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Coral Bleaching in the Vatu-I-Ra Seascape: How Bad Is It?

By Sangeeta Mangubhai

[This is the fourth in a series of blogs by WCS-Fiji Director Sangeeta Mangubhai assessing the damage to coral reefs caused by Cyclone Winston, a Category 5 storm that hit Fiji on February 20]

Before Cyclone Winston hit Fiji, we were following closely the El Niño cycle, the drought, and reports of coral bleaching from dive operators. The local newspaper, the Fiji Times, ran a number of stories about fish kills and there was a lot of speculation about whether this was caused by the elevated sea surface temperatures we were experiencing across Fiji.

Bleached Acropora coral continues to provide a home for blue chromis fish. Photo by Sangeeta Mangubhai ©WCS.
Bleached Acropora coral continues to provide a home for blue chromis fish. Photo by Sangeeta Mangubhai ©WCS.

Temperatures on inner reef flats along the Coral Coast recorded temperatures as high as 35°C. A similar story emerged from Vanuatu.

I have been spending part of each dive collecting data on the scale and intensity of bleaching across a range of habitats – including fringing patch and lagoonal reefs, channels, and bommies – using a rapid assessment technique developed by my colleagues Dr. Tim McClanahan and Dr. Emily Darling at the Wildlife Conservation Society.

Large bleached 3m diameter Porites coral. Photo by Sangeeta Mangubhai ©WCS.
Large bleached three-meter diameter Porites coral. Photo by Sangeeta Mangubhai ©WCS.

Over the last four days, I have documented mild levels of bleaching, with common coral genera like Acropora, Pocillopora, Porites (massive forms), Montipora and Pavona mostly affected.

By mild, I mean that corals are either iridescent or slightly pale, rather than fully white (i.e. bleached). The tissue on these corals is still very much alive. A few very large colonies of Porites and Pavona are severely bleached in the shallow lagoon at Gau Island, but again still alive.

A bleached anemone on lagoonal reefs at Gau. Photo by Sangeeta Mangubhai ©WCS.
A bleached anemone on lagoonal reefs at Gau. Photo by Sangeeta Mangubhai ©WCS.

For most part the bleaching is patchy and affecting corals living at 5-15m depth. Water temperatures in the Vatu-i-Ra Seascape have dropped by about 2°C since the cyclone to 27°C. If these cooler water conditions continue, we can expect that most pale or bleached coral colonies will return to normal over the upcoming weeks.

It is going to be even more important that we look after our reef resources over the next 12 months. We must give our reefs the best chance of recovery so that they can continue to feed and sustain us here in Fiji. How well we care for our reefs will determine how well they recover from both climate-induced temperature stress and the mechanical damage caused by Cyclone Winston.

A four-meter wide bleached Pavona coral continues to provide a home for blue chromis and purple anthias fish. Photo by Sangeeta Mangubhai ©WCS.
A four-meter wide bleached Pavona coral continues to provide a home for blue chromis and purple anthias fish. Photo by Sangeeta Mangubhai ©WCS.

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Dr. Sangeeta Mangubhai is Director of the Fiji Program for WCS (Wildlife Conservation Society). Follow Sangeeta on Twitter at: @smangubhai.

 

Previous blogs in Sangeeta Mangubhai’s series exploring the damage to Fiji’s coral reefs following Cyclone Winston:

* After Winston: Assessing Coral Reefs for Cyclone Damage and Coral Bleaching

* A First Post-Cyclone Look at Coral Reefs in the Vatu-I-Ra Seascape

* Diving Nigali Passage in Gau