Some corals are hard and rocky with calcium carbonate skeletons, whereas others are more pliable or even soft-bodied. Sea fans, such as the one shown in the photo from the sea around Utila, are more pliable and sway gently in the currents. Hard corals can be thought of as the “bricks” that are the foundation of the reef. Sponges, sea fans and their relatives, and certain algae are the “mortar” that help hold the bricks together. The rest of the coral reef community, for example, the fish, shrimp, crabs, snails, and octopuses, will not survive in the absence of a living reef.
Many species of coral have specific types of algae living inside their tissues. Both the coral and the algae benefit from this relationship. Coral “bleach”, that is– lose the algae from their tissues and turn white when they are stressed. Eventually, many die if they are bleached for too long. Each species on Earth, including coral species, has optimal conditions under which it survives, including temperature. Even tropical water corals cannot stand water that is too hot. Water temperature above the coral’s optimum temperature range stresses the corals and they bleach. Although the reef around Utila appears healthy in comparison to other places that Dr. Kathryn Goddard has visited, there have been multiple coral bleaching events in the past decade in this area. The bleaching events have been due to periods of water temperature that is too high. In addition to bleaching events, the abundance of two major reef builders, staghorn coral and elkhorn coral, plummeted due to disease in the 1980s.
To grow coral to restore it to the reef, pieces of some types of coral are grown on coral “trees”. Coral trees are made of plexiglass pipes or other materials on which pieces of coral are hung from the trees by fishing line. The coral pieces are taken from existing coral colonies. Sometimes pieces broken off from being struck by boats are used. Hanging from the coral tree, and thus surrounded on all sides by water rather than being down in low lying areas of the reef, allows the coral pieces access to more of the plankton on which they feed. In addition, the algae in the coral tissues get more light. The coral on the trees can grow faster. The pieces of coral are given the opportunity to grow into larger pieces on the trees so that they can be returned to the reef in areas where coral has been lost by bleaching in order to provide a solid, yet living structure to regrow the reef. The type of coral grown in the photo is staghorn coral Acropora cervicornis.
Hannah Merges, environmental studies major and marine science minor, is doing an internship in Utila, Honduras summer 2020 studying coral disease.