Predation and parasitism can have a huge effect on a reef ecosystem. Damage caused to corals by predators and parasites can leave them open for further damage and maybe even death, if this happens on a large scale then whole reef systems can be damaged. In tropical coral reefs the parrotfish predates heavily on the coral reefs, it’s an herbivorous fish that uses its ‘beak-like’ mouth to feed on the algae on and within the coral. The parrotfish bites chunks of the coral off and extracts the algae during digestion, the waste coral material is then secreted back onto the reef. Another great predator of tropical coral is Acanthaster planci or commonly known as the crown-of-thorns starfish, this predatory echinoderm is known to eat large amounts of coral in the Great Barrier Reef, Australia (van der Laan & Hogeweg 1992).
Cold-water coral ecosystems are once again different from their tropical equivalent; there can be large abundances of fish species found around cold-water coral reefs, these are usually the shallower reefs as the very deep ones are not accessible to most vertebrate species, however, when these species have been observed there has been no herbivorous, coral grazing fish species e.g. the parrotfish (Freiwald et al. 2004).
Alike the tropical reefs, cold-water reefs are home to the echinoderms, the main difference is that there is not a large predatory relationship between cold-water corals and echinoderms. However, a study carried out by Krieger & Wing (2002) where they looked at the predation of megafauna on the coral Primnoa resedaeformis in the Aleutian Islands, showed that the starfish Hippasteria heathi was directly predating on the Primnoa. Starfish, along with over invertebrate species such as gastropods and crustaceans tend to feed on the mucus that grows on the cold-water corals and this does not actually pose a great threat to the coral or reef (Freiwald et al. 2004).