55_ 



constructed flat taxa richness at this time may reflect a change in community structure from 

 the pioneering stage to a later more diverse assemblage, i.e., high diversity was due to the 

 presence of both assemblages. Other lines of evidence include high variability in taxonomic 

 composition of constructed flat samples (NMDS results), which is suggestive of infaunal 

 response to disturbed conditions (Warwick and Clarke, 1993) and domination of 

 constructed flat benthos by Capitella sp. and P. elegans, opportunistic species which are 

 early colonizers of disturbed sediments (e.g., Shull, 1997; Thiel and Watling, 1998). 

 Alternatively, both taxa were dominant at both sites and were equally or more abundant in 

 later samples (Appendix Table 2). As previously noted these species have also been 

 reported as summer dominants under undisturbed conditions (Trueblood, Gallagher, and 

 Gould, 1994). It is unclear from the available information whether or not a pioneering 

 assemblage was detected. What is clear, is that by 1991 the infaunal community of the 

 constructed flat was similar in most regards both to the reference site and other intertidal 

 flat assemblages in the North Atlantic. 



Beals Island, an example of a thirty year old flat resulting from intertidal disposal of 

 dredged material, appears to have been somewhat less successful. Unlike Sheep Island, a 

 commercially viable soft-clam population has not been established, however, there is a 

 substantial clam-worm population. Reasons for the relative failure of the soft-clam are 

 uncertain but may be related to substrate. Sediments at the Beals Island constructed flat are 

 far more cohesive than corresponding sediments at Sheep Island (personal observation). 

 The cohesiveness of Beals Island sediments may be less conducive for the shallow 

 burrowing behavior of the clam. The more intense dismrbance of the Beals Island 

 reference flat by worm-rakers may also result in increased clam mortality (Emerson, 

 Grant, and Rowell, 1990). Differences in clam-worm abundances between Beals Island 

 sites may also be related to substrate. The cohesive sediments of the flat are difficult to 

 traverse and may be avoided by professional worm-rakers. The rakers have limited time 

 between tides to gather their harvest and any delay means lost income. Although the 

 constructed flat caimot be considered a success in the sense of direct harvest it still 

 represents a "seed bank" of worms to replace animals harvested from the remainder of 

 Alley Bay and elsewhere. 



The infaunal community of the Beals Island constructed flat was also somewhat less 

 developed than at the reference area. AlUiough taxa richness and taxonomic composition 

 were roughly equivalent between sites (Figure 3-20; Appendix Table 3), constructed flat 

 abundance and biomass were much lower than reference area values (Figure 3-21; Figure 

 3-22). The differences in abundance and biomass were not restricted to a single group as 

 evidenced by similar biomass composition (Figure 3-23), but are more general in nature. 

 Reasons for the difference between constructed flat and reference area values are most 

 likely related to substrate, elevation and vegetation (intertidal Zostera marina beds). 



Ecological Monitoring of a Constructed Intertidal Flat at Jonesport, Maine 



