PATCHINESS AND NUTRITIONAL CONDITION OF ZOOPLANKTON 



IN THE CALIFORNIA CURRENT 



Stewart W. Willason, John Favuzzi, and James L. Cox 1 



ABSTRACT 



Zooplankton and water samples were collected from 81 stations off the California coast in April 1981 

 during CalCOFI cruise 8104 aboard the RV David Starr Jordan. Abundance, weight (wet and dry), 

 digestive enzyme activity (laminarinase), and biochemical composition of three zooplankton species were 

 determined. The indices measured provided estimates of zooplankton nutritional history on time scales 

 of 1 day to 3 weeks. 



Upwelling was taking place along the California coast, from Point Conception to San Francisco dur- 

 ing the study period. The resulting low surface temperatures were most evident south of San Francisco 

 and just north of Point Conception. Just south of these areas patches of high phytoplankton standing 

 crop (up to 14.7 mg chlorophyll a/m 3 ) were found. The two herbivorous species, Euphausia pacifica and 

 Calanus pacificus, showed highest laminarinase activity in areas with the highest density of phytoplank- 

 ton: enzyne activity was particularly high in the waters off Point Conception. Zooplankters in the southern 

 and offshore regions of the sampling grid showed very low digestive enzyme activity. The larger size (weight) 

 and higher lipid content of C. pacificus near Point Conception and south of San Francisco in comparison 

 to animals in other parts of the California Current suggest that animals in these areas experience pro- 

 longed periods of better nutrition. Nematoscelis difficilis, which is not a herbivore, did not show these 

 patterns. This study illustrates the importance of upwelling regions, such as Point Conception, and shows 

 the large spatial variability of trophic interactions within the California Current System. 



The nearshore, pelagic marine environment is ex- 

 tremely variable and heterogeneous. Spatial hetero- 

 geneity of physical conditions elicit behavioral or 

 physiological responses from marine organisms 

 which contribute to biological patchiness (Haurey et 

 al. 1978; Steele 1978). Patchiness of pelagic marine 

 organisms occurs on all temporal and spatial scales 

 (Haury et al. 1978); one of the most important of 

 these is the mesoscale (a few kilometers to 100's of 

 kilometers, and a few weeks to months). Mesoscale 

 processes, such as coastal upwelling, play a major 

 role in structuring the physical and biological en- 

 vironment at all scales (Haury 1982). Although up- 

 welling regions are very productive (eg., Ryther 

 1969), trophic interactions within these important 

 areas are poorly understood. 



Along the California coast episodic upwelling takes 

 place during the spring and summer months (Reid 

 et al. 1958; Bernstein et al. 1977; Owen 1980; Lasker 

 et al. 1981; Parrish et al. 1981). Upwelling results 

 in mesoscale phytoplankton patchiness along the 

 coast and in the southward flowing California Cur- 

 rent (Owen 1974; Cox et al. 1982; Smith and Baker 

 1982; Pelaez and Guan 1982). It is thought that phy- 

 toplankton patchiness in this area influences the sur- 



^arine Science Institute, University of California, Santa Bar- 

 bara, CA 93106. 



vival and physiological condition of larval fish popula- 

 tions (Lasker 1975; Lasker and Smith 1977; Lasker 

 and Zweifel 1978; O'Connell 1980). In addition, nutri- 

 tion of herbivorous zooplankton (estimated by diges- 

 tive enzyme activity) is influenced by phytoplankton 

 patchiness (Cox et al. 1982; Cox et al. 1983; Willa- 

 son and Cox in press). 



This study investigates the impact that mesoscale 

 and larger scale phytoplankton patchiness have on 

 zooplankton populations within the California Cur- 

 rent along the central and southern California coast. 

 Results of measurements of temperature, phyto- 

 plankton biomass, zooplankton abundance, and zoo- 

 plankton nutrition are presented. Nutritional status 

 was evaluated using intrinsic properties which reflect 

 previous feeding conditions. Short-term feeding his- 

 tory was estimated from measurements of the acti- 

 vity of the digestive enzyme, laminarinase Although 

 digestive enzyme levels of zooplankton do not always 

 provide a good measure of instantaneous digestive 

 or feeding rates (Hassett and Landry 1983; Head 

 et al. 1984; Willason and Cox in press), the level of 

 activity in field captured animals does give an indica- 

 tion of relative feeding history on the order of 1 to 

 5 d (Cox 1981; Cox and Willason 1981; Cox et al. 

 1983; Willason 1983). Longer term nutritional con- 

 dition was assessed from biochemical composition 

 and animal size (wet and dry weight) measurements. 



Manuscript accepted April 1985. 



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