Seagrass meadows enhance benthic microalgal growth in a coral reef ecosystem under global warming scenario- a mesocosm study

The effects of presence of seagrass bed on microalgal assemblages under increasing CO2 concentrations and temperature were examined using mesocosms that simulate coral reef ecosystem. We assessed changes in chlorophyll a and diversity of benthic algal communities grown with/without seagrass bed, at 25 oC and 28 oC, under high CO2 conditions (800~1000 μatm). Total alkalinity, pCO2, and the aragonite saturation state, were all similar between seagrass and control groups, in both temperature treatments. Phytoplankton chl a concentration were similar between seagrass and control groups, however the benthic microalgal chl a concentrations were significantly higher in seagrass group, at both 25 oC and 28 oC. Chlorophyte decreased whereas diatoms increased under 28 oC without seagrass bed, and algal parasites Syndiniales increased at both groups under 28 oC. Our results suggest that seagrass bed will enhance benthic microalgal primary productivity, and the ecosystem favor chlorophyte over diatom growth.