Photo courtesy of John Pye. Coral reefs are sensitive environments that require pristine coastal water quality. Corals are very efficient marine organisms that thrive in nutrient-poor environments. This is because coral polyps contain zooxanthellae -unicellular, symbiotic algae that produce food for their hosts through photosynthesis. Photosynthesis requires sunlight, and the depth and intensity of sunlight penetration is reduced by suspended sediments.
Silt can also settle out on corals and interfere with feeding and recolonization.
Corals can survive occasional short-term siltation events. When stressed they produce mucus, which helps them shed the fine-grained sediments that have settled upon them. However, repeated or chronic silt plumes or a single large event will kill coral. Nutrient loading is also harmful to coral reefs. Excess nutrient levels in coastal waters can lead to algal blooms , which compete with coral colonies for space and light and disrupt the coral reef ecosystem.