November 16, 2013
Abundant, Dominant Corals Still Face Threat Of Extinction
April Flowers for redOrbit.com - Your Universe Online
Scientists generally assume that corals do not face a risk of extinction unless they become very rare, or their range is restricted. A new study, published in the journal Bioscience, reveals that global changes in climate and ocean chemistry affect corals whether scarce or abundant, and often it is the dominant, abundant corals with wide distributions that are affected the most.
A research team, led by Charles Birkeland from the University of Hawaii – Manoa (UHM), including researchers from the Joint Institute for Marine and Atmospheric Research (JIMAR) and the National Oceanic and Atmospheric Administration (NOAA), evaluated both the geologic record of past extinctions and recent major events to assess the characteristics of dominant corals under various conditions. During periods favorable to coral growth, the team found that natural selection favors corals with traits that make them more vulnerable to climate change.
The past 10,000 years have been extremely favorable for corals. Due to their rapid growth, Acropora species like table coral, elkhorn coral and staghorn coral, were favored in competition. Such rapid growth may have been developed, in part, as a defense against predation, hurricanes, or warm seawater. Acropora species of coral have extra thin tissue, porous skeletons and low concentrations of carbon and nitrogen in their tissues. During the present interglacial period, the abundant corals have taken an easy road to living a rich and dominating life. The payback, however, will come when the climate becomes less hospitable.
The research team suggests that the conditions driven by excess carbon dioxide in the ocean cause mortality at rates that are independent of coral abundance. Reproductive success is affected by this density-independent mortality and psychological stress, and can lead to the decline of corals. Although some coral species are abundant across a broad geographical range currently, the findings of this study show that this will not safeguard them against global threats, such as changing ocean chemistry and rising temperatures.
Almost all prior assessments and evaluations of the risk of extinction for a species of coral are made on the basis of how scarce or restricted the range is. The new study, however, highlights the vulnerability of abundant and geographically dispersed corals as well as those that are rare and/or have restricted ranges.
The researchers from the UHM School of Ocean and Earth Science and Technology (SOEST); the National Marine Fisheries Service (Southeast Fisheries Science Center, Northwest Fisheries Science Center, and Pacific Islands Fisheries Science Center); NOAA National Ocean Service; and NOAA Coral Reef Watch hope that their findings will strengthen the case for directly addressing the global problems related to coral conservation.
The authors stress that although handling local problems is a good thing, it will take more than just handling all the local problems to make a positive impact.