FISllKKV HILLKTIN; VOL. 86, NO. 4 



Table 5.— Food of adult Sebastes mystinus relative to near-surface plankton during downwelling episodes of winter. 



n = 4. 



Shoreward transport can be either wind-driven 

 (Ekman transport), or result simply from relaxation 

 of the forces that drive up welling. But in either case 

 our observations indicate that shoreward flowing 

 surface waters override the colder waters near 

 shore, a process we refer to as downwelling. Usually 

 the term downwelling is limited to conditions that 

 result from shoreward Ekman transport (e.g.. Gross 

 1977), but we have found that relaxation of upwell- 

 ing has essentially the same effect on the nearshore 

 ecosystem, the difference being simply in degree of 

 effect. 



Some studies have concluded that warming of the 

 nearshore surface waters during relaxation of up- 

 welling results from alongshore advection (e.g., 

 Send et al. 1987), but even though zooplankters 

 entering our study area during downwelling gen- 



erally moved southward along the coast, the char- 

 acteristic presence of such forms as thaliaceans, 

 ctenophores, and pteropods indicate that the advec- 

 tion is from offshore. So despite the complexities 

 of circulation and mixing that occur in the coastal 

 waters off northern California (e.g., Winant et al. 

 1987), the net result affecting the trophic relations 

 of S. mystinus are alternations between seaward 

 and shoreward transport. 



These water movements follow a strong seasonal 

 pattern that is evident in upwelling indices for lat. 

 39°N (which crosses Mendocino) produced by the 

 Pacific Fisheries Environmental Group of the South- 

 west Fisheries Center, NMFS, NOAA. In addition 

 to the seasonal trend, short-term episodes of sea- 

 ward and shoreward transport produce day-to-day, 

 even hour-to-hour, changes in the foods available to 



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