THE NUTRITION OF COPEPODS IN RELATION TO THE FOOD-CYCLE OF THE SEA

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Abstract
1. The importance of copepods in the economy of the sea and the inconclusive and contradictory nature of previous observations on their food make it desirable to investigate the nutrition of these animals in a thorough manner. For this purpose and in order to develop a satisfactory method of culturing copepods in the laboratory so that their physiology might be studied under carefully controlled conditions, feeding experiments were undertaken using Centropages, Labidocera, Acartia, and particularly Calanus. 2. Small containers without stirrers appeared to be suitable provided that over-crowding was avoided and a low temperature maintained. The materials which were tested as possible sources of food included the organisms present in the harbor water and "persistent" cultures of certain diatoms and green flagellates. 3. Although the survival of the first three copepods mentioned was prolonged by the addition of the diatoms and green flagellates, the majority died off after about two weeks. In the case of Calanus only a slight improvement resulted from this treatment and a large proportion survived when no food organisms were added. 4. Further experiments revealed that the sterilization of the culture water and the removal of particulate matter from it was accompanied by a high mortality of Calanus and that the addition of bacteria to the water resulted in improved survival. To test the possibility that the copepods were utilizing the smaller types of microörganisms for food, the growth of bacteria, etc. was minimized by passing membrane-filtered water continuously through flasks in which certain of the copepods were confined. These copepods failed to molt and died off rapidly, whereas those in flasks through which paper-filtered water flowed remained alive and molted in large numbers. 5. These experiments therefore indicate that bacteria and other constituents of the nannoplankton may be an important food for copepods in the sea. Diatoms and other larger organisms may possibly serve as a source of nourishment indirectly through the bacteria, etc., which feed upon them and their excretions.

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