HOBSON and CHESS: TROPHIC RELATIONS OF THE BLUE ROCKFISH 



Table i . 



-Conditions during sampling sessions off Salmon Point, Mendocino 

 County, 1978-81. 



'Plankton condition. D = Downwelling condition: zooplankters considered to be off- 

 shore species, especially relatively large gelatinous forms, numerous. U = Upwelling con- 

 dition: offshore zooplankters absent. M = Mixed condition: some offshore zooplankters 

 present. 



kelp, Nereocystis leutkeana, which is the major com- 

 ponent of the kelp forests. These same seas, often 

 heavily laden with sediment, had also scoured the 

 seafloor of much of the algal understory, as well as 

 many of the sedentary invertebrates. Once the up- 

 welling season had been established, however, the 

 habitats changed rapidly. 



Often during early-season upwelling the water 

 was relatively transparent, although after rains visi- 

 bility often was limited by suspended sediment dis- 

 charged into the nearshore habitat from coastal 

 streams. By mid-May, however, the numbers of 

 planktonic diatoms (primarily Chaetoceros sp. and 

 Nitzchia sp.) had greatly increased to depths of 



Event 9— In the last major upwelling of this upwelling season, sea temperatures fell to 9.4°C on 2 September after 10 con- 

 secutive days of 5-8 K northerlies. 



Event 10— Sea temperatures rose steadily to 11.4°C on 17 September after 1-3 day periods of 4-8 K northerlies had alter- 

 nated with 1-4 day periods of 4-8 K southerlies through the first half of that month. 



Event 11— Sea temperatures fell to 10.5°C on 24 September after 7 consecutive days of 5-15 K northerlies. A shift to southerlies 

 on 25 September started another climb, and the transition to the downwelling season clearly was under way. This transition, 

 however, was not nearly so well defined as that which had introduced the upwelling season 6 months before. 



721 



