Genetic diversity of coral reefs

Coral reefs are widely known for their stunning array of color, shape and forms of life, making them a model for extreme biodiversity. Hidden within the multitude of reef inhabitants, but no less important, is their genetic diversity which is linked to adaptive capacity, extinction risk of species, and the overall functioning of ecosystems, so conservation strategies often call for preserving areas of high genetic diversity.

However, there is little direct data to guide debates such as whether many small versus one large reserve would be better to protect genetic resources. Researchers from the University of Hawai'i at Mānoa (UHM) School of Ocean and Earth Science and Technology, the University of California, Santa Barbara (UCSB), University of St. Andrews, and University of Melbourne discovered that large areas of intact coral reef with extensive live coral cover, not disturbed by humans or climate change, harbor the greatest amount of genetic diversity.

The colleagues assessed genetic diversity from over 17,000 samples taken from 47 common reef-associated species across the Hawaiian Archipelago and found that genetic diversity varies across the inhabited Main Hawaiian Islands, extending the argument for targeted protection of reefs throughout the Main Hawaiian Islands. Notably, Hawai'i Island has the greatest amount of coral reef area, harbors the greatest proportion of genetic diversity, and serves a unique, and particularly influential role due to its large size at the margin of the chain. Nihoa and Ni'ihau, which sit at the transition between Papahānaumokuākea Marine National Monument and the Main Hawaiian Islands, also stand out and warrant future research and protection due to intriguing combinations of high genetic divergence and unusual fish composition.

Genetic diversity is widely accepted as critical for adaptation to a changing climate. Although coral bleaching in Hawaii has been relatively rare over the past few decades by comparison to many other places in the Pacific, this stressor still exerts a large impact on the reef communities studied. Research shows that areas which experienced the most frequent coral bleaching conditions also showed depressed levels of genetic diversity, not just for corals but for the entire community of fishes and other invertebrates associated with those habitats.

This negative impact of thermal stress on genetic diversity suggests that climate change will compromise the adaptive capacity and genetic integrity of not just corals but the entire coral reef community.

Identifying features of the landscape that are associated with biodiversity hotspots is one of the key strategies for conservation. The researchers involved in the study plan to follow up on evidence in their dataset that the same large-scale ecological rules that predict species diversity also predict genetic diversity. If that is true it would allow rapid assessment of species diversity using DNA analysis and thereby new metrics of resilience and adaptive capacity.