Sewage Discharge Impacts On Coral Reef Communities

Sewage discharges may potentially impact coral reef communities through nutrient enrichment, sedimentation of effluent solids, and bioaccumulation of toxic contaminants. The cumulative impacts of a large discharge in poorly-flushed waters may disrupt reef community structure by stressing sensitive coral species and modifying competitive interactions. High nutrient loading favors the growth of opportunistic species (e.g., benthic green or blue-green algae, bryozoans, tunicates), which out-compete slower growing corals for a limited substrate resource. Excessive sedimentation may lead to altered growth forms and severe decreases in coral cover, taxonomic richness, and colony size. Available data for predicting the effects of toxic contaminants on coral reef systems are limited, but suggest that toxic substances may inhibit coral growth, alter metabolic functions, and reduce recruitment. Based on information available in the literature, a tentative scale of sedimentation impacts is proposed for reef slope communities.