Swaying palms, white beaches, and coral reefs—these are the "postcard" symbols of the idyllic tropical haven. Yet, there is trouble in paradise; the world's coral reef systems are in danger of disappearing. Found off the coasts of nearly 100 nations, today they cover only 0.1% of the world ocean's expanse.
Coral reefs are colonial systems of small animals called "polyps" that extract calcium carbonate from seawater to build the stony structures in which they live. They feed on plankton drifting by their fixed locations by using small tentacles to trap the microscopic organisms. Polyps also have masses of algae living within their bodies to supply them with needed calcium carbonate. In addition, the algae are the source of corals' vibrant colors and provide additional food to their hosts.
There are more than 1,500 species of corals; the majority are found in shallow tropical waters 15-30 feet deep where average growth rates are 1-2 inches a year. Most of a reef structure, however, is not alive—the living part may sit on top of as much as 4,000 feet of dead coral. Clear, moving seawater, warmer than 70°F, is required for optimum growth. This means reefs are found mostly between latitudes 30°N and 30°S.
The term "coral reef system" describes the massive coral structure, the polyps that are the living part, and the organism community that depends on the reef. It has been estimated that one million species are supported by these systems. These "rain forests of the sea" greatly benefit those who visit or live there, from microscopic plankton to humans in diving gear.
Over the past two decades, nearly 25% of the world's reef systems have died. Some experts say that by 2010 more than 40% will be gone. By "dying" it is meant that the polyps die and eventually the reef structure will be eroded away by the sea.
The most recognizable cause of die off is human activity. Coastal communities drain harmful sewage and agricultural wastes into coastal waters and sediments from dredging cover the corals. In addition, some people use their local reefs for fishing and building materials. Fishing using explosives or poisons permanently damages the structures. Blowing up coral to extract limestone for the production of cement not only kills the polyps but also permanently removes coastal protection provided by the reef structure.
While this cause and effect by coastal populations is easily seen and understood, fixing it can be difficult. These stresses tend to occur in lesser-developed nations where alternatives, infrastructure, and funding are not available to remedy the problems. Remove these stresses and the reef system can recover.
Human-caused damage, however, is relatively trivial compared to the longer-term problem of the gradual heating of the sea caused by global warming. While corals need seawater warmer than 70[degrees]F, it cannot be too much warmer than this. An increase of about 8[degrees]F over a reef's normal sea temperature will cause its death. As sea temperature increases it stresses the polyps, their plankton food source is not as abundant, and degenerative diseases spread more easily.
Coral reef systems are not an optional feature of the tropical seas—they are a vital part of their ecosystem and represent a considerable generator of economic value. It is estimated that reefs contribute about $375 billion a year to the global economy (mostly in the form of tourism-related activities). Without a healthy reef offshore the picture of our tropical paradise will change drastically. An encroaching sea will erode beaches. This can be countered feebly by putting dredged sand back on the beach and constructing protection structures such as seawalls, bulkheads, and groins, but the sea eventually wins and this work must be continuous.
It is doubtful the global die off of coral reef systems can be arrested to any great extent. The primary solution is to mitigate global warming, and it is not clear that the major cause of warming is soluble either. This is because the major component of warming is not caused by human activities; it is a natural cycle in the earth's climate, a pattern of long-term cycles over thousands of years that brings both global warming and cooling. Man's activities can aggravate the natural cycle, but he will not be able to control it.