Epilithic algal communities (EACs) can trap sediments on hard substrata of coral reefs. The distribution of sediments and the relationship between EACs and sediment loads were investigated on windward reef zones near Lizard Island in the northern Great Barrier Reef, Australia. The load (accumulated weight) and grain size composition of sediments within EACs differed significantly among zones. EACs on the reef crest contained consistently low loads of sediments (1-2 g dm−2) which were poorly sorted, containing even proportions of sediment grains from silt to coarse sand size. With leeward distance from the crest, sediments increased in average load (up to 56 g dm−2) and became locally patchy and relatively well sorted. The modal size class was predominantly 500-1000 μm. Sediment load on substrata was related to algal functional groups; coverage of crustose and small branching forms displayed negative and positive correlations with sediment load respectively. The heights of EACs were significantly correlated with sediment loads (r = 0.83; P < 0.001). Sediment loads were reduced during a period of rough weather, with corresponding reductions in the heights of EACs. The results indicate that physical features of EACs influence sediment distribution on coral reef substrata and may mediate the effects of sedimentation on reef biota.
Purcell, SW 2000, 'Association of epilithic algae with sediment distribution on a windward reef in the northern Great Barrier Reef, Australia ', Bulletin of Marine Science, vol. 66, no. 1, pp. 199-214.