Substratum requirements are related to feeding type and mode of living. 

 Detrital feeders are most abundant in fine sediments of silt and clay 

 containing organic detritus. The detrital feeders pass the sediment through 

 their bodies, digest the bacteria, and excrete fecal material, which is again 

 colonized by bacteria and reconsumed (Young 1971). 



Organisms that feed on suspended (filter feeders) material, either 

 phytoplankton or detritus, exist almost anywhere that the currents are strong 

 enough to provide a sufficient amount of food. They are found most commonly, 

 however, in sandy or rocky environments, where deposit feeders are not as 

 successful. Other requirements include shelter for animals (e.g., lobsters), 

 hard substrates for nonmobile organisms (e.g., anemones), appropriate 

 sediments for making tubes and algal substrates for some polychaetes and 

 bryozoans. See chapter 12, "Commercially Important Invertebrates," for a 

 complete description of nine important benthic invertebrates. 



Squid . Although they have no shell, these invertebrates are related to 

 clams and mussels. They live in the water column and are active swimmers that 

 shoot backwards through the water. Squid are carnivores and feed on mackerel, 

 herring, krill and shrimp and are preyed upon by other carnivores, such as 

 large fish and whales. 



Finfish . The marine system in Maine supports a slightly higher diversity 

 of finfish species than the estuarine system (73 vs. 61). Seventeen species 

 are strictly marine inhabitants. Temperature is a major factor determining 

 the seasonal and local distribution of marine fish. Fish populations in the 

 marine system of coastal Maine are dominated by resident demersal (bottom- 

 dwelling) species (e.g., cod, pollock, flounders, sculpins, and skates; table 

 4-5). A number of summer migrants to coastal Maine add to the seasonal 

 diversity of fish. Finfish are important components in the energy flow of 

 both marine and estuarine systems due to their abundance (biomass) and 

 representation on many levels of aquatic food chains; they are primary, 

 secondary, and tertiary consumers. Fish support a wide variety of seabird and 

 waterfowl populations. 



Many researchers have held the belief that, in the context of the total 

 ecosystem, organisms (fish or otherwise) could be considered as groups 

 occupying defined feeding niches (Langton and Bowman 1978). These niches are 

 defined according to the fishes' feeding habits and size or life stage. 

 Finfish are discussed from an ecological perspective here, in terms of their 

 feeding habits and habitats. A single species may utilize several different 

 feeding strategies during its various life stages, from larvae through mature 

 adult. Species that share the same feeding habits may be functionally but not 

 taxonomically related. 



Marine fish can be classified on the basis of their principal feeding habits 

 as planktonic, nektonic, or demersal/semidemersal (figure 4-11). The marine 

 system is dominated by demersal/semidemersal feeding finfish populations, 

 followed by nektonic and then planktonic feeders. The cunner and Atlantic cod 

 are both nektonic and demersal feeders. Planktonic feeders such as the 

 herrings, (Atlantic herring, alewife, blueback herring and American shad) 

 Atlantic menhaden, and American sand lance are water-column feeders that 

 consume primarily pelagic crustaceans; copepods , mysids, euphausiids, and 

 amphipods. The nektonic feeders utilize pelagic crustaceans and fish. These 



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