Benthic dinoflagellate blooms in tropical intertidal rock pools: elucidation of photoprotection mechanisms

Intertidal rockpools (RPs), forming a ubiquitous component of rocky shores, are biologically rich ecosystems influenced by short-term (hours–days) and long-term (days–seasons) fluctuating environments. So far, studies on RP biology are scarce and received no attention in India. This study elucidates planktonic microalgal composition and photoprotection mechanisms [dynamic photoinhibition, non-photochemical-quenching (NPQ), and photoprotective pigments production)] from the RPs located at high tide (HT), mid tide (MT), and low tide (LT) zones on the rocky shores of Anjuna, Goa (India) facing the Arabian Sea. MT-RPs and LT-RPs were dominated by diatoms and HT-RPs by dinoflagellates due to the blooms of autotrophic benthic dinoflagellates belonging to Amphidinium sensu stricto and Bysmatrum . The detailed microscopic analysis of these dinoflagellates showed morphological and cellular features similar to Amphidinium carterae (known harmful algae of concern) and Bysmatrum caponii . This study reports B. caponii for the first time from India as well as from northern Indian Ocean. The fast-repetition-rate-fluorometer measurements of RP microalgae suggested lower quantum efficiency ( F v / F m ) and functional absorption cross section for HT-RPs followed by MT-RPs and LT-RPs. The observed differences can thus be attributed to the microalgal composition differences and to differences in experienced irradiance of these communities. Dynamic photoinhibition was more prominent in LT-RPs followed by MT-RPs and HT-RPs. The high accumulation of photoprotective pigments in HT-RPs (due to prolong exposure to solar radiation) could be the reason for the differences. The presence of reduced de-epoxidation state and the mid-day depression in F v / F m coupled with elevated σ PSII confirmed dominance of NPQ of reaction centres in HT-RPs compared to other pools. This study concludes that RP planktonic microalgae are eurythermal, euryhaline, and euryphotic. Concerned with increasing harmful algal bloom events further studies on diverse aspects of RP microalgae (including chemical mediated interactions) needs attention.