Distribution and statistical aspects of Ostracoda from the Pulicat lagoon, Tamil Nadu: Implications on siltation and microenvironment

Abstract

Ostracods are bivalved tiny Crustaceans; inhabit almost all types of aquatic environments. In order to study the systematic and distribution of recent brackish water Ostracoda from the Pulicat lagoon, near Chennai, Tamil Nadu, a total of twelve surface sediment samples and one core were collected from Pulicat lagoon. A total of a total of 37 ostracod taxa belonging to 24 genera, 14 families, 2 superfamilies, and 2 suborders of the order Podocopida have been identified. Among these, Cytherelloidea leroyi belong to suborder Platycopa and the remaining 36 species to suborder Podocopa are recorded from Pulicat lagoon.Geochemical and sedimentological parameters such as CaCO 3 , Organic matter and sand-silt-clay ratio were estimated. An attempt has been made to study the relation between the sediment characteristics (the substrate of the Pulicat lagoon samples consists of sand and silty-sand) and Ostracoda population, and evaluate the favourable substrate for the population abundance in the area. From the distribution of Ostracoda, it is inferred that the sandy substrate is congenial sediment type for the population abundance and distribution. The implications of the proxies like Ostracod surface ornamentation, carapace and valve ratio and other environmental interpretations from the Pulicat lagoon are presented in this paper. The ratio between the carapaces and open valves of Ostracoda has been taken into consideration for determining the rate of sedimentation. Among a total of 1910 Ostracod shells recovered in surface and core, specimens 1469 are carapaces, while the remaining 441 specimens are open valves. Based on this observation, it may be concluded that a relatively rapid rate of sedimentation prevails in the Pulicat lagoon.