There is about 205 hard coral species and about 120 soft coral species found here at Ras Mohamed colonizing the reef walls and competing for space and nutrients. These different corals have different functions in the formation of the reef walls. Different species live at different depths due to their different light requirements. Again, it is the branching corals that tend to dominate the shallow parts of the reef while the deeper parts have more massive colonies which take on a flattened, plate-like growth form to maximise their light capture.
There is believed to be six genera of corals here at Ras Mohamed. These are:
- Acropora- scleractinian corals:
This is a branching coral. These corals are commonly known as Stagshorn coral because they have pointed branches which look like the tip of a stag's horn. It also has a large apical corallite. These corallites usually part the surface looking like small tubes.
- Fungia- scleractinian corals:
These are the corals that look like a brain or a mushroom
- Millepora-hydrozoan corals
- Pocillopora- scleractinian corals
- Porites- scleractinian corals
- Stylophora- scleractinian corals
There are also many Faviids of the faviidae family of corals. These include genera such as Echinopora, Favia, and Favites.
Most corals are colonial. They consist of adjacent polyps which are linked together by extensions of the coelenteron. The polyp sits within a cup-shaped skeletal structure called a corallite. The epidermis (the lower layer of which secretes the skeleton) and gastrodermis forms a very thin layer over the skeleton, so that you can clearly see the skeleton beneath.
Another thing that you will notice when on the reef, is that most corals have the tentacles withdrawn and they only extend them at night.
Acropora, Stylophora and Pocillopora are branched
Porites and the Faviids are massives (i.e. like half boulders or pebbles, depending on size)
Fungia looks like the underside of a mushroom (and is never attached to the reef)
Millepora (Fire coral) can be either encrusting or finely branching. It is pale yellow in colour, with white tips. It produces a sting like a nettle. (You will quickly learn to identify this one!).
Characteristic features for identification:
Acropora
Pocillopora Rounded ends to branches. Surface covered with small ‘warts’. Tiny corallites, appearing as dark dots on the surface.
Stylophora Rounded ends to the branches. Surface relatively smooth (i.e. no warts).
Porites Massive, with very tiny corrallites . So surface appears to consist of pores.
Faviids Massive. Much larger corrallites
Now look at the drawings of the features of these corals and try to systematically memorise the key points.
Insert coral identification graphics
The most southerly true coral structures are Fawn and Saunders Reefs near the border between Eritrea and Sudan. Further south, coral grows on sandy areas or the volcanic sub-strate of the Yemeni islands. The broccoli-like soft corals (dendonephyta and lytophiton), often bright red (below), or yellow, are a characteristic of the Red Sea. Unlike most other corals, they have no algae living in symbiosis with them, so they must absorb nutrients that pass on the current. They do not take part in theformation of the reef because they have no calcarean skeleton. Gorgonian corals (right), or sea fans proliferate only where there is a good flow of water. Echinoderms like the crinoid featherstar or basketstar also feed on nutrients that pass by. However, they are able to move about and choose their spot at night or hide during daylight hours.
