Coral reefs can be severely affected by sedimentation and turbidity but, conversely, some corals are tolerant of low light and have efficient sediment rejection mechanisms that allow them to thrive in muddy conditions on inshore reefs (Stafford-Smith and Ormond 1992), adjacent to rivers or areas of coastal development (Craik and Dutton 1987; Fisk and Harriot 1989; Ayling and Ayling 2000). There is considerable anecdotal evidence and some historical photographic evidence that inshore reefs are muddier and have less coral and more algal cover than previously (Brodie 1997).

 

Cortes and Risk (1985) studied a reef in Costa Rica under siltation stress from adjacent deforestation. They found low coverage and growth rates for live coral. Wesseling et al. (1999) examined damage to and recovery of corals in the Philippines subjected to experimental sediment burial for up to 68 hours. After twenty hours of burial corals showed tissue discolouration; after 68 hours about 50% of tissue disappeared leaving bare coral skeleton exposed or covered with algae whilst up to 90% of the remaining tissue was bleached. Recovery to the preburial state occurred after three to four weeks. Acropora sp. which is found at 5m depth died after 20 hours of burial. These authors concluded that complete burial caused considerable whole-colony mortality, at least in Acropora, and thus may result in a permanent loss of some coral taxa from reefs subject to intense or brief (less than one day) sedimentation events. Less sensitive taxa incur substantial damage but show significant recovery after several weeks (Wesseling et al. 1999). Periodicity of the sedimentation events is an important component about which there are few data. The available data show that impacts and the recovery periods between stress events for individual taxa will obviously vary but details must await further experimental studies.



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