Marine Reserves Promote Coral Reef Resilience by Mitigating Human Impacts Through the Restoration of Parrotfish Populations, Increasing Their Reproductive Output and Seeding Neighboring Overfished Reefs

Abstract

Coral reefs are some of the most productive ecosystems on the planet, providing fisheries resources for over a billion people with billions of dollars in revenue from tourism for developing nations. Coral reefs are under threat from overfishing and water pollution, resulting in less productive algae dominated reefs. Marine reserves are widely expected to promote the resilience of reefs by protecting and increasing the abundance of herbivorous fishes that can graze on algae, therefore directly or indirectly preventing coral to algal phase shifts. However, the ability of marine reserves to mitigate human impacts, restore herbivorous fish populations and seed nearby reefs is still poorly known. The study location was within the central Philippines wherein 58 reefs (30 marine reserves and 28 sites open to fishing) were surveyed and sampled. This study examined the relationships between anthropogenic stressors and reef health through regression analyses, determined shifts in sizes of reproductive female parrotfishes and how this restores reproductive output and utilized genetic techniques in detecting migration patterns. Results revealed that marine reserves were able to prevent the proliferation of algae and loss of coral in the face of increasing anthropogenic impacts, while the increase in parrotfish biomass within reserves was implicated in these benefits. Additionally reproductive female size and abundance increased within reserve boundaries compared to fished areas resulting in an exponential increase in egg production with increasing years of protection. Genetic analyses identified several related pairs of parrotfishes sampled at over 400kms apart, while migration analyses supported a north to south dispersal of immigrants. When coupled with ocean currents, reefs within the Sibuyan Sea or further north were highlighted as potential sources for reefs to the south in the Bohol Sea and Sulu Sea. These results are potentially encouraging for managers within the Philippines, indicating that marine reserves can promote the resiliency of coral reefs by preventing algal proliferation and promote coral growth. Additionally these reserves can restore the reproductive potential of ecologically important herbivorous fishes (i.e. parrotfishes) and seed nearby reefs