Approaching the black box in zooplankton feeding: Behavior related feeding rates in nauplii of Oithona davisae and Acartia grani

Ingerslev Henriksen & IH Casper

Student thesis: Master thesis

Abstract

It is hypothesized that velocity differences are what is driving all encounter processes in the ocean and therefore the relative velocity differences between a copepod and its prey lead to different ingestion rates. The ability of a copepod to detect a prey is defined by their particular feeding strategy. Thus, a better understanding of the predator and prey motility will give us a tool to predict the predation rates. First, predation rates of nauplii of the calanoid Acartia grani and the cyclopoid Oithona davisae were obtained by incubation experiments with two different prey items presented separately. The prey were the motile dinoflagellate Heterocapsa sp. (ESD=12.8 μm) and the non-motile diatom Thalassiosira weissflogii (ESD=14.4 μm). Maximum ingestion rates showed 303 % body C ingested d-1 for Acartia predating on Heterocapsa sp., 185 % body C ingested d-1 for Acartia presented with Thalassiosira weissflogii, and 121 % body C ingested d-1 for Oithona when presented with Heterocapsa sp. Feeding was not observed in the case where Oithona were presented with Thalassiosira weissflogii. The behavioral patterns demonstrated that Acartia grani nauplii move in a high frequent hop-like pattern while nauplii behavior of Oithona davisae best can be described as a low frequent jump-sink behavior. Both species showed clear evidence of a higher jump frequency when presented with the motile prey, and Oithona dedicated less time in sinking when presented with the motile prey. This indicates that the nauplii are capable of adjusting their feeding behavior to the prey present, thereby optimizing their feeding. Motility traits found in adults of Oithona davisae reported by Uchima & Hirano [1988] have not been found in nauplii of the same species from the present work. This supports the evidence of ontogenic behavioral changes in nauplii of Oithona davisae. Furthermore, it is hypothesized that the observed no-feeding in Oithona davisae nauplii when presented Thalassiosira weissflogi, is due solely to the use of mechanoreceptors. A simple prey encounter model was applied to the observed behavioral data and yielded a clearance rate which showed the same tendency to what was estimated directly from the functional response experiments. Motility of predator and prey is an important factor that helps define the encounter rates between copepod nauplii and algae cells. The encounter model can be used to predict nauplii clearance rates. However, constraints of the theoretical model such as the absence of limiting factors like handling time, assuming a 100% feeding efficiency and differences in receptor sensitivity all influence on the final result and the effect of these factors on the model should be better studied.

EducationsEnvironmental Biology, (Bachelor/Graduate Programme) Graduate
LanguageEnglish
Publication date1 Jan 2005
SupervisorsWinding Hansen & WH Benni

Keywords

  • zooplankton, feeding, functional response, Oithona davisae, Acartia grani, behavior, calanoida, cyclopoida