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Coral Reef Restoration Reef Life
Increasin coral reef biodiversity

Healthy coral reef ecosystems are like bustling cities, with buildings made of coral and thousands of marine inhabitants coming and going, interacting with one another, carrying out their business. In this sense, coral reefs are the sea’s metropolises. Coral reefs provide shelter for nearly one-quarter of all known marine species. And over the last 240 million years, reefs have evolved into one of the largest and most complex ecosystems on the planet. They are home to more than 4,000 species of fish, 700 species of coral, and thousands of other species of plants and animals. Scientists estimate that, in total, more than one million species of plants and animals are associated with the coral reef ecosystem. With the demise of so many coral reefs, the diversity is waning and needs to be reestablished in many areas. 

Caribbean coral reef life is far richer than 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 coral reef life. 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.”



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 reef life needs saltwater to survive and requires 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”).


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 and coral reef life 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.

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