A knowledge of the growth rates and feeding behaviour of planktonic copepods at natural food concentrations is important for an understanding of food-chain dynamics in the sea. In many areas of the open oceans average concentrations of particulate organic carbon rarely exceed 100 µ carbon 1-1, and even in coastal regions the maximum levels are probably only one or two orders of magnitude higher (Parsons, 1975). Thus, most herbivorous marine copepods live in a nutritionally dilute environment (Conover, 1968). In contrast to natural conditions, many laboratory investigations have been carried out at unnaturally high food concentrations, often more than one order of magnitude higher than those which might be expected in the sea.