Micro-tidal dependent phytoplankton C-biomass dynamics over two shallow tropical coral reefs

Abstract

This study investigates micro-tidally induced variations in micro-phytoplankton carbon biomass (C-biomass), concentrations of chlorophyll a, nitrate, phosphate and silicate, temperature, salinity and pH at three zones (near-coast, lagoon and reef) at two sites (Flic-en-Flac (FEF) and Belle Mare (BM)) on two consecutive days covering two high and low tides in August (winter) and in November (summer) 2011. At FEF, 36 different genera of micro-phytoplankton were recorded, including 29 bacillariophyceae, 5 dinophyceae and 2 cyanophyceae. At BM, 34 different genera of micro-phytoplankton were recorded, including 31 bacillariophyceae, 3 dinophyceae and 2 cyanophyceae. At low tides the total micro-phytoplankton C-biomass (TMPB) and nutrient levels were significantly higher compared to those at high tides.  At both sites, zonal variation in TMPB was evident with significantly higher C-biomass at the near-coast. Only bacillariophyceae and dinophyceae C-biomass along with nutrient levels exhibited seasonal variation with higher values in summer. Bacillariophyceae was dominant, followed by cyanophyceae and dinophyceae, irrespective of micro-tidal changes indicating their ability to tolerate a wide range of micro-tidally induced environmental changes. These findings provide insights on the effect of micro-tidal cycle on micro-phytoplankton dynamics and might have implications for carbon cycling over shallow tropical coral reefs and other inter-connected coastal ecosystems.