SHEPARD ET AL.: ECOLOGY OF CERIANTHARIA 



we had no adjacent slope dives to compare with the 

 canyon dives, Ceriantharia were common in canyons 

 and have been suggested to be canyon "indicator" 

 species (Rowe 1972). In the future, we hope a 

 canyon-slope comparison of Ceriantharia species' 

 diversity and abundance will be made. 



Relation to Bottom Water Temperature 



Wigley and Theroux (1981) found that total macro- 

 faunal density in the Middle Atlantic Bight generally 

 increased directly with increasing temperature 

 range (A T). Ceriantharia occurrence at grab sam- 

 ple stations followed this trend until A T reached 

 15.9°C, after which it decreased (Fig. 4). Why an 

 intermediate temperature range may be favorable 

 to Ceriantharia is unknown. Wide ranges might en- 

 tail harmful extremes of temperature, while nar- 

 rower ones may be too constant at an unfavorable 

 level, or larval stages may benefit from some degree 

 of fluctuation for maximal development ( Andrewar- 

 tha and Birch 1954, p. 129-205). Information on how 

 temperature affects ceriantharian metabolism, 

 activity patterns, and development is lacking. 



Marine organism distributions are largely con- 

 trolled by temperature (Hutchins 1947; Crisp 1965; 

 Gosner 1971). The most obvious effect of tempera- 

 ture on invertebrate distributions is exclusion of 

 species from areas with unsuitable thermal regimes 

 (Kinne 1970). Submersible data on ceriantharian 

 geographic and bathymetric distribution demon- 

 strate allopatric speciation which we believe is 

 primarily a response to temperature. 



Relation to Sediments 



The presence of silt is characteristic of deposi- 

 tional areas which may be favorable to suspension 

 feeders (Rowe and Menzies 1969). Wigley (1968) 

 described Ceriantharia as common inhabitants of 

 silty-sand sediments on Georges Bank. Through 

 resuspension, surficial deposits are potential food 

 for Ceriantharia (Rhoads 1974). In addition to low 

 deposition, substrate instability may account for the 

 scarcity of Ceriantharia in 100% gravel and rippled 

 coarse sand substrate. Shifting substrates, such as 

 the 100% gravel sediments at grab sample stations 

 or the rippled sand dunes observed from submer- 

 sibles, may harm suspension feeders through 

 clogging of feeding apparatus, or the burial of lar- 

 vae (Sanders 1956; Ross 1968; Rhoads and Young 

 1970; Rhoads 1974). 



However, Ceriantharia were generally cosmo- 

 politan with respect to substrate (Fig. 4; Appendix 



Tables 1, 2). They are well adapted to withstand 

 strong currents, sediment movement, and extreme 

 deposition of fine material because their tubes pro- 

 vide firm anchorage (Frey 1970) and protection 

 against clogging or burial (Pearce 1972). Pearce et 

 al. (1976) found Ceriantharia were dominant macro- 

 fauna in fine carbon-rich sediments stressful to other 

 benthic species, near New York Bight sewage sludge 

 disposal sites. 



Just as 100% gravel substrate is unfavorable for 

 burrowing, a gravel veneer might also be expected 

 to limit space available for burrowing. However, on 

 submersible dives, Ceriantharia were frequently 

 seen in gravel-covered areas (less than about 50% 

 gravel cover). These deposits, probably Pleistocene 

 ice-rafted glacial debris, are exposed in areas which 

 usually experience higher currents than adjacent 

 areas (Valentine et al. 1980; Valentine in press), a 

 favorable consideration for suspension feeders. 



Spatial Pattern 



Local conditions of food supply, substrate, or 

 micro topography, may enhance Ceriantharia aggre- 

 gation (Fig. 7). Local differences in food supply may 

 allow Ceriantharia to survive in aggregations. 

 Grassle et al. (1975) observed that strongly clumped 

 suspension-feeders were able to maintain aggrega- 

 tions because their food supply was continually 

 renewed. Unusually high Ceriantharia abundances 

 near a sewage sludge/dredge spoil disposal area may 

 have occurred owing to the increased amounts of 

 organic matter (Pearce et al. 1976). 



Grassle et al. (1975) found Ceriantharia, similar 

 to Cerianthid A, more randomly distributed on the 

 continental slope, south of Cape Cod (depth of 1,465 

 to 1,830 m, homogeneous sandy silt-clay substrate). 

 In comparison, substrata in canyon heads where 

 aggregations were observed from submersibles are 

 heterogeneous (Hecker et al. 1980; Valentine et al. 

 1980). Our grab samples showed the same contrast 

 between heterogeneous substrata shallower than 

 500 m and homogeneous silt-sands and clays down- 

 slope (Shepard and Theroux fn. 4). Since inver- 

 tebrates are capable of substrate selectivity (Thor- 

 son 1966; Gray 1974), a variable substrate may be 

 characterized by patchy inhabitant distributions 

 (Hecker et al. 1980). 



The Cerianthid B aggregation in Lydonia Canyon 

 (Fig. 7), located on a knoll, may benefit from 

 elevated positioning and swifter currents (Hughes 

 1975; Sebens 1984), thus aggregations may also 

 form in response to local changes in surface 

 elevation. 



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