Acute physiological reactions of Calanus pacificus to selected dinoflagellates: direct observations

Calanus pacificus (Copepoda: Calanoida) females were collected off the California (USA) coast from November 1984–April 1985. A video system was used to observe and record the behavior of restrained individual females presented with a variety of dinoflagellate prey. Two species, Gonyaulax grindleyi and Ptychodiscus brevis, elicited acute physiological reactions. In 40% of the trials (n=10), copepods fed G. grindleyi regurgitated after 45 to 120 min and, in nearly all cases, did not maintain full guts. Copepods in the presence of P. brevis exhibited rapid heart rate and loss of motor control. Scrippsiella trochoidea elicited an intermediate response by C. pacificus. The copepods occasionally displayed mouthpart twitching or failure to maintain gut fullness. Olisthodiscus luteus elicited no unusual behavior in an intermediate temporal range (sec-hours), although the mouthpart movements appeared different than in copepods fed Gyrodinium resplendens (used as control). Placing the copepods in G. resplendens suspension restored normal feeding behavior in all cases.