JPR Advance Access originally published online on June 17, 2009
Journal of Plankton Research 2009 31(9):1045-1058; doi:10.1093/plankt/fbp049
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Testing the relationship between primary production and Acartia tonsa grazing pressure in an estuarine lagoon
1 Sección Oceanología, Universidad de la República, Uruguay 2 Sección Limnología, Dpto. Ecología, Facultad de Ciencias, Universidad de la República, Uruguay
* CORRESPONDING AUTHOR: dcalliar{at}fcien.edu.uy
Received on February 23, 2009; accepted on May 27, 2009
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Abstract |
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Flow of carbon to large consumers in marine environments is mediated by copepods. Globally, copepod grazing removes a small fraction of pelagic primary production, and that fraction decreases from oligotrophic to productive ecosystems. Such a pattern should result from mechanisms whose validity has not been explicitly tested. We analysed the relationship between primary production and copepod herbivory pressure (HP) in a subtropical lagoon under the hypothesis that HP is higher during periods of low, compared to periods of high productivity. On 18 occasions during 2 years, we estimated primary production as 14C incorporation, and herbivorous grazing (as gut fluorescence) and egg production rates for the dominant zooplankter Acartia tonsa. Primary production varied between 18 and 407 mg C m–2 day–1; A. tonsa HP was low (max. of ca. 5% or 18%, depending on assumptions) and followed a non-linear negative pattern with primary production consistent with expectations. The herbivorous fraction of A. tonsa diet was usually <50%, suggesting strong trophic links with microbial processes. Despite sustained high fecundity (11–83 eggs female–1 day–1), population density of A. tonsa was moderate or low, which contributed to low HP. Top-down control on copepods, also suggested by earlier studies in this ecosystem, may be one factor constraining fluxes via the herbivory pathway.
Corresponding editor: Roger Harris