Coral Bleaching Guam 2013

With the onset of human-induced climate change, marine scientists are taking a closer look at how marine organisms respond to warming temperatures, sea-level rise, and more acidic oceans.  One way in which corals respond to climate change and warming temperatures is through coral bleaching.  Coral bleaching is what happens when a coral animal becomes stressed and expels its symbiotic zooxanthellae (a special kind of algae that lives inside the coral).  These zooxanthellae are what give coral a lot of its color, so when corals expel their algae they appear white (hence the name coral bleaching).  Bleached corals may regain their zooxanthellae and become healthy and colorful again, but if unusually warm water temperatures persist and the corals are without their important algae partners for too long, they can die.  With temperatures getting warmer and warmer, at a faster rate than normal, it is likely that the world’s coral reefs will see much more frequent and increasingly severe coral bleaching events.  Since corals are an important part of coral reef ecosystems, the death of corals and loss of the structure they provide can have a negative impact on the whole ecosystem.  The structures that coral form not only provide homes to many fish, but corals are also a food source to some fish and invertebrates.  For Guam, corals are important because of the shelter they provide to a lot of fish that we enjoy consuming, they are one of the main reasons why Guam gets over one million tourists every year, and they also help protect the island from large waves.  For these reasons local coral reef managers are interested in better understanding how Guam’s corals and the coral reef ecosystem as a whole are affected by coral bleaching, and whether or not we can expect our reefs to adapt to the changing conditions.

In August of this year, Guam’s coral reef managers and scientists found that Guam was experiencing bleaching island wide, and that several different species at various depths were affected.  Several of Guam’s coral reef management partners (Guam Long-term Coral Reef Monitoring Program, NOAA, Guam EPA, the National Park Service, the University of Guam, and Guam DAWR) conducted approximately 17 separate qualitative assessments around Guam to get an idea of the scale and severity of the bleaching.  As it became apparent that this was a widespread, potentially severe event, these partners decided to take action and begin a formal quantitative assessment of approximately 50 sites around Guam.

So far, data has been collected regarding species affected, the severity of bleaching, and the size class of the corals which are bleaching.  This information has been collected at 48 sites island-wide, mainly in the shallow water just beyond where the waves break.   These data will not only help us understand which corals may be more or less resistant  to coral bleaching, but it will also help us understand how bleaching may affect corals in the future and ways to prepare for these events.  A special targeted effort by the Guam Long-term Monitoring Program is also underway to assess bleaching effects on Guam’s shallow-water staghorn Acropora patches.  Data has already been collected at several sites around Guam and these areas will be revisited over the coming months to assess this coral’s response to bleaching.  As these staghorn patches provide critical habitat to key fisheries species and have been shown to be decreasing in total cover over the past 30 years, these surveys will help illuminate the susceptibility and resilience of these important coral patches to bleaching and other climate effects.  On top of the survey efforts, public talks have been given to approximately 250 students and 50 adults to educate them about coral bleaching, what is looks like, and how the public can help by sending in pictures and reports of what they are seeing.  With these efforts, Guam will have a better handle on bleaching effects and perhaps what to expect in coming years with the anticipated growing effects of climate change.  

Posted by
Roxanna Miller
7:10 am
Wednesday, January 1, 2014
Location: Hagatna, Guam

UOG Marine Laboratory student performing a benthic photoquadrat survey.  Photo taken by Dave Burdick.

A massive Porites sp. coral which is bleached.  Some areas have already begun to die as evidenced by the algae covered areas.  Photo taken by Dave Burdick.

Landscape view of coral bleaching at Pago Bay.  Photo taken by Laurie Raymundo.

Bleached colonies at Ritidian National Wildlife Refuge in northwestern Guam.  Photo taken by Roxanna Miller.

Staghorn Acropora sp. bleaching survey quadrat.  Photo taken by Roxanna Miller.