MULLIN and CONVERSE: EUPHAUSIID AND ZOOPLANKTON BIOMASSES 



copepods particularly decreased moving off- 

 shore. The biomasses of both categories were 

 larger in 1955 and 1956 (pre-El Nino years) than 

 in 1958 and 1959 (El Nino years; see also Chel- 

 ton et al. 1982). This suggests that biomasses of 

 euphausiids and of the smaller copepods respond 

 similarly to interannual climatic or environ- 

 mental variation. 



Our results, which are summarized in Figure 

 2, were 



1) Biomasses of euphausiids and copepods were 

 significantly less in the southern area than in 

 the northern area, both before (1955-57) and 

 during (1958-59) the El Nino, in agreement 

 with Colebrook's (1977) conclusions, and the 

 ratio of euphausiid to copepod biomasses did 

 not change significantly. Analysis of data 

 from only the inshore subareas yielded the 

 same results, except that the euphausiid bio- 

 mass did not differ significantly between 

 northern and southern inshore areas during 

 1958-59. 



2) Biomasses of euphausiids and copepods were 

 significantly less during El Nino than before 

 it, both in the complete areas and in the in- 

 shore portions (also agreeing with Cole- 

 brook's result), and the euphausiid/copepod 

 biomass ratio did not change significantly. 



3) Neither the euphausiid nor the copepod bio- 

 masses were significantly different between 

 inshore and offshore subareas, nor were the 

 ratios significantly different (comparison not 

 shown in Figure 2); this result differs from 

 Colebrook's conclusion. 



Overall, we conclude that it is reasonable to 

 use the biomass of small zooplankton to correct 

 or scale the biomass of euphausiids for effects of 

 geography or interannual climatic variation in 

 order to test for changes due to factors specific 

 to the euphausiids. 



Interannual Variation in 1960-69 off 

 California 



Averaged over the entire decade, there were 

 significantly lower biomasses of euphausiids and 

 of small zooplankton offshore than inshore, both 

 in the southern area by itself and in the com- 

 bined areas (unlike our result for 1955-59). 

 Thus, for testing hypotheses (such as Hm) con- 

 cerning biomasses, the inshore/offshore distribu- 

 tion of samples should be similar in the sets be- 

 ing compared (as was true in our case). We were 

 unable, however, to reject the null hypothesis 

 that the median ratio of biomasses in the off- 

 shore subset of stations equalled the median 



PERIOD 



Category 



1955-'57 



1958-'59 



< 

 111 



< 



(U 



copepods 



34. 



c 



0) 



O 

 V) 



(36.) 

 (37.) 



*; euphausiids 24. 



O 



2 euph./cop. 0.49 (0.81) 



copepods 12, (13.) 



euphausiids 5.0 (7.0) 



euph./cop. 0.40 (0.44) 



19. (19.) 



9 . 1 (9.3) 



0.29 (0.22) 



7.5 (8.5) 



4.1 (3.2) 



0.52 (0.47) 



Figure 2. — Overall and (inshore subset) medians for each space/time block in the 1950s, for 

 wet weight biomasses (mgm"^) of copepods and euphausiids, and for the ratios at 

 individual stations. Arrows connect medians which differed significantly iP < 0.05 for H,, = 

 no difference); a thick arrow indicates that the comparable medians of the inshore sub.sets of 

 data also differed significantly. All comparisons were "vertical" or "horizontal"; no "oblique" 

 comparisons were tested (e.g., no comparison between northern, 1960-65, and southern, 

 1966-69). 



637 



