Swimming and feeding behaviour of the planktonic copepod Clausocalanus furcatus

The objective of this study was to quantify motion and feeding behaviour ofthe small calanoid Clausocalanus furcatus, which is acommon and abundant species in oligotrophic environments. Adult femaleswere video recorded at 60 fields s^-1 using videoequipment which allowed us to follow each free-swimming individualcontinuously in 3 1 vessels. At 20C underdark conditions, C.furcatus moved continuously alongconvoluted small loops at a mean speed of 10 mms^-1 (corresponding to 10 body lengthss^-1). This motion was occasionally interrupted bysudden somersaulting performed at very high speed (up to 17 mms^-1). The copepods only occasionally sank. There wasno evidence that C.furcatus created feeding currents.Dinoflagellate cells offered as food appeared to be perceived by directencounter at high speed, being instantaneously captured and ingested orrejected. The capture rates were correlated with the frequency ofsomersaulting. By moving fast and by associating a high turning rate with ahigh frequency of crossing the previous tracks,C.furcatus searched 22-26% of the explored volumes.The motion and feeding behaviour of C.furcatus showthat the foraging tactic of this species is to explore small volumes ofwater rapidly. This strategy appears, so far, to be unique among smallplanktonic copepods.