Mesozooplankton community structure and trophic interactions in the Southern Patagonian Shelf (SW Atlantic, Argentina, 47°-55°S)

SABATINI, M.E.; AKSELMAN, R.; NEGRI, R.; SILVA, R.; SANTINELLI N., ; SASTRE, V.; DAPONTE, C.; ANTACLI, J.C.; LUTZ, V.; SEGURA, V.; RETA, R.; GIL, M.

Pucón

Simposio; 5to Simposio Internacional de Producción de Zooplancton; 2011

Center for Oceanographic Research in the Eastern South Pacific (COPAS), Universidad de Concepción, North Pacific Marine Science Organization (PICES), International Council for the Exploration of the Sea (ICES)

The ecosystem of the Southern Patagonian Shelf is highly productive and includes a variety of commercially important fisheries and large mammal and bird populations. Knowledge of the pelagic food web structure that supports the richness of this system is still developing, but there are broad indications that mesozooplankton occupy a pivotal position as vital prey for fish and consumers of smaller plankton. For the first time, all plankton communities in the size 2 µm to 20 mm were surveyed simultaneously in the region in October 2005. Plankton data and trophic relationships were examined through multivariate statistics. Nanoplankton and microplankton were taxonomically (diatoms, dinoflagellates, ciliates, flagellates) and functionally (autotrophs, heterotrophs) sorted within each size fraction. Copepods largely dominated the > 200 µm fraction. Three mesozooplankton assemblages typical of the inner, middle, and outer shelf were identified. The inner and middle shelf assemblages overlapped slightly but were spatially separated from the outer shelf community. Adults and late copepodids of Drepanopus forcipatus were typical of the inner shelf assemblage. Middle-shelf species included the copepod Ctenocalanus vanus, the amphipod Themisto gaudichaudii and the chaetognath Sagitta tasmanica, while an assortment of taxa characterized the outer sector. Latitudinal patterns in mesozooplankton community composition were less apparent than cross-shelf patterns. No clear pattern of phytoplankton and protozooplankton assemblages was apparent when the whole < 200 µm plankton community structure was considered. In contrast, communities in the optimal size food for copepods (> 10 µm) were slightly different across shelf. Overall, spatial patterns of mesozooplankton and copepod prey communities matched weakly. Significant correlations were found particularly with large autotrophs and heterotrophs.