Widespread overfishing in the region over many decades has led to very low levels of herbivorous fish, which normally play an important part in keeping algae from overgrowing reefs. In the absence of herbivorous fish, the role of keeping algae levels in check fell to a species of grazing sea urchin. When an epidemic nearly wiped out the beneficial urchins on Jamaican reefs in the early 1980s, algae quickly overgrew and killed the corals. Some scientists claim this is a harbinger of events to come as reefs around the world continue to be overfished. Coastal development also gives rise to several harmful effects.
Direct effects come from coral mining, shoreline filling for land reclamation, and harbor dredging.
Indirect effects, however, are more pervasive. Algal blooms resulting from nutrient-laden sewage released nearshore can block sunlight in the water column, stunting coral growth and interfering with reproduction. Shoreline construction disturbs sediments, which smother corals. Even tourism, where it is unregulated, can pose a threat. The prospect of widespread reef losses is particularly worrisome given the critical role they play in fostering the productivity of the tropical oceans.