Zooplankton structure and succession at the EPEA coastal station (northern Argentina):Dominance of the smaller size fractions

VIÑAS, M.D. ; NEGRI, R.; SILVA, R.; CAPITANIO, F; DAPONTE, M.C; HERNÁNDEZ, D

Pucon

Congreso; 5 th zooplankton production symposium; 2011

The community structure and seasonal succession of zooplankton was studied at the EPEA (Estación Permanente de Estudios Ambientales) coastal station (38°28´S 57°41´W) during an annual cycle (March 2000-April 2001). Monthly samples were obtained with a small bongo net (mesh size 67 μm). Small copepods (< 1mm total length), represented mostly by Oithona nana and members of Paracalanus-Ctenocalanus, dominated the mesozooplankton throughout the study year, outnumbering larger copepods by two orders of magnitude. In summer, small copepods were also dominant in terms of biomass. Highest densities of large copepods (>1 mm total length) Calanoides carinatus and Ctenocalanus vanus were observed mostly in winter and early spring. Oikopleura dioica and Penilia avirostris were the dominant appendicularian and cladoceran species respectively. They exhibited increased densities in summer. Noctiluca scintillans was strongly dominant during spring and early summer whereas Sagitta friderici showed increased densities in fall and summer. Lamellibranch larvae peaked during winter and early spring, coinciding with the reproductive cycle of the adults. Zooplankton community succession exhibited two clearly different periods throughout the year: 1) a cold winter-spring period characterized by a classical, largely herbivorous food web, in which large copepods C. carinatus, C. vanus and lamellibranch larvae were associated with lowest temperatures and highest densities of Chl-a and microphytoplankton, and 2) a warm spring-summer period dominated by small copepods and microbial filter-feeders like O. dioica and P. avirostris, and characterized by highest density of picoplankton and lowest concentration of Chl-a. The potential implications of the zooplankton seasonal succession for higher trophic levels are discussed.Monthly samples were obtained with a small bongo net (mesh size 67 μm). Small copepods (< 1mm total length), represented mostly by Oithona nana and members of Paracalanus-Ctenocalanus, dominated the mesozooplankton throughout the study year, outnumbering larger copepods by two orders of magnitude. In summer, small copepods were also dominant in terms of biomass. Highest densities of large copepods (>1 mm total length) Calanoides carinatus and Ctenocalanus vanus were observed mostly in winter and early spring. Oikopleura dioica and Penilia avirostris were the dominant appendicularian and cladoceran species respectively. They exhibited increased densities in summer. Noctiluca scintillans was strongly dominant during spring and early summer whereas Sagitta friderici showed increased densities in fall and summer. Lamellibranch larvae peaked during winter and early spring, coinciding with the reproductive cycle of the adults. Zooplankton community succession exhibited two clearly different periods throughout the year: 1) a cold winter-spring period characterized by a classical, largely herbivorous food web, in which large copepods C. carinatus, C. vanus and lamellibranch larvae were associated with lowest temperatures and highest densities of Chl-a and microphytoplankton, and 2) a warm spring-summer period dominated by small copepods and microbial filter-feeders like O. dioica and P. avirostris, and characterized by highest density of picoplankton and lowest concentration of Chl-a. The potential implications of the zooplankton seasonal succession for higher trophic levels are discussed.