Long-term and seasonal zooplankton dynamics in the northwest Iberian shelf and its relationship with meteo-climatic and hydrographic variability

Long-term and seasonal dynamics of zooplankton abundance and taxonomic composition and its relationship meteo-climatic and hydrographic factors were investigated on the northwest Iberian shelf. Zooplankton were collected (1995–2011) at two locations within and off the Rı´a of Vigo (Station 1 and Station 3, respectively). abundance of zooplankton (NZT) varied annually following on average a unimodal cycle, with peak values late spring and early autumn. In the long term, the time series of NZT exhibited three contrasting periods: ) 1995–2001, characterized by low abundance and low amplitude seasonality, with a stepped increase towards 2001; B) 2001–2006, of high abundance and marked seasonality enclosing the maximum values of the time series; C) 2006–2010, of intermediate abundance and amplitude of the seasonal cycle. The most common taxonomic showed similar long-term and seasonal patterns. Principal component analysis revealed a shift in zooplankton from 2001 onwards, which affected annual averages and seasonality of all taxa. The observed changes in dynamics were concomitant with sustained trends for upwelling intensity (increasing), precipitation (decreasing) Gulf Stream North Wall position (equatorward) between 2000 and 2005. The results stress the importance hydrodynamics, driven by meteo-climatic conditions, in the control of the abundance levels of zooplankton at and long-term interannual scales.