232 Gordon A. Riley 



1955), so that the deficiency obviously does not approach the extremity of laboratory 

 cultures, in which the nitrogen content may be reduced to one-third normal (Ketchum 

 and Redfield, 1949). 



It is beyond the scope of this paper to discuss seasonal succession in detail, but one 

 other major feature is apparent in Fig. 4, which compares chlorophyll analyses with 

 Conover's cell counts. The latter comprised mainly diatoms and armoured flagellates. 

 In addition, occasional examinations of fresh material in summer have revealed two 

 to five miUion naked flagellates per litre and many millions of small, unidentified 

 Chlorella-Wkc cells. These small species are believed to be largely responsible for the 

 disparity between chlorophyll and routine cell counts in summer. Long Island Sound 

 seems to resemble, to a much less extreme degree, the situation described by Ryther 



( 1954) in Great South Bay and Moriches Bay, Long Island, where there was an exces- 

 sive summer dominance by " small forms ". These were shown by Ryther's experi- 

 ments to be favoured in their competition with diatoms by reduced salinity, high 

 temperature, a low N:P ratio, and the presence of nitrogen primarily in forms other 

 than nitrate. Similar environmental tendencies have been noted in Long Island Sound. 

 It is perhaps significant in this connection that the slightly higher nitrate values 

 during the summer of 1952 were accompanied by much larger quantities of diatoms. 



In the locality described by Ryther, the nannoplankton appeared to have a distinctly 

 toxic effect on shellfish. There is no evidence of a similar situation in the Sound. 

 LoosANOFF et al. (1947; 1953) have studied feeding rates and toxicity reactions of 

 lamellibranchs, using a variety of nannoplankton species as food organisms. Their 

 work indicates that the concentration of organisms required for toxic effects is well 

 above the level of the population found in the Sound. On the other hand, R. Conover 



(1955) found that Acartia, the dominant genus of copepods in these waters, feeds 

 much more effectively on diatoms than on nannoplankton. Hence the value of the 

 latter as zooplankton food is somewhat questionable. 



Quantitative aspects of the total zooplankton population, as depicted in Fig. 3, 

 provide little material for generalization except that there is a minimal population 

 in autumn and early winter, a larger but rapidly fluctuating crop in spring and summer, 

 and a vast diflference from one year to the next. Similar variability in the level of the 

 summer population has been noted in previous studies during the summers of 1938 

 to 1941. There is no satisfactory explanation, although it may be argued on rather 

 tenuous grounds that a causal relation exists between the relative abundance of nitrate, 

 diatoms and zooplankton in 1952 as compared with their scarcity the following year. 



According to Deevey (1955), copepods are the dominant zooplankton organisms 

 in the Sound, the most important species being Acartia clausi and A. tonsa, with 

 smaller but significant quantities of Temora longicornis, Pseudocalanus minutus, 

 Paracalanus crassirosths, and Oithona spp. Several other copepods and three species 

 of Cladocera occasionally constituted as much as 5 % of the population, as did the 

 larvae of various bottom invertebrates. In general, the species composition was 

 quite limited, and several species that are common in the outer coastal waters and are 

 known to have a wide salinity tolerance were unable to maintain significant numbers 

 in the Sound. 



R. Conover (1955) has made a descriptive and experimental study of the two 

 species of Acartia with particular reference to problems of seasonal succession. A. 

 clausi appeared in November or December and increased to a maximum in May of 



