Assessing coral reefs for cyclone damage and coral bleaching

BY: Sangeeta Mangubhai

On Saturday, 20 February 2016, Fiji with a population of 900,000 was hit by Category 5 Cyclone Winston. It was one of the largest cyclones we had experienced with winds of up to 185mph. Over a 24-hour period the cyclone left a trail of destruction through the centre of the country, and through the Vatu-i-Ra Seascape where the Wildlife Conservation Society (WCS) works. The Fijian Government immediately announced a 30 day state of emergency, calling for coordinated assistance from NGOs, private sector and humanitarian aid agencies. As images flood in from across the country, we are getting the full sense of the damage that has been done especially within the communities we work, and the long recovery road that is ahead of Fiji.

Much of our effort so far, has been around providing food and water relief to our communities until authorities and humanitarian organisations can step in. However, over the next 10 days, through the generous support of Nai’a Cruises, a live-aboard ship that has been diving in Fiji since 1993, I have the opportunity to survey coral reefs throughout the Vatu-i-Ra Seascape to assess the damage caused by cyclone Winston, and collect data on coral bleaching.

Why is this important? Fijians are highly reliant on their coral reef for both food and for livelihoods. In fact, fish is the main source of protein, and therefore healthy productive coral reefs and their associated fisheries, are critical to Fiji’s food security.

I will be using two main techniques to assess the reefs. Firstly, I will be taking a series of random underwater photos from about half a meter above the reef surface at 12-15m depth. They have to be random because I have to be careful not to bias my sampling and favour one type of substrate (e.g. coral) over another (e.g. sand). So what I do is close my eyes for about five to ten kicks of my fins, open my eyes and wherever I land I point the camera down and take a photo. All the photos are later analysed in software specifically designed to help capture how much hard coral covers the reef, versus soft coral, algae, sand or rock.

Secondly, I will be assessing the scale and intensity of coral bleaching across different reefs throughout the Vatu-i-Ra Seascape. Just before the cyclone, there were increasing reports from dive operators and local scientists of coral bleaching throughout Fiji, caused by the El Niño cycle. Coral bleaching occurs when a coral is stressed which more often is in response to increases in sea surface temperatures. Under stress, coral will sever the unique relationship they have with an algae living inside them called zooxanthellae. The algae gives coral their colour and turn sunlight into food. Without zooxanethellae corals become pale to white (hence the term coral bleaching), and slowly start to starve.

On this trip, I will visit both sites I surveyed in 2001 with Nai’a Cruises, as well as explore new areas. The data I will collect can also serve as a baseline for both measuring changes on coral reefs, as well as the recovery of reefs, post-cyclone and post-bleaching. The ability of our reefs to either resist stresses like from cyclones and high sea surface temperatures will affect how healthy they are, and therefore their ability to support local fisheries in Fiji.

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