abstract
A review of published literature on the sensitivity of corals to turbidity and sedimentation is presented,
with an emphasis on the effects of dredging. The risks and severity of impact from dredging (and other
sediment disturbances) on corals are primarily related to the intensity, duration and frequency of exposure to increased turbidity and sedimentation. The sensitivity of a coral reef to dredging impacts and its
ability to recover depend on the antecedent ecological conditions of the reef, its resilience and the ambient conditions normally experienced. Effects of sediment stress have so far been investigated in 89 coral
species (10% of all known reef-building corals). Results of these investigations have provided a generic
understanding of tolerance levels, response mechanisms, adaptations and threshold levels of corals to the
effects of natural and anthropogenic sediment disturbances. Coral polyps undergo stress from high suspended-sediment concentrations and the subsequent effects on light attenuation which affect their algal
symbionts. Minimum light requirements of corals range from 14 days complete burial) for very tolerant species. Hypotheses to explain substantial differences
in sensitivity between different coral species include the growth form of coral colonies and the size of the
coral polyp or calyx. The validity of these hypotheses was tested on the basis of 77 published studies on
the effects of turbidity and sedimentation on 89 coral species. The results of this analysis reveal a significant relationship of coral sensitivity to turbidity and sedimentation with growth form, but not with calyx
size. Some of the variation in sensitivities reported in the literature may have been caused by differences
in the type and particle size of sediments applied in experiments. The ability of many corals (in varying
degrees) to actively reject sediment through polyp inflation, mucus production, ciliary and tentacular
action (at considerable energetic cost), as well as intraspecific morphological variation and the mobility
of free-living mushroom corals, further contribute to the observed differences. Given the wide range of
sensitivity levels among coral species and in baseline water quality conditions among reefs, meaningful
criteria to limit the extent and turbidity of dredging plumes and their effects on corals will always require
site-specific evaluations, taking into account the species assemblage present at the site and the natural
variability of local background turbidity and sedimentation