Turbidity (number of particles per unit water volume) and sedimentation both have adverse effects on reef-building corals. Turbid waters intercept light and reduce the photosynthesis possible.
Sedimentation tends to smother coral colonies and inhibit feeding and the extension of the polyps’ crowns of tentacles. Blankets of sediment also may encourage the growth of disease-causing bacteria.
Corals with relatively flat surfaces (e.g., brain corals) tend to produce large amounts of mucus, which traps the sedimented particles. The polyps can then transport the material off the colony.
Erect corals intercept less material and usually have a lower capacity to produce mucus.
The overall effect of turbidity and sedimentation reduces the development of corals. For example, the coast of Venezuela is very turbid, and coral development there is quite poor. In waters greater than 20 km offshore, coral growth is better developed.