Chemicals leaking from plastics disrupt the two most critical processes for reef survival – the reproduction of adult corals and the settling of their larvae, a new study to have emerged from the University of Hawai’i at Manoa has found.

The research is among the first to demonstrate the hidden dangers of plastic pollution and may go some lengths to help explain why some reefs are failing to recover following mass-bleaching events, scientists believe.

“When people think of threats to coral reefs, microplastics are often unnoticed,” said Keiko Wilkins, the researcher behind the study and a recent PhD graduate from the University of Hawai’i at Manoa Marine Biology Graduate Programme.

“Not only do corals eat microplastics, microplastic-associated chemicals may have hidden impacts. My research highlights this issue, urging us to see plastic pollution as a complex stressor to our reefs.”

Conducted at the Kewalo Marine Laboratory, Wilkins’ work has been published in two parts. The first study has appeared in Integrative and Comparative Biology and showed that plastic leachates – these are chemicals released from plastics into the water – significantly reduced fertilisation rates in corals.

The second study – published in Frontiers in Marine Science went on to demonstrate that these same chemicals negatively affected the ability of coral larvae to settle onto reefs, a step essential for replenishing coral populations.

“Keiko’s research is timely and essential in supporting efforts at the protection of coral reefs and all who depend on them,” said Bob Richmond, director of the Kewalo Marine Laboratory and Wilkins’ advisor. “Her results provide proof of the unseen, damaging effects of plastic pollution and the need to urgently address this problem if we are to leave a legacy of vital coral reefs for future generations.”

Coral samples were collected from protected areas including the Papahānaumokuākea National Marine Sanctuary and the Hawaiian Islands Humpback Whale National Marine Sanctuary. Wilkins is now investigating how many microplastic particles are being ingested by corals in these regions.

Her full paper, ‘Microplastic Leachate Negatively Affects Fertilisation in the Coral Montipora capitata’ has now been published in the journal Integrative and Comparative Biology. Her study ‘Unseen threats: negative effects of microplastic leachate on coral planulae settlement’ is now published in Frontiers in Marine Science.

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