The National Marine Fisheries Service is developing a recovery plan for elkhorn and staghorn corals. We want the plan to set a specific target of 350 ppm for atmospheric CO2. Reversing the trend of carbon build up is necessary to slow coral bleaching. NMFS’s plan has merits because it sets helpful criteria for ocean warming and acidification.
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Elkhorn and staghorn corals inhabit the waters of Florida, the Bahamas, and the Caribbean. The two corals are sometimes found interspersed together, though elkhorn coral lives in shallow water of 1 to 5 meters in depth, while staghorn coral lives in deeper water, of 5 to 20 meters. Elkhorn coral is the largest acroporid coral. It has brown to tan branches that spread like flat fans with white on the outer growing margins. Staghorn is quite different, golden yellow to medium brown, and again with white edges, but its form is a thicket of branching rods of up to 5 cm (2 inches) in diameter. Living elkhorn is relatively scarce off of Broward County and is more common to the south, but staghorn coral can be found as far north as Palm Beach Florida.
Elkhorn and staghorn corals are particularly dependent on sunlight, whereas other corals can catch particles and zooplankton for energy. Therefore, decreases in water clarity are more detrimental to elkhorn and staghorn as they may not be able to switch from feeding on photosynthesizing algae to other food sources. This inability makes them less resilient to bleaching events and more susceptible to climate change factors.
The Draft Recovery Plan reports: Recent work on Pacific Acropora spp. suggests that acidification may reduce the threshold at which bleaching occurs; however, elkhorn and staghorn corals have yet to be subjected to similar acidification studies. In addition to effects on growth and calcification, recent laboratory experiments have shown that increased CO2 also substantially impairs fertilization and settlement success in Acropora palmate.
Staghorn and elkhorn reefs in Florida and the Caribbean have declined up to 97 percent since the 1970s. The corals face ongoing declines due to bleaching from increasing ocean temperatures, pressures from disease, fishing, dredging and pollution, and impacts from ocean acidification.
We strongly urge the Fisheries Service to add a recovery criterion to the final plan that specifies the target atmospheric CO2 concentration at 350 ppm, or the CO2 concentration range needed to achieve the recommended temperature and acidification (pH) targets. We commend the recovery team and the Fisheries Service for the draft recovery plan which provides an important roadmap for reducing key threats to elkhorn and staghorn corals.
Please join with us in signing our letter to the National Marine Fisheries Service.