The use of a deep tank in plankton ecology. 2. Efficiency of a planktonic food chain1

Populations of copepods and ctenophores were maintained in a quasi‐steady state in a 70‐m3 tank supplied with phytoplankton and harvested regularly for several months. Paracalanus parvus replaced Acartia tonsa as the dominant copepod; in the absence of ctenophores, the yield of copepods was 10.4–12.5% of the phytoplankton supplied as food. When the carnivorous ctenophores were present, their yield was 2.6% of the phytoplankton supplied but could have been as high as 3.2% had not copepods been harvested simultaneously.