Acropora palmata

Elkhorn Coral

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Elkhorn Coral Elkhorn Coral Elkhorn Coral

 

Description

Elkhorn coral (Acropora palmata) is a large, branching coral with thick and sturdy antler-like branches. It is a member of the Acropora genus, the most abundant and species-rich group of corals in the world.

Colonies of Elkhorn coral are fast growing - branches increase in length by 2-4 inches (5-10 cm) per year, with colonies reaching their maximum size in approximately 10-12 years. Over the last 10,000 years, elkhorn coral has been one of the three most important Caribbean corals contributing to reef growth and development, as well as providing essential fish and marine invertebrate habitat.

While once the most abundant stony coral on shallow reef crests and fore-reefs of the Caribbean and Florida reef tract, by the early 1990s elkhorn coral had experienced widespread losses through its range. Multiple factors are thought to have contributed to coral declines, including impacts from hurricanes, coral disease, mass coral bleaching, climate change, coastal pollution, overfishing, and damage from boaters and divers. In 2006, elkhorn coral and a close relative, staghorn coral (Acropora cervicornis) were listed as threatened under the US Endangered Species Act.

Geography

Elkhorn coral is found on coral reefs in southern Florida, the Bahamas, and throughout the Caribbean. Its northern limit is Biscayne National Park, Florida, and it extends south to Venezuela; it is not found in Bermuda. Once found in continuous stands that extended along the front side of most coral reefs, the characteristic "Acropora palmata zone" supported a diverse assemblage of other invertebrates and fish. These zones have been largely transformed into rubble fields with few, isolated living colonies

Ecosystem

Elkhorn coral is found in shallow water, generally ranging from 1 to 5 meters deep. Elkhorn coral is a tropical species and inhabits waters with a temperature range of 66 tol 86 degrees F. This coral tolerates salinities within the normal range of 33 to 37 parts per thousand. Elkhorn coral often establishes in heavy surf close to shore, where the preferential exposed reef crests create an optimal habitat.

 

Conservation

This species is listed as Critically Endangered as there has been a population reduction exceeding 80% over the past 30 years due, in particular to the effects of disease, as well as other climate change and human-related factors. This species is particularly susceptible to bleaching. Although the current population is persisting at a very low abundance and the current population trend appears to be stable, there are places where populations continue to decrease and others where there seems to be moderate or localized recovery. Whether mortality continues to exceed growth and recruitment or not, this species requires immediate investigation and monitoring on a regional scale.

 

Threats

Major Threats
The major threat to this species has been disease, specifically white-band disease which is believed to be the primary cause for the region wide acroporid decline during the 1980s (Aronson and Precht, 2001a,b) and is still ongoing (Williams and Miller, 2005). Other major threats include thermal-induced bleaching, storms, and other diseases (Rodriguez-Martinez et al. 2001,Precht et al. 2002,Patterson et al. 2002,Acropora BRT 2005).

Localized declines are associated with: loss of habitat at the recruitment stage due to algal overgrowth and sedimentation; predation by snails; mortality by endolithic sponges; ship groundings, anchor damage, trampling, and marine debris. The long-term threat of reduced skeletal integrity due to ocean acidification is of particular concern due to the species' presence in wave-swept environments.

In general, the major threat to corals is global climate change, in particular, temperature extremes leading to bleaching and increased susceptibility to disease, increased severity of ENSO events and storms, and ocean acidification.

Coral disease has emerged as a serious threat to coral reefs worldwide and a major cause of reef deterioration (Weil et al. 2006). The numbers of diseases and coral species affected, as well as the distribution of diseases have all increased dramatically within the last decade (Porter et al. 2001, Green and Bruckner 2000, Sutherland et al. 2004, Weil 2004). Coral disease epizootics have resulted in significant losses of coral cover and were implicated in the dramatic decline of acroporids in the Florida Keys (Aronson and Precht 2001, Porter et al. 2001, Patterson et al. 2002). Escalating anthropogenic stressors combined with the threats associated with global climate change of increases in coral disease, frequency and duration of coral bleaching and ocean acidification place coral reefs at high risk of collapse.

Localized threats to corals include fisheries, human development (industry, settlement, tourism, and transportation), changes in native species dynamics (competitors, predators, pathogens and parasites), invasive species (competitors, predators, pathogens and parasites), dynamite fishing, chemical fishing, pollution from agriculture and industry, domestic pollution, sedimentation, and human recreation and tourism activities. 

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