Influence of climate change and other impacts on rocky intertidal communities of the Azores

Abstract

Biodiversity is under increasing pressure from human activities driving global environmental change. Global climate driven change interacts with regional (e.g. eutrophication) and local scale impacts (e.g. overexploitation). Long-term and broad scale data are required to distinguish human-induced changes from natural fluctuations. The aim of this thesis was to explore the responses of intertidal ecosystems to climate change and other impacts, using the Azores as a model system, by describing patterns and experimentally testing processes. Relevant long-term environmental data on surface air and sea temperature testing processes. Relevant long-term environmental data on surface air and sea temperature plus wave action were collected. Baseline data collected in the 1980s was compared to the 2010s. Descriptive studies examined the patterns at the individual and community level providing evidence of long-term changes in response to greater stress due to changing environmental conditions. At the individual level, changes in phenology of two Azorean species of limpets (Patella aspera and Patella candei gomesii) were assessed over time (1980s versus 2010s) and space across the Archipelago. Evidence of temporal and spatial changes were found in the reproductive cycle of the limpets; these can probably be related with climate change and spatial gradients in environmental conditions across the Archipelago. At the community level, long-term changes in distribution of key intertidal species were assessed. Changes were found not only in the abundance but also in the vertical distribution of the species. Some of these may be ascribed to recent climate change, whereas other may be better explained by the overexploitation of keystone limpet grazers. Finally, community response to the loss of a key intertidal northern species (Fucus spiralis) was experimentally simulated. Fucus spiralis showed fast recovery rates and, unlike expected, its loss had minimal effect on the associated assemblages. Overall, results indicate that there have been some significant changes on the Azorean rocky shores. These included changes in the phenology, abundance and distribution of species. My results suggest F. spiralis in the Azores is not a key species as found elsewhere; so its potential loss may have little to no impact on the remainder of the community. My research highlights the key role of enforced marine reserves in distinguishing between the long-term effects of changes in climate from other anthropogenic activities such as fishing. Whilst there was some evidence of climate driven change, it is likely that human overexploitation of limpets has a greater effect.

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