New paper: Biophysical and anthropogenic influences on the status of Tonga’s coral reefs and reef fish fishery

Tonga’s coral reefs are increasingly threatened by both local (e.g. overfishing and pollution), and global (e.g. climate change) impacts. However, there is very little information on the current status of their coral reefs, or what the main threats are, and it is very difficult to manage and conserve an ecosystem for which there is little information. In this recent paper, we present the first national assessment of Tonga’s coral reefs and reef fish fishery using ecological survey data from 375 sites throughout the country. We assessed seven key metrics of reef health and fish resource status: Fish diversity, density and biomass, and live benthic cover of hard coral, soft coral, turfing algae, and crustose coralline algae. We then used a modelling approach called Boosted Regression Trees to assess and describe the relative importance of 11 socio-environmental variables (see previous blog post) on these key metrics of reef condition. Overall, we found clear spatial patterns in the status of Tonga’s coral reefs, with some areas in very poor condition, while others were better. Surprisingly, the places with the lowest live coral cover were not those with the most people, but instead the northern Vava’u archipelago, where live coral cover was on average less than 10%, and in many places 0. We think that this is mainly to do with poor water quality and limited flushing by clean, cool, oceanic water, due to the geography of the islands. Overall, the status of both Tonga’s coral reefs, and reef fish fishery, were healthiest in the middle, Ha’apai island group, where there is plenty of clean water and limited fishing. This study provides critical baseline information for Tonga’s coral reefs that we hope will facilitate ongoing conservation and management efforts.