418 FAOEK [CHAP. 19 



the community and can be made relatively sound taxonomically with the 

 assistance of specialists in the groups encountered. The thermodynamic 

 approach involves the danger that guesses at functions may seem obvious and 

 yet be quite incorrect. For example. Sanders (1960) has demonstrated that a 

 species of the gastropod genus Turbonilla, all members of which were formerly 

 believed to be highly specific ectoparasites, is a deposit feeder and that species 

 of the polychaete genera Nephythys and Ninoe, which would ordinarily be con- 

 sidered carnivorous, are also deposit feeders. There is no question that the 

 determination of the rates and pathways of energy flow is a basic and necessary 

 part of any complete study of a community, but it is just a part and as such 

 largely ignores behavioral, physiological and populational differences between 

 species in the same trophic level. As Bray (1958) says: "If the natural history 

 approach has sometimes failed to quantify its methods, it is also possible that 

 the mechanist approach has occasionally forgotten the problem." In the 

 present distressing state of the taxonomy of many groups, particularly among 

 the invertebrates, the third approach is attractive. It is, however, an almost 

 universal experience that such a procedure results in failure to separate morpho- 

 logically similar species which may have quite different functions. 



In addition to the biological and philosophical difficulties discussed above, 

 there are the technical ones associated with the necessity of using several 

 different sampling methods, of summarizing and understanding great masses 

 of data, of long-term repetitive work in a limited area, of defining the area, of 

 accounting for import into and export from the area, etc. Despite these difficul- 

 ties, the complexity of nature is a fact and an attempt should, therefore, be 

 made to study it. 



2. Definition of Community 



No formal definition of community has yet been given. The writer feels that 

 this should be an operational definition such as: a group of species which are 

 often found living together. As pointed out earlier, the decision on what is 

 sufficiently "often" must ultimately be a subjective one, though objective 

 procedures can help and will promote consistency. The decision as to whether 

 species are "living together" or not depends upon an estimate or determination 

 of the mobility, activity and sphere of influence of individuals and of the inter- 

 spersion of the populations. As most marine studies, except possibly in the 

 intertidal zone, will depend upon samples take over areas or volumes which are 

 unseen, some care is necessary in interpreting co-occurrence in a sample as 

 indicating that the organisms were "living together". This definition puts no 

 limits on the size of communities: any assemblage from the algae and associated 

 invertebrates on a spider crab carapace to the plankton in the upper 50 m over 

 broad areas in the North Pacific Ocean may qualify. There may be some value in 

 identifying as major communities those which are essentially independent of all 

 external sources of energy except the sun (Park. 1949) but these are only one 

 end of a continuum in terms of the relative importance of internal and external 



