by Meadows and Campbell, 1972; Gray, 1974). However, within a given 

 set of environmental variables, biological interactions may determine 

 much of the observed community structure via such control mechanisms 

 (e.g., predation, competition for space) as have been demonstrated 

 experimentally for other marine communities (Connell, 1972, 1974). 

 Unfortunately, infaunal communities have not been amenable to similar 

 types of manipulation or direct observation, so these interactions 

 have received little attention. 



The biocoenosis view of stable coadapted species assemblages in 

 long-term equilibrium with the environment has been revised by more 

 recent approaches of ordination and multifactorial analysis (see 

 Mills, 1969; Lie and Kelley, 1970) which have shown how infaunal 

 species distributions may be viewed as loose co-occurrences or aggre- 

 gations along continua of the physical environment. Probably varying 

 degrees of both situations exist within any observed pattern. Knowledge 

 of infaunal distribution patterns has suffered from a lack of experi- 

 mental verification of degrees of physical control, and from few 

 attempts to define biological interactive and coactive determinants of 

 structure. Hutchinson (1953) discusses these factors. 



1. Physical-Chemical Factors . 



The sediment-water interface is a biologically active boundary 

 supporting a complex of interacting invertebrates and fishes which 

 derive energy primarily from carbon and nitrogen sources in organic 

 detritus, either directly or through trophic steps (Rowe, 1971; Har- 

 grave, 1973). Although little information is available on actual 

 nutritive values of detritus (Darnell 1967; Tenore, 1977), the 

 qualitative composition and magnitude of detrital flux to the sediment 

 strongly influence species composition, abundance and biomass, with 

 greater faunal densities occurring along gradients of increasing 

 detrital supply (Sanders, 1969; Sanders and Hessler, 1969). However, 

 in very shallow water where sediments are regularly disturbed by wave 

 activity, this relationship does not hold. Margalef (1968, 1975) has 

 pointed out that in changing, unstable environments, ecosystems are 

 energetically expensive to operate because excess fecundity is necessary 

 to compensate for loss of individuals. On the positive side is their 

 ability to function under a wider range of conditions. This serves to 

 explain why shallow, nearshore communities in relatively productive 

 waters generally have lower biomass and species abundance than offshore 

 communities of the continental shelves where sediments are more stable 

 (Barnard, 1963; Lie and Kisker, 1970). 



The overriding importance of sediment grain size as a controlling 

 community variable has been emphasized by Jannson (1967) and Thorson 

 (1957), and reviewed by Gray (1974). This importance derives from its 

 control over biologically meaningful variables such as porosity. 



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