Commmunity structure, biomass and productivity of epilithic algal communities on the Great Barrier Reef; dynamics at different spatial scales

Abstract

Epilithic algal communities (EAC) covered a high proportion of the reef flats (50-80%) and reef slopes (30-70%) on coral reefs of the Great Barrier Reef (GBR). Crustose coralline algae and turf algae dominated the EAC in reef flat habitats, except in the nearshore region where turf algae predominated. Turfs also dominated the EAC on reef slopes. Patches of crustose coralline algae had a higher biomass, but a lower photosynthetic rate than the equivalent area of fine turf algae. The net result was that these two main forms of epilithic algae had comparable rates of areal productivity. The productivity of turf-dominated communities was inversely correlated with algal biomass. Epilithic algal communities from various reef habitats at the same depth had equal areal and biomass-specific productivity, regardless of location on transects extending both across and also along the GBR. EAC productivity changed in a predictable manner with season (maximum in summer, minimum in winter) and depth (decreasing with depth). -from Authors