Coral bleaching in the Vatu-i-Ra Seascape – how bad is it?

BY: Sangeeta Mangubhai

Bleached Anemone

Bleached Anemone

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. Temperatures on inner reef flats along the Coral Coast recorded temperatures as high as 35°C. A similar story emerged from Vanuatu. http://www.huffingtonpost.com/lagipoiva-cherelle-jackson/fish-kills-reported-in-fiji_b_9233612.html

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 Dr. Tim McClanahan and Dr. Emily Darling from the Wildlife Conservation Society.

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.

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, to 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 recovery from both climate-induced temperature stress and the mechanical damage caused by cyclone Winston.

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