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Fishery Bulletin 106(4) 
sites display a more pronounced, negative response to 
increased fishing effort. Depth has also been shown 
to influence the abundance and biomass of other ben- 
thic taxa (i.e., amphipods and the brittle star Ophiura 
robusta) in the southern portion of CA-II (Link et al., 
2005). 
Species in the class Polychaeta play diverse ecologi- 
cal roles (e.g., carnivores, deposit feeders, suspension 
feeders), use different habitats (e.g., infauna, epifauna), 
and display different mobility patterns (e.g., errant and 
tubicolous lifestyles), all of which influences how they 
respond to bottom fishing. Many polychaetes exhibit a 
high intrinsic rate of growth allowing them to quickly 
colonize barren substrate and recover rapidly from 
disturbances. This high rate of growth explains why 
the free-living polychaetes in the North Sea remain 
unaffected by bottom fishing at trawling frequencies 
as high as six times per year (Jennings et al., 2002). 
In contrast, tubicolous polychaetes are often heavily 
affected by bottom fishing because of both their pro- 
duction of calcareous and sediment-encrusted tubes 
that can be crushed by fishing gear and their need for 
stable substrate on which to build tubes. This appears 
to be the case at the deep depth stratum on Georges 
Bank, where F. implexa was less abundant at disturbed 
sites. Similarly, the inception of bottom fishing was 
implicated in the declining abundance of four spe- 
cies of tubicolous serpulid polychaetes in the Irish Sea 
(Bradshaw et al., 2002) and the sabellid polychaete 
Myxicola infundibulum on Fippennies Ledge in the 
Gulf of Maine (Langton and Robinson, 1990). A few 
species do prove that there are exceptions to the rule 
that most tubicolous polychaetes are negatively affected 
by mobile fishing gear. Such examples include the tube- 
heads formed by the serpulid polychaete Pomatoceros 
spp. that were not significantly affected by biannual 
beam trawling in the eastern Irish Sea (Kaiser et al., 
1999) and the Spirorbis spp. tubes whose abundance 
was elevated at fished sites on Georges Bank (Collie 
et al., 2000a; Asch, 2006). The small size of Spirorbis 
spp. tubes makes them extremely difficult to remove 
from their substrate and may provide this species with 
a competitive advantage over other species more sensi- 
tive to bottom fishing (Collie et al., 2000a). Similarly, 
the resistance of the Pomatoceros spp. to bottom fishing 
may be related to the fact their tubes are small enough 
to pass through the 80-mm mesh used by Kaiser et al. 
(1999) during experimental trawling. 
Because of their low, encrusting growth form, en- 
crusting bryozoans have proven to be resistant to physi- 
cal disturbances from natural sources (Sebens et al., 
1988) and appear to be less sensitive to anthropogenic 
disturbances, as well. The cover of encrusting bryozo- 
ans is generally greatest in disturbed areas of Georges 
Bank. This effect is significant at shallow sites and 
marginally significant at deep sites. Encrusting bryo- 
zoans whose substrate may be overturned by a trawl 
or dredge are capable of recovering quickly because 
of their fast growth rates and rapid ability to repair 
structural damage (Bradshaw et al., 2002). This set 
of life history characteristics may provide encrusting 
bryozoans with a competitive advantage in highly dis- 
turbed environments. 
The abundance of cultch in disturbed areas of north- 
east Georges Bank can be explained by the fact that 
most cultch at our study sites consists of P. magellani- 
cus shells that were either discarded by scallop fishing 
crews or killed by mobile fishing gear, but not landed. 
In areas where cultch accumulation is linked to high 
levels of predation on bivalves or to current patterns 
concentrating shell fragments, bottom fishing may have 
a negative effect on this resource. Such is the case in 
studies of the effect of mobile fishing gear on patches 
of cultch on Stellwagen Bank and in a more southern 
area of Georges Bank (Auster et al., 1996; Lindholm 
et al., 2004). 
Noncolonial organisms 
As part of a related research project, naturalist dredge 
samples of noncolonial megafauna have been collected 
since 1994 at the same study sites where benthic pho- 
tographs in the present study were taken (Collie et al., 
2005), allowing for comparisons to be made between 
these two sampling techniques. The results of the cur- 
rent study are similar to those obtained by Collie et 
al. (2005) in that they both indicated that P. magel- 
lanicus, S. droebachiensis, and Pagurus spp. increased 
in abundance inside CA-II. The increased density of 
P. magellanicus in the closed area is likely related to 
both direct and indirect effects of bottom fishing. As 
a commercially targeted species, P. magellanicus is 
removed from areas where scallop dredging occurs. 
The adverse effect of dredging and otter trawling on 
sponge cover may also serve to reduce P. magellanicus 
abundance, because some scallop species maintain a 
mutualistic relationship with sponges that helps them 
escape predation. In a laboratory experiment where 
this mutualistic relationship was examined, scallops 
with sponges encrusted on their shells had to exert 
20-30 times less effort to overcome the adherence of the 
tubefeet of a seastar predator than did scallops whose 
shells were cleaned of sponges (Bloom, 1975). A third 
factor influencing the distribution of P. magellanicus 
may be that the seastars (Asterias spp.), which are key 
scallop predators, obtained slightly higher abundance 
outside the closed area. Asterias spp. may be particu- 
larly abundant at disturbed sites because members of 
this genus are also scavengers that have been reported 
to feed upon organisms damaged by trawls (Ramsay et 
al., 1998). 
The sea urchin S. droebachiensis may have also ben- 
efited from the elevated cover of colonial epifauna in 
CA-II because this species is known to eat sponges, 
hydroids, bryozoans, tunicates, and amphipod and poly- 
chaete tube complexes at locations where macroalgae 
and kelp (the preferred diet of sea urchins) are absent 
(Briscoe and Sebens, 1988). The elevated number of S. 
droebachiensis in photos taken in CA-II corroborates 
the findings of Hermsen et al. (2003), who identified 
