Zooplankton community modulated by spatial and tidal changes in the Bahía Blanca Estuary, Argentina

The variability of the zooplankton community over a spatial and a tidal scale, the relationship between physico-chemical variables, and the abundance of zooplankton were studied in the temperate and turbid Bahía Blanca Estuary (Southwestern Atlantic, Argentina). Samples were taken by pumps during 12-h tidal cycles, at 3-h intervals, from two depths and three sites across the main channel in the inner and middle estuary zones. The zooplankton was dominated by the copepods Acartia tonsa and Euterpina acutifrons, and larvae of the invasive Pacific oyster Crassostrea gigas. The physico-chemical variables that most influenced the zooplankton community were salinity, temperature, suspended particulate matter, and chlorophyll a Most taxa showed higher abundances in the inner estuary, which corresponds to a turbid and shallow area. The abundance of A. tonsa was higher in the inner estuary while that of E. acutifrons was higher in the middle estuary. This spatial distribution is consistent with the tidal distribution of these species as in the inner estuary the abundance of A. tonsa peaked at ebb tide and that of E. acutifrons peaked at flood tide. Significant differences in the zooplankton community structure both across the channel and between depths were detected by multivariate analyses, but no clear patterns were found in the abundance of each taxon by a species-level analysis. The results provide insight into the patterns of zooplankton distribution and abundance in a temperate, turbid, and human-impacted coastal ecosystem, considering different spatial and short-term scales. These results will be useful to design efficient sampling programmes in highly dynamic environments.