Abstract
Laboratory feeding experiments were conducted to study the functional response and prey size spectrum of the young naupliar stages of the calanoid copepod Paracartia grani Sars. Experiments were conducted on a range of microalgal prey of varying sizes and motility patterns. Significant feeding was found in all prey of a size range of 4.5–19.8 μm, with Holling type III functional responses observed for most prey types. The highest clearance rates occurred when nauplii fed on the dinoflagellate Heterocapsa sp. and the diatom Thalassiosira weissflogii (respectively, 0.61 and 0.70 mL ind-1 d-1), suggesting an optimal prey:predator ratio of 0.09. Additional experiments were conducted to examine the effects of the presence of alternative prey (either Heterocapsa sp. or Gymnodinium litoralis) on the functional response to the haptophyte Isochrysis galbana. In the bialgal mixtures, clearance and ingestion rates of I. galbana along the range of the functional response were significantly reduced as a result of selectivity towards the larger, alternative prey. Paradoxically, relatively large prey trigger a perception response in the nauplii, but most likely such prey cannot be completely ingested and a certain degree of sloppy feeding may occur. Our results are further evidence of the complex prey-specific feeding interactions that are likely to occur in natural assemblages with several available prey types.
Highlights
Zooplankton grazing is a key process in pelagic ecosystem functioning as a driver and modulator of the vertical particle flux in the water column [1], [2]
Maximum clearance rates reached the highest values when feeding on T. weissflogii and Heterocapsa sp., and showed the lowest values for I. galbana
When expressed in terms of carbon and nitrogen weight-specific rates, the maximum daily rations by P. grani nauplii were highest when feeding on the dinoflagellates G. litoralis (274% body C d-1 and 291% body N d-1) and Heterocapsa sp. (270% body C d-1 and 224% body N d-1), followed by T. weissflogii (136% body C d-1 and 94% body N d-1), I. galbana (115% body C d-1 and 64% body N d-1), and lowest for R. salina (74% body C d-1 and 53% body N d-1)
Summary
Zooplankton grazing is a key process in pelagic ecosystem functioning as a driver and modulator of the vertical particle flux in the water column [1], [2]. Small planktonic copepods are likely the most abundant metazoans on Earth, and have an important role as grazers and as a source of prey for fish and their larvae in coastal as well as pelagic ecosystems (reviewed by Turner [3]). Aspects of their feeding ecology, including behaviour and the quantification of feeding rates, draw much scientific interest. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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