NO A A PROFESSIONAL PAPER 11 



A B 



FIGURE 9. 1-2.— Scanning electron micrographs of C iripos showing sulcal opening (A) and three dimensional structure (B). Sulcal opening 

 IS 33 M-m wide and does not appear to be covered by cell wall plates. Original magnification of B is 490 x . (Courtesy of M. Ledbetter, 

 Brookhaven National Laboratory.) 



66, 72), a strong narrow band maximum developed as 

 diatom populations disappeared. The layer consisted al- 

 most entirely of C. tripos (>90% of total cells) and was 

 between 0.3 and 3 percent light depths in association with 

 the 10° to 13° C isotherms. The depth of the layer, which 

 was 1 to 3 m thick, decreased gradually from 35 m at 

 station 98 (75 km offshore) to 20 m at station 72 (10 km 

 offshore. ) This trend apparently persisted as thermal strat- 

 ification continued to develop so that by May and June 

 (fig. 9.1-7) most of the C. tripos population was concen- 

 trated in a thin layer immediately below the thermocline, 

 in association with the 10° C isotherm and between the 

 0. 1 and 10 percent light depths. Because of nannoplankton 

 blooms in the upper 10 m and high concentrations of det- 

 ritus, the C. tripos maximum was below the 1 percent light 

 depth in the Apex and south along the New Jersey coast 

 within 20 km of the shoreline to about Barnegat Inlet (39° 

 45'N). 



Horizontal Distribution in Maximum Chlorophyll Layer 



Areal distributions of C. tripos cell density in terms of 

 population size must be interpreted in the context of tem- 

 poral variations in the vertical distribution of cells. The 

 population was distributed over the upper 30 to 40 m 

 during January-March when the water column was well 

 mixed and was aggregated near the base of the thermoc- 

 line during April-June when the water column was ther- 

 mally stratified. 



Within the Apex in February and March, population 

 size increased with distance from the mouth of the estuary, 

 especially along the New Jersey coast (fig. 9.1-8). This 

 pattern was closely related to the flow of estuarine water 

 (fig. 9.1-9) so that cell densities were lowest when the 



proportion of estuarine water was greatest. Conversely, 

 maximum chlorophyll-a concentrations (fig. 9.1-10) par- 

 alleled the distribution of low-salinity estuarine water, re- 

 flecting the rapid response of diatom populations (domi- 

 nated by Nitzschia seriata, with 5. costatum and Rhizosolenia 

 sp. abundant) to nutrient enrichment. 



This pattern continued across the shelf along a southeast 

 transect originating in the Apex and extending to the shelf 

 break in late March (fig. 9.1-11). C. tripos reached max- 

 imum cell density (60/ml) near the shelf break; Nitzschia 

 seriata was most abundant in the Apex. Based on these 

 observations and the degree to which C. tripos clogged 

 zooplankton nets during March (fig. 9.1-12), high dens- 

 ities of C. tripos had developed throughout New York 

 Bight by the end of March; maximum densities occurred 

 in offshore reaches of the outer Bight (midshelf to the 

 shelf break). This inshore-offshore increase in cell density 

 apparently persisted into April (fig. 9.1-5). 



As the water column stratified, distribution shifted so 

 that by mid-May an inshore-offshore decrease in abun- 

 dance was observed; maximum cell densities were located 

 in the Apex near the head of the Hudson Shelf Valley 

 (fig. 9.1-13). Nannoplankton accounted for most of the 

 chlorophyll a in the surface layer throughout the Bight 

 except for the center of high chlorophyll a (6 jig/l) off 

 Long Island and a very patchy region off New Jersey where 

 a maximum of 10 \i.gl\ was reported. C. tripos accounted 

 for more than 85 percent of the chlorophyll a at all depths 

 at these two locations. As thermal stratification continued 

 to develop, C tripos distribution shifted to the southeast 

 (fig. 9.1-14) so that by mid-June the center of maximum 

 abundance was in about 60 m of water 80 km east of 

 Seaside Park, N.J. (39°55'N, 73°15'W). Surface chloro- 

 phyll-a concentrations were low throughout the outer 



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