Love et al ; Fish assemblages around oil platforms in the Santa Barbara Channel area 



111 



2-, 



• Species diversity (H') 

 ^ Number of species 



X 



> 



■5 



CO 



1.5 



1 - 



0.5- 



15 



-10 



— I- 

 o 



H 



■a 

 o 



West 



o 



East 



3 

 a- 



-20 



-15 



-10 



CO 



5' 





Figure 7 



(A) Species richness (number of species) and species diversity (Shannon- 

 Weaver diversity index, H') and (B) density (fish/100 m^) and biomass 

 ( kilograms/m- ) on the midwater transects of seven platforms in the Santa 

 Barbara Channel area. Platforms are ordered by geography from northwest 

 (Irene) to southeast (Gail). 



bination with the wells, crossbeams, and pilings pro- 

 vide a greater degree of habitat complexity and thus, 

 may allow a greater number of species to coexist. 



Platforms north of Pt. Conception in the Santa 

 Maria Basin contain far more YOY rockfishes than 

 those in the Santa Barbara Channel to the south. 

 This geographic difference is almost certainly due 

 to the difference in water masses of the two areas. 

 Platforms north of Pt. Conception are more exposed 

 to the California Current; those south of the Point 

 are more influenced by Southern California Bight 

 water (Brink and Muench, 1986; Hickey, 1992). There 



is considerable evidence that, within much of the 

 Southern California Bight, juvenile rockfish recruit- 

 ment has been poor for a number of years (Ste- 

 phens et al., 1984, 1994; Love et al., 1998), probably 

 due to decadal-long changes in oceanographic condi- 

 tions. Since the late 1970s, waters off Southern Cali- 

 fornia have warmed significantly and upwelling has 

 declined. This situation has led to reduced zooplank- 

 ton production (Roemmich and McGowan, 1995) and 

 a reduction in the survival of many marine fish spe- 

 cies in early life stages (Holbrook and Schmitt, 1996). 

 The present regime is probably part of a long-term 



