By Sangeeta Mangubhai
[This is the sixth and final blog in a series 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]
After 10 days at sea, traveling over 500km and completing 26 dives, I have solid data on the scale and intensity of damage to the Vatu-i-Ra Seascape from Cyclone Winston – a tropical storm 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.
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. Both windward and leeward reefs sustained equal damage and there really was no easy way to predict which reefs would be damaged and which ones would remain unscathed.
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 30 meters 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 showed signs of coral bleaching of up to 20 percent caused by thermal stress from the El Nino cycle we are in. Post-cyclone, the temperature has dropped a couple of degrees and now ranges 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 saw large schools of barracuda, big-eye trevally, fusiliers, surgeonfish, and colourful anthias.
So what’s next for Fiji’s reefs?
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 little about the timing of spawning in Fiji and what factors result in good pulses of recruitment onto reefs.
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 that our reefs have had 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 grow, remain healthy, and can continue to sustain us.
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: