Ecological Impacts of the North Atlantic Oscillation (NAO) in Mediterranean Ecosystems

Large-scale climate indices have received much attention in recent years in ecology-climate research due to the advantages they have over typically used local weather variables, such as temperature or rainfall. In the Mediterranean, the North Atlantic Oscillation (NAO) is a major forcing of climate patterns, especially precipitation. More than 60 studies to date have demonstrated the effects of the NAO on both terrestrial and aquatic Mediterranean ecosystems. In terrestrial ecosystems, the NAO affects the phenology and growth of plants and crop yields. It also affects the condition and diet of mammals and disease-related mortality in amphibians. The effects of the NAO are probably better known in marine ecosystems, where the impact on the hydrodynamics of the water column and currents is felt in the dynamics of populations from plankton to fishes in both pelagic and benthonic environments. Additionally, birds are an especially well studied taxon when it comes to effects of the NAO. The NAO has been shown to affect the population dynamics of water birds by impacting the availability and extent of their habitat and by influencing dispersal decisions of individuals. The NAO plays an essential role in the migration of birds throughout the Mediterranean basin, and it is probably a reason for the observed advance of arrival dates during the spring in Europe. In spite of the notable number of studies carried out to date, we are far from knowing accurately the ecological impacts of the NAO on Mediterranean ecosystems. More efforts are needed to understand regional differences in the NAO effects within the Mediterranean basin and how they compare with more northern latitudes of Europe.