Underwater Adventures: Coral Reefs of Puerto Rico

What is a coral reef?

Coral reefs are one of  the most attractive and most complex biological communities on the  planet. The word “coral” is used to describe a group of tiny organisms,  from the phylum Cnidaria, that secrete hard calcareous skeletons and  live in colonies in the form of polyps.

In the Caribbean, there  are more than 70 stony corals, whose skeletons are complex structures we  call coral reefs. Associated with these are soft or horny corals, some  Zoantharia, and millepora or “stinging corals”.

Biology and ecology of coral reefs

The biological combination of colonial organisms and associated flora  and fauna make up the coral reef, one of the biological systems in which  nature expresses its greatest splendor and complexity. Slow but steady  coral growth takes thousands of years; the accumulation of sediment and  fragments that are generated in the reef allows corals to survive,  despite increases in sea level. The vertical growth, at the rate of 0.5  to 1.5 cm per year, allows the reef to adjust to these changes. Many of  the modern reefs were established less than 15 thousand years ago when  sea level was 85 meters (279 feet) below the current level, and island  platforms began to flood as a result of the rapid rise in sea level.

Coral  polyps have tentacles with which they capture zooplankton that swims  freely in the water. The most unique characteristic of polyps is that  they have unicellular algae, known as zooxanthellae, inside.

Numerous  hiding places between coral blocks provide shelter to a wide variety of  animals including sponges, worms, mollusks, crustaceans, sea urchins,  sea stars, holothurians, and fish that are characterized by vivid,  contrasting colors. This complex community of organisms, closely  integrated as a result of a long evolution, gives rise to the ecosystem  of coral reefs. The deployment of colors found in the reef is not an  accident but rather the result of the complexity of that biological  community.

In Puerto Rico, there are three types or forms of reefs:

• Fringing reef  – This type of reef surrounds a non-coral coastline. It is often  separated from the coast by a lagoon or shallow, narrow body of water  whose floor is covered in calcareous sands and seagrass. This type of  reef is one of the most common in Puerto Rico; but because of its  proximity to the coast itself, it is also the one most degraded by human  activity.

• Barrier reef – This type of reef  occurs further away from the coast. In Puerto Rico, this type is  represented by a reef which lies at the edge of the island shelf at depths of 20 meters (65 feet).

• Bank reefs  – Bank reefs are located on the platform between the two previous  types. This type of structure is known as coral platform or  bank-barrier. These reefs often acquire crescent shapes because the  coral grows and consolidates preferably towards the waves.

(from Enciclopedia De Puerto Rico)