CHAPTER 10 



Above the pycnocline, inorganic phosphorus concen- 

 trations (fig. 1()-4B) were less than 0.4 p,M/l, except near 

 the estuary where they reached 1.1 |xM/l. Away from the 

 estuary, phosphate concentrations generally were higher 

 below the pycnocline than above. The highest concentra- 

 tion (3.6 p.M/1) was observed just below the pycnocline 

 at station 213 in the anoxic area (fig. 10-5). 



Silicate concentrations were generally highest (5-20 

 |xM/l) in the subpycnocline waters throughout the area 

 sampled, particularly where oxygen was low (fig. 10-4B). 

 No silicate was detected in surface waters except at es- 

 tuarine stations and at stations 200, 201, and 207 just north 

 of the anoxic area. The highest concentrations of silicate 

 (up to 20 \iMI\ ) were found in or just below the pycnocline 

 at stations 226, 213, and 217 in and adjacent to the low 

 D.O. area (fig. 10-5 and Thomas et al., in press). 



According to Richards (1965), during anaerobic decom- 

 position sulfide should accumulate over phosphorus in an 

 atomic ratio of 53:1. Our observed ratios of S:P (1.8:1 to 

 12.2:1) were considerably less. However, the anoxic sys- 

 tems examined by Richards et al. (1965). such as Lake 

 Nitinat, have a deep subpycnocline layer (100-200 m) 

 where anoxia occurs at some distance below the oxygen 

 interface. The thickness of the subpycnocline layer in the 

 anoxic area for this study was 6 to 15 m. There was a 

 direct relationship between S:P ratios and distance below 

 the pycnocline (r = +0.82, n = 5). Oxygen appears to 

 have diffused downward through the pycnocline to oxidize 

 the sulfide, and thereby decreased (oxidized) the sulfide 

 concentrations to the levels observed (A. Draxler and C. 

 Byrne, NMFS, in press). 



ORGANIC CARBON AND 

 PHYTOPLANKTON 



The DOC concentrations ranged from 1 to 13 mg C/1 

 (figs. 10-6 and 10-7A) and are considered unusually high 

 compared to other areas (ch. 4). Concentrations generally 

 decreased from the estuary to the shelf (fig. 10-6). How- 

 ever, the highest concentrations of DOC were found in 

 the middle and outer portions of the Apex (stations 41, 

 109, 34, 86, 76, 51; figs. 10-6 and 10-7A). 



Particulate organic carbon (POC) concentrations de- 

 creased seaward from the estuary (fig. 10-6). At station 

 102 near the estuary, POC was generally distributed uni- 

 formly with depth. Farther south along transect 102-227, 

 progressively larger concentrations of POC were meas- 

 ured in and below the pycnocline (fig. 10-7A). 



The ratio of integral DOC to integral POC. integrated 

 from surface to bottom, ranged from 3:1 to 25:1 and was 

 generally highest in the outer portion of the APEX where 

 standing stocks of DOC were highest. Thus, most of the 

 organic carbon in the New York Bight is in dissolved 



forms, which is generally true of most marine environ- 

 ments (Riley 1973). 



Chlorophyll-a (Chla) concentrations generally de- 

 creased from 3 to 6 mg/m^ near the estuary to 0.4 to 0.8 

 mg/m' offshore (fig. 10-6). Especially high concentrations 

 of phytoplankton (16 mg Chla/m') occurred at station 34 

 near the sewage sludge disposal site (fig. 10-6). At stations 

 outside the Apex, adjacent to the New Jersey coast, and 

 in the oxygen-depleted area, large increases in chloro- 

 phyll-a concentrations were observed in the pycnocline 

 and directly above the seabed (fig. 10-7B). Most of the 

 chlorophyll a was attributable to nannoplankton (<20 ixm) 

 (fig. 10-7B). Proceeding away from the estuary, netplank- 

 ton (>20 |xm) increased in relative abundance over nan- 

 noplankton. However, the maximum netplankton contri- 

 bution to the phytoplankton community biomass was only 

 66 percent at station 227. (See chapter 9, part 1.) 



Identification and enumeration of phytoplankton in 

 whole water samples collected from the surface, pycnoc- 

 line, and bottom water at stations 102, 109, 76, 201 . 217, 

 and 227 further confirmed that nannophytoplankton pre- 

 dominated over netphytoplankton. A spherical phyto- 

 plankton species 1.5 to 3 |xm in diameter and fitting the 

 description of Nannochloris alomus given by Ryther 

 (1954) and Patten (1959) was numerically dominant in the 

 21 samples examined. Its cell densities in surface water 

 generally decreased from 270.000 cells/ml near Sandy 

 Hook (station 102) to 90.000 cells/ml offshore at stations 

 217 and 227. Cell densities for the remainder of the phy- 

 toplankton community were 100 to 900 cells/ml. Other 

 than the small chlorophyte (probably Nannochloris ato- 

 mus), chain-forming diatom species such as Skeletonema 

 costatum, Nitzchia seriata, Melosira sp.. Rhizosolenia de- 

 licatula, and Chaetoceros curvisetum dominated in samples 

 collected near bottom and in the pycnocline, whereas flag- 

 ellated species such as Heterocapsa triquetra. Massartia 

 rotundata. ( = Katodinium rotunatum), Peridinium tro- 

 choideum. and Olisthodiscus liiteus dominated counts in 

 surface samples. Ceratium tripos was not seen in any of 

 the 21 samples examined. Mahoney (ch. 9, pt. 2) also 

 noted the absence of C. tripos in his samples from late 

 August. These findings verify that the C. tripos bloom, 

 which occurred earlier in the year (Malone 1978), had 

 dissipated by the end of August. 



Mandelli et al. (1970) observed that C. tripos was the 

 dominant species in their sampling area during June-Au- 

 gust 1966. They also noted a decline in diatom (netplank- 

 ton) abundance during the summer. This finding has been 

 confirmed by Malone ( 1976) and O'Reilly et al. ( 1976) for 

 the Bight Apex and the Hudson-Raritan estuary. 



The general depletion of silicate in surface waters 

 throughout the offshore and oxygen-depleted areas may 

 have contributed to the relative abundance of nannophy- 

 toplankton (phytoplankton requiring little or no silicate) 



239 



