Abundant corals in a shallow Hawaiian lagoon. (Photo by Keoki Stender)

Researchers Erik Franklin, Paul Jokiel and Megan Donahue from the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology developed species distribution models of the six dominant Hawaiian coral species around the main Hawaiian Islands, including two species currently under consideration as threatened or endangered. They found the order of coral abundance (from highest to lowest) around the main Hawaiian Islands to be Porites lobata, Montipora patula, Pocillopora meandrina, Montipora capitata, Porites compressa, and Montipora flabellata. The study was published in Marine Ecology Progress Series.

Environmental factors—wave energy, shape of the seafloor, water clarity, depth, rugosity (roughness of the seafloor), geological island age and organic sediment content—are known to influence Hawaiian reefs. This is the first study to systematically examine the influence of these factors on the distribution and abundance of coral species across the entire seascape of shallow reefs in the main Hawaiian Islands.

“Average wave height and maximum wave height were the most influential variables explaining coral abundance in the Hawaiian Islands,” reported Franklin, lead author of the study and assistant researcher at the UH Mānoa Hawaiʻi Institute of Marine Biology. “Our models also identified relationships between coral cover and island age, depth, sunlight, rugosity, slope and aspect (direction a slope faces).”

In general, coral cover was predicted to be highest in primarily wave-sheltered coastlines and embayments. Reefs with highest cover were concentrated in Kāneʻohe Bay on Oʻahu; the wave-sheltered reefs of Molokaʻi, Lānaʻi, Maui, and Kahoʻolawe; and the Kohala coast of Hawaiʻi.

Regional-scale mapping of coral species from these models provide a framework for population modeling and marine spatial planning of Hawaiian coral reefs. The geographic characterization of coral reefs would benefit greatly from the improved coral distribution and abundance information generated from coral distribution models. Data from these models can be incorporated into marine conservation plans or used for threat assessments to reefs.

“For example, our results were recently used in the management plan review process of the Hawaiian Islands Humpback Whale National Marine Sanctuary as they considered the distribution and abundance of animals other than whales, ” Franklin says.

Franklin and colleagues are in the process of extending the modeling approach to include additional marine species in Hawaiʻi, such as reef fish and include additional environmental variables to try to improve the predictive capacity of the models. Ideally the results will continue to inform marine resource management in the Hawaiian Islands.

Read the School of Ocean and Earth Science and Technology news release for more information.

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