Inner Shelf Substrate Characteristics and Their Impacts on the Distribution of Recent Benthic Foraminifera from the Southern Part of Gulf of Mannar, Southeast Coast of India

Abstract

The present study elaborates the relationship between sediment characteristics and benthic foraminiferal population distribution from off the coast of Theresapuram, Sippikulam, Mookaiyur and Valinokkam representing the southern part of Gulf of Mannar, Southeast coast of India. A systematic collection of sediment and bottom water samples were made at 28 sampling stations, keeping seven samples each, along the four traverses. The samples were collected for three seasons, representing pre-monsoon (October), post-monsoon/winter (January) and summer (April) and thus the collections amounted to a total of 84 samples. The benthic foraminiferal studies from the sediments collected have led to the recognition of 124 benthic foraminiferal species belonging to 59 genera, 39 families and 21 super families of 5 suborders. Among the 124 species, Ammonia beccarii, A. tepida, Asterotalia infllata, Elphidium advenum, Noninoides boueanum, and Quinqueloculina seminulum are considered to be abundant and widespread in the present study area. It has been observed that the maximum population is observed during summer (April) with 2335 specimens and the minimum with 1934 specimens during monsoon (October). Spatially, the middle segment (stations 3-5) of all traverses of all the collections encounter with relatively higher population. Impact of spatial and seasonal variation in substrate characteristics on the benthic foraminiferal population revealed that the calcium carbonate content shows a positive correlation with the fauna of the study area and the organic matter content has somewhat inverse relationship with the population abundance. In the present study, organic matter content is not an effective factor that controls the population abundance, but along with other parameters plays a supporting role. Out of 12 possible sediment types of Trefethen’s classification, the sediments in the study area fall only in three types’ viz., sand, siltysand and claysand. The most favourable substrate for higher benthic foraminiferal population seems to be siltysand. In general, the benthic foraminiferal population of the present study is directly proportional to the calcium carbonate content of the sediments along with lower organic matter (0.7 -0.93%) and the accommodative substrate for higher reproduction is silty sand.