Shallow Water Coral Reefs

Shallow water coral reefs are found throughout the tropics in waters generally shallower than 70 m depth. The Department of Interior has jurisdiction over 24 different coral areas, including coral reefs found off the coasts of Florida, the U.S. Virgin Islands, and Hawaii. Over 800 species of reef-building coral are known to exist worldwide and are often described as the rainforests of the sea because they harbor such a great quantity of biodiversity. Reefs provide homes, nurseries, feeding grounds and spawning sites to more than a quarter of life in the ocean—a diversity of life that is virtually unparalleled in the world. More than 100 million people depend economically on corals reefs, and many more rely on reefs for protection from storm surges, tsunamis and coastal erosion. Resources such as food and recreation provide $30 to $172 billion annually to the global economy.  Unfortunately, due to climate change, coral reef communities will become much less common.

A Home for Threatened & Endangered Species

Coral reefs are living habitats, and many species of coral are threatened by extinction.  Elkhorn coral (Acropora palmata) and staghorn coral (Acropora cervicornis) are both critically endangered. Dozens more corals have been petitioned for listing as endangered by the US Fish and Wildlife Service. Coral reefs also provide important habitat for many endangered marine species, including sea turtles and fish and food for marine mammals.

Climate Change Threats

Coral reefs are vulnerable to ocean acidification and rising sea surface temperatures. As absorbed CO2 increases the acidity of the oceans, coral reefs find it more difficult to secrete their calcium carbonate skeletons. The slowed growth rates coupled with warming temperatures, which causes tropical corals to bleach, can result in death. Coral reefs are predicted to become functionally extinct if CO2 levels continue to rise: at CO2 levels of 450 ppm in the atmosphere calcareous corals will decline; above 500 ppm coral reefs are likely to be crumbling habitats; at 560 ppm (expected to be reached by the middle of the century) reefs will likely be eroding globally. These impacts may be especially severe for elkhorn and staghorn corals that are already critically endangered.  

Endangered fish may already be negatively affected by rising temperatures and acidifying waters. In the future the fish may have to spend more energy on respiration versus growth or reproduction.  These vulnerable fish will also lose the structural complexity of the reef that they use to hide, find food and raise young. Endangered reef fish include giant sea bass, totoaba, plain goby, Warsaw grouper, and strawberry grouper. Top predators capture prey from the reef. Species that rely on food from reefs include the Caribbean monk seal, Hawaiian monk seal, Borneo Shark, Pondicherry Shark, whitefin topeshark, Maltese skate or ray, giant devilray, Caribbean electric ray, Queensland sawfish, common guitarfish, scalloped hammerhead, and sawback angelshark.

Needed Conservation Measures

Coral reefs are not only threatened by ocean acidification and climate change, but also from a number of local and regional threats that are rapidly decreasing coral cover. These include destructive fishing practices such as bottom trawling and dynamite fishing, coastal development, depletion of grazers, and run-off pollution. Mitigation of these threats would boost the resiliency of coral reefs in the face of rising acidity and temperature. However, the removal of these threats will only begin to solve the problem of reef destruction and death. We must stabilize atmospheric CO2 if we want healthy coral reefs and the animals that depend on them for future generations.  (See the Arctic profile for more on stabilizing CO2 levels.)