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

Abstract

Long-term and seasonal dynamics of zooplankton abundance and taxonomic composition and its relationship
\nwith meteo-climatic and hydrographic factors were investigated on the northwest Iberian shelf. Zooplankton were collected
\nmonthly (1995–2011) at two locations within and off the Rı´a of Vigo (Station 1 and Station 3, respectively).
\nTotal abundance of zooplankton (NZT) varied annually following on average a unimodal cycle, with peak values
\nbetween late spring and early autumn. In the long term, the time series of NZT exhibited three contrasting periods:
\nA) 1995–2001, characterized by low abundance and low amplitude seasonality, with a stepped increase towards
\n2001; B) 2001–2006, of high abundance and marked seasonality enclosing the maximum values of the time series;
\nand C) 2006–2010, of intermediate abundance and amplitude of the seasonal cycle. The most common taxonomic
\ngroups showed similar long-term and seasonal patterns. Principal component analysis revealed a shift in zooplankton
\ndynamics from 2001 onwards, which affected annual averages and seasonality of all taxa. The observed changes in
\nzooplankton dynamics were concomitant with sustained trends for upwelling intensity (increasing), precipitation (decreasing)
\nand Gulf Stream North Wall position (equatorward) between 2000 and 2005. The results stress the importance
\nof hydrodynamics, driven by meteo-climatic conditions, in the control of the abundance levels of zooplankton at
\nseasonal and long-term interannual scales.