Small-Scale Habitat Structure Modulates the Effects of No-Take Marine Reserves for Coral Reef Macroinvertebrates

Pascal Dumas,Mehdi Adjeroud,Haizea Jimenez,Christophe Peignon,Laurent Wantiez,Fabiano Thompson

doi:10.1371/journal.pone.0058998

Abstract

No-take marine reserves are one of the oldest and most versatile tools used across the Pacific for the conservation of reef resources, in particular for invertebrates traditionally targeted by local fishers. Assessing their actual efficiency is still a challenge in complex ecosystems such as coral reefs, where reserve effects are likely to be obscured by high levels of environmental variability. The goal of this study was to investigate the potential interference of small-scale habitat structure on the efficiency of reserves. The spatial distribution of widely harvested macroinvertebrates was surveyed in a large set of protected vs. unprotected stations from eleven reefs located in New Caledonia. Abundance, density and individual size data were collected along random, small-scale (20×1 m) transects. Fine habitat typology was derived with a quantitative photographic method using 17 local habitat variables. Marine reserves substantially augmented the local density, size structure and biomass of the target species. Density of Trochus niloticus and Tridacna maxima doubled globally inside the reserve network; average size was greater by 10 to 20% for T. niloticus. We demonstrated that the apparent success of protection could be obscured by marked variations in population structure occurring over short distances, resulting from small-scale heterogeneity in the reef habitat. The efficiency of reserves appeared to be modulated by the availability of suitable habitats at the decimetric scale (“microhabitats”) for the considered sessile/low-mobile macroinvertebrate species. Incorporating microhabitat distribution could significantly enhance the efficiency of habitat surrogacy, a valuable approach in the case of conservation targets focusing on endangered or emblematic macroinvertebrate or relatively sedentary fish species

Highlights

While coral reefs provide a wide array of environmental and economic services, concerns about their sustainability have dramatically increased over recent decades [1,2]
Study area In New Caledonia, reef and lagoon formations together cover an area of approximately 22 200 km2, encompassing a significant level of biodiversity based on a large variety of benthic habitats [18]
The ecologically closely-related trochus species Trochus niloticus and Tectus pyramis had a similar range of density and were widely distributed across the study area

Summary

Introduction

While coral reefs provide a wide array of environmental and economic services, concerns about their sustainability have dramatically increased over recent decades [1,2]. As a main consequence of overfishing, populations of many subsistence or commercial fish/invertebrate species are seriously collapsing, creating local risks for food security throughout the IndoPacific [4]. In this context, there is an urgent need to promote relevant management solutions to reverse these alarming trends. Little work has focused on invertebrates, especially in tropical areas. Despite their importance for the coastal fisheries of most Pacific insular countries, very few quantitative studies have investigated the ecological responses of traditionally harvested macroinvertebrates to protection [11]

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Conclusion