Responses of benthic habitat and fish to severe tropical cyclone Winston in Fiji

Tropical cyclones can dramatically reduce coral cover, coral diversity and structural complexity, which can all cause flow-on effects to fish communities. In 2016, Fiji sustained extensive damage from one of the most severe cyclones recorded in the southern hemisphere (Category 5 cyclone Winston). We assessed the impacts of cyclone Winston on the coral reef habitat and fish assemblages in Kubulau and Levuka districts in Fiji. Wave modelling showed that cyclone-generated waves were substantially larger and persisted longer in Levuka than Kubulau. Damage to live corals was spatially variable and highest in Levuka, with the extent of damage highly correlated to the exposure, height and duration of waves at each site. We recorded increases in macroalgae directly after the cyclone and increases in encrusting coralline algae two years after the cyclone. We did not detect many changes in the fish assemblage caused by cyclone Winston. Obligate corallivores, and species within this group, Chaetodon baronessa and Labrichthys unilineatus, were the only fish to show a decline post-cyclone, most likely caused by declines in coral cover. We found that the modelling of cyclone wave dynamics (wave height, duration and exposure) explained the variation and damage to live corals better than proximity to the cyclone path, providing a useful tool to predict cyclone damage. Future climate models predict that more cyclones will reach the highest intensities. Understanding the impact this will have on vulnerable coastal communities that are dependent on marine resources and are protected from wave energy by reefs is essential for effective mitigation and adaptive management plans.