shallowest depth station (30 m) (Fig. 2). There were very few 

 other encrusting organisms besides the bryozoans . Only three of 

 these organisms covered significant area, the polychaetes 

 Spirorbis spp. and Filograna implexa , and the bivalve Anomia 

 sp. . None of these species accounted for more than five percent 

 cover on any group of plates, but the latter two species were 

 most abundant at the deepest station (80 m) Spirorbis was most 

 common at 50 m (Fig. 5). 



Among the erect bryozoans, Idmidronea atlantica was clearly 

 the spatial dominant and appeared to overgrow all other species 

 on the panels including the related species Tubulipora lilliacea 

 which produces more robust but shorter upright processes from a 

 broad encrusting base. Idmidronea grows as a much-branched but 

 loose hemispherical mound (open fan) arising from a small central 

 base. Idmidronea was abundant on the 50 m plates, covering over 

 50 percent of the plate surface, and covered over 20 percent of 

 the space on panels at 30 and 65 m depth. Harmelin (1973) 

 reports that this species produces a less densely branched colony 

 with less water movement. It was more abundant on inner surfaces 

 (Fig. 2) at all depths, whereas T. lilliacea was most abundant at 

 30 m and was more abundant on outer surfaces at 30 and 50 m but 

 was equal at 65 m and rare at 80 m. The wholly encrusting 

 Tubulipora f labellaris was of equal abundance on both sides of 

 the 50 m plates and reached less than one percent cover on all 

 others ( Fig. 2 ) . 



Encrusting bryozoans were most abundant at 30 m where they 

 occupied more than 40 percent of the space, or more than 65 

 percent if T. lilliacea is considered an encrusting species given 

 its wide encrusting base and short upright branches. Encrusting 

 species were of approximately equal abundance on inner and outer 

 plate surfaces at all depths, but accounted for less than ten 

 percent cover at all depths below 30 m. Since plates from 50 m 

 had so much cover by Idmidronea , there was a negative correlation 

 between this species and the cover of encrusting bryozoans. 

 There was also a strong negative correlation between the 

 abundance of Idmidronea and the abundance of Tubulipora lilliacea 

 at 30-50 m for all plates combined (Fig. 3). 



Among the common encrusting species, only Callopora 

 craticula was present in approximately equal abundance at all 

 depths (1-3 % cover). The other common species were generally 

 restricted to a single depth each. Celleporella hyalina covered 

 approximately 20 percent of the surface on the 30 m plates, but 

 was extremely rare at other depths. Porella proboscidea reached 

 three percent cover at this depth and also appeared only as 

 scattered small colonies at deeper stations. Schizomavella 

 auriculata averaged approximately 0.8-2.5 percent cover at 50 m 

 and 1.6 percent on outer plates at 80 m but appeared rarely on 

 all other plates. Lepralia americana was common only at 65 m 

 (outer plates) at 3.2 percent cover and occurred at 0.9 percent 

 cover at 80 m (inner) but was less than 0.1 percent cover on all 

 other plates. Other encrusting species never accounted for more 



58 



