Effects of extreme seasonality on community structure and functional group dynamics of coral reef algae in the southern Red Sea (Eritrea)

Abstract

Spatial and temporal variation in the biomass of four functional groups of coral reef algae (canopy algae, foliose algae, turf algae and crustose corallines) was investigated in the southern Red Sea. This region is characterised by extremely high summer temperatures (ca. 35°C). Strong seasonal shifts in the relative contribution of each group to the total macroalgal biomass were observed. On the reef flat, canopy and foliose algae dominated in winter, retaining low biomass in summer. On the fore reef, crustose corallines accounted for most of the macroalgal biomass throughout the year. Turf algae contributed least to the total biomass in all reef zones; biomass peaks shifted from midsummer on the inner reef flat to winter in the deeper zones. Biomass correlated negatively with seawater temperature in most groups, but the correlation was positive for turf algae on the shallow reef flat. We hypothesise both direct and indirect effects of the strong seasonality.