Corals
Corals are a group of marine invertebrates belonging to the Anthozoa class. They are made up of individual polyps within a protective skeleton, and each polyp are around 1- 3cm in diameter (Fig. 2)
Acropora nasuta
Fig.2 The visible polyps of a Nosey coral species in the Maldives [8]. |
Symbiotic single- celled algae called Zooxanthellae are found in almost all reef building scleractinian corals and this is what gives them their colour. They produce energy for the coral host through photosynthesising; with 90% of their production being passed to the coral polyps. The polyps put this energy into building the reef and also to support the food webs of the reef.
Corals feed on particulate matter and zooplankton and are mostly nocturnal. They reproduce both asexually and sexually; asexual reproduction extends the colony and sexual reproduction allows dispersal to establish new colonies. The relationship between coral and algae is extremely delicate and they have specific physical requirements in order to survive. This includes a certain amount of light, low turbidity, specific temperature ranges, normal oceanic salinity and a low nutrient status. Corals grow at different rates with dome colonies growing at around 1- 2cm each year, and branched colonies growing up to 10cm per year. However erosion caused by waves and other organisms means that the growth can be much slower, with rates of around 10m in 1000 years being estimated. |
Some other examples of coral species that can be found in tropical reef systems are;
Species: Acropora cf. hyacinthus (Table coral)
Size: 3- 10m Ecology: One of the most abundant types of corals, often providing the greatest cover on many reefs. Sensitive against high water temperatures, coral bleaching can frequently be observed in table corals [8]. |
Species: Sarcophyton sp. (Mushroom leather coral)
Size: 5- 10m Ecology: Common across the entire Indopacific. There are around 36 different species recorded and it grows on reef tops and slopes [8]. |