Small Marine Protected Areas in Fiji Provide Refuge for Reef Fish Assemblages, Feeding Groups, and Corals

Abstract

The establishment of no-take marine protected areas (MPAs) on coral reefs is a common management strategy for conserving the diversity, abundance, and biomass of reef organisms. Generally, well-managed and enforced MPAs can increase or maintain the diversity and function of the enclosed coral reef, with some of the benefits extending to adjacent non-protected reefs. A fundamental question in coral reef conservation is whether these benefits arise within small MPAs (<1 km2), because larval input of reef organisms is largely decoupled from local adult reproduction. We examined the structure of fish assemblages, composition of fish feeding groups, benthic cover, and key ecosystem processes (grazing, macroalgal browsing, and coral replenishment) in three small (0.5-0.8 km2) no-take MPAs and adjacent areas where fisheries are allowed (non-MPAs) on coral reefs in Fiji. The MPAs exhibited greater species richness, density, and biomass of fishes than non-MPAs. Furthermore, MPAs contained a greater abundance and biomass of grazing herbivores and piscivores as well as a greater abundance of cleaners than fished areas. We also found differences in fish associations when foraging, with feeding groups being generally more diverse and having greater biomass within MPAs than adjacent non-MPAs. Grazing by parrotfishes was 3-6 times greater, and macroalgal browsing was 3-5 times greater in MPAs than in non-MPAs. On average, MPAs had 260-280% as much coral cover and only 5-25% as much macroalgal cover as their paired non-MPA sites. Finally, two of the three MPAs had three-fold more coral recruits than adjacent non-MPAs. The results of this study indicate that small MPAs benefit not only populations of reef fishes, but also enhance ecosystem processes that are critical to reef resilience within the MPAs.

Fig 1. Study sites.

Marine protected areas (red) and adjacent areas, where fisheries are allowed (green), at three village sites (Votua, Vatu-o-lalai, Namada) along Fiji’s Coral Coast.

Fig 2. Herbivorous fishes.

Box plot for fish density and biomass (120 m^-2) of four categories of herbivorous fishes (browsers, grazers, excavating parrotfishes, and scraping parrotfishes) in MPAs and adjacent non-MPAs at three village sites (Votua, Vatu-o-lalai, and Namada) along the Coral Coast of Fiji. * signals the comparisons in which the 95% credible interval indicates a significant effect of protection status.

Fig 3. Non-herbivorous fishes.

Density and biomass (120 m^-2) of five categories of Non-herbivores. Study sites and symbols as in Fig 2.

Fig 4. Grazing by parrotfishes.

Rates of substratum grazing by parrotfishes (% grazed area d^-1, mean ± SE) in MPAs and adjacent non-MPAs at three village sites (Votua, Vatu-o-lalai, and Namada) along the Coral Coast of Fiji. * and ** indicate paired bars with significant (p < 0.05) or highly significant (p < 0.001) differences, respectively. Note the different scales of the y-axes.

Fig 5. Macroalgal browsing.

Rates of macroalgal removal by herbivores (% of algae consumed in 5 h, mean ± SE). Study sites and symbols as in Fig 2.

Fig 6. Benthic cover.

Percentage cover (mean ± SE) of four categories of benthos (scleractinian corals, macroalgae, eplithic algal matrix and others) in MPAs and adjacent non-MPAs, at three village sites (Votua, Vatu-o-lalai, Namada) along Fiji’s Coral Coast. * and ** indicate, respectively, paired bars that differ significantly (p < 0.05) and highly significantly (p < 0.001).

Fig 7. Coral recruits.

Density (mean ± SE) of coral recruits m^-2 of plot area (see text for details). Study sites and symbols as in Fig 2.