Oxygen Depletion and Associated Benthic Mortalities 

 in New York Bight, 1976 



Chapter 9. Plankton Dynamics and Nutrient 



Cycling 



Part 2. Bloom Decomposition 



John B. Mahoney^ 



' Sandy Hook Laboratory, Northeast Fisheries Cen- 

 ter, National Marine Fisheries Service, NOAA, High- 

 lands, NJ 07732 



INTRODUCTION 



As discussed in part 1 of this chapter the combined 

 BOD of the respiration of the Ceralium tripos population 

 and the cell decomposition during the bloom decline and 

 ultimate collapse would have been sufficient to produce 

 the 1976 oxygen depletion in the New York Bight. This 

 section is concerned with C. tripos decomposition. 



In early July, when the magnitude of the problem first 

 became evident, divers observed a layer of flocculent 

 material several meters thick at the thermocline and a 

 denser accumulation at least 1 cm thick on the bottom. 

 The floe was present throughout the oxygen-depleted area 

 and persisted during the summer. Examination of initial 

 samples of this material established that it was an aggre- 

 gate of phytoplankton dominated by C. tripos. Signs of 

 decay in this aggregate were obvious. The phytoplankton 

 in the affected area was surveyed during the summer to 

 obtain information on the time sequence and geographical 

 pattern of the decomposition of the C. tripos population. 



METHODS 



Samples, mostly 1 liter in polyethylene bottles, were 

 collected by divers or taken by water sampler casts. Since 

 viability of the C tripos cells and the activity of other 

 microorganisms and meiofauna were considered impor- 

 tant assessments, use of a preservative was avoided when- 

 ever possible. Live samples were kept cool until they 

 reached the laboratory where they were refrigerated at 

 2° C. They were examined within 24 hours. Samples that 

 could not be returned to the laboratory within a day were 

 preserved with Lugol's iodine or buffered Formalin. 



Since the phytoplankton in most of the samples was 

 clumped, only qualitative estimates of the relative abun- 



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