FISHERIES BULLETIN: VOL. 84, NO. 1 



Lipid content, size, and water content of a zooplank- 

 ton species reflect feeding history on the order of 

 1 to 3 wk (Omori 1970; Lee et al. 1970, 1971; Bam- 

 stedt 1975; Childress 1977; Boyd et al. 1978; Vidal 

 1980; Hakanson 1984). Spatial patterns derived from 

 these data are used to estimate relative differences 

 in feeding and nutritional condition of zooplankton 

 from different areas within the California Current. 

 An understanding of the interrelationships of these 

 variables in different areas may provide insights in- 

 to mechanisms which generate and maintain physical 

 and biological mesoscale features. 



METHODS 



Species Studied 



Two euphausiid species, Euphausia pacifica Han- 

 sen and Nematoscelis difficilis Hansen, and the 

 copepod, Calanus pacificus Brodsky were chosen for 

 the present study because 1) all are common in the 

 California Current region (Fleminger 1964; Brinton 

 1967b), 2) all have been used in previous digestive 

 enzyme studies (Cox 1981; Cox and Willason 1981; 

 Hassett and Landry 1982, 1983; Cox et al. 1983; 

 Willason 1983; Willason and Cox in press), and 3) 

 a large base of information exists on the sizes, 

 feeding rates, and energetics of these zooplankters 

 (Brinton 1967a; Mullin and Brooks 1976; Vidal 1980; 

 Ross 1982; Cox et al. 1983; Torres and Childress 

 1983; Willason 1983; Hakanson 1984; Willason and 

 Cox in press). Euphausia pacifica, the most abun- 

 dant euphausiid in the California Current (Brinton 

 1967b; Brinton and Wyllie 1976; Youngbluth 1976), 

 and C. pacificus, the most abundant copepod along 

 the California coast (Fleminger 1964; Star and 

 Mullin 1981), are considered primarily herbivorous 

 (Mullin and Brooks 1976; Ross 1982; Willason and 

 Cox in press). By contrast, N. difficilis does not ap- 

 pear to be a herbivore (Nemoto 1967; Mauchline and 

 Fisher 1969; Willason and Cox in press). 



Sample Collection 



The sampling program was conducted off the Cali- 

 fornia coast from 7 to 27 April 1981 in conjunction 

 with the California Cooperative Fisheries Investiga- 

 tion (CalCOFI) survey. Zooplankton and water sam- 

 ples were collected from 81 stations during CalCOFI 

 cruise 8104 aboard RV David Starr Jordon. Figure 

 1 shows the stations sampled and the sampling se- 

 quence during the cruise. The grid covered an area 

 of about 270,000 km 2 ; nearshore stations were 

 sometimes within 1 km of the coast and offshore 



stations were located up to 300 km from the 

 coast. 



Although the mean flow of the California Current 

 is south through the sampling grid at this time of 

 the year (Lynn et al. 1982), smaller regions within 

 the grid are often subjected to different hydro- 

 graphic influences. For example, the waters of the 

 offshore regions intergrade with the waters of the 

 Central Pacific Gyre (Bernstein et al. 1977); the 

 nearshore region south of Point Conception (the 

 Southern California Bight) is characterized by a 

 semipermanent, counterclockwise eddy and is hydro- 

 graphically distinct from the other areas of the grid 

 (Owen 1980); and the nearshore area adjacent to and 

 north of Point Conception is characterized by periods 

 of intense coastal upwelling during the spring and 

 summer months (Parrish et al. 1981). To compare 

 the biological and nutritional properties of zooplank- 

 ton in the different hydrographic regions, the sam- 

 pling grid was divided into four sections: southern 

 nearshore (I), northern nearshore (II), southern off- 

 shore (III), and northern offshore (IV) (Fig. 1). 



Surface chlorophyll a concentration (depth of 2 m) 

 was used as an indicator of phytoplankton standing 

 crop. Previous studies have shown that there are 

 positive correlations between surface chlorophyll a, 

 integrated chlorophyll a, and primary production in 

 the waters of the California Current (Lorenzen 1970; 

 Hayward and Venrick 1982). Measurements of sur- 

 face chlorophyll a, therefore, give a relative approx- 

 imation of phytoplankton biomass within the sam- 

 pling grid. 



Two replicate water samples (0.25 to 2.0 L) for 

 chlorophyll a analysis were taken at each of the 81 

 stations from a depth of about 2 m using the ship's 

 seawater pumping system. Each sample was filtered 

 through a 4.5 cm Whatmann GF/C filter; two drops 

 of a seawater-saturated MgC0 3 solution were add- 

 ed during filtrations. The filters were folded in half 

 and stored frozen in aluminum foil at -20°C. An 

 additional 15 water samples were taken for chloro- 

 phyll a analysis along the cruise track adjacent to 

 and immediately south of the Point Conception 

 region while the ship was under way. Measurements 

 of surface water temperature (±0.1°C) were also 

 taken at each station using a glass mercury thermo- 

 meter. 



Paired bongo nets (designated net 1 and net 2) with 

 mouth openings of 0.396m 2 and mesh openings of 

 505 ptm were used for the collection of zooplankton 

 samples. A General Oceanics 2 flowmeter was mount- 



2 Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



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