62 



(Table III). No grab samples were taken in any part of this environment, 

 which must account for the relative scarcity of infaunal species as com- 

 pared to regions sampled elsewhere in the Gulf where grab samplers were 

 occassionally used. As can be seen in the lists of living animals from both 

 the northern and southern portions (Table II), crustacean and prosobranch 

 species far outnumber any other kind of organisms, and these kinds of 

 animals are most likely to be taken by dredges and trawls. 



Even though no grab samples were taken, which might serve to show 

 a true difference between nearshore and intermediate shelf faunas, there 

 is no doubt that the intermediate shelf assemblage is a distinct one, with 

 depth boundaries at about 27 to 65 meters. The fact that decapod cru- 

 staceans proved to be important index species in providing a characteristic 

 set of stations for this environment, both in the north and the south, 

 lends more support to this idea, since these animals are motile, and would 

 be expected to range over several communities or environments, unless 

 the physical boundaries might be fairly sharp. The contingency matrix 

 indicated a close association between 18 invertebrate species in the Tiburon 

 region in depths from 25 to 76 meters. The distribution of these stations 

 and three other closely associated stations is shown in fig. 19. As shown 

 in Table III, these stations were taken by 7 shell dredges, 4, 3-meter 

 otter trawls and 2 rock dredges. Although the list of associated species, as 

 given by the matrix is primarily an epifaunal one, and the mollusks are 

 both living and dead species, it is given here for reference. The complete 

 list of invertebrates identified so far from the Tiburon intermediate shelf 

 region is given in Table II. 



