174 



Fishery Bulletin 104(2) 



taxa fall <0.1'7(). Black corals had the largest incidence 

 of associated animals (15.3% of individuals), followed by 

 vase (3.9%), barrel (2%), foliose (1%), shelf (0.7%), and 

 flat (0.5%) sponges. Fish were most commonly observed 

 on black corals (1.3%) but were also observed on vase 

 sponges, including an attached egg case. No organisms 

 were observed living on gorgonians. 



The frequency of fish species near sponges, gorgoni- 

 ans, and black corals was significantly different from 

 the frequency of those same species found elsewhere 

 along transects (chi-square, all P<0.01; Table 4). Of the 

 108 species adjacent to these large invertebrates, six 

 species were found at significantly higher frequencies 

 than predicted by their density along transects: cowcod, 

 bank rockfish iSebastes rufus). swordspine rockfish 

 iSebastes ensifer). shortbelly rockfish iSebastes jordani), 

 pinkrose rockfish iSebastes simulator), and members of 

 the rockfish subgenus Sebastomus (Table 4). 



600 



Cnnoids 



nn^nnnrir^nn 



■^^-^L. 



The distribution of mean nearest-neighbor distances 

 between fishes and large invertebrates varied from 0.1 

 to 9.9 m (Fig. 10). Overall median distances varied from 

 0.9 m (shelf sponges) to 1.8 m (black corals). However, 

 there were no statistical differences between the me- 

 dian distances for each group (Kruskal-Wallis, H=WA; 

 df=6; P=0.11). For the six fishes that were found more 

 frequently near large invertebrates than on transects, 

 the overall median distances to the invertebrates were 

 5.5 m (cowcod). 1.0 m (bank rockfish), 1.3 m (swordspine 

 rockfish), 1.5 m (shortbelly rockfish), 1.7 m (pinkrose 

 rockfish), and 1.4 m (Sebastomus). 



The overall incidence of damaged and dead sponges, 

 gorgonians, and black corals was low (0.3% of total num- 

 ber observed). Black corals were more commonly damaged 

 (1.7%) or dead (1.1%), followed by vase sponges (0.6% and 

 0.1%, respectively), barrel sponges (0.5% and 0%), and 

 foliose sponges (0% and 0.1%). No dead or damaged flat 

 or shelf sponges or gorgonians were observed. 

 Damage in black corals included portions of the 

 colony that appeared discolored; dead black cor- 

 als lacked polyps and were discolored. Among 

 sponges, the most common damage was individu- 

 als that had broken from the substratum and 

 were lying on their side or broken colonies. 



Basket stars 



I 



r^ r^ .J. r^ n r;-! 



fi 



ri r^ Pn .=,,—, Pn Fl 



900 - 



Brittle stars 



^r^^OUO 



' I ' ' t ' ' I ' ' 1 



n 



JL 



^n^^ 



500 



E 

 o 



Bractiiopods 



^^^^ 



^1 1^ 



2 n 



White plumed anemone 



i 



rJ^ 



^ , ^ , 



200 - Fragile sea urchins 



1 



.n. 



o ^. 



-Oa 



50 



Sea pens 



rjl ^ -^ -, p O rp [7] 



n=9,726 



X 



n_ 



TT RR RIVl BB BC BS CB MB SB CS SC SP MG SG MM MS SS 

 Habitat code 



Figure 5 



Mean density of structure-forming invertebrates in habitat patches 

 of each substratum type. Vertical bars are + one standard error. 

 See page 169 for definitions for the substrate abbreviations along 

 the X axis. 



Discussion 



Several groups of invertebrates were distin- 

 guished by their large size, such as black corals, 

 sponges, crinoids, basket stars, anemones, and 

 sea pens. Organism size is an important aspect 

 of structural habitat because it contributes to 

 vertical relief and increases the availability of 

 microhabitats. For example, yelloweye iSebastes 

 rube?Ti?nus) rockfish may use the large gorgo- 

 nian coral Primnoa as a vantage point to prey 

 upon small fishes (Krieger and Wing, 2002). 

 Size variation among structure-forming inver- 

 tebrates was significant. Individual black corals, 

 sea pens, and sponges greater than 1 m in height 

 represented only 0.1% of all organisms, and 90% 

 of the individuals were <0.5 m high. 



Similarly, the complex structures of crinoids, 

 gorgonians, black corals, and basket stars may 

 increase the availability of microhabitats and 

 create a high surface area for settlement or 

 retention of other organisms. Fish egg cases 

 have been observed attached to both gorgonians 

 (Etnoyer and Morgan') and vase sponges (pres- 

 ent study. Table 3). 



High-density aggregations have not been used 

 as a criterion for defining structure-forming 

 invertebrates, but there are several examples 

 that illustrate the potential importance of these 

 aggregations. High density "forests" of crinoids 

 provide refuge and substrata for a wide variety 

 of small fishes and invertebrates in rocky areas 

 (Lissner and Benech, 1993; Puniwai, 2002). 



