GULF OF MEXICO 



205 



sapidus, aiul the two shrimp, Penaem setiferm 

 and P. aztecus, all important components of the 

 fauna. This system of bay waters forms a rim 

 along: the whole northern Gulf coast. Although 

 certain species such as tlie cyprinodont fishes, the 

 common oyster, and the various species of palae- 

 monid shrimp remain in the baj's and are found 

 nowhere else, the bays are not faunistically isolated 

 from the shallow Gulf, despite narrow connections 

 through the passes, but form a system with it. 

 The dominant life of the region has perforce 

 become adapted to this estuarine-sea water system 

 and moves back and forth within it during the 

 life cycle. 



Gunter also emphasized the importance of two 

 gradients connected or correlated with salinity. 

 One, an ostensible relation between salinity and 

 size, depends on the fact that most motile animals 

 move out from shallower waters as they grow larger 

 and go toward or to the sea. This migration is 

 accelerated by the onset of cool weather in the 

 fall when large movements from the bays to the 

 Gulf take place amounting almost to a general 

 exodus for some species. 



The other gradient is a decline in the number of 

 species as the salinity falls. As he pointed out, 

 the bay fauna is marine, and although practically 

 all species can live in high salinities they only 

 tolerate varying degrees of low salinity, and thus 

 the numbers of species present become less as the 

 salinity falls along the gradient. The difference 

 in numbers of species in the Gulf and Copano Bay 

 is particularly striking in winter. At that season 

 the fresher, shallower, and thus cooler waters of 

 Copano Bay are dominated by only four or five 

 motile species. The importance of these general 

 phenomena to paleoecological studies was specially 

 mentioned (Gunter 1947). 



Since ecological studies by Gunter did not 

 include the sessile, poorly motile or burrowing 

 forms in the area they are incomplete. Never- 

 theless, they go a long way toward describing 

 the communities of the shallow Gulf. Readers 

 interested in details should consult the original 

 papers. As for the deeper water communities, 

 virtually nothing is known except the results 

 of sporadic dredging stations by the Blake and 

 Albatross more than 50 years ago. There has 

 been no attempt to list the findings of these dredg- 

 ings b}^ stations, a difficult task of reassembling 

 in view of the scattered publication of reports on 



the various animal groups. Hence, our knowledge 

 of the deep-water life of the Gulf of Mexico is still 

 that of Agassiz' Three Cruises of the Blake. 



Investigations of recent facies 



A relatively new development is the study of 

 assemblages of living (and dead) organisms as 

 potential fossil assemblages. In such studies, 

 groupmgs or facies correlated with environmental 

 conditions are emphasized. Such facies may be 

 the same as a natural community (especially that 

 of the oyster reefs) , or they may have no particular 

 relationship to the communities in which they 

 occur especially if they include such remains as 

 mollusk shells and coral fragments carried there 

 by physical forces. In his study of moUuscan- 

 foraminiferan assemblages in San Antonio and 

 Aransas Bays, Texas, Ladd (1951) recognizes a se- 

 ries of facies roughly corresponding to the salinity 

 gradient: bay head, inter-reef, reef, polyhaline 

 bay, passes, open gulf (near- and offshore), 

 beaches, and highly saline lagoon. A similar 

 series, based exclusively on foraminifera is recog- 

 nized in the same region by Parker, Phleger, and 

 Peirson (1953) ; river, marsh, bay, beach and open 

 gulf. The distribution of various foraminifera 

 along several transects in the northern Gulf from 

 Florida to Texas in relation to sedimentary facies 

 is discussed by Lowman (1949). 



Community terminology 



The matter of terminology and classification 

 of marine communities, in general, is not settled. 

 The ambitious attempt of Clements and Shelford 

 (1939) to classify the biota of the North Atlantic 

 into various biomes and their component as- 

 sociations has served principally to emphasize 

 that the criteria of terrestrial biomes have but 

 limited application to the marine environment. 

 The term biome was accepted somewhat uncriti- 

 cally by Jones (1950) who classified the North 

 Atlantic bottom communities into various hard 

 and soft bottom "biomes." It is suggested in 

 the recent monumental treatise of Allee et al. 

 (1949), that self-sustaining communities within 

 the sea are difficult to recognize, and that biomes, 

 as defined on land, do not exist : "The major marine 

 community despite its great regional biotic varia- 

 tion, is so lacking in effective barriers to dispersal, 

 is so much subject to slow continuous circulation 

 of its medium and exhibits so much interdepend- 



