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Finding A New Future for Corals
Photo Credit: Caroline Rogers/US Geological Survey
By Sarah Heberling
Coral species around the world face numerous threats that vary from natural to human-induced, severe to slight, and global to local in scale. Unfortunately, few first-hand observers of the once biologically diverse "rainforests of the sea" remain. Most people today only know of such healthy coral reefs through photographs. Some of the threats to coral reefs are well understood, while others we are just beginning to comprehend.
In 2006, the once dominant Caribbean reef-building species of elkhorn (Acropora palmata) and staghorn (A. cervicornis) corals became the first to be listed under the Endangered Species Act (ESA). Both coral species are distributed throughout the Caribbean from the Bahamas to Venezuela, from Mexico to Florida, and in Puerto Rico and the U.S. Virgin Islands. These species were once so common that entire reef zones were named after them. Now, it is estimated that less than three percent of their populations remain.
The decline of these species, and their eventual listing as threatened, resulted mainly from disease, climate change (which increased bleaching1 in response to elevated sea surface temperatures), and hurricane impacts. Other threats contributing to their decline include damage resulting from boating, fishing, diving, and snorkeling, as well as impacts of coastal development, including sewage and stormwater discharges. If these threats continue, so will the decline of elkhorn and staghorn corals.
Although we know the threats contributing to the decline of threatened elkhorn and staghorn corals, we do not yet know how these threats affect individual coral species or how individual threats acting together affect the overall physiology and health of these corals. The research conducted by scientists within and outside of the National Marine Fisheries Service (NMFS) will play an important role in managing threats and eventually recovering these species.
Photo Credit: Michael Barnette/NOAA
At the 11th International Coral Reef Symposium, held this year in Ft. Lauderdale, Florida, elkhorn and staghorn corals were the subject of 46 oral and poster presentations. Much of the research on these species presented at the symposium focuses on reproduction and genetics. Other research centers on coral diseases, including physiological responses and environmental conditions associated with disease. The causes of disease in these coral species remain undetermined. Other investigations seek to identify coral restoration techniques in an on-going response to damage resulting from such disturbances such as vessel groundings and storms. Developing successful techniques may lead to the largerscale reef restoration efforts needed to achieve recovery. In the meantime, we still need accurate estimates and maps of species numbers and distribution.
Gaps in knowledge and understanding can affect our ability to stem the decline of elkhorn and staghorn corals, but these uncertainties need not stop development of research and management strategies. For example, four years of data on elkhorn colonies in the Upper Florida Keys, collected by Dana Williams at the University of Miami Rosenstiel School of Marine and Atmospheric Science’s Cooperative Institute of Marine and Atmospheric Studies and Margaret W. Miller at the NMFS Southeast Fisheries Science Center, is being used by Tali Vardi, a graduate student at Scripps Institution of Oceanography, to develop a population viability analysis model for this species. Different types of datasets can be incorporated into the model to show how those parameters change the long-term viability of elkhorn coral populations. These datasets may include annual bleaching, monitoring, or abundance data; climate change modeling data, such as long-term prediction data for future hurricane intensities, frequencies, and storm tracks; and changing ocean pH and calcium carbonate levels, which affects the rate at which corals form their outer skeletons. In turn, this may help the Acropora Recovery Team develop recovery objectives and compare recovery strategies.
Elkhorn and staghorn corals are unique in the world of ESA-listed species. These animals are immobile colonial invertebrates that also provide habitat for a multitude of species. These relatively fast-growing corals provide the branching framework for reef creatures in search of a safe place to live, eat, and grow. Therefore, conservation and recovery of threatened corals is inherently coupled with the conservation of an entire ecosystem. The unique nature of these threatened species means that existing examples of ESA-listed species management and recovery may not be appropriate. Thus, future research objectives and the data collected from past and on-going research initiatives will need to be formulated and applied in potentially new and creative ways to develop and implement practical recovery actions.
1Bleaching is when a heat-stressed coral colony expels all of its symbiotic algae and only the white coral skeleton is left, giving the coral a "bleached" appearance.
Sarah Heberling, a NMFS natural resource specialist/Acropora Implementation in St. Petersburg, Florida, can be reached at 727-824-5312.
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