PICRC solves the mystery of slow coral recovery from typhoon damage on east coast of Palau

Protecting our marine environment requires investment – investment in funding, time, human resources, information and patience.  A recent publication by Palau International Coral Reef Center (PICRC) and their collaborators from Australia in the peer-reviewed journal, Marine Ecology Progress Series, both enlightens and reminds us the critical importance of continued investment in our environment.

Palau’s coral reefs are confronted with multiple threats at the same time, both local and global.  Among the biggest local threats are overfishing and sedimentation, while global threats include coral bleaching from increasing water temperatures; ocean acidification from increasing concentration of carbon dioxide in the water; and broken reef systems from increased frequency and intensity of typhoons – all of which are due to the changing global climate and increased deforestation and land-use in Babeldaob Island.

Six years after the last super typhoon Haiyan, the eastern reefs of Babeldaob were showing a low average of 6-7% overall coral cover.  “A 7% live coral cover is less than half of what we expected” stated Dr. Yimnang Golbuu, Chief Executive Officer of PICRC and one of the co-authors of the study. “Recovery of the eastern reefs is important, not only for the communities on the east coast, who rely on it for food security, protection and income, but also for the whole nation, as they make up more than a quarter (28%) of Palau’s total reef area.”

This paper, titled, “Modelled larval supply predicts coral population recovery potential following disturbance”, provided an explanation for the relatively slow recovery of coral cover on the eastern side of Babeldaob and Koror, compared to the rest of Palau, after the super typhoons Bopha in 2012 and Haiyan in 2013.  The researchers determined that the direction, timing, frequency and strength of the currents that pass through the east coast ultimately result in a low supply of coral larvae to these areas. By contrast, the rest of the Palau archipelago has an abundant supply of larvae both from local reefs and also from reefs elsewhere in Palau.  For this reason, unlike the east coast of Palau, they can recover much faster from typhoon damage. This finding resulted from biophysical computer modelling that used satellite altimetry data.  The model was validated by field data from the PICRC’s long-term coral reef monitoring studies. 

How are these findings useful to Palau? In at least two ways! Firstly, as our coral reefs remain vulnerable to multiple threats, especially the climate-induced threats for which we have limited influence and control in preventing, we need to protect and strengthen our Marine Protected Areas to ensure that they can provide larvae to repopulate damaged reefs. Secondly, the areas that receive fewer coral larvae, such the eastern side of Babeldaob and Koror, needs enhanced protection as they are less robust because of a lesser supply of coral larvae. “This study demonstrates that there are reefs around Palau that receive much less larvae than others after large coral spawning events. Knowing where these reefs are located is useful for management actions that aim at optimizing reef recovery”, stated Dr. Marine Gouezo, former PICRC researcher and lead author of the study.

According to Professor Eric Wolanski from James Cook University in Australia and one of the co-authors of the study, “The biophysical computer model that we used in this study has applications beyond this study.  The model can also be used to explain the spatial patterns of reef fish recruitment and fish populations in Palau and its susceptibility to fishing; it can thus guide fishing management to ensure the long-term survival and well-being of our reef fish.”