4. If algal cells and their culture medium 

 are moderately infected with bacteria, it is not 

 possible to predict how algal biochemistry and 

 morphology affect the growth and development 

 of phytoplankton- consuming larvae, 



5. Although Palaemonetes larvae consumed 

 all of the species of phytoplankton offered 

 them, their growth was not predictable. Ac- 

 cording to the calculated assimilation indices, 

 Palaemonetes is almost unable to digest any 

 of the plant material used in this experiment. 



UTILIZATION OF DETRITUS FROM THE 



SEDIMENT BY MACROBENTHIC 



INVERTEBRATES OF THE 



PAMLICO RIVER ESTUARY 



Kenneth Tenore 



Objective: 



To investigate sediment detritus as a source 

 of nutrition for dominant species found in the 

 Pamlico River, N.C. estuary. 



Justification: 



A study of the benthic community of the 

 Pamlico River estuary has shown a correla- 

 tion between the density of the fauna and the 

 percentage of organic matter in the sediment. 

 One cause of this correlation might be the 

 capacity of these benthic forms to utilize 

 sediment organic matter as food. Knowledge 

 of the rate of accumulation of sediment detritus 

 would be useful in a study of the energy flow 

 in the estuarine ecosystem. The use of isotope 

 tracers in studying the feeding activities has 

 certain advantages. The utilization and assimi- 

 lation of labeled food material can be measured 

 directly by determining the presence of the 

 label isotope in the animal tissue. Research 

 on the feeding of benthic animals has, in gen- 

 eral, relied on such indirect indices as growth 

 and mortality. 



Experimental Procedure: 



Detrital nnatter will be prepared from algae 

 labeled with phosphorus 32 and nnixed with a 

 sand sediment. Dominant species of the estuary 

 (bivalves, Macoma balthica and Rangia cuneata ; 

 polychaete. Nereis succinea ; amphipod, 

 Cyathura polita ) will be introduced into trays 

 containing this sediment. The animals will later 

 be analyzed for phosphorus 32 content by liquid 

 scintillation techniques, and the rate of utiliza- 

 tion of the detrital matter calculated for each 

 species. 



NUTRIENT FACTORS CONTROLLING 



ESTUARINE PHYTOPLANKTON 



PRODUCTION 



Gordon Thayer 



Objective: 



To measure the concentrations of nutrients 

 in estuaries near Beaufort, N.C., to identify 



the nutrient or nutrients limiting phytoplankton 

 production in these estuaries, and to estimate 

 the turnover rates of phosphorus between conn- 

 partments of the open-water portion of the 

 ecosystem. 



Justification: 



Research on the production and standing 

 crop of estuarine phytoplankton has, in general, 

 been descriptive rather than analytical. In- 

 vestigators of shallow embayments have ob- 

 served pronounced seasonal cycles in standing 

 crop and production correlated with the sea- 

 sonal cycle in water temperature and have 

 suggested that the phytoplankton cycle is con- 

 trolled by the rate at which benthic microflora 

 regenerate nutrients. Evaluation of this possi- 

 ble interrelation among temperature, nutrients, 

 and microfloral metabolism would yield insight 

 into factors that control part of the organic 

 production in estuaries and thus affect the 

 movement of radionuclides in the estuarine 

 ecosystem. 



Experimental Procedure: 



The concentration of nutrients in estuaries 

 near Beaufort, N.C, is being chemically 

 analyzed at regular intervals. The limiting 

 nutrients are identified by comparison of the 

 rate of photosynthesis of unenriched controls 

 with the rate of water samples enriched with 

 various nutrient mixtures. A radioactive 

 tracer, phosphorus 32, is being used to de- 

 termine the rates at which phosphorus under- 

 goes the following transformations in estuarine 

 waters : 



inorganic _j. particulate ^dissolved inorganic 

 phosphorus"^ phosphorus^ phosphorus 



Results: 



1. Phytoplankton production has varied from 



3 -1 



an average of 1.2mg.C/m. day" to 0.4 



mg.C/m.'^day"' ; maxima are in September 

 and May. ^^ 



2. The variation in production is correlated 

 with standing crop and a seasonal cycle in 

 water temperature. 



3. Phosphate-phosphorus concentrations 

 have shown only slight seasonal variation-- 

 minimum concentration of 0.15 //g. at./l. 

 and a maximum concentration of 0.5 ^g. 

 at./l. 



4. Nitrate-nitrogen concentrations have 

 varied between 0.1 and 1.2 /ig. at./l., and the 

 variation appears to be correlated with tem- 

 perature. 



5. Enrichment experiments have shown that 

 among the main nutrients being measured, 

 nitrate is the most limiting. Phosphate is also 

 limiting but not as much as nitrate. 



6. The use of an organic substrate (glucose 

 or organic detritus) in the enrichment studies 

 indicates that bacteria may extract nutrients 



