Distribution of dinoflagellate cysts along the salinity gradient in two tropical estuaries along the West coast of India

Abstract

Dinoflagellate cysts are known to be potential seed banks which have an essential role in providing bloom history and also serve as useful indicators of eutrophication in marine environments. The present study is focused on the surface distribution of dinoflagellate cysts along the salinity gradient in two tropical estuaries, namely Chapora and Sal in Goa along the West coast of India. Surface sediments and water samples were collected monthly from February 2016-March 2017 which included all three seasons (pre-monsoon, monsoon, post-monsoon). A total of sixteen species of dinoflagellate cysts belonging to the order, Gymnodiniales, Gonyaulacales, and Peridiniales were recorded in the surface sediments. Cysts of heterotrophic dinoflagellates dominated the assemblage in both estuaries. Based on Redundancy Analysis (RDA), it was observed that the distribution of the dinoflagellate cysts were influenced by various physico-chemical parameters in both estuaries with salinity and grain size being the main explanatory variable. Nitrate limitation is noted to be a triggering factor for dinoflagellate cyst formation. Also, yessotoxin producer species, such as Gonyaulax spinifera, encountered in both estuaries showed an inverse relationship with nitrate concentration. This suggests that, high nitrate input in these estuaries might lead to excystment of Gonyaulax spinifera eventually leading to harmful blooms under eutrophic conditions.