Coastal pollution reduces genetic diversity of corals, reef resilience

A new study published in the journal PeerJ by researchers at the University of Hawaii found that human-induced environmental stressors have a large effect on the genetic composition of coral reef populations in Hawaii.

The National Science Foundation-funded scientists confirmed that there is an ongoing loss of sensitive genotypes in nearshore coral populations due to stressors from poor land-use practices and coastal pollution. This reduced genetic diversity compromises reef resilience.

This research provides valuable information to coral reef managers in Hawaii and around the world who are developing approaches and implementation plans to enhance coral reef resilience and recovery through reef restoration and stressor reduction.

The study identified that genetic relationships between nearshore corals in Maunalua Bay, Oahu, and those from sites on West Mau were closer than relationships to corals from the same islands, but farther offshore.

This pattern can be described as isolation by environment in contrast to isolation by distance. This is an adaptive response by the corals to watershed discharges that contain sediment and pollutants from land.

"While the results were not surprising, they demonstrate the need to control local sources of stress while addressing the root causes of global climate change," said Robert Richmond, director of the Kewalo Marine Laboratory and co-author of the study. "The findings show the need to track biodiversity at multiple levels."

While the loss of coral colonies and species is easy to see with the naked eye, molecular tools are needed to uncover the effects of stressors on the genetic diversity within coral reef populations.

"This study shows the value of applying molecular tools to ecological studies supporting coral reef management," stated Kaho Tisthammer, lead researcher on the paper.

The work was a collaborative effort among researchers at the university’s Kewalo Marine Laboratory, Pacific Biosciences Research Center, and the Hawaii Institute of Marine Biology.

"This work highlights the importance of limiting pollution, sediment, and agricultural runoff to nearshore coral reefs," says Dan Thornhill, a program director in NSF's Division of Ocean Sciences. "Protecting biodiversity is essential, as that diversity is needed in helping corals and other marine life adapt to changing oceans. Selecting for resilience to pollution may eliminate coral genotypes that resist disease, tolerate higher temperatures, and continue to grow in more acidic and oxygen-depleted waters."