PEARCY: MICRONEKTON AND MACROZOOPLANKTON OFF OREGON 



100 



I I I I I 1 I I I I T 1 1 i I i I l; I I I rr 1 1 1 I ! I I I 



. . I I I I 1 1 1 v y I •;• I I I I I I I I 

 jjasond'jf' mamj jasond 



1963 



1964 



JFMAMJJASONDJFMAMJJASOND 



1965 ' 1966 



J F M A M J J 



1967 



Figure 5. — Biomass of macrozooplankton captured in 1-m diameter plankton nets at four 

 stations, 1963-1967. Each point represents one collection. 



differences were for medusae, whose standing 

 stocks in the summer exceeded those in the winter 

 at 28 and 46 km (Mann-Whitney U, P<0.01) and 

 perhaps at 84 km (P = 0.06), and for shrimps at 84 

 km, where again biomass was larger during sum- 

 mer than winter (Table 2). 



Trophic Groups 



To estimate seasonal and inshore-offshore vari- 

 ations in the standing stocks of the lower trophic 

 levels of oceanic consumers, the dry weights of the 

 various taxa were combined. Herbivores were 

 assumed to include copepods, euphausiids, and 

 salps-doliolids. Planktonic carnivores included 

 chaetognaths, medusae, amphipods, and shrimps. 

 Nektonic carnivores included fishes, squids, and 

 shrimps. Although it is recognized that some 

 euphausiids and copepods may be carnivorous, the 

 main species captured off Oregon, Euphausia 

 pacifica, Thysanoessa spinifera, and Calanus spp., 

 are considered to be largely herbivorous. 



Inshore-offshore variations in standing stocks 

 are illustrated in Figure 6. On the average, the 

 biomass of herbivores was greater than planktonic 



40 



35 



^"£ 30 

 O 



^25 



20 



X 



y 15 



g 10 



h^ 



PLANKTONIC j 



CARNIVORE§-.| J._ \ 



NEKTONIC 

 CARNIVORES 



— O'- 



28 



46 84 120 



DISTANCE OFFSHORE (km! 



>I20 



Figure 6. — Inshore-offshore variations in the average biomass 

 (± 1 SE) of herbivores, planktonic carnivores, and nektonic 

 carnivores at five stations. 



carnivores, and the biomass of these organisms 

 was greater than that of micronektonic carni- 



75 



