Decadal change in zooplankton seasonal succession in the Bahía Blanca estuary, Argentina, following introduction of two zooplankton species

Abstract

Seasonal zooplankton succession (mainly of the mesozooplankton) in the inner zone of Bahı ́a Blanca estuary during the period 1990–1991 was compared to that from the period 1979–1980 in order to detect changes having taken place in 10 years. Taxonomic composition, zooplankton abundance, species occurrence and temperature–salinity conditions were studied within the two annual cycles. This estuarine ecosystem has been deeply affected by a population increase and by the rapid growth of industrial activity and maritime traffic over the last two decades. Several changes in the zooplankton assemblage composition and structure were detected, probably due to temperature– salinity gradient patterns, which showed discernible differences. Dominance, during winter–spring, of two new invading species, namely, the cirriped Balanus glandula and the copepod Eurytemora americana, causing a decrease in the autochthonous key copepod Acartia tonsa, was one of the principal features of the period 1990–1991. Seasonal changes in diversity and species richness, as well as differences in the multivariate general pattern of the zooplankton community structure with a consequent decrease in the community stability during the second period, were also observed.