FISHERY BULLETIN: VOL. 77, NO 3 



lantica varied the least in mean abundance during 

 the study, showing only slight increases during 

 spring and late summer 1975. 



Onshore-Offshore Distribution 



Several of the more abundant zooplankton taxa 

 in the New York Bight showed statistically sig- 

 nificant (P<0.05) differences in mean standing 

 stocks between the onshore (<50 m) and offshore 

 ( >50 m) sectors of the region (Table 5). Taxa which 

 on the average were significantly more abundant 

 onshore during 1974-75 were C. typicus, Penilia 

 avirostris, T. longicornis, Evadne spp., A. tonsa. 

 and doliolids. Those which were significantly more 

 abundant offshore were Calanus finmarchicus, O. 

 similis, O. atlantica, M. lucens, and Clausocalanus 

 pergens. Significant onshore-offshore differences 

 on an annual basis were not observed for 

 Pseudocalanus sp., pteropods, Paracalanus parvus, 

 appendicularians, gastropod veligers, echinoderm 

 plutei, medusae, and S. elegans. Neither total 

 copepods nor total chaetognaths differed sig- 

 nificantly between the two regions, but other zoo- 

 plankton combined were significantly more abun- 

 dant offshore (Table 5). 



Substantial seasonal changes occurred in the 

 onshore-offshore distribution of many of the 

 aforementioned taxa (Figure 2). Certain copepod 

 species which peaked or were otherwise very 

 abundant in the offshore region during winter and 

 spring were much less abundant onshore at those 

 times. However, during the summer, onshore 

 stocks of these species increased to levels ap- 

 proaching those in offshore waters. Species 

 exhibiting this pattern were M. lucens. C. pergens. 

 O. atlantica, Calanus finmarchicus, and P. parvus 

 (Figure 2). Several other taxa which reached 

 maximum levels of abundance during the spring 

 tended to be equally abundant onshore and 

 offshore during most times of the year. This group 

 of ubiquitously abundant taxa included 

 Pseudocalanus sp., O. similis, S. elegans, 

 medusae, appendicularians, pteropods, gastropod 

 veligers, and polychaete larvae (Figure 2). 

 Doliolids and the coastal-estuarine speciesPen(7ia 

 avirostris, T. longicornis, and A. tonsa all peaked 

 in the onshore environment during summer or 

 autumn and were seldom, if ever, abundant 

 offshore (Figure 2). Although Centropages typicus 

 also reached its highest levels of abundance on- 

 shore during the summer, it was usually abundant 

 offshore as well, especially during March and 



April (Figure 2). Echinoderm plutei peaked in on- 

 shore waters during autumn 1974 but also exhib- 

 ited a secondary offshore peak during spring 1975 

 (Figure 2). Evadne spp. exhibited maxima in both 

 the onshore and offshore environments during 

 spring and summer 1975 but were abundant only 

 onshore during autumn 1975 (Figure 2 1. 



Zooplankton Maxima, 



Phytoplankton Blooms, and 



Temperature 



We observed distinct peaks in zooplankton 

 abundance in both onshore and offshore environ- 

 ments in 1975 (Figure 3). In the offshore region, 

 there were two maxima, in March and May. The 

 March peak was dominated by L. retroversa which 

 composed nearly 60% of all offshore zooplankton 

 during that month. The remaining 40'/( of offshore 

 zooplankton in March was composed primarily of 

 the copepods Pseudocalanus sp., O. similis, 

 Paracalanus parvus, and M. lucens. The May 

 maximum was dominated hy Pseudocalanus sp., 

 Calanus finmarchicus, and O. similis, and these 

 species tended to be most abundant over the outer 

 shelf at the eastern end of the study area (e.g., 

 stations F3, F5, G2, G4). The March pteropod- 

 dominated maximum occurred similtaneously 

 with the beginning of the spring phytoplankton 

 bloom when chlorophyll a standing stock biomass 

 (milligrams/square meters) was high (Figure 3) 

 and discrete depth chlorophyll a concentrations 

 exceeded 4 ixg/l throughout the water column at 

 virtually all stations. However, during May when 

 copepods peaked in abundance offshore, the 

 phytoplankton bloom was in decline (Figure 3). In 

 the offshore region, water temperatures in the 

 upper 20 m remained low ( =£10° C) through May. 



We observed a single peak in zooplankton abun- 

 dance in the onshore environment during 1975 

 (Figure 3). This peak occurred in July and was the 

 result of marked increases in the abundance of 

 Centropages typicus and T. longicornis. In July, 

 these two species constituted about 67^^ of all on- 

 shore zooplankton and were especially abundant 

 at stations near the apex of the Bight and off the 

 New Jersey coast (e.g., A2, A4, B3, B5). The early 

 summer rise in C. typicus and T. longicornis stocks 

 occurred during a period when surface water 

 temperatures rose from about 10° to 20° C but 

 when onshore chlorophyll a biomass was low ( Fig- 

 ure 3). At other times during this study various 

 other taxa were dominant onshore, e.g., Penilia 



676 



