Results and discussion
Several problems have arisen during the operation of the system. The more important of these difficulties and their solutions are described below.
Shortly after inoculation of the No. 1 tank with Acartia tonsa, flow through both tanks was halted for system modifications. At that time, the A. tonsa population numbered only about 400, but Acartia clausi had increased to at least 38,000. There were no observations between the fifth and tenth day following the cessation of flow. On the tenth day, although active and showed excellent survival mortality in the A. clausi population was apparently complete. Dissolved oxygen measurements revealed that the A. clausi tank had dropped to 3.2 ppm, whereas the A. tonsa tank was near saturation. When working with relatively low concentrations of Acartia in static dish cultures, I had never found aeration necessary. The bodies were siphoned from the A. clausi tank and the remaining medium was aerated. After 1 day, emergence of a few stage 1 and 2 nauplii indi- cated that some eggs had survived Oa concentrations fatal to all other stages. During normal operation, O2 concentration is now maintained at 9.5 to 9.8 ppm throughout the system.