they begin moving into deeper waters. 

 Haedrich and Hall (1S76) hypothesize that 

 these ontogenetic habitat shifts and the 

 general absence of adults in an estuarine 

 environment act as mechanisms to reduce 

 competitive interactions within species as 

 well as to allow the juvenile stages 

 access to the more productive marine 

 habitats. 



Age-related changes in the use of 

 inshore environments by fish and their 

 subsequent effects on a tidal flat habitat 

 is largely species- or group-specific 

 (i.e., resident vs. migratory species). 

 Those fish most dependent upon tidal flats 

 for feeding are the demersal species 

 (e.g., flatfishes, skates) and small bait- 

 fishes (e.g., silversides, killifishes, 

 and menhaden), while most of the pelagic 

 fishes are probably less dependent upon 

 tidal flats for food items. 



Juvenile fish dominate coastal waters 

 and because of their abundance can consume 

 large quantities of benthic invertebrates 

 and have a conspicuous effect upon the 

 structure of benthic communities. Many 

 demersal fishes form schools (e.g., scup) 

 or may be found in loosely aggregated pop- 

 ulations (e.g., winter flounder) and have 

 caused localized, short-term reductions in 

 the population abundance of polychaetes, 

 small crustaceans, and bivalves. The 



reported seasonal population decline of 

 infaunal invertebrates in a Massachusetts 

 salt marsh habitat was probably due to the 

 appearance of invertebrate predators 

 (e.g., epibenthic crustaceans) and fish 

 predators (Schneider 1978). Tyler (1971b) 

 found that adult winter flounder fed over 

 a Bay of Fundy intertidal flat and sug- 

 gested that destruction of the habitat 

 would reduce the productivity of the fish 

 populations. Others have also noted the 

 presence of large populations of demersal 

 fishes associated with intertidal zones 

 (Hancock and Urquhart 1965; Edwards and 

 Steele 1968). Virnstein (1977) demon- 

 strated experimentally that the effect of 

 demersal fish on the benthos was highly 

 species-specific. Some species like the 

 hogchoker had a minimal ef'fect on benthic 

 population abundance while other species 

 such as the spot ( Leiostomus xanthurus ) 

 reduced both the abundance and species 

 diversity of the infauna in a Chesapeake 

 Bay subtidal site. The relative magnitude 

 of such impact is dependent upon the 

 degree of disturbance associated with for- 

 aging on the bottom (e.g., excavating 

 activities) as well as feeding rates. 

 Species such as skates that can disturb 

 large areas of the bottom when foraging 

 have more pronounced effects on the ben- 

 thos (Van Blaricom 1970) than species that 

 only browse on the sediment surface. 



48 



