189 



Abstract — Understanding the in- 

 teractions between kelp beds and 

 nearshore fish is essential because 

 anthropogenic changes and natural 

 variability in these beds may affect 

 available habitat for fishes. In this 

 study fish communities were inves- 

 tigated in south-central Alaska kelp 

 beds characterized by a range of sub- 

 strate complexity and varying den- 

 sities of both perennial understory 

 kelps and annual canopy kelps. Many 

 of the observed fish species, as well 

 as understory and canopy kelps, were 

 positively associated with structurally 

 complex substratum. Targeted canopy 

 and understory kelp beds supported 

 seasonal populations of adult and 

 juvenile Pacific cod (Gadus macro- 

 cephalus), rockfishes (Sebastes spp.), 

 and year-round populations of green- 

 lings {Hexagrammos spp. I. Monthly 

 changes in kelp and fish communi- 

 ties reflected seasonal changes; the 

 densities of some species were great- 

 est during periods with higher tem- 

 peratures. This work illustrates the 

 importance of structurally complex 

 kelp beds with persistent understory 

 kelp populations as important fish 

 habitat for several commercially and 

 recreationally important fishes. 



Implications of substrate complexity 

 and kelp variability for south-central 

 Alaskan nearshore fish communities 



Judy Hamilton 



Kachemak Bay National Estuanne Research Reserve 

 95 Sterling Highway, Suite 2 

 Homer, Alaska 99603 



Email address: judy_hamilton@fishgame.state.ak.us 



Brenda Konar 



School of Fisheries and Ocean Sciences 

 University of Alaska Fairbanks 

 245 O'Neill Building 

 Fairbanks, Alaska 99775 



Manuscript submitted 10 September 2004 

 to the Scientific Editor. 



Manuscript approved for publication 

 29 August 2006 by the Scientific Editor. 



Fish. Bull. 105:189-196 2007). 



Marine macroalgal communities in 

 the shallow, rocky, nearshore zones 

 are among the most productive aquatic 

 biomes on earth and provide impor- 

 tant habitat for invertebrates, fishes, 

 and marine mammals (Steneck et al., 

 2002). Although the importance of 

 kelp bed variability (including kelp 

 density, distribution, and species com- 

 position) to fishes has been demon- 

 strated in Alaskan waters (Dean et 

 al., 2000; Hegwer, 2003; Hamilton, 

 2004; Calvert, 2005), the role of sea- 

 sonality in these habitats is poorly 

 understood, particularly in regions 

 with seasonal extremes, such as the 

 subarctic (but see Calvert, 2005). Fur- 

 thermore, although the persistence 

 and stability of kelp beds are at least 

 partly determined by suitable space 

 and substratum type (Dayton, 1985), 

 the importance of overall habitat com- 

 plexity (i.e., kelp cover and substrate 

 topography) to kelp-associated fish 

 species has not been investigated in 

 Alaska. 



Previous studies in Alaskan kelp 

 beds have shown positive correla- 

 tions between the presence of fishes 

 and the density (or biomass) of un- 

 derstory algae (Dean et al., 2000; 

 Hegwer, 2003; Hamilton, 2004). Re- 

 searchers elsewhere have also agreed 

 with these findings (Dayton, 1985) 

 but have demonstrated relationships 

 between fish density or biomass and 

 the relative abundance of the canopy 

 kelp Macrocystis pyrifera (Bodkin, 



1986; Carr, 1994). Macrocystis forms 

 dense stands that are generally stable 

 and provide persistent habitat; beds 

 composed of this perennial species 

 exhibit relatively little seasonal and 

 annual variation in structure (Day- 

 ton, 1985; Steneck et al., 2002). In 

 contrast, northern Pacific canopy 

 kelps are annuals (Alaria fistulosa 

 and Nereocystis luetkeana [hereafter 

 Nereocystis]) that afford much less 

 midwater structure. As a result, ver- 

 tical relief in northern Pacific kelp 

 beds is often seasonally restricted to, 

 and is more consistently provided by, 

 physical structure of the seafloor and 

 the perennial understory kelp species. 

 The importance of physical structure 

 (described by the measures of rugos- 

 ity, substrate size, and verticality) 

 to temperate and tropical reef fish 

 assemblages has been documented 

 (Aburto-Oropeza and Balart, 2001; 

 Garcia-Charton and Perez-Ruzafa, 

 2001), but little is known about the 

 importance of the physical structure 

 of kelp and substrate to fishes in 

 the northern Pacific rocky nearshore 

 zones. 



The objectives of this study were to 

 assess relationships of fish to habitat 

 structure and to seasonal variability 

 in kelp communities. We determined 

 the relationship of fishes to habitat 

 structure (classified according to ru- 

 gosity, size of substrate, and vertical- 

 ity) and kelp densities. Because north 

 Pacific macroalgal communities vary 



