CIESM Workshop 40 Phytoplankton Response to Mediterranean Environmental Change Toxic phytoplankton response to warming in two Mediterranean bays of the Ebro Delta. Margarita Fernández-Tejedor 1 , Maximino Delgado 1,2 , Esther Garcés 2 , Jordi Camp 2 , Jorge Diogène 1 1 IRTA Carretera del Poblenou km 5.5, 43540 Sant Carles de la Ràpita Spain margarita.fernandez@irta.cat 2 Institut de Ciències del Mar, Passeig Marítim de la Barceloneta, 37-49, E-08003 Barcelona ABSTRACT The analysis of the phytoplankton and environmental parameters of the time series in Alfacs and Fangar bays (north western Mediterranean) from 1990 to 2009 shows some trends. There is an increase in the average water column temperature, 0.11, 0.01, 0.80 and 0.23 ºC for spring, summer, fall and winter respectively in Alfacs Bay and 1.76, 0.71, 1.33, 0.89 ºC for spring, summer, fall and winter in Fangar Bay. The trends in phytoplankton populations show a shift in the timing of occurrence of Karlodinium spp. blooms and an increase of the Pseudo-nitzschia spp. abundances. There is a lack of correlation between the average seasonal temperatures and the toxic phytoplankton abundances. INTRODUCTION The linear warming trend of global surface temperature over the 50 years from 1956 to 2005 is 0.13 [0.10 to 0.16] °C per decade, (IPCC, 2007). In the Western Mediterranean, during the same period of time the linear trend is 0.002 - 0.009 ºC per year, 0.025 ºC per year for the period 1973-2005 at the station placed in Estartit in the Catalan coast 1