stations, depth ranges from 1.6 m (station V1, October) to 18.5 m (station V9, May). Stations V1, T1 and A1 are the nearest stations with depth ranges from 1.6 m –2.4 m and stations V9, T9 and A9 are the farthest with depth ranges from 16.8 m –18.5m (Figure 4a, 4c, 4e). It is observed that in all seasons the diversity and the foraminiferal number (living and total) were found to be minimum at near shore stations and maximum at the farthest stations (V9, T9 and A9). It may be concluded that the depth along with other parameters played an important role in controlling the population and diversity of foraminifera in the present study.

5.3. Distribution and Ecology of Abundant and Widespread Foraminifera

The following five species viz. Ammonia beccarii, Ammonia tepida, Asterorotalia inflata, Nonioniodes boueanum, and Quinqueloculina seminulam are considered to be widespread and abundantly occurring since they are found as living in all the samples collected and studied and their LFN for a season is greater than other species of the present area. The living foraminiferal number of these five abundant and widespread living foraminifera in actual number of specimens for all the samples collected during May, October and January is given in Figure 6, Figure 7 and Figure 8 respectively while the temporal distribution is clearly exhibited in Figure 9.

Figure 6. LFN of Abundant and Widespread Foraminifera (May 2016)

Figure 7. LFN of Abundant and Widespread Foraminifera (October 2016)

Figure 8. LFN of Abundant and Widespread Foraminifera (January 2017)

Figure 9. Temporal Distribution of Abundant and widespread Species

Kumar and Manivannan [33] recorded eight abundant and widespread species of foraminifera in the Palk Bay, off Rameshwaram and concluded that the increase in temperature, salinity and dissolved oxygen content are the causative factors for the abundance of the living population. According to Twinkle Jacob and Kumar [23] the distribution of benthic foraminifera in the shelf part of Bay of Bengal, east coast of India is chiefly controlled by nature of sediments and bathymetry coupled with hydrodynamic condition, salinity and dissolved oxygen.

Ecological and distribution study of the abundant and wide spread foraminiferal species of the study area revealed the following:

• The LFN of all the five abundant and wide spread fauna were found to be maximum during May followed by January and minimum during October.

• The lesser LFN encountered during October and January was mainly because of the bay depression and monsoon rains and the resultant modifications of the bottom water parameters.

• Spatially, the LFN of all these abundant species were less in stations nearer to the shore and gradually increasing in stations away from the shore. Lesser population noticed in near shore stations were mainly due to wave agitation.

• The environmental conditions that prevailed during May (summer) were congenial for higher reproduction and higher LFN.

• In general, the living foraminiferal number increases with increasing temperature, salinity and dissolved oxygen content of bottom water.

• The LFN was positively correlated with depth and found to be more in samples collected in comparatively deeper waters.

6. Summary and Conclusion

Influence of bottom water parameters on the distribution of recent benthic foraminifera from the shallow shelf sediments of the Palk Bay, off the coast of Tiruchendur have been studied in detail and the conclusion are summarised below:

For the study, sediment and bottom water samples have been collected at 27 stations, along three traverses viz. From off Veerapandianpattinam, off Tiruchendur and from off Alandurai, during May 2016, October 2016 and January 2017 representing the seasons summer, pre monsoon and winter respectively. A total of 105 benthic foraminiferal species belong to 47 genera, 32 families, 16 super families and 4 suborders have been identified. Among these 105 species, the following five species viz. Ammonia beccarii, A. tepida, Asterorotalia inflata, Nonioniodes boueanum and Quinqueloculina seminulam were found to be abundant and widespread. Various bottom water parameters like temperature, salinity, dissolved oxygen content and pH were determined and correlated with the distribution of LFN and the distribution of wide spread foraminiferal species. Bottom water parameters showed negligible variations between stations of a season but exhibited a distinct variation among seasons. It was observed that higher temperature, salinity and dissolved oxygen content of the bottom waters influence the proliferation of the living population during summer (May 2016). Optimum conditions for the higher population and abundance of foraminifera are: Temperature: > 32.0oC, Dissolved oxygen: > 6.0 mg/l, Salinity: >32 ppt and pH >8.1. The population is found to be more in samples collected in comparatively deeper waters as the other ecological variables which determine the abundance and diversity of foraminifera are directly associated with changes in depth.

Acknowledgements

The authors are greatly indebted to the authorities of the National College, Tiruchirappalli for granting permission to utilise the laboratory and library facilities. The first author acknowledges with gratitude the financial assistance provided by the Rajiv Gandhi National Fellowship Programme (UGC) for carrying out the research work.

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