Spatial and temporal scales of environmental forcing of Acartia populations (Copepoda: Calanoida) in the Canal de Mira (Ria de Aveiro, Portugal)†

Abstract Zooplankton and hydrological data were collected from August 2000 and June 2002 at six stations distributed throughout Canal de Mira (Ria de Aveiro, Portugal). The abundance of Acartia clausi and Acartia tonsa adults and juveniles of Acartia spp. for each station and month were combined in a three-way data matrix, which was decomposed into three two-way matrices corresponding to different modes: biological, time, and space. Cluster analysis applied on the space mode revealed the existence of three different zones as a consequence of zooplankton composition. At each mode, principal component analysis showed strong seasonal variations in zones 1 and 2. A different spatial pattern was found between the periods November 2000–April 2001 and November 2001–April 2002, with the displacement of the highest abundance levels from the middle estuary to near the mouth. The congeneric populations were segregated in space: the A. clausi population was restricted to downstream stations (zone 1), whereas the A. tonsa population dominated the middle estuary. Significant correlations between hydrological parameters and copepod abundance were found to differ from zone to zone. The statistical methodology was a valuable tool to (i) discriminate spatial and seasonal distribution patterns, (ii) define estuarine sections based on the faunistic composition, and (iii) evaluate delayed effects of phytoplankton.