Part 6: How do humans harm corals?

M/V Alec Owen Maitland vessel grounding in Florida Keys National Marine Sanctuary, October 25, 1989.

Anthropogenic (human-caused) sources of reef mortality include pollution, physical impacts and overfishing.

Climate change detrimentally impacts coral in several ways. Levels of atmospheric carbon dioxide are increasing, causing rises in sea surface temperature (SST). The rise in SST, in turn, increases the frequency and severity of coral bleaching. Levels of carbon dioxide are also increasing in seawater, resulting in weaker coral skeletons, reduced coral extension (growth) rates, and an increased susceptibility to erosion on reefs. Climate change is also linked to greater frequencies of severe storms, which are a major cause of physical damage to reefs.

Land based runoff, including excess nutrients, pollutants, and sediments, can harm coral, particularly when these impacts are ongoing.

Coral reef habitats are also sensitive to physical disturbance. Ship groundings, which destroy reef structures, create coral rubble that can do further damage when storms pound the reef. Large debris, from shipwrecks or other sources, can have similar impacts.

Overfishing is pervasive on many coral reefs, even in areas previously considered undisturbed. Heavy fishing both decreases biodiversity (reduces the number of species living in an area) and shifts the ecosystem structure of fish and reef communities. (Although the evidence isn't conclusive, ecologists generally believe that losing biodiversity makes an ecological community more unstable, and hence more vulnerable to stresses.) Destructive fishing practices, such as the use of dynamite and poisons, common in some areas of the Pacific, directly damage and kill coral.