Other factors that could produce the patterns observed 

 might act after initial recruitment. Differential mortality due 

 topredation, overgrowth competition, or physical disturbance 

 could modify the initial recruitment pattern. Clearly predators 

 are finding the granite blocks and the settling panels. However, 

 there is no indication from our community level predation studies 

 that any of the large invertebrate or fish predators prey on 

 bryozoans as a large part of their diet. The seastar Henricia 

 has been observed feeding on bryozoans as have small Asterias 

 vulgaris and Leptasterias sp. These seastars, and several small 

 gastropods, were common on granite blocks at 50 m and were 

 observed frequently at 30 m as well, although they were not 

 quantified at that depth. They were, however, rare at the 

 deeper two stations. Predation does not appear to be limiting 

 bryozoans to the shallower zones. If anything, predation is more 

 intense at the shallower depths. Competition is also most 

 intense at the 30 and 50 m stations as seen by the lack of bare 

 or unoccluded space at these depths, but is far less frequent at 

 the two deeper stations where much space exists for colonization 

 and lateral growth. Competition must surely be affecting the 

 species composition of the assemblages on the shallower plates. A 

 study of overgrowth competition in this assemblage will be the 

 topic of a later publication on these experiments. 



In summary, early community development proceeds more 

 rapidly at the shallower depths (30-50 m) in the rocky subtidal 

 zone of the Gulf of Maine. The early successional assemblage is 

 bryozoan-dominated in the first year, with other phyla becoming 

 common only in the second year of the settling plate experiments. 

 Particular species have distinct depth maxima, and certain 

 species such as Idmidronea show clear patterns of abundance on 

 inner versus outer plates in the array. Predation and 

 competition are likely to be important local structuring 

 processes at the shallower depths, but these may not become 

 important until several years later at the deeper sites (65-80 m) 

 because of lower overall colonization and possibly growth rates 

 of the encrusting species. The first year, and even the second 

 year, assemblages look very different than the communities we 

 observe on undisturbed vertical walls which are dominated by 

 sponges, ascidians, sea anemones, polychaetes, and bryozoans. 

 However, we have seen natural patches on the rock walls that 

 contain assemblages very similar to those on our settling plates. 

 It thus appears that bryozoans are the rapid colonizers in this 

 system and that they colonize and occupy space primarily within 

 the first two or more years, possibly giving way gradually to the 

 more massive species neighboring their originally cleared patch. 

 The importance of bryozoans in this community, and their 

 successional status, would not have been understood without 

 colonization experiments of this type. Analysis of the remaining 

 years' data, and the results from granite substrata, will tell us 

 how closely the settling plates mimic the natural surfaces and 

 will give us more information on the role of benthic predators at 

 this stage of community development. 



63 



