Immediately after disturbance, sediments rapidly 

 become anoxic and inhospitable to infaunal or- 

 ganisms at even shallow depths below the surface. 

 Only through time are the disturbed sediments 

 utilized at depth by species which appear later 

 during succession, after bioturbation by earlier 

 colonists has irrigated the sub-surface sediments 

 and has worked some usable organic material into 

 deeper deposits (Rhoads et al. 1977). After per- 

 turbation, a true successional sequence occurs 

 during the recolonization of muddy sediments in 

 shallow waters. Early, short-lived opportunists 

 colonize the surface zone and are replaced by 

 long-lived species which can now live deeper in 

 the sediments only after their preparation by the 

 biological activity of the initial colonists (Rhoads 

 etal. 1978). 



Opportunistic species tend to have variable 

 densities through time (Rhoads et al. 1978). Spe- 

 cifically, they show strong seasonality in most 

 shallow-water sediments (McCall 1977). One pos- 

 sible explanation of the great seasonal fluctuation 

 in abundance of opportunists in the soft-sediment 

 benthos is their susceptibility to predation (Mc- 

 Call 1977, Rhoads et al. 1978). Many studies have 

 shown that the shallow-burrowing benthic in- 

 fauna are most subject to predation (Blegvad 

 1928, Virnstein 1977, Nelson 1978, Woodin 

 1978). Caging experiments in soft sediments have 

 also demonstrated that opportunists respond 

 most rapidly when released from predation 

 (Young et al. 1976, Virnstein 1977, Lee 1978, 

 Reise 1978). Such results suggest that opportunis- 

 tic species may often be controlled by predation 

 in the soft sediments of shallow marine waters 

 and may be responsible for most of the energy 

 flow from the benthic invertebrates to fishes, 

 crabs, and shorcbirds. 



Although available data suggest that predators 

 prey most heavily upon the opportunists among 

 the benthic infaunal invertebrates, this conclusion 

 must remain tentative. Cage artifacts obscure the 

 results of virtually all of the caging experiments 

 in soft substrates (Peterson 1979). Full cages, 

 which are designed to exclude predators, also 

 have the effect of slowing down water currents 

 and thereby causing increased organic deposition. 

 These organic-rich deposits represent food fcjr 

 many opportunistic deposit feeders. The great in- 

 crease in opportunistic species inside full cages 



may be a consequence of this organic enrichment 

 rather than an indication that opportunists suffer 

 the highest mortality from predators. Future re- 

 search must be done to separate these two possi- 

 bilities before it can be unequivocally stated that 

 densities of benthic opportunists are controlled 

 primarily by predation. 



Given that opportunistic benthic infauna 

 undergo large seasonal fluctuations in abundance 

 in the sediments of shallow-water marine habitats 

 and assuming that these species contribute sub- 

 stantially to the energy flow to higher trophic 

 levels, Rhoads et al. (1978) suggested that careful 

 seasonal timing of dredging activities in shallow 

 waters can minimize the impact on natural estu- 

 arine systems. Dredging during winter months 

 should have minimal impact on this entire system, 

 in part because the new set of opportunistic spe- 

 cies, upon which higher trophic levels are depen- 

 dent, does not occur until springtime. Winter 

 dredging will not interfere with that process 

 unless the sediments are altered in some way 

 which makes them unsuitable for colonization. 

 This suggestion can only be tested by an in situ 

 pilot experiment in the actual system in question. 

 Such winter dredging would also cause minimal 

 damage from increased turbidity because phyto- 

 plankton production is lowest during winter. 

 Although this model of the impact of dredging on 

 soft-sediment systems was developed to describe 

 the shallow subtidal benthos of Long Island 

 Sound, it possesses much broader applicability. 

 Specifically, it can undoubtedly be extrapolated 

 to the intertidal mud flats of North Carolina 

 where seasonal pulses of recruitment by oppor- 

 tunistic infauna are evident (Commito 1976) and 

 where predation on these species is substantial. 



One reason that the intcrtitlal benthic com- 

 munities of tidal flats can be perturbed so greatly 

 with relatively little damage to their ecological 

 functioning is that they are extremely resilient 

 systems (Boesch 1974). A resilient system is one 

 which recovers quickly after perturbation. Al- 

 though estuarine systems are characterized by 

 relatively low species diversities and low persis- 

 tence stabilities (i.e., possess quite variable popu- 

 lation abundances and community composition), 

 their resilience stability may be relatively great 

 (Boesch 1974). The physical environment is so 

 variable and predators and benthic disturbers 

 are so common in the benthic communities of 



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