93 



not necessary that the genera, or even families, are the same for the 

 dominant organisms in these parallel communities, so long as the dom- 

 inants perform the same function within the community. These "ecological 

 parallel communities" have been designated "ISO-communities" by 

 Thorson (1957, p. 504); although this concept has recieved earlier dis- 

 cussion by TiscHLER (1950, 1951) and Gaspers (1950). For this reason, 

 a preliminary analysis of the feeding types (when known) of the char- 

 acteristic animals of each environment was made, and a few conjectures 

 as to the organization of the assemblages as to other biological factors 

 are presented in the discussion of the results of this study. These assem- 

 blages have also been compared with similar assemblages or communities 

 studied elsewhere in the tropics and sub-tropics, and in particular those 

 described previously by the author from the Gulf of Mexico. Finally, 

 an attempt is made to determine which of the environmental factors 

 exerts the greatest influence upon the assemblage as a whole. The discussion 

 of these assemblages follows in the same order as the earlier descriptoins. 



I. The Intertidal and Shallow Rocky Shores: 



In all probability, the rocky shore habitat in the Gulf of California 

 may offer one of the richest examples of this sort in the variety of species 

 and numbers of individuals known in the world. The rocky shores of the 

 temperate or boreal regions may be richer in numbers of individuals but 

 there are far fewer species. The rocky shores of most tropical islands also 

 seem to be relatively poor in numbers of species and individuals, at least 

 from personal observations made on islands in the Indian Ocean, on 

 Easter Island and in the Bahamas. Longhurst (1958, pp. 54-59) cites 

 relatively few intertidal rocky shore invertebrates in his discussion of the 

 shallow, hard substrate community along the coast of Sierra Leone, West 

 Africa. This would indicate that it is not the tropical climate alone which 

 is responsible for the large number of species found on the rocky shores of 

 the Gulf of California. 



Although this assemblage of animals is found everywhere in the world 

 where rocky shores exist, there was no exact counterpart in the Gulf of 

 Mexico, with which this author is most familiar. The closest approximation 

 to this assemblage off Texas is the fauna of the rock jetties at the major 

 passes along the northern Gulf coast, described by Whitten, Rosene 

 and Hedgpeth (1950). There is little resemblance between their list and 

 the one given here, except for a few moUusks. This is not surprising, since 

 there are no natural rocky shores for the recruitment of the species adapted 

 to this habitat along the coast of the northern Gulf of Mexico, while it is 



