management sourcebooks 1
E N V I R O N M E N T A L
B A C K G R O U N D
Coral reefs are an important component of the Caribbean coastal system.They may lie very close to the shore or many kilometres from it. Among the most ecologically diverse systems in nature, coral reefs play an important role in the protection and formation of many Caribbean beaches.
A living coral reef is a community composed of thousands of different members living in harmony with each other. The coral reef is made up of many tiny animals called coral polyps. These animals secrete limestone to surround themselves with a hard skeleton. The skeletons all join together to form the coral reef.
A healthy coral reef is home to many different plants and animals. These include algae, sponges, worms, starfish, sea urchins, lobsters and fish.
There are two basic types of coral. Stony or hard corals are the main reef builders and come in many shapes and sizes. Examples are elkhorn coral (Acropora palmata), brain coral (Diploria clivosa) and star coral (Montastrea annularis). Soft corals are flexible with their skeleton being inside the animal. The sea fan (Gorgonia flabellum) is an example of a soft coral.
Coral reefs require warm, clear waters in which to grow. Reefs may be classified according to their position relative to the shore. The main types of reefs found in the Caribbean are: fringing reefs, which border a shoreline; patch reefs, which are isolated clumps of coral sometimes only measuring a few metres in diameter; and barrier reefs, which are separated from the shoreline by a deep lagoon or channel. Figure 27 shows sections and plans of fringing and barrier reefs.
|Figure 27. Fringing and barrier reefs. The
former are situated
close to the shore, while the latter may lie several kilometres
from it (adapted from Bacon, 1978).
Coral reefs are especially important to beaches because they protect the shoreline from high waves. Fringing reefs and barrier reefs often grow very close to the sea surface. Incoming waves break and expend their energy on the reef, thereby sheltering the adjacent coastline. (See Figure 2 8.) There is, nonetheless, some wave action at the beach sheltered by a coral reef. Often the waves reform between the reef and the beach. However, the wave energy is much less at the beach than if the reef were not present. Thus, in many respects, reefs are natural breakwaters and perform the same functions as those described for offshore breakwaters in Case 4 .
|Figure 28. Coral reefs and
beach protection. The
living reef, with its high relief and varied
topography, causes the waves to break and
thus protects the beach. Once the reef is dead
and flattened, higher wave energy is experienced
at the beach. Erosion begins (adapted from
Crown of Thorns Newsletter, 1990a).
|Coral reefs act as natural breakwaters protecting beaches from high wave energy.|
Since even a dead coral reef may continue to act as a breakwater for adjacent beaches, dead reefs should always be left intact.
|A dead coral reef may still provide some protection to adjacent beaches.|
Coral reefs are also important to many beaches because they act as a sand source. Many fish actively feed on the coral. For example, the parrot fish (Scarus) can bite off chunks of coral, digesting the living material and excreting coral sand. Other fish also feed on the coral. The butterfly fish (Chaetodon) and trigger fish (Balistes) are two examples. As a result, sand is formed which may eventually end up on the beach. However, as was seen in Case 3, not all beaches are made up of coral sand. Many Caribbean beaches are composed of land-based sand and others consist of a mixture of coral and land-based sands.
|The coral reefs are a source of sand for many beaches.|
Coral reefs are vulnerable to natural forces and many human activities. Waves generated by storms and hurricanes can break off large pieces of coral. A beautiful elkhorn reef can be transformed overnight into a bare rubble reef. Sometimes, this coral rubble is thrown up onto the beach. Rising seawater temperatures occasionally give rise to coral bleaching whereby corals turn white. The same phenomenon occurs when fishermen or -women use bleach to stun fish. Large influxes of freshwater may also damage the corals.
|Photograph 33. Coral rubble resulting from
Hurricane Luis, Cove Bay, Anguilla, 1995.
Mounds of coral debris bear testimony to the
underwater damage caused by the hurricane.
