Corals and Other Invertebrates
The Caribbean Sea and adjacent waters including Florida and the Gulf of Mexico
Class Anthozoa (corals, anemones, and relatives), Order Scleractinia (stony corals)
The elkhorn coral is named for the antler-like shape of its colonies. It is a fast growing species and is one of the most important reef-building species in the Caribbean. It was formerly one of the most common corals on reefs throughout its range. Today, it is very rare and is considered critically endangered by reef scientists.
Elkhorn coral structures are actually colonies of several genetically identical animals living together. These colonies can reproduce both sexually and asexually, and they are hermaphroditic – each animal produces both eggs and sperm. During just a few days surrounding full moons in the fall, elkhorn corals release bundles of eggs and sperm that float to the surface, break apart, and mix. Sperm do not fertilize eggs from the same colony, so several colonies release their gametes at the same time, in a process known as broadcast spawning. The fertilized egg quickly hatches and the baby coral spends a few days in the water column before settling on the reef and beginning to form a new colony. Elkhorn coral colonies can also reproduce through fragmentation (asexually). When a storm or some other disturbance breaks apart a colony, each piece is able to reattach to the reef surface and begin growing again. Through this process, and as a result of its fairly rapid growth rate, the elkhorn coral was historically responsible for building large areas of Caribbean Reefs. Numerous species (including caribbean spiny lobsters, parrotfishes, tube blennies, and others) directly rely on elkhorn coral as their primary habitat.
Like most shallow-water corals, elkhorn corals have symbiotic algae living within their cells, providing the corals with excess energy that they make via photosynthesis (the use of sunlight to convert carbon dioxide into food/energy). Nearly all species of shallow-water corals and several other groups of reef invertebrates have symbiotic relationships with these algae, so it is important that they live in clear, shallow water. Like all stony corals, the elkhorn coral builds a skeleton of calcium carbonate – a compound that will become increasingly more rare as the ocean acidifies (a phenomenon caused by the ocean’s absorption of acidic carbon dioxide from the atmosphere).
As a result of disease, pollution, coral bleaching, and storm damage, populations of elkhorn corals have crashed. Throughout its range, it has become more and more rare, and scientists now consider it to be critically endangered (very highly vulnerable to extinction). As it is a keystone species and ecosystem engineer, its endangerment threatens many other coral reef species. Without careful management of the threats that elkhorn corals experience, one of the most important species of reef-building corals in the Caribbean could be lost.
Note on a closely related species: The elkhorn coral’s sister species, the Staghorn Coral (Acropora cervicornis) is similar in appearance, biology, and ecology and is another ecosystem engineer on Caribbean reefs. Unfortunately, it has recently suffered a similar fate and is also critically endangered.
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