FISHERY BULLETIN: VOL. 84, NO. 3 



munity's species composition) to Ceriantharia 

 distribution exist at about 500, 900, and 1,600 m. 



Our submersible data indicate that shelf species 

 were confined to depths of less than about 400 m, 

 and the bathyal species (Cerianthid A) was seen 

 between 1,600 and 2,000 m. Published reports in- 

 dicate another unidentified species lives deeper than 

 about 1,000 m (Grassle et al. 1975; Hecker et al. 

 1980; Sebens in press). Similar depth zonation of 

 slope fauna inhabiting the study area have been 

 reported for isopods (Menzies et al. 1973), demer- 

 sal fishes (Musick 11 ), and megafauna captured in 

 trawls (Haedrich et al. 1980). Some environmental 

 factors, suggested as causes for observed distribu- 

 tions, are temperature, sedimentation rates, and 

 substrate types (summarized by Haedrich et al. 

 1975, 1980). 



The depth interval between about 400 and 600 m 

 on the continental slope south of New England is 

 a temperature transition zone; shallower bottom 

 waters experience larger seasonal temperature 

 variations than stable deeper waters (Sanders and 

 Hessler 1969; Haedrich et al. 1975). Depth-temper- 

 ature profiles (Fig. 6) made on A Ivin dives in Veatch 

 Canyon showed larger depth related temperature 

 variations also occurred shallower than 500 to 600 

 m. The shelf species (Cerianthids B, C, and D) may 

 not be able to tolerate and/or thrive in the cold stable 

 conditions below 500 m. 



The Cerianthid A population, we saw deeper than 

 1,600 m in the axis of Oceanographer Canyon, in- 

 habited sediments high in biogenic carbonates; 

 canyon axes may act as settling basins for suspended 

 matter being funneled downcanyon (Valentine et al. 

 1980). Rowe and Menzies (1969) attributed increases 

 in suspension-feeder concentration, in photographs 

 from the upper slope (200-800 m) and at the slope 

 base (3,000 m) off North Carolina, to increased 

 detritus accumulation resulting from downslope 

 movement and concentration by the prevailing bot- 

 tom currents. Haedrich et al. (1980) stated, in 

 reference to the depth zonation of megabenthic 

 fauna on the slope off southern New England, that 

 "zonation must result to some degree from vary- 

 ing strategies that promote success along a food 

 resource gradient". 



Haedrich et al. (1975) suggested boundaries to 

 zones of larger epifauna, at about 400 and 1,000 m 



n Musick, J. A. 1976. Community structure of fishes on the 

 continental slope and rise off the Middle Atlantic Coast of the 

 U.S. Manuscript presented at Joint Oceanographic Assembly, 

 Edinburgh, September. (Copies available from: J. A. Musick, 

 Virginia Institute of Marine Science, Gloucester Point, VA 23062, 

 USA). 



on the continental slope south of New England, 

 result from physical changes in the slope environ- 

 ment. Macllvaine (1973, p. 30-70) reported on the 

 physical environment in the same area (sediment 

 type, suspended sediments, and slope gradient). The 

 zone between 400 and 1,000 m consists largely of 

 homogeneous silt-sand substrate, near-bottom sus- 

 pended sediments at 520 m were 50 to 60 \xglh 

 (about 25% organics), and the slope gradient is about 

 1.4°. Deeper than about 1,000 m there are more 

 variable sediment features (stiff clayey silt sedi- 

 ments which are smooth or hummocky, talus slopes, 

 and rock outcrops), suspended sediments were 20 

 ^g/L (about 45% organics) at 1,000 m and 80 /ig/L 

 (about 80% organics) at 1,670 m, and the slope 

 gradient is steeper (7.6°). 



Suspension feeders rely on current velocity and 

 nutrient load for their food supply. Substrate vari- 

 ability deeper than 1,000 m may enhance Cerian- 

 tharia occurrence down to 2,000 m: Features such 

 as hummocks may act as perches for suspension 

 feeders, placing them up higher where current is 

 swifter and their food supply is replenished more 

 rapidly (Hughes 1975; Dyer 1980; Sebens 1984). 

 Higher suspended sediments and percentage of 

 organics may further enhance Ceriantharia occur- 

 rence below 1,600 m, as compared with 1,000 or 520 

 m. The lesser slope gradient between 400 and 1,000 

 m probably results in lower near bottom current 

 velocities; near the shelf-slope break in Ocean- 

 ographer Canyon, bottom currents are swifter at 

 105 to 300 m than at 650 m, due primarily to a dif- 

 ference in slope gradient (Valentine in press). Thus, 

 increased slope gradient may enhance Ceriantharia 

 occurrence below 1,000 m. 



Other mechanisms may affect ceriantharian depth 

 zonation such as the direct effects of pressure 

 (Siebenallar and Somero 1978), or predators (Paine 

 1966; Rex 1976); however, data were not available 

 to evaluate these factors. 



Submarine canyons received particular attention 

 during submersible dive activities because of the 

 potential entrainment of discharges from oil explora- 

 tion activities into productive canyon environments 

 (Cooper and Uzmann fn. 8). Bathymetric zonation 

 of slope fauna may be altered and/or species abun- 

 dance enhanced by submarine canyons (Rowe 1971; 

 Haedrich et al. 1975). The conduitlike nature and 

 substrate heterogeneity of canyons have both been 

 implied as explanations for observed faunal enrich- 

 ment in canyons as opposed to adjacent noncanyon 

 slope areas (Rowe and Menzies 1969; Rowe 1971, 

 1972; Haedrich et al. 1975; Hecker et al. 1980; 

 Valentine et al. 1980; Rowe et al. 1982). Although 



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