PETERSON and MILLER: SEASONAL CYCLE OF ZOOPLANKTON ABUNDANCE 



I00 r 



ACARTIA CLAUSII 



\CENTROPACES 



A LONGIREMIS 



CALANUS ' NAUPLII \pARACALANUS 



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FIGURE 4. — Seasonal cycle of relative abundance (percent of total catch) of the most abundant zooplankton species (all copepods) at 

 stations NH 1, NH 3, NH 5, and NH 10 along the Newport, Oreg., transect over the 3-yr study period. Centropages were C. abdominalis, 

 A. longiremis were Acartia longiremis , Calanus were C. marshallae, Paracalanus were P. parvus, and Oithona were O. similis. 

 Pseudocalanus sp. are represented by the white area at the bottom of each graph. All remaining zooplankton are represented by the 

 white area at the top of each graph. 



most dominant during the spring. Paracalanus 

 parvus and Oithona similis have their highest rel- 

 ative abundance during the winter. 



Different years were different at NH 1, as previ- 

 ously noted (Peterson and Miller 1975). 

 Pseudocalanus sp. had a much higher relative 

 abundance during the 1969 and 1971 upwelling 

 seasons than in 1970. During the 1970 upwelling 

 season, A. clausii and Pseudocalanus sp. shared 

 numerical dominance in many samples. Centro- 

 pages abdominalis was less important during the 

 1971 upwelling period than in earlier years. Acar- 

 tia longiremis was about equally dominant at var- 

 ious times during all three upwelling seasons. 

 Oithona similis was more important during the 

 summers of 1969 and 1971. Paracalanus parvus 

 was a significant fraction of the plankton over 



broader time intervals in 1969 and 1970 than in 

 1971. 



At NH 3 the most striking aspect of the annual 

 cycle compared with NH 1 is the greatly decreased 

 importance of Acartia clausii and generally in- 

 creased importance of A. longiremis and Calanus 

 marshallae. Acartia clausii made up a large frac- 

 tion of the catch only during October 1970. Acartia 

 longiremis and C. marshallae were major compo- 

 nents over broader intervals in 1970 and 1971 at 

 NH 3 than at NH 1. The annual cycle of Pseudo- 

 calanus sp. relative abundance at NH 3 was about 

 the same as for NH 1, except for two periods: July 

 of 1970 and 1971. During both times Pseudo- 

 calanus sp. was dominant at NH 1, whereas A. 

 longiremis was dominant at NH 3. 



The NH 5 plot is similar to that for NH 3, par- 



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