However, human beings pose probably the greatest threat to corals. Silt resulting from offshore dredging, the removal of mangroves and vegetation clearing can literally smother a reef. Ships' anchors cause physical damage and sometimes divers may damage or break off pieces of coral simply by touching the delicate corals with their fins. Pollution, whether large-scale resulting from sewage or small-scale from water draining a field treated with pesticides, poses another threat to corals.
It may take many years before the damage to a coral reef is manifest on the beach. If a reef is lowered by one hurricane, it may not be until the next tropical storm or hurricane that the reduced breakwater effect is evident through heightened beach erosion.
|There is often a time lag of several years before the effects of coral reef damage are seen on the beach.|
Besides being valuable in their own right, coral reefs are also vitally important for many Caribbean beaches. Therefore, every effort should be made to protect and conserve them.
|Wherever coral reefs exist, their health is of vital importance to adjacent beaches.|
Another rock formation, this one often found on the beach or just seaward of the shore, is beachrock. Beachrock consists of sand grains cemented together with calcium carbonate (lime). It forms within the body of a beach, beneath the sand surface and near the water table. (See Figure 29.) Once the covering sand has been stripped away, the beachrock formation hardens into rock. Exposure of beachrock ledges is indicative of an eroding shoreline. Beachrock became exposed on many beaches in the eastern Caribbean after hurricanes eroded the sand in 1995. As beaches continue to erode and retreat inland, beachrock ledges may be left out in the sea. These offshore beachrock ledges may then act as breakwaters reducing the incoming wave energy. Sometimes, sea pools behind these rock ledges form sheltered swimming areas.
|Figure 29. Beachrock formation. Stage A.
Beachrock forms within the body of the beach.
Stage B. As the sand covering the beachrock is lost,
the rock exposure hardens and is visible on the
beach. Stage C. As the coastline continues to retreat
inland, the beachrock is left as a rock exposure out
in the sea and may eventually function as an
offshore breakwater helping to protect and stabilize
|Photograph 34. Beachrock
ledge, Vieux Fort,
Saint Lucia, 1989. Over the years, this beach
has retreated landwards (eroded), leaving this
beachrock ledge out in the sea. Now, the rock
ledge is acting as a breakwater protecting the
beach from high waves.
P R A C T I C A L
R E S P O N S E S
Preserve and protect coral reefs.
Coral reefs are important in their own right, besides being so in relation to beaches. They are already experiencing stress from such natural factors as hurricanes and higher seawater temperatures. The need is therefore all the greater to preserve and protect them from additional stress caused by human activities. It should be everyone's goal to preserve and protect coral reefs, be they a private individual, developer, fisherman or -woman, diver or government representative. There are several actions that individuals can take on their own:
|Do not clear the land until you are ready to build and always replant the land as soon as possible.|
Look for alternative sites if development projects require alteration to coral reefs.
If a proposed development scheme, such as a marina, requires major or minor alteration to a coral reef, look for alternative sites for the development. This rule applies whether the coral reef is alive or dead. Even dead reefs protect the shoreline.
|Reefs should not be altered for development purposes. Look for alternative sites.|
Do not undertake offshore dredging activities close to coral reefs.
If an offshore dredging project is planned, perhaps to nourish a beach, ensure that there are no coral reefs in the immediate vicinity of the proposed dredging site or nearby. Currents can carry sand and silt many kilometres away from the immediate dredging site. Ensure that detailed studies are undertaken before dredging is permitted.
|Environmental impact assessments are required before dredging can be permitted.|
Retain beachrock ledges.
Coastal property owners sometimes wish to remove beachrock ledges to improve sea bathing conditions. This is generally not a good practice. The existence of beachrock is an indicator of erosion. Furthermore, the beachrock itself protects the beach, particularly when it is out in the sea and detached from the beach.
Retain dead coral reef structures.
As with beachrock ledges, the dangers related to removing dead coral reefs in the nearshore area to improve sea bathing conditions well outweigh the advantages. In most instances where dead coral has been removed, erosion increases dramatically. Even when dead, coral reefs continue to protect the beach and, in some cases, help to anchor the shoreline.