Assessing the Namena Marine Reserve off Vanua Levu
March 16, 2016
Fading Fast
March 23, 2016

BY: Sangeeta Mangubhai

After 10 days at sea, travelling over 500km and completing 26 dives, I have solid data on the scale and intensity of damage to the Vatu-i-Ra Seascape, from Tropical Cyclone Winston that passed through Fiji on the 20 February 2016. Coupled with cyclone damage, I assessed coral diversity and coral bleaching patterns throughout the seascape, on fringing reefs, bommies, underwater pinnacles and reef channels.

Sangeeta on board NAI'A exploring the damage to Fiji’s coral reefs following Cyclone Winston

Sangeeta on board NAI’A exploring the damage to Fiji’s coral reefs following Cyclone Winston

Damage to coral reefs was highest in the north, and lowest in the south, which as expected, followed the pathway Cyclone Winston took through Fiji. It was clear that where the eye of the cyclone passed, corals sustained damage. However, the level of destruction was highly variable and patchy between reefs. [pullquote_left] There really was not easy way to predict which reefs would be damaged and which ones would remain unscathed – both windward and leeward reefs equally sustained damage.[/pullquote_left]

Sadly Fiji experienced significant losses of sea fans (gorgonian corals) and soft corals at almost all of the sites. Table and staghorn Acropora (branching) corals were broken off at the stems, often sitting upside down on the substrate or obliterated into small pieces. You still see flashes of colour from sea fans and soft corals, but now you have to look a little harder to find them. Sides of fringing reefs, bommies and pinnacles had large scoured out areas, with clean white surfaces or covered in a fine layer of turf algae. Large volumes of old and new rubble accumulated in between reef structures, shifting around with the currents. The Nasi Yalodina, a shipwreck sitting at 30m in the eastern Bligh waters had been pushed down to deeper depths and was no longer visible to divers.

In addition to sustaining mechanical damage from the cyclone, the reefs had coral bleaching (ranging from 0-20%), caused by thermal stress from the El Nino cycle we are in. Post-cyclone, the temperature has dropped a couple of degrees and now rangeds from 27-28°C, which if continues, will help corals return to normal. Thankfully, the fish, shark and manta life were flourishing. We dived and snorkelled with 10 mantas across the Vatu-i-Ra Seascape, and large schools of barracuda, big-eye trevally, fusiliers, surgeonfish, and colourful anthias.

Bleached-Acropora-coral-continues-to-provide-a-home-for-blue-chromis-fish

Bleached-Acropora-coral-continues-to-provide-a-home-for-blue-chromis-fish

So what next for Fiji’s reefs? Well, the road to recovery will depend on how well corals successfully reproduce and their larvae settle onto reefs. Some species like Pocilloporids (which provide shelter for fish and other cryptic invertebrates like crabs and shrimps), usually spawn multiple times, releasing fully formed larvae into the water column that are ready to settle immediately onto reefs. Other hermaphroditic species like branching Acroporids, will release eggs and sperm into water column and fertilised eggs will develop into larvae, before settling onto reefs. We know so little about the timing of spawning in Fiji, and what factors result in good pulses of recruitment onto reefs.

Large bleached 3m diameter Porites Coral

Large bleached 3m diameter Porites Coral

My concern is that corals that are under bleaching stress, will invest their energy in staying alive, and will forfeit reproduction for up to 12 months. If this happens, the recovery of Fiji’s reefs might be slow or delayed. This is the first time I am aware of, where our reefs have to deal with both climate-induced bleaching stress and the mechanical damage from a cyclone.

It is going to be even more important over the next 12 months and longer for us to look after our coral reefs in Fiji, to give them the best fighting chance of recovery. Instead of seeing them as infinite resources for us to use without limit, we should see them like our gardens and plantations, needing care and maintenance to ensure they are grow and are healthy, and can continue to sustain us.

 

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