Nutrient pollution/eutrophication

Abstract

Nutrient pollution or eutrophication has severely degraded many coastal reefs around the world. The three main pathways of reef damage by nutrient pollution are release of nutrient limitation (nitrogen, phosphorus, or organic matter), light limitation from increased turbidity, and flowon effects from altered sediment properties. While nutrients, light, and sediments also vary greatly in areas unaffected by humans, they are often elevated from land clearing, agricultural and urban runoff, and aquaculture. Eutrophication leads to reduced recruitment and species richness in reefs and altered trophic structures (corals being replaced by macroalgae in shallow water and by heterotrophic communities in deeper water). On Indo-Pacific reefs, nutrient pollution may also lead to increased frequencies of outbreaks of the coral-eating starfish, Acanthaster planci. The vulnerability of a specific reef area to damage by eutrophication is greatest if it is located in a poorly flushed location or surrounded by a shallow sea floor. Reefs that are frequently disturbed and reefs with low abundances of herbivorous fishes are also sensitive to degradation by nutrient pollution. In contrast, reef areas that are flushed by fast currents or surrounded by a deep water body and reef areas with abundant herbivores are relatively resistant to exposure to nutrient pollution.