Calanidae and Harpacticidae 225 



conveniently collected with a tea strainer or any sort of net. It is rarer 

 and sometimes even difficult to find after a severe storm has washed out 

 the pools which it inhabits, but in a few weeks is as numerous as ever. 



The animal may be raised in Syracuse dishes or in any larger con- 

 tainers. The natural medium is seawater, which may be diluted as much 

 as half, or concentrated to as much as 8% total salinity. The animal 

 can withstand very rapid changes within these limits. I have usually 

 used natural strength seawater. 



The food of these copepods probably consists of bacteria, but this has 

 not been determined. They multiply rapidly if there is plenty of decay- 

 ing vegetable matter in the medium, such as bits of seaweed, or even a 

 piece of cheesecloth. The richest culture I ever obtained had a heavy 

 growth of Platymonas subcordaejormis in it. The alga may have served 

 as food, or simply to aerate the medium. 



If the food supply is at all abundant, it is necessary to use rather 

 shallow containers or to employ compressed air for oxygenation. In 

 either case, care must be taken to see that evaporation does not increase 

 the salinity of the medium beyond the tolerance of the copepod. 



The optimum temperature seems to be about 25-30 C. 



CALANUS FINMARCHICUS, AND OTHER PELAGIC COPEPODS 



These copepods are not easily kept alive in the laboratory, and it 

 is very difficult to raise adults from eggs. The greatest mortality seems 

 to be in passing from the last copepodid stage to the adult. A number 

 of different methods, however, have met with at least partial success. 

 Miss Lebour* and others recommend the Plymouth plunger jar. [See 

 p. 21.] For old stages I have had equal success with 500 cc. Erlenmeyer 

 flasks containing about 300 cc. of seawater in which 4 to 6 copepods were 

 kept. 



Probably the natural food consists mainly of small diatoms and other 

 unicellular algae, Protozoa, and bacteria. Enough food is contained in 

 seawater filtered through coarse filter paper if the water is kept flowing. 

 Otherwise Nitzschia [For culture see p. 33.], Dunaliella [For culture 

 see p. 134.] , or, still better, Platymonas subcordaejormis [For culture see 

 p. 135] may be added (1-5% of algal culture). 



Calanus is found in waters with temperatures from about 4° to above 

 20 C, but has a rather sharp upper limit of tolerance, which appears 

 to be different in races from different regions. Specimens taken off 

 Pacific Grove, California, lived several weeks at 17.5 C. Those from 

 near Woods Hole died quickly above 15 C. It should generally be 

 safe to keep the animals between 12 ° and 15 C. 



*Sci. Progr., London, 27:494, 1933. 



