Hydrological and meteorological features in relation to the distribution of zooplankton of Tuticorin coast in the Gulf of Mannar are described. Seasonal variations in the surface temperature and salinity show similarity in general trends. A bimodal cycle in the distribution of these major factors was noticed. An increasing trend in the dissolved oxygen content was observed during postmonsoon months. The relation between pH and oxygen appeared to be inverse. The annual cycle of production of plankton in the region was found to be dicyclic. Copepods and chaetognatbs reached their maximum when the salinity was low. Copepods and lucifer showed an inverse relationship when the latter dominated the plankton. Poor percentages of copepods and lucifer were noticed when molluscan larvae and fish eggs constituted high percentages. The bulk of the larval stock consisted with planktonic stages of decapods, lamellibranch, gastropod and fish. Maximum occurrence of larvae coincided with the rainfall. The seasonal variations and the inter-relationship of the planktonic organisms are discussed.