Nine of the ten most common sponge species on the fore-reef slope of Davies Reef(Great Barrier Reef) contain symbiotic cyanobacteria. Six of the ten are net primary producers, with three times more oxygen produced by photosynthesis than is consumed during respiration. Light interception is enhanced by morphological flattening, thereby increasing the potential for phototrophic nutrition, a factor crucial in the ecology of most sessile coral reef invertebrates.