YEAR-TO-YEAR VARIATIONS IN THE PLANKTOLOGY OF 

 THE OREGON UPWELLING ZONE 



William T. Peterson and Charles B. Miller' 

 ABSTRACT 



Sampling results from Oregon coastal waters show that plankton abundance in 1971, a year of reduced 

 coastal upwelling, was lower than in 1969 or 1970. This was correlated with greater frequency and 

 abundance in 1971 for species usually found more offshore and with a general reduction in the number 

 and density of the most strictly neritic species. It is proposed that these changes are related to changes 

 in nearshore fisheries which, therefore, appear to depend upon the general stimulation of production by 

 upwelling. 



In this paper we describe the nearshore zooplank- 

 ton community found off the Oregon coast during 

 the upwelling seasons of 1969, 1970, and 1971. 

 Differences in species composition and abundance 

 between the individual upwelling seasons will be 

 described and related to differences in upwelling 

 strength, hydrographic conditions, and wind pat- 

 terns. Our research on coastal zooplankton is cen- 

 tered upon understanding the dynamics of the 

 nearshore community found within 18 km of the 

 beach. We have concentrated our efforts in this 

 area because it has been shown to be the location 

 of the most intense coastal upwelling. Effects of 

 upwelling are present farther offshore, but the 

 phenomenon is most pronounced within 10 km of 

 shore (Huyer 1974). The importance of under- 

 standing coastal upwelling and its effect upon 

 biological production is well established. 



PREVIOUS ZOOPLANKTON STUDIES 

 IN THE OREGON AREA 



Distribution and abundance of Oregon coastal 

 zooplankton has been the subject of several theses 

 at Oregon State University. Seasonal variations in 

 distribution and abundance along a single line of 

 latitude have been studied by Hebard (1966) off 

 Newport (Figure 1) and by Laurs (1967) off 

 Brookings. Both seasonal and spatial variations 

 were considered by Cross (1964) from data collect- 

 ed off Astoria, Newport, Coos Bay, and Brookings. 

 Lee (1971) looked at samples collected from a grid 

 of stations during one brief interval in August 

 1963. Both Hebard and Laurs employed plankton 



'School of Oceanography, Oregon State University, Corvallis, 

 OR 97331. t. h- J 6 J, 



nets with a mesh size of 570 ju.m while Cross and 

 Lee used nets with 240-/xm mesh. Since the larger 

 mesh retained only very large forms, some very 

 different conclusions about the relative impor- 

 tance of zooplankton species were reached by the 

 different authors. Hebard found that the 

 euphausiid Euphausia pacifica was numerically 

 dominant, and Laurs found that this animal 

 dominated the zooplankton biomass. Copepods 

 were unimportant in their studies. Conversely, 

 Cross and Lee found that the copepods Oithona 

 similis, Pseudocalanus, and Acartia longiremis 

 were numerically dominant. A forthcoming paper 

 by Pearcy (in litt.) will summarize the results of a 



.40' 



44°30'N 



I24°W 



Figure l.-Map of the study area showing the Newport 

 hydrographic line (solid dark line) and the sampling positions. 



Manuscript accepted October 1974 

 FISHERY BULLETIN: Vol. 73, No. 3, 1975 



642 



