Does Herbivorous Fish Protection Really Improve Coral Reef Resilience? A Case Study from New Caledonia (South Pacific)

Laure Carassou,Michel Kulbicki,Marc Léopold,Laurent Wantiez,Nicolas Guillemot,Richard Kf Unsworth

doi:10.1371/journal.pone.0060564

Abstract

Parts of coral reefs from New Caledonia (South Pacific) were registered at the UNESCO World Heritage list in 2008. Management strategies aiming at preserving the exceptional ecological value of these reefs in the context of climate change are currently being considered. This study evaluates the appropriateness of an exclusive fishing ban of herbivorous fish as a strategy to enhance coral reef resilience to hurricanes and bleaching in the UNESCO-registered areas of New Caledonia. A two-phase approach was developed: 1) coral, macroalgal, and herbivorous fish communities were examined in four biotopes from 14 reefs submitted to different fishing pressures in New Caledonia, and 2) results from these analyses were challenged in the context of a global synthesis of the relationship between herbivorous fish protection, coral recovery and relative macroalgal development after hurricanes and bleaching. Analyses of New Caledonia data indicated that 1) current fishing pressure only slightly affected herbivorous fish communities in the country, and 2) coral and macroalgal covers remained unrelated, and macroalgal cover was not related to the biomass, density or diversity of macroalgae feeders, whatever the biotope or level of fishing pressure considered. At a global scale, we found no relationship between reef protection status, coral recovery and relative macroalgal development after major climatic events. These results suggest that an exclusive protection of herbivorous fish in New Caledonia is unlikely to improve coral reef resilience to large-scale climatic disturbances, especially in the lightly fished UNESCO-registered areas. More efforts towards the survey and regulation of major chronic stress factors such as mining are rather recommended. In the most heavily fished areas of the country, carnivorous fish and large targeted herbivores may however be monitored as part of a precautionary approach.

Highlights

Coral reefs are one of the ecosystems the most susceptible to climate change [1,2]
A total of 111 species of herbivorous fish were observed in the 14 sites surveyed in New Caledonia (Fig. 1; Appendix S1a)
Besides a high social cost in a region where small-scale fishing represents an important matter for both rural and urban populations, an exclusive protection of all herbivorous fish species in New Caledonia would not be capable of mitigating climate change effects on coral reefs

Summary

Introduction

This is due to 1) the high sensitivity of reef-building corals to rising water temperature, leading to bleaching events, and 2) their tropical distribution that makes them susceptible to physical destruction by hurricanes [3,4] These climate-induced disturbances, combined with other stress factors such as fishing [5,6], predator outbreaks [7,8], diseases [9,10], or pollution [11,12] have resulted in a significant decline of coral reefs worldwide during the last decades [3,13]. Management strategies that may improve the resilience of coral reefs to climate change, in particular by mitigating the appearance and persistence of coralmacroalgae phase-shifts, and by facilitating the recovery of corals after natural disasters (e.g., bleaching events, hurricanes), are required

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Results

Discussion

Conclusion