Algal constraints on copepod grazing. Growth state, toxicity, cell size, and season as regulating factors

• Published in: ICES Journal of Marine Science
• Main Authors: Nejstgaard, J. C., Båmstedt, U., Bagøien, E., Solberg, P. T.
• Format: Text
• Language: English
• Published: Oxford University Press 1995
• Subjects: Articles; Calanus finmarchicus
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/52/3-4/347; https://doi.org/10.1016/1054-3139(95)80050-6

The copepod Calanus finmarchicus was used to quantify effects on the grazing rate due to prey algae characteristics. Laboratory cultures of the haptophytes Emiliania huxleyi, Prymnesium patelliferum , and Pavlova lutheri , the diatoms Thalassiosira nordenskioeldii, T. anguste-lineata , and Chaetoceros calcitrans f. pumidus , and the cryptophyte Rhodomonas baltica were used as food. There was no significant difference in clearance rate between exponential and stationary cultures. Feeding rate increased rapidly with cell diameter (ESD) of the algae in the size range 7–17 μm, while there was no apparent relationship for algae between 3 and 7 μm. E. huxleyi was a suboptimal food with low clearance rates (0–1.6 ml cop−1 h−1) and estimated maximum daily food: body carbon ratios (18%). Feeding rate was not affected by variation in coccolith coverage of the cells. In contrast to the diatoms, there was a pronounced seasonal shift in feeding rate on E. huxleyi . The highest grazing rates coincided with the maximum abundance of E. huxleyi (May-June), and may be caused by seasonal adaptation of the copepod. The feeding on P. patelliferum was lower (0–1 ml cop−1 h−1) than expected from its cell size, and decreased further during incubations > 24 h. A hepatocytic cell test demonstrated a high toxicity of the P. patelliferum strain, although the vitality of C. finmarchicus was not influenced during a two-day exposure in dense suspensions (106 cells ml−1). Thus sublethal toxicity may protect P. patelliferum from copepod predation, being a competitive advantage compared with non-toxic algae.