Volumen 45 - Número 1: 35-42 | 2010
Article

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Functional response of Sagitta setosa (Chaetognatha) and Mnemiopsis leidyi (Ctenophora) under variable food concentration in the Gullmar fjord, Sweden

Odette Vergara-Soto^1*, Danilo Calliari^2,3, Peter Tiselius³, Rubén Escribano^1,5, M. Lorena González⁴ and Samuel Soto-Mendoza⁶

¹Pelagic Laboratory and Mesozooplankton (PLAMZ) of COPAS Center, Marine Biology Station,Universidad de Concepción, P.O. Box 42, Dichato, Concepción, Chile

²Sección Oceanología, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400, Montevideo, Uruguay

³Sven-Loven Centre for Marine Research-Kristineberg, Marine Ecology Dept., Göteborg University, S-450 34 Fiskebäckskil, Göteborg, Sweden

⁴Program for Regional Studies in Physical Oceanography and Climate (PROFC), Universidad de Concepción, Box 160-C, Concepción, Chile

⁵Center for Oceanographic Research in the Eastern South Pacific (COPAS), Department of Oceanography, Universidad de Concepción, Box 160-C, Concepción, Chile

⁶Laboratorio de Oceanografía Pesquera y Ecología Larval (LOPEL), Departamento de Oceanografía. Universidad de Concepción, Cabina 10, Box 160, Concepción, Chile

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Gelatinous carnivores are important components of the pelagic system and potentially key organisms in trophic webs, since they prey on several groups of organisms. In the Gullmar fjord many species of gelatinous organisms have been found exerting an important predatory impact on Acartia clausi, a dominant copepod of the mesozooplankton in this ecosystem. This work aims at evaluating the predatory impact of M. leydi and S. setosa on the community of copepods of the Gullmar fjord. These experiments were of functional-response type. In addition, length-weight regressions for predator biomass estimates were obtained. S. setosa showed a functional response Type II. By contrast, M. leidyi showed a linear functional response (Type I) with maximum ingestion (Imax) rates of 7 copepods ind^-1 h^-1 for individuals of length size between 7 and 15 mm. Sagitta setosa exhibited an Imax of 3.96 (copepods pred^-1 h^-1) with individuals in the size-range between 6 and 7 mm. The predatory impact of S. setosa and M. leidyi was high, suggesting that these species exert a strong impact on the mesozooplankton community of the Gullmar fjord.

Key words: Functional response, ingestion rate, chaetognath, ctenophore, copepod

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