192;! ] Esterly: Marine Copepoda at La Jolla 429 



mine the presence of organisms at times when they are not produced. 

 Herdman and Scott (1908, p. 193) state that many seasonal variations 

 are caused "simply by the normal sequence of stages in the life 

 histories of organisms throughout the year." The reasonableness of 

 this statement seems self-evident. In studying the changes of the 

 plankton so far as it consists of Copepoda, it is highly important to 

 know the developmental stages of these Crustacea. 



The occurrence of phytoplankton undoubtedly has something to do 

 with the occurrence of the Copepoda. The ecological relation between 

 the two groups has not been taken up in the work at La Jolla, though 

 extensive studies of the phytoplankton have been carried on for 

 several years by Mr. Allen. It would be well worth while to know 

 whether there is any relation between the maximal occurrence of a 

 species or group of species of copepods and some component of the 

 phytoplankton. So far as our own work is concerned, however, we 

 must simply state that no facts have been ascertained regarding such 

 matters. But when we consider the well established significance of 

 both phytoplankton and copepods in the food cycle of the sea as 

 affecting certain fisheries (see Michael, 1921, p. 555 ; Allen, 1921, p. 

 538; Herdman, 1922, pp. 166-169) the need of ascertaining whether 

 there is a relation between abundance of copepods and, for example, 

 abundance of diatoms, will be emphasized. Aside from its ultimate 

 bearing on fisheries, such a question is worth investigating because 

 of the general relationship it bears to the ecology of the copepods 

 taken alone, since they feed upon the plant cells. Does the seasonal 

 occurrence of the micro-crustacea depend on the occurrence of the 

 organisms on which they feed? May not some of the variability in 

 distribution of the copepods be bound up with irregular occurrence 

 of their food supply? We are not in a position to answer such 

 questions as yet, but they are interesting and important subjects for 

 investigation. 



Nothing in our results is more striking than the difference in 

 seasonal occurrence of the two species of Acartia. Herdman obtained 

 similar results in his work in the Irish sea, though his tables deal 

 with separate genera instead of species in the same genus. Herdman 

 found, for example, that Temora longicornis has its maximum in 

 December, January, and February, while Paracalanus parvus is most 

 abundant in September and least abundant in June (Herdman, Scott 

 and Lewis, 1915, p. 233). It is almost certain that just as striking 

 differences will be found between the genera or species of the small 

 calanids and the Podoplea as between the species of Acartia. 



