Table 5.— A) The recommended geometric mean regressions for interconversion between displacement volume (DV) and dry 

 weight (DW) in the Gulf of Maine area; and B)the relative abundance of the major taxa(>l%) associated with the particular equa- 

 tion, expressed as percent of total numbers. Copepods are broken down into major species (>1%) with their abundance expressed 

 as percent of total copepod numbers (in parentheses). Zooplankton data from Sherman et al. (1978, 1979). 



bined and a new regression equation calculated. 

 These equations, and the equations showing sig- 

 nificant differences between years, are the rec- 

 ommended equations for conversion between the 

 biomass measures (Tables 3-5). Choice of which 

 regression to use should be based on area, season, 

 and species composition. Confidence limits can 

 be calculated for any predicted dry weight or dis- 

 placement volume by using the method outlined 

 by Ricker (1973) or Wiebe et al. (1975). A listing 

 of values for predicting dry weights and dis- 

 placement volumes within 95% confidence limits 

 is given in Table 6. 



The limitations of the method for the area 

 under study are as follows. The presence in sam- 

 ples of organisms such as salps, jellyfish, and 

 doliolids, which have a high displacement vol- 

 ume to dry weight ratio due to a greater reten- 

 tion of intracellular water, can significantly 

 affect the accuracy of dry weight estimates 

 (Wiebe et al. 1975). This was also observed in our 

 data, but only on rare occasions were these or- 

 ganisms encountered. Chaetognaths were also 

 mentioned by Wiebe et al. as organisms that 

 could alter the biomass relationship. Since they 

 are common, but not dominant, components of 

 the plankton throughout the year in our sampling 

 areas, the seasonal regressions account for their 

 continuous presence and are therefore appli- 



cable to samples where they are present. This 

 study revealed two additional situations in which 

 sample composition caused a deviation in the bio- 

 mass relationship. Twenty samples collected 

 during late winter 1977 from the GOM and GB 

 contained high concentrations of diatoms, pri- 

 marily Rhizosolenia sp. and Thalassiosira sp., 

 and microzooplankton not normally captured by 

 0.333 mm mesh nets. The samples resembled 

 thick "pea soup" and many hours were required 

 for draining in order to obtain a displacement 

 volume reading. Since their dry weight to dis- 

 placement volume ratios were very low com- 

 pared with other samples collected during the 

 same period, the samples were eliminated from 

 the general analysis and a separate regression 

 calculated (r = 0.962) for them (Table 1). The 

 second situation was observed in autumn 1978 

 when the siphonophore population increased 

 dramatically, especially off SNE and in the 

 GOM. Since these delicate colonial aggregations 

 are easily fragmented during collection, their 

 abundance could not be measured quantitatively. 

 For these samples, displacement volume to dry 

 weight ratios were disproportionally high be- 

 cause of the intracellular water retained by their 

 nectophores. The regression line calculated with 

 data only from siphonophore-dominated samples 

 was significantly different (P<0.05) in both 



637 



