Long-term changes in seaweed communities of NW Iberiaresults and tools for future studies

Abstract

Macroalgae are main foundation species in temperate coastal rocky shore ecosystems. In recent years, changes in the distribution and abundance of seaweeds hove been detected. These changes hove been attributed to climate change as well as to local stressor that are disturbing marine ecosystems worldwide. The conservation status of marine macroalgae in the NO of Iberia is poorly known. In this thesis, the changes in the abundance of intertidal seaweeds and the potential mechanisms behind these changes were studied. In Chapter 1, changes in the frequency of occupation of 33 common perennial intertidal seaweeds in NW Iberia over the last 15 years were recorded; these changes were compared with time trends in potential environmental drivers. In Chapters II and III, global change lactors such as water warming and a weakening of the Iberian Upwelling system were experimentally investigated as potential drivers of the trend detected in the lield (Chapter I). Finally, in Chapter IV the impact of local activities such as the exploitation of intertidal mussel seed banks on the accompanying non-target sessile community was assessed.