6. Reef fish and other major predators

Fish, like corals, have geographical patterns across regions and across individual reefs, being structured in the latter case by wave energy and depth. The thousands of species show a variety of feeding patterns. Detritus feeders are very abundant, feeding on the detritus on the seabed, especially in the fine, filamentous algal turf on apparently bare rock. Plankton feeders are common also, and herbivorous fishes show a large abundance, perhaps a quarter of the total species present, cropping algae that otherwise would grow unchecked and smother coral. Since turf algae also contain many micro-species and detritus, most herbivores also ingest much food other than simple plant material. Carnivores range from extreme specialists, such as polyp-picking butterflyfish, to generalists. Sharks and barracuda only consume other fish and generally are at the top of their food chains. The complicated ecological structure of the food webs can be clarified by analysing nitrogen isotope ratios in their tissues. Other important coral carnivores include the crown of thorns starfish, which can remove almost all living coral on a reef when it develops into plagues. Overfishing by humans greatly disturbs the equilibrium of a reef, and this is increasingly causing reef degradation.