Estimation of copepod trophic niche in the field using amino acids and marker pigments

Abstract

In this study, marker pigments analysed in incubation feeding experiments and monthly amino acid composition (AAC, weight percentage of total amino acids yields) of copepods collected over 1 yr from the field were used to estimate the food niche of 4 co-occurring copepod species: Acar- tia clausi, Oithona nana, Temora longicornis and Euterpina acutifrons. Both marker pigments and AAC of copepods are good indicators of copepod food niche. Marker pigments are indicators of the autotrophic food ingested by copepods and AAC is an indicator of both autotrophic and non- autotrophic food needed by copepods to maximise reproductive success. Marker pigments showed that copepod species fed selectively on the phytoplankton community and that copepod species had different diets. A. clausi fed mainly on chlorophytes and diatoms, E. acutifrons on diatoms and chloro- phytes, T. longicornis on dinoflagellates and diatoms, and O. nana on dinoflagellates and prymnesio- phytes. Each copepod species had its own specific AAC and, furthermore, there was a significant relationship between similarity in AAC among copepod species and similarity in the phytoplankton classes ingested by them, indicating that the differences in the AAC among copepod species were due to different food resources. As a higher copepod reproductive success is observed when the AAC of the food is more similar to the AAC of the copepods, this selective feeding behaviour could be due to the necessity of a diet with an AAC balanced in an optimal proportion. The food niche partitioning observed in this study might contribute to the coexistence of these copepod species in their habitat.