Coral Reefs

Coral reefs are extremely diverse habitats and are like “underwater rainforests” (Attenborough, 2001.). There are over 6000 known species of coral (Twan et al., 2006.). Corals are large skeleton structures created by generations of hermatypic (reef-building) coral. These encase polyps; a sea anemone like organism that feeds on plankton.

Hermatypic corals have a symbiotic relationship with zooxanthellae; the small algae that photosynthesise on the surface of the coral. These zooxanthellae are what give corals their bright colour and though many polyps are carnivorous the zooxanthellae also provide important sources of nutrition to them (Rowan & Powers, 1991.).

The world’s first coral reefs appeared over 500 million years ago (Wood, 1983.). They can reproduce sexually and asexually. Asexual reproduction occurs via fragmentation; where broken pieces of coral land on a suitable substrate and creates a new colony. This type of reproduction is common in branching corals like Acropora cervicornis.

Sexual reproduction occurs via mass spawning. Mass spawning is when many species of corals release their eggs and sperm into the sea all during a 24 hour period (Wallace, 1994.). In some Montastraea and Acropora species, the eggs and sperm are released in a sack. They then float to the surface where they separate and fertilisation takes place. When the eggs are fertilised it creates zygote larvae called a planula.

 Mass spawning of coral (Bunch, 2003.).

Due to mass spawning, coral reefs are now present across the globe. The diagram below created by NASA in 2004 shows the distribution of coral populations.

 Global distribution of coral (NASA, 2004.).