New research shows that ocean corals previously thought to be at low risk of extinction may be facing risks after all. A team of scientists are challenging the traditional assumption that corals do not face a risk of extinction unless they become very rare or have a very restricted range. Some coral species are abundant across a broad geographic range, but the new findings show that this does not safeguard them against global threats, including changing ocean chemistry and rising temperatures.
A team of researchers from the University of Hawaii at Manoa (UHM), Joint Institute for Marine and Atmospheric Research (JIMAR) and the National Oceanic and Atmospheric Administration (NOAA) revealed that global changes in climate and ocean chemistry affect corals whether scarce or abundant. They have also determined that often it’s the dominant, abundant corals with wide distributions that are affected the most.
Traditionally, the risk of extinction for a species of coral was made on the basis of how scarce or restricted its range. But the new findings show that abundant and widely dispersed corals–as well as corals that are rare and/or have restricted ranges–may be vulnerable.
The researchers looked at both past extinctions and recent major events to determine the characteristics of dominant corals under various conditions. They concluded that–during periods advantageous to coral growth–natural selection favors corals with traits that make them more vulnerable to climate change.
Various species of corals have been fairly stable for the last 10 thousand years. Certain types of coral–including acropora species (table coral, elkhorn coral and staghorn coral)–were favored in competition due to their rapid growth. The rapid growth may have been advantageous due in part to neglecting investment in few defenses against predation, hurricanes or warm seawater.
Acropora species have porous skeletons, extra thin tissue and low concentrations of carbon and nitrogen in their tissues. The abundant corals have taken an easy road to living a rich and dominating life during the present interglacial period, but there may be negative consequences when the climate becomes less hospitable.
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 propose that the conditions driven by excess carbon dioxide in the ocean cause mortality at rates that are independent of coral abundance. This density-independent mortality and physiological stress negatively affect reproduction, leading to the decline of corals.
The scientists hope to strengthen the case for directly addressing the global problems related to coral conservation.
Photo of table coral: Nick Hobgood/Wikimedia Commons