WHAT CORALS TO LOOK FOR DURING A SWIM AND/OR DIVE IN THE VIRGIN ISLANDS/CARIBBEAN

For the novice snorkeler or diver in the Caribbean, the fascinating array of creatures, colors and shapes found on coral reefs can be a bit overwhelming at first. As one becomes accustomed to both equipment and surroundings, more attention can be paid to the reef's details. Throughout the Caribbean, including the Virgin Islands, there is little variation in the region between the number and types of coral species commonly found among the reefs(Edmunds et al. 1990). What can be found in St.Thomas can be found in Jamaica or Bonaire as well. However, there are variances in abundances of species between sites.

With a little practice and a good waterproof ID chart, identifying these corals will become fun and sometimes challenging.

Corals have readily seen pores in which its polyps live and greatly aid identification by factors such as pore size, relief from the coral or distance between them (for more information see "Coral Anatomy" or read the overview on the homepage). One of the most commonly seen corals in this region isn't really a coral: it's a hydroid. The infamous "fire coral" (Millepora spp.) is orange-yellow in color and doesn't seem to have any pores. It does have visible stinging structures which can be painful to come into contact with. This organism forms encrusting colonies which can assume the shape of its support structure.

Another predominant Caribbean coral is Montastrea annularis, or "mountainous star coral". This coral is considered to be an important reef former and builds massive colonies(Greenberg 1986). This species has three morphotypes which may actually be different species, but this matter is far from resolved(Weil and Knowlton 1994). Its cups are slightly raised above the coral surface and its shape can be columnar, encrusting, knobby, or keeled. There is no uniform color for this species. Its relative, "cavernous star coral"(Montastrea cavernosa) is more readily distinguished by its very large and raised cups.

If you see a coral that looks fuzzy and the whole structure looks like giant fingers, it is probably "pillar coral" (Dendrogyra cylindrus). The tentacles of this coral are extended during the day, unlike most other species, and its "fingers" can grow to several feet in height.

There are many species of "brain coral" (Diploria spp.) whose distinctions can baffle experts; therefore, this genera will generalized. Colonies can reach three feet in diameter and are usually rounded heads: the really huge (6 ft. diam.) brain corals are Colpophyllia natans. The common name refers to the fold and grooves on the corals' surfaces. The differences between the grooves are the keys to proper identification: I suggest picking up a good coral ID book to satisfy any further curiosity.

Two related and easily discerned species are the two local varieties of Acropora.

Elkhorn coral (A. palmata) has wide, flattened branches and its raised polyps give it a nubby texture. Staghorn coral (A. cervicornis) has thinner, tapering branches and looks almost fragile. This species also has the nubby texture. Both varieties are a bright burnt-orange color and can be very dense in certain areas.

If you encounter a coral that looks like lettuce leaves with ridges, then it is in the genus Agaricia. These are also called "leaf corals", due to the foliose morphology. This group also can be difficult to identify to species, so we will leave well enough alone.

Another coral which can be very abundant locally is "finger coral"(Porites porites). It has large pores, grows in thick colonies, and has branches which are swollen at the tips. It is distinctly gray and its tentacles are often exposed in the daytime. Its cousin, P. asteroides, forms yellow or green lumpy masses which generally grow to about 1 ft in diameter. Both can be found in shallow water.

There are many more corals to be found in the Virgin Islands and throughout the Caribbean. However, this report is very introductory and several excellent field guides are available which can greatly enhance one's species identification. Hope to see you at Buck Island or Magen's Bay sometime!

Bibliography:

Edmunds, P.J., D.A. Roberts and R.Singer.1990. Reefs of the northeastern Caribbean I. Scleractinian populations. Bull. Mar. Sci. 46(3):780-789.

Greenberg, Idaz. 1986. Guide to Corals and Fish. Seahawk Press:Miami, Fla.

Weil, Ernesto and Nancy Knowlton. 1994. A multi-character analysis of the Caribbean coral Montastrea annularis (Ellis and Solander, 1786) and its two sibling species, M. faveolata (Ellis and Solander, 1786) and M. franksi(Gregory, 1895).Bull. Mar. Sci.. 55(1):151-175.7/5/95