Predicting River Macroinvertebrate Communities Distributional Shifts under Future Global Change Scenarios in the Spanish Mediterranean Area

Several studies on global change over the next century predict increases in mean air tem-peratures of between 1 degrees C to 5 degrees C that would affect not only water temperature but also river flow. Climate is the predominant environmental driver of thermal and flow regimes of fresh-water ecosystems, determining survival, growth, metabolism, phenology and behaviour as well as biotic interactions of aquatic fauna. Thus, these changes would also have consequences for species phenology, their distribution range, and the composition and dynamics of communities. These effects are expected to be especially severe in the Mediterranean basin due its particular climate conditions, seriously threatening Southern European ecosys-tems. In addition, species with restricted distributions and narrow ecological requirements, such as those living in the headwaters of rivers, will be severely affected. The study area corresponds to the Spanish Mediterranean and Balearic Islands, delimited by the Koppen climate boundary. With the application of the MEDPACS (MEDiterranean Pre-diction And Classification System) predictive approach, the macroinvertebrate community was pre-dicted for current conditions and compared with three posible scenarios of watertempera-ture increase and its associated water flow reductions. The results indicate that the aquatic macroinvertebrate communities will undergo a drastic impact, with reductions in taxa richness for each scenario in relation to simulated current conditions, accompanied by changes in the taxa distribution pattern. Accordingly, the distribution area of most of the taxa (65.96%) inhabiting the mid-high elevations would contract and rise in altitude. Thus, fami-lies containing a great number of generalist species will move upstream to colonize new zones with lower water temperatures. By contrast, more vulnerable taxa will undergo reduc-tions in their distribution area.