Seasonal succession of zooplankton in coastal waters of the Argentine Sea (Southwest Atlantic Ocean): prevalence of classical or microbial food webs

Abstract

The demographic characteristics of marine zooplankton make it especially suitable for examining the variability of marine ecosystems. The zooplankton annual succession was studied at a permanent coastal station in the Argentine Sea (38°28′S, 57°41′W) in relation to physical conditions and phytoplankton size fractions. Small copepods (<1 mm total length), mainly represented by Oithona nana (Cyclopoida) and adults and copepodites of Calanoida, numerically dominated the metazooplankton throughout the year. In summer, small copepods also exceeded large copepods in biomass. Larvaceans (mostly <1 mm total length) were the second most important metazooplankton group, with strong dominance of Oikopleura dioica. The zooplankton succession exhibited two main periods throughout the year: (1) a cold winter–spring period characterized by a dominant classical herbivore food web in which the large copepod Calanoides carinatus and lamellibranch larvae were associated with the lowest temperatures and highest Chl-a and microphytoplankton, and (2) a warm summer period dominated by a microbial food web in which microbial filter-feeders such as Oithona nana, Paracalanus spp., Oikopleura dioica and Penilia avirostris predominated and the highest density of picophytoplankton and lowest concentrations of Chl-a were recorded. The implications of the present findings for the growth and survival of fish larvae distributed in the study area are discussed.

Keywords:

• mesozooplankton succession
• small copepods
• larvaceans
• phytoplankton fractions
• EPEA station
• Argentine Sea
• Southwest Atlantic Ocean

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

The Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP) provided financial support for sample collection. A part of the equipment used in this work was financed by grants from the Agencia Nacional de Promoción Científica y Tecnológica (PICT 15227/03) and Universidad Nacional de Mar del Plata (15/E393) to MDV and a grant from the Universidad de Buenos Aires (UBACyT X413) to FLC. We are grateful to the captain and crew of the RV Capitán Cánepa for the shipboard assistance. We also thank Vivian Lutz and Daniel Cucchi Colleoni for providing data on Chl-a and Marina Marrari for English editing. Two anonymous reviewers provided very constructive comments that substantially improved an earlier version of the manuscript. This is INIDEP contribution No. 1760.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark