stramin nets. Clarke, Pierce, and Bumpus 

 (1943) gave the dates of these cruises and 

 the station numbers and locations. A discus- 

 sion of papers concerned with the distribution, 

 abundance, and ecology of zooplankton and 

 phytoplankton based on information collected 

 during these cruises follows. 



A detailed report of the productivity of 

 Georges Bank based on data from 1Z0 stations 

 made on the cruises during September 1939 

 and January, March, April, May, and June, 

 1940 was given by Riley (1941). His report 

 includes an analysis of the methods of meas- 

 uring phytoplankton which" shows that the 

 plant pigment method gives results most 

 nearly representative of the abundance of 

 phytoplankton. The main body of this work 

 concerns the vertical and horizontal distri- 

 bution of plant pigments, nitrate, phosphate, 

 and oxygen at various seasons of the year. 

 The data show that the quantity of plant pig- 

 ments has marked seasonal and regional vari- 

 ations, that the quantity of plant pigments was 

 lowest and of nutrients highest in January, 

 that the spring diatom bloom began in March 

 and lasted until May, and that during the 

 spring diatom bloom there was a pronounced 

 inverse relation between plant pigments and 

 nutrients. Plant pigments, the percent satura- 

 tion of oxygen, and experimental determina- 

 tions of oxygen production showed positive 

 correlations with light and negative ones with 

 temperature. He discussed the seasonal cycle 

 of productivity and the physical and biological 

 factors affecting productivity and gave meas- 

 urements of the mean standing crop of plank- 

 ton and the mean total productivity. 



Sears (1941) analyzed the abundance, dis- 

 tribution, and species composition of diatoms 

 collected during the surveys of Georges Bank 

 from the latter part of March to the end of 

 June 1940. She obtained water bottle samples 

 of phytoplankton at depths of 1 , 10, 30, 50, 

 and 80 m., and determined the number of 

 cells per 0.1 m. of sea surface. These data 

 show that the period of diatom abundance was 

 more prolonged on Georges Bank than in most 

 parts of the Gulf of Maine, and that production 

 generally was greatest in the deep water along 

 the periphery of the bank. Chaetoceros 

 decipiens and Ch. dibilis were the most charac- 

 teristic species of the spring flora, and 

 Leptocylindrus minimus was the most abundant 

 diatom in late June. 



In a study of the causes underlying the 

 initiation of spring diatom flowering, Riley 

 (1942) made an extensive statistical analysis 

 of the relation of the phytoplankton crop (as 

 indicated by the quantity of plant pigments) to 

 depth and stability (as indicated by the dif- 

 ference in density between the surface and 

 30 or 50 m.) based on observations made 

 during March, April, and May, 1941. He 

 found the relation between plankton and sta- 

 bility zero in March, positive in April, and 



negative in May. Data from the April cruise 

 support the theory that when the thickness of 

 the euphotic zone and rates of photosythesis 

 and respiration are constant, the rate of 

 increase in the plankton population is a linear 

 function of the reciprocal of the zone of 

 vertical turbulence. He discussed the reasons 

 for the seasonal change in the relation of 

 plankton abundance to stability. 



As a continuation of these studies, Riley 

 (1943) compared laboratory experiments on 

 the growth of Nitschia closterium ( = Phaeo- 

 dactylum tricornatum ) with experiments of 

 natural phytoplankton associations on Georges 

 Bank during the spring of 1941 in an attempt 

 to describe some of the physiological factors 

 involved in spring diatom flowerings. He de- 

 scribed the growth curves of the laboratory 

 culture of Nitschia under varying conditions 

 of light, temperature, and nutrients and dis- 

 cussed the relative importance of certain 

 chemical and physical factors at different 

 stages of the population cycle. In a parallel 

 study on natural populations on Georges Bank, 

 he found that many of the species passed 

 through a population cycle similar to the 

 laboratory culture of Nitschia , and noted 

 similarities in the relations of the population 

 curves with respiration and photosynthetic 

 activity. He discussed generally the physio- 

 logical factors involved in spring flowerings. 



A study of the abundance, distribution, and 

 seasonal cycle of reproduction of Sagitta 

 elegans on Georges Bank based on collections 

 made during all 11 Atlantis cruises was made 

 by Clarke, Pierce, and Bumpus (1943). They 

 found the greatest concentrations of S. elegans 

 within the central homogeneous water mass 

 of the bank throughout the year; this species 

 recommends itself as an indicator for tracing 

 movements of the mixed bank water. The 

 chief period of reproduction centered in April 

 and May. S. serratodentata and ^. enflata 

 occurred entirely outside the margin of the 

 mixed area. They compared the distribution 

 of S. elegans to that of two species of cope- 

 pods, Calanus finmarchicus and Pseudocalanus 

 minutus . 



Riley and Bumpus (1946) discussed phyto- 

 plankton- zooplankton relations on Georges 

 Bank based on estimates of the abundance of 

 total phytoplankton and of total and of individual 

 species and genera of zooplankton from Sep- 

 tember 1939 through June 1940. They demon- 

 strated a significant inverse relation between 

 the horizontal distribution of phytoplankton 

 and total and individual species of zooplankton 

 and presented evidence that grazing caused 

 this inverse relation. They suggested that 

 turbulent mixing tended to redistribute the 

 populations so that correlation was not fully 

 developed. They attempted on theoretical 

 grounds to determine grazing rates and to 

 estimate the effect of turbulent mixing on the 

 populations of zooplankton and phytoplankton. 



