Corals are delicate yet strong – vulnerable to degradation with changes in the environment, yet they serve as protective barriers that shelter our coasts from powerful storms. The importance of coral reefs is indisputable, providing billions of dollars in coastal protection, tourism, and support of a prosperous fisheries industry. Despite their economic importance, coral reefs are on the decline worldwide due to climate change, bleaching, and disease. The good news is that restoration efforts are underway to aid recovery. There are pockets of reef that thrive despite inhospitable conditions—evidence of real-time adaptation to a changing environment. This indicates that humans might be able to help, and new USGS science published in the journal Endangered Species Research can help guide the way.

Most corals are colonial animals related to jellyfish and sea anemones, and can reproduce by fragmenting, that is breaking off into genetically identical colonies, and sexually by releasing eggs and sperm into the water. Sexual reproduction blends genes from parent corals, leading to new genetic variations that, through natural selection, lead to coral populations that are better adapted to the environment and novel stress factors such as new coral diseases. On many reefs across the world, individual corals are too spread out for successful sexual reproduction. So, providing potential mates through “managed relocation” could allow existing populations, which consist of genetically identical clones, to start sexually reproducing again. USGS science shows that one way to help might be to assist corals in migrating to parts of their range they formerly occupied to help jump start sexual reproduction within remaining coral populations.

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The elkhorn coral, Acropora palmata, is severely threatened, but is critical to reversing coral-reef ecosystem collapse in the western Atlantic. The elkhorn coral is especially important, as it is the only species in this region that forms the upper reef crest—the area of the reef that causes waves to break—thereby reducing storm damage to our coastal communities. Elkhorn corals are one of several species of corals struggling to naturally produce new colonies. This has led to the implementation of restoration efforts, including raising elkhorn coral fragments in nurseries until they are large enough to plant on the reef tract. But how can restoration groups determine which corals will be successful? And where should they be planted to maximize their success?

USGS marine biologist Dr. Ilsa Kuffner and her colleagues conducted an experiment with six different genetic strains of nursery-grown elkhorn coral to find out where they can be successful and grow fastest—knowledge that could help restoration groups jump-start natural reproduction in strategic locations. “If we can introduce enough genetic diversity to restart sexual reproduction, the coral populations will have a better chance of responding to stress and seeding future populations that are better adapted to the changing environment,” says Kuffner.

The scientists transplanted 54 small nursery-grown elkhorn coral fragments supplied by the Coral Restoration Foundation of different genetic strains to locations spanning 200 miles of the Florida reef tract. They worked with partners from the National Park Service at Dry Tortugas National Park and Biscayne National Park, along with the NOAA Florida Keys National Marine Sanctuary, to obtain permission to do this research. From May 2018 to October 2019, they repeatedly visited the corals to photograph, weigh, and measure the size of each coral fragment.

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The corals transplanted to the two sites in the Dry Tortugas flourished—growing nearly double the size and about 85% faster than the corals that survived in the Upper and Middle Keys—indicating that conditions for elkhorn coral growth may be better there. The successful introduction of five genetic strains of elkhorn to this isolated but well-connected location has potentially supplied the one, remaining native Dry Tortugas genetic strain with potential mates to help propagate future generations. The team is continuing their research, collaborating with the Ohio State University, to discover what causes the corals to grow better in the Dry Tortugas. Some explanations could include temperature, water flow, or food supply.

“Our partnership with the USGS and their research directly informs our coral conservation efforts at Dry Tortugas and Biscayne National Parks,” said Pedro Ramos, superintendent of Everglades and Dry Tortugas National Parks. “The results of this study will help to identify locations for replanting nursery-grown corals and assist in the restoration of a more genetically robust, reproductive population.”

The results of this study are being shared with partners involved in managing and restoring elkhorn coral populations throughout the Florida Keys. USGS plans to continue their coral research to help conserve the economic and ecological benefits of this critically important species.

Read the publication here.