Corals as endangered species

September 20, 2010, 3:46 pm

Corals have a global distribution, occurring mostly in tropical waters. Up until recently their wide-spread range has prevented any possible listing of corals as endangered species either locally or globally. However, as the intensity and number of threats to coral reefs increase, coral decline has become so prevalent in some areas that it has begun to warrant efforts to list corals as endangered species. In May of 2006, two species of Acropora corals were listed by the United States as Vulnerable under the Endangered Species Act. More recently however, ten corals were added to the World Conservation Union’s (IUCN) Red List of Threatened Species. Each process for listing coral species follows certain procedures and although all twelve corals have not been assessed under both listings, the take home message is the same: corals are facing serious decline.

US Listing of Corals as Endangered Species

caption Acropora cervicornis, Staghorn Coral. (Photo credit: Colin Ackerman)

In May 2006, the United States listed Acropora palmata (Elkhorn coral) and Acropora cervicornis (Staghorn coral) as vulnerable under the Endangered Species Act due to their widespread decline throughout their Caribbean range. Although numerous factors such as habitat degradation, storm and anchor damage, coral bleaching and competition have contributed to the Acropora decline, coral disease was identified as the major cause of coral loss throughout the region. The widespread decline changed many reefs from three-dimensional dense thickets to flat rubble areas.

Corals and Acroporids specifically, have inherent characteristics that make their assessment under the Endangered Species Act challenging. Because corals are invertebrates, a listing determination must be based on the species’ status throughout ‘all or a significant portion’ of its range. Staghorn and Elkhorn coral are located throughout the Caribbean, southeast Florida, and the Gulf of Mexico, making assessment difficult because of its large range. Although some populations of Acroporids in the Caribbean are still in decline, other populations are increasing and some remain unchanged, making population estimates and future predictions conflicting and confusing. Consensus remains, however, that the current abundance of elkhorn and staghorn corals has declined drastically from their historic abundances throughout their entire range. Both species undergo sexual (production of larvae) and asexual (fragmentation of branches that can yield new attached and growing colonies) reproduction. The extent to which each occurs and under what environmental conditions remains unknown, making estimates of recovery, connectivity, and identifying genetic individuals difficult at best.

caption Acropora palmata, Elkhorn coral. (Photo credit: Lindsay Aylesworth)

For these reasons and the mandate that any invertebrate be assessed according to the entirety of its range, the listing of elkhorn and staghorn corals as vulnerable under the Endangered Species Act has been a long and drawn out process. The National Marine Fisheries Service (NMFS), as designated by the National Oceanographic and Atmospheric Administration (NOAA) and the Secretary of the Interior, is responsible for gathering and analyzing information on marine species for assessment and listing of the Endangered Species Act (ESA), and has considered listing both corals since 1991. Because listing decisions are made “solely on the basis of the best scientific and commercial data available…after conducting a review of the status of the species,” the lack of detailed biological information and threats throughout its range was the main cause of delay in finalizing the assessments. In 2004, the Center for Biological Diversity (CBD) petitioned the NMFS again to consider both corals for listing, and in 2005, NMFS organized an Atlantic Acropora Status Review. These findings, followed by a public comment period, led to the final inclusion of elkhorn and staghorn corals as vulnerable under the ESA.

The ESA, enacted in 1973, is the legal basis for most of the protection afforded imperiled marine wildlife species and the ecosystems upon which they depend. A species is considered ‘endangered’ when it is in “danger of extinction throughout all or a significant part of its range.” A species is listed as “threatened when it is likely to become an endangered species within the foreseeable future.” For both Acropora species, "within the foreseeable future" was determined, based on life history characteristics, to mean within 30 years.

In order to determine whether a species is either endangered or threatened under the Endangered Species Act, the presence of one or more of the following factors is sufficient to support a listing:

  1. the present or threatened destruction, modification or curtailment of its habitat or range;
  2. overutilization for commercial, recreational, scientific, or educational purposes
  3. disease or predation;
  4. the inadequacy of existing regulatory mechanisms;
  5. other natural or manmade factors affecting its continued existence.

