168 



Fishery Bulletin 104(2) 



Deep-sea corals, such as gorgonians (sea fans), antipa- 

 ththarians (black corals), scleractinians (stony corals), 

 and hydrocorals, are of particular interesc because they 

 are often long-lived and slow-growing (Andrews et al., 

 2002; Heifetz, 2002), poorly studied (Etnoyer and Mor- 

 gan'), and in certain situations vulnerable to human 

 activities (e.g., mobile fishing gear) (Watling and Norse 

 1998; Freese et al., 1999; Krieger, 2001; Dayton et al., 

 2002: Fossa et al., 2002; NRC, 2002;). Other megafau- 

 nal invertebrates, such as crinoids, basket stars, and 

 sponges also may enhance the structural components 

 offish habitat (Puniwai, 2002) and may be disturbed 

 or destroyed by some fishing activities 'Freese, 2001; 

 Krieger, 2001). 



The potential for invertebrates to add functional 

 structure to benthic communities has centeicd large- 

 ly around their size and complex morphology. A size 

 threshold of 1 m has often been used as an indicator 

 of structure-forming species because marked changes 

 in benthic community structure have been observed 

 in areas where rocky substrata exceed 1 m (Lissner 

 and Benech, 1993). The complex structure of deep-sea 

 corals also has been discussed as an important factor 

 that contributes to microhabitat diversity (Krieger and 

 Wing, 2002; Etnoyer and Morgan'). In this article, be- 

 sides forming complex structure and large size, we also 

 believe that megafaunal invertebrates form structure 

 if they aggregate in high numbers, especially in areas 

 of low relief For example, aggregations of sea urchins 

 and sea pens may provide significant structural relief 

 for fishes in mud- and sand-dominated habitats (Bro- 

 deur, 2001). 



An important question is the extent to which struc- 

 ture-forming invertebrates are ecologically important to 

 fishes, especially those of economical value. Most studies 

 have focused on "associations" between structure-form- 

 ing invertebrates and fishes as a measure of ecological 

 importance at several spatial scales. Fishes have been 

 considered to be associated with invertebrates if they 

 are found in the same trawl sample (Heifetz, 2002), 

 if fishing is higher in areas with corals than without 

 corals (Husebo et al., 2002), if they are found together 

 within similar habitats observed from a submersible 

 (Hixon et al.-), or if they are observed "among or within 

 1 m" from corals (Krieger and Wing, 2002). In this 

 article we investigated association at three different 

 levels: 1) fishes that are physically touching large in- 

 vertebrates; 2) fishes that are found statistically more 

 frequently near large invertebrates in relation to their 

 overall abundance patterns; and 3) fishes that are found 

 as nearest neighbors to large invertebrates. 



The goal of this study was to describe patterns in 

 the density, distribution, and size of structure-forming 

 megafaunal invertebrates on deep rocky banks and 



outcrops off southern California. Given the recent inter- 

 est in these organisms as potentially important habitat 

 for groundfishes, and thus targets for protection from 

 fishing activities, these organisms deserve a critical 

 examination of their potential to contribute structure 

 to continental shelf and slope ecosystems and an ex- 

 amination of their associations with fishes and other 

 marine organisms. Accordingly, our specific objectives 

 were the following: 



• Identify structure-forming invertebrates based on cri- 

 teria of size, morphological complexity, and density; 



• Quantify the density and size distributions of these 

 invertebrates according to depth and substratum 

 types; 



• Quantify associations between large, structure-form- 

 ing invertebrates and other organisms, particularly 

 fishes; and 



• Assess the health of these organisms in terms of 

 obvious physical damage. 



Materials and methods 



Underwater surveys were conducted off southern Califor- 

 nia by using nonextractive video-transect methods and 

 direct observations from an occupied research submers- 

 ible (Delta) from 8 October to 6 November 2002. These 

 surveys were conducted as part of a larger investigation 

 into the abundance, size, and distribution of cowcod 

 (Sebastes levis) and associated benthic fishes and habi- 

 tats inside and around the newly established Cowcod 

 Conservation Areas (CCAs) off southern California (Fig. 

 1). The CCAs, which encompass 14,750 km- and are 

 closed to groundfish harvest in water depth >37 m, were 

 established in 2001 to assist in rebuilding the depleted 

 cowcod population off southern California. 



Digital, georeferenced maps of seafloor substratum 

 types, interpreted from side-scan sonar, multibeam ba- 

 thymetry, seismic reflection, and other past geophysical 

 surveys, were used to identify and select sites of rocky 

 habitats (Greene et al.'). We attempted to restrict the 

 substratum types to mixed sediment and rock and to 

 30-330 m depth (i.e., likely cowcod habitat). 



The Delta submersible was tracked by using an ORE 

 Trackpoint II plus (ORE Offshore, West Wareham, MA) 

 USBL system and WINPROG (vers. 3.1, FUGRO. San 

 Diego, CA) software. We linked the tracking system to 

 our ArcView"^ GIS (vers. 3.2, ESRI Corp., Redlands, CA) 

 seafloor mapping project and tracked the submersible 

 real-time in relationship to depth and seafloor habitat 

 maps. 



2 Hixon, M. A., B. N. Tissot, and W. G. Pearcy. 1991. Fish 

 assemblages of rocky banks of the Pacific northwest, Heceta, 

 Coquille, and Daisy Banks. OCS Study MMS 91-0052. 

 410 p. U.S. D.I. Minerals Management Service 770 Paseo 

 Camarillo. 2"'' Floor, Camarillo, CA 93010. 



3 Greene, H. G., J. J. Bizzarro, D. M. Erdey. H. Lopez, L. 

 Murai, S Watt, and J. Tilden. 2003. Essential fish habi- 

 tat characterization and mapping of California continental 

 margin. Moss Landing Marine Laboratories Technical Pub- 

 lication Series No. 2003-01, 29 p., 2 CDs. Moss Landing 

 Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, 

 CA 9.5039. 



