Nonselective, nonsaturated feeding by three caltinid copepod species in the Labrador Seal

Copepod grazing experiments were conducted in suspensions of natural particulate matter during the spring bloom in the Labrador Sea to examine the phenomena of saturated ingestion rates and particle selection, There was no critical concentration of available food at which ingestion rates were saturated. Calanus finmarchicus, Calanus glacialis, and Calanus hy-perboreus removed all phytoplankton in direct proportion to their abundance at chlorophyll a concentrations ranging from 0.53 to 12.1 pgeliter-‘. For phytoplankton>20 pm in diameter there appeared to be no selective ingestion according to the size, shape, or species of cell. The filtration rate for a given copepod species did not change over time or space. Weight-specific ingestion rate increased as copepod body weight increased. The current quantitative understand-ing of copepod feeding behavior rests al-most entirely on the results of experi-ments conducted in highly artificial particulate environments (reviewed by Marshall 1973; Conover 1978). A ques-tion of paramount importance remains unanswered: do copepods exhibit the same feeding behavior in their natural environment as they do under laboratory conditions? In laboratory studies of copepod feed-ing, ingestion rates become saturated at some critical concentration of food; this relationship can be described by a recti-lineair mode1 (Frost 1972), an Ivlev curve (Parsons et al. 1967), or a Michae-lis-Menten model (Mullin et al. 1975). This effect has been demonstrated for several planktonic filter feeders and has been incorporated into many models of copep’od feeding (e.g. Lehman 1976; Steele and Frost 1977). Feeding experi-ments have also shown that copepods are able to selectively ingest certain particles from simple mixtures according to their size or nutritional value (Frost 1977; Pou