With the listing comes designation of critical habitat, which is comprised of physical or biological features that require special management and are essential to conservation. For any coral, critical habitat could include certain temperature or salinity requirements, availability of food or nutrients, a location that has a presence or absence of predators or competitors, or any other requirement necessary for corals to thrive. Because these are general factors that require lots of data the National Marine Fisheries Service has not, as of November 2007, been able to designate any areas as critical habitat. With another species, such as a dolphin, it would be easier to identify important habitat that is essential for breeding or feeding because their behavior can be observed only in several distinct locations, but with stationary corals that have the ability to photosynthesize, spawn and fragment, identifying essential habitat is difficult because it can occur everywhere within the species range.

With the listing of any species under the Endangered Species Act, recovery plans are drafted and areas that are important to the species survival, i.e. critical habitat, are designated and protected. With the listing of any species, also comes a higher level of awareness and publicity about the issues surrounding its decline and conservation. It is in this way that elkhorn, (Acropora palmata) and staghorn (Acropora cervicornis) benefit from protection of the Endangered Species Act.

Corals and the IUCN Red List of Threatened Species

In September of 2007, the World Conservation Union (IUCN) published its latest updates to the Red List of Threatened Species. For the first time since its inception in 1963, the Red List included ten coral species. These coral species, endemic to the Galapagos Islands, demonstrate that the myriad of threats coral reefs face are finally taking their toll on these ancient marine invertebrates.

caption IUCN Categories. (Source: IUCN Red List of Threatened Species)

The IUCN Red List of Threatened Species is a categorized assessment of species based on extinction risk ranging from extinct to least concerned.

The Red List process was developed based on population biology and assesses the probability that a species will become extinct some time in the relatively near future on the basis of various characteristics of population biology. Three major attributes are used: the area the species occupies (and how fragmented that area is); the size of its population; and the rate of change of the population. The smaller or more fragmented the area a species occurs in, the more susceptible it is to wholesale changes in its habitat or to a single catastrophic event such as an El Niño event, the introduction of a disease or new predator. Even if a population is apparently widespread and abundant it may be seriously threatened if its population is declining rapidly enough. The smaller a population is, the more likely random fluctuations in population numbers can drive it to a level at which it can no longer successfully reproduce. On the basis of one or more of these attributes species are assessed and placed into a category reflecting the estimated severity of the extinction risk.

The overall aim of the Red List is to convey the urgency and scale of conservation problems to the public and policy makers, as well as to motivate the global community to try to reduce species extinctions. It identifies and documents those species most in need of conservation action and provides information to help establish conservation priorities at the local level. The Red List also helps influence national and international policy. The Red List process can be applied to assess extinction risk on a national scale, which has been done in Colombia. By creating a national Red List that records species native to Columbia and their associated threat levels, Columbia has begun to identify species that are in need of conservation within its own borders and implement appropriate management policies. At the international level, information from the Red List is used to set policy and priorities in international agreements such as the Convention on Biological Diversity (CBD) and the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). By drawing attention to the magnitude and importance of threatened corals, the Red List increases awareness of threats that reefs face. With the first assessment of a coral species completed, albeit limited to the Galapagos Islands, 10 corals made an appearance on the Red List. Out of the 10 species listed, two species (Wellington’s Solitary Coral and Floreana Coral) were assessed as Critically Endangered and another, Polycathea isabela, as vulnerable. The main threats to the Galapagos Corals were from El Niño and climate change and were indicative of massive declines in the population over a short time period. This reiterates that corals can be the early warning indicators for the harmful effects of climate change on marine species. More corals are expected on the Red List next year as additional data from assessments in the Pacific and Caribbean are completed.

Further Reading



Aylesworth, L. (2010). Corals as endangered species. Retrieved from


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