Tissot et al : Invertebrates on deep banks off southern California 



171 



(Allocentrotus fragilis [4%]), and sea pens 

 (suborder Subselliflorae; [2%]; Fig. 4). 



The density of common structure-forming 

 invertebrates was variable across habitat 

 types; some species were found over a wide 

 range of habitats. Crinoids and basket stars 

 were found on all 17 habitat types but were 

 most dense on either high-relief rock or low- 

 relief mixed rock (Fig. 5). In contrast, brittle 

 stars and brachiopods were dense in low-re- 

 lief mixed rock but rare or absent in low-re- 

 lief mixed sediment. White sea urchins were 

 most dense in habitats with sand, whereas 

 fragile sea urchins were most dense in habi- 

 tats with mud. White-plumed anemones were 

 most dense in mud-gravel habitats, and sea 

 pens were most dense in low-relief mixed- 

 sediments (Fig. 5). 



Deep sea corals and sponges were the larg- 

 est structure-forming invertebrates but were 

 relatively uncommon (27^ of total) (Table 2). 

 Gorgonians were difficult to distinguish and 

 were categorized into one group (order Gor- 

 gonacea). The black coral is a new species 

 that recently has been described and named 

 the Christmas tree coral (Antipathes den- 

 drochristos) (Opresko, 2005). Sponges were 

 categorized into five groups based on their 

 structure and shape: flat, barrel, shelf, vase, 

 and foliose sponges (Fig. 6). 



Gorgonians and black corals were most 

 dense on low-relief mixed rock areas (Fig. 7). 

 However, gorgonians were found in only four 

 habitat types at 144-163 m depth, whereas 

 black corals were found on 12 habitat types 

 at 100-225 m depth, including pinnacle, boulder, and 

 sand areas. These differences may be due to the un- 

 equal number of observations (i.e., 27 gorgonian vs. 135 

 black coral colonies). 



The five morphological groups of sponges displayed 

 broad distributions across habitat types but were espe- 

 cially dense on high-relief rock and low-relief mixed rock 

 (Fig. 7). Flat, barrel, vase, and foliose sponges were found 

 in all habitats; shelf sponges were found in all habitats 

 except MM, MS, and SS. Foliose sponges were found 

 at significantly deeper depths (mean=191 m; SE = 53; 

 n=1259) than were other sponge groups (pooled mean=152 

 m; SE = 0.6; n=7545), which were not significantly dif- 

 ferent from each other (Kruskal-Wallis //=594; df=4; 

 P<0.01). Generally sponge size increased with increasing 

 depth, although the correlation was low (/■=0.07; P<0.001; 

 n = 6551). Although sponges were found throughout the 

 study area, gorgonians and black corals were restricted in 

 their distribution to a small number of sites (Fig. 8). 



Structure-forming invertebrates displayed wide varia- 

 tion in size; maximum height ranged from 4 cm for 

 brachiopods to 2.5 m for black corals (Table 2). There 

 was no significant correlation between size of the in- 

 vertebrate taxa and structural relief of the substratum 

 types (r=0.28, P=0.30, /z = 15). 



20 



10 



< 90 m. n =770 patcties 



IJ 



nH^^n 



r-1 n 



20 - 



10 - 



126-175 m. n=751 patcties 



n 



CL 



- n 



20 - 



10 



>175m, n =570 patches 



_a 



n^rin 



LX 



TT RR RM BB BC BS CB IV1B SB CS SC SP IVIG SG IVIIV1 fVIS SS 

 Habitat code 



Figure 3 



The frequency of habitat patches of each substratum type, stratified 

 by depth. See page 169 for definitions for the substrate abbrevia- 

 tions along the .r axis. 



Gorgonians and black corals had different size distri- 

 butions (Fig. 9). Black corals ranged from 10-250 cm 

 in height (mean=33.6; SE=1.9; n=195) and most indi- 

 viduals were in the 10-50 cm size category. Individuals 

 were found in three color forms: gray-to-white (SO'/f ), 

 rusty-brown-to-red (47%), and gold (3%). Gorgonians 

 ranged in size from 10 to 40 cm (mean=21.7; SE = 1.2; 

 n=27) and were found in multiple morphological forms 

 from elongate to fan-like (Fig. 6). 



Sponges displayed similar size distributions to those 

 of gorgonian corals, but had different mean and max- 

 imum sizes (Fig. 9). Mean sizes of flat, barrel, and 

 foliose sponges were not significantly different from 

 each other (pooled mean=19.8 cm; SE = 0.1; ;!=7373) but 

 were significantly smaller than vase and shelf sponges 

 (pooled mean = 20.9 cm; SE = 0.2; ?! = 1289), which were 

 not different from each other (one-way ANOVA; F=4.52; 

 df=4,8657; P=0.001). The maximum observed height 

 was 50 cm for shelf sponges, 60 cm for foliose sponges, 

 and 100 cm for barrel, flat, and vase sponges (Fig. 9). 



Most (98.2% by number) sponges, gorgonians, and 

 black corals by number did not have any other organ- 

 isms living on them (Table 3). Overall, crinoids (1.4%) 

 were most commonly associated with these large in- 

 vertebrates, followed by sponges (0.1%), and nine other 



