MEPS 210:13-24 (2001)  -  doi:10.3354/meps210013

Gelatinous zooplankton assemblages associated with water masses in the Humboldt Current System, and potential predatory impact by Bassia bassensis (Siphonophora: Calycophorae)

F. Pagès1,*, H. E. González2, M. Ramón1, M. Sobarzo3, J.-M. Gili1

1Institut de Ciències del Mar (CSIC), Plaça del Mar s/n, 08039 Barcelona, Catalunya, Spain
2Instituto de Biología Marina, Universidad Austral de Chile, Casilla 567, Valdivia, Chile
3Centro EULA-Chile, Universidad de Concepción, Casilla 160-C, Concepción, Chile

ABSTRACT: Large numbers of gelatinous zooplankton were collected off Mejillones Peninsula, Chile (Humboldt Current System) in January 1997 during an oceanographic cruise. The area was characterized by the mixing of 3 water masses and the development of coastal upwelling. Siphonophores were the predominant group at most of the stations and the calycophoran Bassia bassensis was overwhelmingly the most abundant species. Five group associations were distinguishable in relation to the water masses identified. Siphonophores were associated with Subtropical Surface Water, the ctenophore Pleurobrachia sp. with Subantarctic Water, the pelagic tunicate Salpa fusiformis with Equatorial Subsurface Water, an assemblage of all gelatinous groups with mixed waters, and a low occurrence of gelatinous groups with upwelled Equatorial Subsurface Water. Molluscs were the group least associated with any water mass. The potential percentage of small copepods removed by B. bassensis ranged between 2.9 and 69.3%. Our results indicate that B. bassensis was the most important secondary predator in the top 50 m of the water column, and could therefore have had a significant trophic impact on the population of small copepods off the Mejillones Peninsula during the sampling period, where small copepods constituted 80.6% of the total mesozooplankton community. This siphonophore potentially ingested an average of 17.3% of the total copepod biomass.


KEY WORDS: Siphonophores · Ctenophores · Salps · Molluscs · Water masses · Humboldt Current · Bassia · Copepods · Predation


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