COMMUNITY STRUCTURE AND DYNAMICS OF THE AZOREAN ROCKY INTERTIDAL: EXPLOITATION OF KEYSTONE SPECIES

Abstract

Experimental work has shown the importance of grazing by patellid limpets in structuring intertidal assemblages. Little is known, however, about the effects of a largescale and chronic removal of limpets. Here I investigate the ecology of Patella candei, a seldom-studied limpet endemic to Macaronesia, and how its long-term fishery impacts the Azorean rocky intertidal. The specific aims of this thesis are to: examine the processes that affect the distribution of limpets in the Azores at a range of spatial scales; investigate the role of grazing by P. candei in structuring the Azorean rocky intertidal and if its harvesting has impacted the dynamics and functioning of this ecosystem. The distribution of limpets was variable at a range of spatial scales. At the scale of islands, inter-island variation in harvesting intensity affected the abundance and size structure of populations of limpets as well as the balance between grazers, algae and barnacles. Stocks of limpets showed clear signs of exploitation and there was evidence that current legislation, including limpet protected zones, have been largely ineffective in protecting these populations. At smaller spatial scales, substratum micro-topography influenced the distribution and sui-vival of limpets. I also showed that the experimental provision of microhabitats could be used as a measure to mitigate the effects of coastal urbanisation, whilst promoting a local enhancement of the stocks of limpets. Overall my results provide evidence for the population and community level effects of limpet harvesting and show that limpet harvesting has a strong impact on the structure and fiinctioning of the Azorean rocky intertidal.