FISHERY BULLETIN: VOL. 84, NO. 3 



Functional Role 



An increase in structural complexity of the sub- 

 strate vertically and/or horizontally increases the 

 number of microhabitats, and if the appropriate 

 colonizers and mortality sources are present, within- 

 habitat diversity will likely be increased (Steimle and 

 Stone 1973; Abele 1974; Hughes 1975; Woodin 1976, 

 1978; Connell 1978; Suchanek 1979; Hulbert et al. 

 1982). Ceriantharia tubes may increase species 

 diversity and abundance on featureless soft bottom 

 areas by 1) attracting motile megafauna seeking 

 refuge near tubes and 2) serving as a favorable 

 substrate for epifauna and infauna, particularly 

 suspension-feeders and tubiculous species. 



By acting as a three-dimensional refuge, the tubes 

 may ease predation pressure on smaller motile 

 species (Ware 1972; Whoriskey 1983). Demersal fish 

 and crustaceans similar to those we observed have 

 been noted by others in association with Cerian- 

 tharia (Uzmann et al. 1977; Hecker et al. 1980; 

 Valentine et al. 1980). The species most commonly 

 observed near tubes, Helicolenus dactylopterus, 

 Sebastes sp., and Bathynectes sp., characteristical- 

 ly exhibit thigmotactic behavior. 



Associations similar to the ones we found between 

 suspension feeders and Ceriantharia tubes in Block 

 Canyon (Figs. 3D, 8), and polychaetes and tubes 

 from Oceanographer Canyon (Appendix Table 3), 

 have been recorded for Ceriantharia and polychaetes 

 (Kingsley 1904; O'Connor et al. 1977), phoronids 

 (Ponder 1971; Emig et al. 1972; Hartog 1977), and 

 bivalves (Ponder 1971). These associations have 

 been alternately referred to as commensalism or in- 

 quilinism; we prefer the latter definition as it high- 

 lights the role of the ceriantharian tube. Emig et 

 al. (1972) speculated that Cerianthus maua Carlgren 

 tentacles may act as baffles, causing waterborne 

 food particles to settle out, and become available to 

 suspension feeders (Phoronis australis Haswell) in- 

 habiting the C. maua tubes, in which case the term 

 commensalism may be more appropriate. However, 

 Emig et al. also stated that increased food supply 

 is probably a secondary benefit to the phoronids and 

 that the suitability of the tube as a settlement sur- 

 face for larvae motivates the association. O'Connor 

 et al. (1977) studied a Pachycerianthus multiplicatus 

 Carlgren population inhabiting deposit substrates 

 (85% silt-clay, 15% sand) off Ireland and suggested 

 tubes were prime settlement surface for the larvae 

 of inquiline filter-feeding polychaetes, Myxicola in- 

 fundibulum (Renier). The associates (sponges, 

 hydroids, and colonial anemones) of Ceriantharia 

 tubes in Block Canyon are generally nonmotile so 



they probably had to arrive on the tubes as larvae. 

 More unstable substrate surrounding the tubes may 

 be less suitable as a settlement surface for larvae 

 of suspension feeders (Rhoads and Young 1970, 

 1971; Rhoads 1974). 



The vertical aspect of Ceriantharia tubes may 

 enhance diversity and abundance by 1) allowing ver- 

 tical stratification of trophic types (MacArthur and 

 Levins 1964; Hughes 1975; Schoener 1975; Ausich 

 and Bottjer 1982), and 2) affording inhabitants, such 

 as the filter feeder Potamilla neglecta, elevated feed- 

 ing stations where clogging by resuspended sedi- 

 ments is less likely, and current velocities tend to 

 be greater (Dyer 1980), thus the food supply is more 

 rapidly renewed (Hughes 1975; Sebens 1984). 



The stable nature of the tubes may serve species 

 behaviorally inclined to attach themselves to firm 

 substrate. The three species of polychaetes, Poly- 

 cirrus eximius, Marphysa sp., and Potamilla neglec- 

 ta, most abundant on ceriantharian tubes caught in 

 Oceanographer Canyon, but rarely found in the ad- 

 jacent sediments (Appendix Table 3), usually attach 

 their tubes to solid surfaces such as stones, algae, 

 or hydroids (Gosner 1971; Fauchald and Jumars 

 1979). 



Infaunal species may also gain relief from preda- 

 tion pressure by inhabiting ceriantharian tubes. The 

 feltlike tubes are generally more consolidated that 

 the sediments surrounding them, thus more difficult 

 to graze. Ponder (1971) viewed protection as the 

 principal benefit to a leptonid bivalve, Montacutona 

 ceriantha Ponder, inquiline with Cerianthus sp. in 

 Japanese waters. Protection may be enhanced for 

 tubiculous infauna since their retraction may be 

 stimulated by a similar response to disturbance by 

 the host ceriantharian (Emig et al. 1972). 



Ceriantharia tubes may serve as a preferential 

 food source for some infauna. O'Connor et al. (1977) 

 noted sipunculids, Golfingia elongata (Keferstein), 

 inquiline with Pachycerianthus multiplicatus had 

 tube remains in their guts. Scavengers, such as Mar- 

 physa sanguinea may benefit from the inquilinism 

 for this reason. 



Ceriantharia may also negatively affect the in- 

 fauna in sediments adjacent to the tubes; large 

 motile species, attracted to the tubes for shelter, 

 might selectively graze near tubes. We hope to in- 

 vestigate Ceriantharia "forest" communities more 

 thoroughly on future submersible cruises: Substrate 

 collections taken away from tubes will further define 

 their functional role. We believe Ceriantharia influ- 

 ence the ecology of the northwest Atlantic contin- 

 ental shelf and slope more than has been revealed 

 from data collected by conventional surface tech- 



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