Figure 3.— Changes in median displacement vol- 

 umes and dry weights for A) Southern New 

 England, B) Georges Bank, and C) Gulf of Maine 

 waters. Dashed lines represent intersurvey peri- 

 ods. Similar abundance trends are portrayed by 

 both indexes, but discrepancies in magnitude be- 

 tween measures occur for Georges Bank summer 

 samples and throughout the year in the Gulf of 

 Maine. Displacement volumes are from Sherman 

 et al. (1977, 1978). 



E 

 O 

 O 



o 



o 



O 



> 



LU 

 LlI 



o 



< 



_l 



Q. 



< 



Q 

 LlI 



120 



100 



80 



60 



40  



20 • 



- 

 120 - 



100 



80 



60 



40 



20 



- 

 120 

 100 

 80 

 60 

 40 

 20 







SOUTHERN NEW ENGLAND 



DISPLACEMENT 

 VOLUMEK^^ 



DRY ^\ 



/ WEIGHT \ 



£ 



*. 



5 



t~ i i i i i r~i i I i i r~i n m i r 



GEORGES BANK 



h 



\ \ DRY 



\ '■ *" WEIGHT 



l DISPL ACE MEN T " - * 



VOLUME 



h 





I I I I I I I I I I I I 



© 



i i i i I I I I I ! 

 GULF OF MAINE 



DRY 

 WEIGHT 



/A. 



y/ 



V 



10 

 -8 



- 6 



- 4 



- 2 



- 



I I i i i i I I I II II I I I I I I I I ! I I 



JFMAMJJ AS0MDJF MAMJJ A S N D 



-10 

 -6 

 6 

 4 

 2 

 



— 12 



— 10 

 8 

 6 

 4 



— 2 



— 



fO 



E 

 O 

 O 



E 



>- 

 rr 



Q 



Q 



LlI 



1977 



1978 



o 

 o 



E 

 en 



O 



I- 

 <J 

 IT 



O 

 > 



>- 



tr 

 o 



< 



14 - 

 12 



10 - 

 8 - 



GULF OF MAINE 



SOUTHERN NEW ENGLAND 



i i i i i i i i i i i i i i ! i i i : i i i i 



FMAMJJASONDJFMAMJJASOND 



1977 



1978 



winter and represent a substantial biomass 

 underestimated by displacement volumes. 



Autumn increases in dry weight were not ob- 

 served for GB or SNE, though both areas sup- 

 port large populations of Calanus in the spring 

 and summer. In general, overwintering Calanus 

 remain in deep water and do not migrate ver- 

 tically (Marshall and Orr 1955). The only concen- 

 trations of preadult Calanus found in these areas 

 were at a few stations located near or below the 

 100 m contour line during late autumn. These 

 samples had higher dry weight-displacement 

 volume ratios than Calanus free stations. The 

 G0M is able to support a large population of over- 

 wintering Calanus in deepwater basins. 



Figure 4.— Seasonal changes in dry weight/displacement vol- 

 ume ratios for the three sampling areas. Points are placed at 

 the midpoints of the survey cruises. Gulf of Maine samples have 

 higher values throughout the year. 



calanus minutus or Centropages typicus were 

 abundant. The preadult Calanus apparently 

 store lipid reserves for survival through the 



Discussion 



The linear relationship between displacement 

 volume and dry weight is affected by the sea- 

 sonal changes in species composition and age 

 structure which occur throughout the year in 

 zooplankton communities. Accurate intercon- 

 version between them is possible only with a ser- 



639 



