Lavamegos Vertical distribution of euphausnd life stages 



309 



St. 120 60 120.50 120 45 



100 

 200 

 300 



05 O 05 05 O 05 OS O 05 





 100 



200 

 300 





 100 

 200 

 300 







'111 



''.Oil 



12060 12050 12045 



S aHme 

 Postlarvae 





S Longtcome' 

 Postlarvae | 



02 O 02 02 O 02 02 O 02 



002 O 002 002 002 002 002 





 100 

 200 



'J 10 



100 

 200 

 300 



Larvae 



II 



01 O 01 Ol 01 01 O Ol 





 100 

 200 

 100 



1 



N ftexipes 

 Postlarvae 





05 05 05 O 05 05 05 



02 O 02 02 02 02 O 02 



002 002 002 O 002 002 O 002 



01 01 01 O 01 01 01 



Abundance (ind/nf) 



Figure 8 



Vertical distribution of Stylocheiron affine, S. longicorne, S. maximum, 

 Thysanoessa gregaria, and Nematobrachion flexipes off Point Eugenia. 

 ND = no data. 



periods of weak upwelling, with descent even to 

 depths lacking oxygen (i.e. Santa Barbara Basin, 

 Alldredge et al., 1984). In the present study, no ag- 

 gregations of euphausiids analogous to copepods in 

 diapause were found. For some euphausiid species, 

 a low concentration of oxygen might limit migration 

 at depth during daytime. This case apparently oc- 

 curs in Saanich Inlet ( British Columbia ), where dense 

 aggregations of Euphausia pacifica were observed 

 directly above the anoxic layers ( 100-150 m ) ( Mackie 

 and Mills, 1983). Near this site, in the temperate fjord 

 of Dabbob Bay (Washington), a seasonal variation in 

 the vertical migratory range of E. pacifica was recorded 

 (Bollens et al., 1992). During the day, larvae of this 

 species occurred deeper in the water column in late 



summer and fall than in spring. However, they were 

 always above the depth levels of juveniles and adults 

 (50-125 m) during the day, the entire population mi- 

 grating to the surface at night (Bollens et al., 1992). 



The relation between vertical distribution of eu- 

 phausiids and low oxygen concentration has been 

 discussed for the eastern tropical Pacific (ETP) 

 (Brinton, 1979; Sameoto et al., 1987). In ETP the 

 layer of strongly depleted oxygen (<0.1 mL/L) is 

 present beneath the thermocline, to depths of 300- 

 400 m. The vertically migrating species in the ETP 

 group (Euphausia lamelligera, E. distinguenda , E. 

 diomedeae, and Nematoscelis gracilis) tolerate in- 

 tense 2 -deficiency at their daytime depths and en- 

 ter the oxygenated mixed layer at night (Brinton, 



