Are marine protected areas useful for the recovery of the Mediterranean mussel populations?

Rius, Marc and Zabala, Mikel (2008) Are marine protected areas useful for the recovery of the Mediterranean mussel populations? Aquatic Conservation Marine and Freshwater Ecosystems, 18 (5), 527-540. (doi:10.1002/aqc.887).

Abstract

1. Mussel beds are important intertidal communities in the Mediterranean Sea and have traditionally been exploited by humans.

2. Marine protected areas are management tools for recovering over-fished populations, normally top predator populations, which may in turn undermine prey abundance. Therefore, mussel populations might not recover inside protected areas, as they are affected by increasing fish populations.

3. To study the effects of both human and fish predation on mussels, three locations were selected: the Reserve (R), where all types of exploitation were banned and fish were abundant; the Partial Reserve (PR), where only angling was permitted, and fish abundance was low; and the Non-Reserve (NR), where no protection existed and fish were rare.

4. Data from mussel bed surveys indicate that recruitment is critical to sustain mussel populations, and similar size structures were found at all three locations. However, the overall biomass in the PR was nearly double that in both R and NR, suggesting disturbance of some sort at these latter two sites.

5. A tethering experiment showed that fish predation greatly affected mussels in R, while the analysis of harvester collections from the NR showed that the most harvested size classes were those least abundant in the mussel bed.

6. Both protected and non-protected areas are unable to increase mussel populations due to trophic cascade effects, while partial reserves, where fish populations are exploited and mussels protected, are areas where the Mediterranean mussel populations can recover.

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