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

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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.