Impacts of copepods on marine seston and resulting effects on Calanus finmarchicus RNA: DNA ratios in mesocosm experiments.

Becker, C., Brepohl, Daniela C., Feuchtmayr, H., Zöllner, Eckart, Sommer, Frank, Clemmesen, Catriona , Sommer, Ulrich and Boersma, Maarten (2005) Impacts of copepods on marine seston and resulting effects on Calanus finmarchicus RNA: DNA ratios in mesocosm experiments. Marine Biology, 146 . pp. 531-541. DOI 10.1007/s00227-004-1459-7.

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We investigated the impact of copepods on the seston community in a mesocosm set-up, and assessed how the changes in food quantity, quality and size affected the condition of the grazers, by measuring the RNA:DNA ratios in different developmental stages of Calanus finmarchicus. Manipulated copepod densities did not affect the particulate carbon concentration in the mesocosms. On the other hand, chlorophyll a content increased with higher copepod densities, and increasing densities had a positive effect on seston food quality in the mesocosms, measured as C:N ratios and ω3:ω6 fatty acid ratios. These food quality indicators were significantly correlated to the nutritional status of C. finmarchicus. In contrast to our expectations, these results suggest a lower copepod growth potential on higher quality food. However, in concordance with earlier studies, we found that when copepods were in high densities the large particles (>1000 µm3) decreased and that the smaller particles (<1000 µm3) increased in number. These patterns were closely linked to the condition of C. finmarchicus, which were of better condition (RNA:DNA ratios) with increasing biovolumes of large particles, and, conversely, lower RNA:DNA ratios with increasing biovolumes of smaller particles. Consequentially, the selective grazing by copepods stimulated increased biovolumes of smaller plankton, and this increase was responsible for the increased food quality, in terms of C:N and ω3:ω6 ratios. Thus, we conclude that the decreasing growth potentials of C. finmarchicus were a result of a decrease of favourably sized food particles, induced by copepod grazing.

Document Type: Article
Keywords: Food Treatment, Plankton Community, Mesocosm Experiment, Food Quantity, Copepodite Stage
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EV Marine Evolutionary Ecology
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-BI Biological Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1007/s00227-004-1459-7
ISSN: 0025-3162
Date Deposited: 11 Feb 2010 14:22
Last Modified: 03 Jul 2019 08:21

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