CORAL REEF - CLOSEUP
Caribbean coral reef life is far richer than of any other marine habitat-type of the entire Atlantic Ocean. There are about 65 species of hard corals recognized and 500-700 reef-associated fish species. Unfortunately, coral cover on reefs of the region has dropped from about 50-60% to less than 15% today. The vacated space is occupied now by a mixture of sponges, algae and bare substrate.
How do fish populate reefs?
Danielle Dixson, a coral reef ecologist at Georgia Tech, has found that smells, in general, are a big part of life on these reefs. Among other things, some fish born away from the reefs use smell to find corals to settle on as adults. Unfortunately, it also works the other way around. Fish are lured by the smells of healthy reefs, but they’re repelled by the smells of unhealthy ones. And that can help lock in that “death spiral.”
WHAT CORAL REEFS ADD TO THE WORLD
WHAT DO CORAL REEFS NEED TO SURVIVE?
Corals need to grow in shallow water where sunlight can reach the morals rarely develop in water deeper than 165 feet (50 meters).
Corals need clear water that lets sunlight through; they don’t thrive well when the water is opaque. Sediment and plankton can cloud water, which decreases the amount of sunlight that reaches the zooxanthellae.
Corals need saltwater to survive and require a certain balance in the ratio of salt to water. This is why corals don’t live in areas where rivers drain fresh water into the ocean (“estuaries”).
WARM WATER TEMPERATURE
Reef-building corals require warm water conditions to survive. Different corals living in different regions can withstand various temperature fluctuations. However, corals generally grow best in water temperatures of 70–85°F. Our warming oceans are posing a life-threatening problem to the coral's existence.
Corals are sensitive to pollution and sediments. Sediment can create cloudy water and be deposited on corals, blocking out the sun and harming the polyps. Wastewater and fertilizers discharged into the ocean near the reef can contain too many nutrients that cause seaweeds to overgrow the reef.
Different species of coral grow at different rates depending on water temperature, salinity, turbulence, and the availability of food. The massive corals are the slowest growing species, adding between 5 and 25 millimeters (0.2–1 inch) per year to their length. Branching and staghorn corals can grow much faster, adding as much as 20 centimeters (8 inches) to their branches each year.
Coral reefs grow best in warm water (70–85°F), and prefer clear, shallow water, where lots of sunlight filters through to their symbiotic algae. It is possible to find corals at depths of up to 300 feet (91 meters), but reef-building corals grow poorly below 60–90 feet. Corals need salt water to survive, so they grow poorly near river openings or coastal areas with excessive runoff.