Indian Journal of Marine Sciences Vol. 28, September 1999, pp. 302-306 Distribution of ostracodes in the innershelf sediments off Kasargod, south west coast of India Rajesh Reghunath & T R Sreedhara Murthy Department of Marine Geology, Mangalore University, Mangalagangotri 574 199, Karnataka, India and Sk. Md. Hussain Department of Geology, University of Madras, A.C.Co\lege of Technology campus, Guindy, Chennai 600 025. India Received 7 January 1998, revised 20 October 1998 Surface sediment samples were collected from the innershelf off Kasargod, west coast of India, to appreciate the distribution of ostracoda fauna and the controls on the same. About 21 ostracode species have been identitied which belong to 17 genera. The depth wise distribution pattern reveals that the fauna is less populated up to 25 m water depth, and thereafter the population increases. Diversity index suggests open marine conditions. The ostracodes distribution pattern is related to water depth, sedimentological aspects, organic matter and carbonate distributions. Correlation analysis reveals that fine grain size, high organic matter and low carbonate content gives the minimum number of ostracodes and vice versa. Linear and multiple correlation also show that deeper depth favours the higher population. Though ostracodes are next to foraminifera in abundance, only a little attention has so far been paid to the study of ostracodes from the west coast of India ' · 4 , which deals mainly with either taxonomy or ecological aspects. Hence, an attempt has been made in this communication to analyse the distribution of ostracodes in relation to the physico-chemical conditions as well as the water depth. Materials and Methods The study is made in the innershelf region off Kasargod (Jat. 12°15'-12°31' N; long. 74°45'-75°E) (Fig. 1). Thirty four grab samples were collected, along three parallel transects, normal to the coast with an interval of 5 km between two adjacent transects, and a distance of roughly 1 km between two successive sampling stations. The area (-250 km 2 ) investigated extends from 6 to 47 m water depth. The Chandragiri river is the major fresh water regime influencing the study area (Fig. 1). The ostracodes were separated based on standard procedures 5 • 7 and the identification was made 8 . 9 . The individual tests of all the species present in each sample is counted separately to get a statistical evaluation of distribution. Results and Discussion Sedimentological, carbonate and organic matter studies of the present study area were reported 10.1 1 earlier. Silty clay and clayey silt sediments dominate the study area with a band of clayey sand sediments at a water depth of >46m . A considerable amount of sand is present (60-71 %) in the stations N12, Mil and S 11 and its mean grain size is in th e very fine sand range. The sedimentological studies indicate that these three sand rich samples are relict in nature, deposited during the lower stands of sea level. The samples located off the river mouth (zone A in Fig. I) are characterised by low carbonate and high organic matter values. Out of the 34 samples studied, ostracodes are confined only to 28 samples and consist 21 species representing 17 genera. All the species are benthic and the absolute abundance cha rt (Table 1) shows that no species is found in all the samples. Six species show widespread occurrence and cover about 50% of the ostracode bearing samples. They are Chrysocythere kezii, Keijella darwini, K. karwarensis. K. whatleyi. Lankacythere coralloides and Phlyctenophora zealandica. The first transect is characterised by the dominance of KeijeL/a I\ :halleyi followed by Chrysocythere keiji. The dominant species in the second transect is Chrysocythere keiji )