Review of the oceanography of Long Island Sound 



231 



favoured the dominance of Thalassiosira and that its tolerance to low light intensity 

 permitted a relatively early flowering. Contrariwise, physical conditions promoted 

 dominance by Skeletonema throughout February and March, 1953, and toward the 

 end of the 1954 flowering. 



In 1955 the flowering was even earlier. The major growth took place during the last 

 ten days of January, and the peak was attained early in February. The New Haven 

 Weather Bureau reported that the percentage of sunshine in January, 1955, was the 

 highest that has been recorded in 55 years of observation, so that an early flowering 

 was not unreasonable. The temperature in the Sound was 3-1 to 3-3' at the beginning 

 of the flowering, and Skeletonema was the dominant species. As the flowering pro- 

 gressed the temperature dropped to about 1 '. At this writing, counts of the phyto- 

 plankton for this period have not been completed. Preliminary indications are that 

 Thalassiosira gained in relative importance but was unable to achieve complete 

 dominance. 



Experiments by S. Conover (1955) showed that the 1954 flowering was terminated 

 largely because of nitrogen deficiency. At this time and again in June, 1954, natural 

 phytoplankton populations were enriched with phosphate, nitrate, iron, and man- 

 ganese, singly and in combination. In all cases nitrogen was the one element that had 

 a significant effect on the population as a whole, although individual species occasion- 

 ally responded to other types of enrichment. Nevertheless, the percentage of nitrogen 

 in the phytoplankton remained nearly constant through the year (Harris and Riley, 



50 



40 



— MILLIONS OF CELLS PER LITER 



pG. CHLOROPHYLL PER LITER 



30 



20 



10 



1952 



Vj 



M 'j 'j ' r' s 'O I n"VT) ' f 'm 'a 'mTT'j 'a 'S '0 'N 'D -J 'F 'M 



1953 



1954 



Fig 4 Phytoplankton cell numbers and chlorophyll concentrations in the surface waters, plotted as 



the average of all values obtained at inshore stations. 



