FISHERY BULLETIN: VOL. 74, NO. 4 



as offshore transport of the more numerous species 

 observed in nearshore waters. 



Distribution of Zooplankton Biomass 



The standing stock of zooplankton was highest 

 at the nearshore stations and decreased with 

 distances seaward. The largest and smallest 

 biomass values occurred along the southern tran- 

 sect and corresponded with high and low phyto- 

 plankton stocks, respectively (Malone 1971). 



Zooplankton were concentrated in the upper 

 100-150 m at most stations, particularly in the 

 mixed layer (ca. 0-40 m). Densities ranged from 10 

 to 580 g wet wt/ 1,000 m ' (Figure 2). Below 100-150 

 m, the amount of zooplankton at approximately 

 100-m intervals was generally between 25 and 150 

 g wet wt/ 1,000 m-'. Diel fluctuations in biomass 

 were greatest in the surface water (0-150 m) 



U1 



LiJ 



K 



UJ 



2 



Q. 



UJ 



o 



100 

 300 

 500 

 100 

 300 

 500 

 100 

 300 

 500 



(a) 



ZOOPLANKTON BIOMASS 



(GM wer WT PEO lOOO m3) 



50 2^ 



450 . 550 



1/1 

 CE 



U 

 »- 

 UJ 



2 



I 

 t- 



Q. 

 llJ 



a 



(b) 



Figure 2.-The vertical distribution of zooplankton biomass. 

 Clear bars indicate day samples; dark bars designate night 

 samples, (a) SOE cruise 22 and (b) CalCOFI cruise 7008. 



increasing at night by factors of 1.2-8. At two 

 nearshore stations, CalCOFI 50.80 and 70.75, large 

 quantities of phytoplankton clogged net meshes in 

 the upper 50 m and prevented any quantitative 

 comparison of day and night catches. Below 150 m, 

 a small but consistent increase in biomass was 

 usually observed at night {P = 0.20, Sign Test). 

 During the day, at some intervals between 250 and 

 400 m, biomass was equal to or slightly greater 

 than concentrations in the upper 150 m. 



Diversity, Density, and 

 Distribution of Euphausiid Species 



Twenty species of euphausiids distributed 

 among seven genera were identified. Thirteen 

 species occurred frequently enough and in 

 sufficient numbers to allow descriptions of their 

 vertical distribution. In the upper 150 m, 8 species 

 formed 50% of the total abundance and 12 made up 

 90%. Nine species were found at more than half the 

 stations. In the total water column sampled (ca. 

 0-700 m), 6 and 11 species composed 50 and 90% of 

 the total species abundance. At most stations one 

 or two species were numerically dominant. 



The distributions of euphausiids at midday and 

 midnight are discussed in the following para- 

 graphs. Only examples of a few species are illus- 

 trated to represent the major patterns observed 

 since a large number of profiles were derived from 

 the data for all the species collected at each station 

 (Youngbluth 1973). In many cases, diurnal changes 

 in vertical distributions were obscured either by 

 patchiness or avoidance or incomplete sampling 

 due to gear failure or foul weather. This account is 

 thus a composite description of the data from all 

 stations. 



Euphausia 



Four species of Euphausia were takeni-E". 

 pacifica, E. recurva, E. gibboides, and E. mutica. 

 With the exception of E. pacifica, these species 

 were only abundant at the offshore stations along 

 the southern transects (SOE 16, 25; CalCOFI 

 50.110). In this region densities of each species 

 usually ranged between 10 and 200/1,000 m^. 

 Juveniles and larvae were often more than twice 

 as numerous as adults. The daytime habitat of E. 

 mutica larvae was between 100 and 400 m. 

 Juveniles of this species were found only in one 

 haul which sampled from 400 to 500 m (SOE 16). 

 Euphausia gibboides and E. recu rva were collected 



928 



