Response of benthic dinoflagellates Amphidinium carterae and Bysmatrum gregarium to salinity changes and prolonged darkness: Elucidation through laboratory experiments

Abstract

This study elucidates the responses of bloom-forming benthic dinoflagellates, Amphidinium carterae and Bysmatrum gregarium (formerly known as B.caponii) to salinity changes and prolonged darkness.Both dinoflagellates are known to inhabit rock pools that experiences significant variations in environmental conditions.In both dinoflagellates, salinity changes did not trigger cyst formation but morphological responses were different under prolonged darkness.B.gregarium underwent encystment while A.carterae showed cell shrinkage and flagella movement (up to 9~days) without cell division.This study documents cyst formation in B.gregarium for the first time.However, both dinoflagellates showed reduced growth and photosynthetic efficiency under lower salinity (< 5) and prolonged darkness.Interestingly, both dinoflagellates did not show a maximum photosynthetic efficiency of 0.65 under optimal growth conditions which could be due to the prevalence of carotenoid-chlorophyll protein complex and diatoxanthin (fluorescence quencher).This study proposes that seasonal rainfall (e.g., Southwest monsoon along the Indian coast) can control the proliferation of both dinoflagellates in rock pools (i.e., just before the onset of monsoonal rainfall) as it hampers cell growth, inhibits photosynthesis, and does not induce cyst formation as adaptive survival strategies.Further findings on their dark survival for several days will have implications in the studies related to the transportation to different locations through the ship's ballast water discharge or to deeper sediments in the intertidal regions.