Gelatinous zooplankton off the Argentinean continental shelf: winter distribution, estimated biomass and significance for pelagic community

SCHIARITI, A.; GIBERTO, D.A.; MIANZAN, H. W.

Hiroshima, Japon

Congreso; 4th International Zooplankton Production Symposium. Human and Climate Forcing of Zooplankton Populations; 2007

Beyond their seasonal fluctuations in abundance, jellies seem to be increasing their numbers on the ocean ecosystems. There are, nevertheless, few historical data to support that perception. Furthermore, their contribution to the production of pelagic environments remains uncertain. Distribution, abundance and biomass of jellyfish were studied using 152 samples (MWT net) off the Argentinean Continental Shelf (39-50ºS; 61-34ºW) in winter of 1988. Multivariate analyses were applied to investigate gelatinous zooplankton community structure and their relationship with water masses. We found 11 species of gelatinous zooplankton. Their distribution patterns were related to the distribution of water masses. The most abundant species were Pegea confederata and Calycopsis sp. (0.002 ind./m3). Jellyfish biomass was dominated by Periphylla periphylla reaching 39% (13.9 mg/m3) of the wet weight (ww), 38.7% (0.5 mg/m3) of the dried weight (dw) and 33.6% (0.01 mg/m3) of the organic Carbon content (org. C). Biomass of the pelagic community was dominated by jellyfish reaching the 66.3% of the ww (35.5 mg/m3). In terms of dw and org. C, however, the pelagic environment was dominated by non-gelatinous species which represented 75.8% of the dw (3.8 mg/m3) and 97.9% of the org. C (1.8 mg/m3). These results suggest that gelatinous zooplankton could play an important role in the pelagic ecosystem as carnivorous or filtering species. However, in winter of 1988, they would not have contributed significantly to the pelagic standing stock. The historical data presented in this work would constitute a baseline for testing possible increases in jellyfish abundance.