4-45 



4-20). This difference may be the result of the net change, i.e., small 

 newly hatched larvae captured in earlier years by the 76ym CB net may 

 have been undersampled by the larger mesh, ISym 1/2-meter net. These 

 small larvae were probably most prevalent in early to late summer and 

 early fall months. Doevcy (1952a) reported polychaete larvae in spring 

 Block Island Sound plankton samples. It may be reasonably assumed that 

 a great many taxa comprise the polychaete group with no one taxon pre- 

 dominating on a yearly basis. 



Veliger larvae of gastropod and bivalve molluscs occurred pri- 

 marily during warmer months in New Haven Harbor (May through November) 

 and in Long Island Sound (Deevey, 1952a) . Again, body-size selectivity 

 of the larger mesh net appears to be the most likely explanation for 

 changes in ranking regarding the bivalves (Table 4-4) and for changes in 

 the appearance of seasonal population fluctuation patterns comparing 

 1973 and 1974 with 1975 through 1977 data for both gastropods and 

 bivalves (Figure 4-21) . The most abundant gastropod veliger was pro- 

 bably Littorina si^p. ; from close examination of a few samples, Mytilus 

 edulis and My a arenaria were the predominant bivalve larvae. Larvae of 

 the American oyster {Crassostrea virginica) probably comprised a small 



but important fraction of the bivalve assemblage in mid- July, with peak 



3 

 densities of 10 to 70 larvae per m during 1977 (NAI, 1978). Though 



these densities of oyster larvae are unexceptional in Long Island Sound 



(Loosanoff and Engel, 1940) , because of the temporal nature of peaks in 



oyster larvae, data from monthly sampling cannot be assumed to give 



representative data on oyster larvae densities. 



Of the major tychopelagic forms represented in New Haven 

 Harbor zooplankton collections , only harpacticoid copepods ranked rela- 

 tively high in overall abundance (Table 4-4) . As in the case of poly- 

 chaete and gastropod larvae, a sharp summer reduction in numbers fol- 

 lowing a late spring peak was observed during the years 1975 through 

 1977 (Figure 4-22) . No summer decline was indicated in 1973. In 1974, 

 however, harpacticoids disappeared completely from Clarke-Bumpus col- 

 lections during July and August. 



(Text continued on page 4-49) 



