induced by selective factors operating on planktonic larval stages. 

 Observed fauna may largely reflect the timing and numbers of larvae 

 available for settlement. Species occurrence at a particular locality 

 usually reflects availability of larvae in the plankton and concomitant 

 suitability of water, physical and biological substrate qualities as 

 cues for settlement. Absence of a species may indicate lack of larvae, 

 unsuitability of cues for settlement, or postsettlement mortality. 

 Specific factors affecting larvae are not well known. Coe (1953) and 

 Barnes and Wenner (1968) showed a high degree of spatial and temporal 

 variation in larval settlement patterns of sand beach macrofauna. 

 Diener and Parr (1977) found that abundances of certain dominant infaunal 

 polychaete species varied up to a hundredfold between sampling periods 

 at 7.6-meter depths off southern California. 



It may be concluded from the unstable nature of the physical 

 habitat and the ephemeral nature of infauna populations as a result of 

 their life-history characteristics, that nearshore sediment populations 

 show wide variations in their numbers both in space and time. Pro- 

 ceeding offshore to more physically stable conditions, populations 

 become more diverse (Day, 1967; Day, Field, and Montgomery, 1971). This 

 conforms with Sanders' (1969) thesis of higher diversity in less physi- 

 cally controlled (offshore) environments. 



Implications of variations in basic life-history characteristics, 

 such as lifespan, fecundity, and age of reproduction in relation to 

 environmental stability have been discussed by Frank (1968), Margalef 

 (1968, 1975), Pianka (1970), and MacArthur (1972). The importance of 

 relating empirical data to considerations of ecological theory and trans- 

 lating this to such applied problems as environmental impacts of man- 

 induced perturbations upon marine benthic communities lies in the fact 

 that environmental impacts of these perturbations are most prevalent in 

 nearshore and coastal regions. Superimposed upon seasonal recruitment 

 patterns, nearshore populations, via the aforementioned life-history 

 strategies, frequently experience periods of population expansion when 

 the environment is not resource limiting or physically disruptive. 

 Furthermore, most species show a high degree of spatial aggregation, 

 even in apparently physically homogeneous areas (Buchanan, 1963; 

 Gardefors and Orrhage, 1968; Gage and Geekie, 1973). It is upon this 

 background of natural variability that detection of responses to 

 perturbations must be discerned. From an engineering standpoint it 

 becomes a problem of signal extraction; statistically based detection 

 of low level responses may be difficult. High variability within 

 these nearshore communities should be recognized as basic features of 

 their existence. Sampling design, statistical treatment, and monitoring 

 have to operate within this framework. 



4. Diversity . 



The classical (and largely theoretical) contention regarding bio- 

 logical diversity is that high diversity should promote resistance to 



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