The ecological value of fully enforced, no-entry, marine protected areas: A case study of harvested limpets

Harvesting of intertidal gastropods can lead to a direct reduction in the biomass of targeted species through a reduction in the numbers and size of individuals, in turn leading to extensive changes to the structure of intertidal communities.In the Azores, two patellid species co-occur, and both are exploited for human consumption. However, one of these species, Patella aspera (Roding, 1798), is larger and has a greater economic value and is thus favoured in comparison to the smaller Patella candei (d'Orbigny, 1840).This study investigates the effects of human exploitation on the interaction between these two species by comparing their densities and sizes within two areas of a marine protected area (MPA): a no-entry area where human access is strictly prohibited and an adjacent area where human access is allowed and collection still occurs despite it being prohibited.Patella aspera attained similar densities in the two areas, but individuals were much larger within the no-entry MPA. In contrast, P. candei were more abundant in the adjacent area but were of a similar size as in the no-entry MPA. Limpet biomass was much greater within the no-entry MPA. The abundance (% cover) of upright macroalgae and barnacles as well as bare rock were also significantly reduced within the no-entry MPA, where grazer-resistant algal crusts cover was significantly greater.This study highlights the influence of human activities and how these may affect the complex dynamics of biotic interactions with wider community-level cascading effects.