452 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



The second region (region 2) of the littoral is 

 composed of the shores of the bars or islands be- 

 tween these run-offs; these areas vary greatly in 

 stability and extent, but appear rather constant 

 in structure and physical nature. But, as men- 

 tioned earlier, this apparent constancy is decep- 

 tive; a more intensive study of the Brownsville 

 region and the Texas shore line immediately north 

 and east reveals the disappearance of the marsh so 

 characteristic of the Mississippi-Alabama-Louisi- 

 ana shore line and its replacement by much more 

 sandy shores facing the sea. This can be seen 

 from any topographic map. There have been no 

 comparative faunal studies of this region but such 

 studies might well be expected to reveal an asso- 

 ciated faunal break. Intensive studies of a few 

 limited localities show the species of a single 

 genus, such as for example, Callianassa, which 

 occur on the ocean side of a bar in the northern 

 Gulf, are definitely more closely related to those 

 in similar habitats in more southern areas than 

 they are to those found along shores with different 

 soil composition in the same climatic zone. Thus 

 it appears that along the northern Gulf, at least, 

 temperature is not a strictly limiting factor. 



In general, the common families of region 2 are 

 the Callianassidae, Albuneidae, Hippidae, and 

 some representatives of the Paguridae; the Por- 

 tunidae represented by the ubiquitous Callinectes 

 of many species, and others of that family; a few 

 Pinnotheridae along the sand bars, especially on 

 the open or widely exposed shores; and in slightly 

 sheltered regions and small transient tidal pools, 

 such Palaemonids as Macrobrachium and Palae- 

 monetes. 



The east coast of Mexico is not too well known; 

 although it differs, as we go south, from the Texas 

 shore line. Limestone, coral sands, coral reefs, 

 and actively growing corals, with strips of rocky 

 cliffs of laval origin, prevail. The underlying rock 

 is limestone with much calcareous sand mixed 

 with coral along the shore line. Theoretically, 

 the coral provides the habitat for the crustacean 

 forms which might be expected to replace here 

 the rocky-shore species of other sections. Wliat 

 we might consider the southern rim of the Gulf, 

 namely, the northern shore line of the Yucatdn 

 Peninsula, is another region not adequately ex- 

 plored nor described. It may be presumed, how- 

 ever, that such reefs as are present would show a 

 more constant and consistent animal life th^n is 



to be found in similar habitats of the northern 

 Gulf, since there is less depositional modification. 

 Here is another key locality for important further 

 study of the Gulf littoral. 



Region 3 of the Gulf littoral comprises scattered 

 shallow bays with muddy or occasionally shelly 

 bottoms. This condition is found along the 

 northern and western Gulf. Here there is a 

 typical mud-bottom fauna living at depths of from 

 a few to 20 or .30 feet, and consisting of many 

 Xanthids, some of the family Porcellanidae, 

 especially Petrolisthes, species of Inachidae, Palae- 

 monidae, and Crangonidae, and a few of the 

 families Calappidae, Parthenopidae, and Maiidae. 

 Other Xanthids are distributed along the muddy 

 shores of these embayments, where their burrow- 

 ing often completely riddles large areas of tidal 

 mud flats. 



There is a further gap in our knowledge: the 

 fauna of large parts of northern Cuba. From 

 the general topography we would expect a rich 

 fauna on these shores. The forms from the 

 northern shore of Cuba as far as they are known 

 belong more to the Caribbean — more precisely, 

 the West Indian fauna — than to that of the Tor- 

 tugas and the Florida Keys. But this may be 

 questioned; the picture is not clear-cut, again for 

 lack of records. 



Region 4 is the reef fauna of western Florida 

 and the Keys. As suggested above, it may be 

 supposed that we would find here a fauna com- 

 parable to that of the West Indies; and as far as 

 the fairly comprehensive studies from the Tor- 

 tugas show the forms found here are indeed 

 similar to those of the larger islands, such as 

 Puerto Rico, which have been fully studied. 

 They grade into those of northern Cuba. Com- 

 parison of this material with that from central 

 and northern South America should show many 

 definitely tropical characters. 



The third major group comprises the fauna of 

 the deeper Gulf. On the whole, this fauna is 

 known only from isolated samples of the popula- 

 tion since thorough study is wanting. Explora- 

 tions so far have not been extensive, though in 

 the neighboring West Indies some records have 

 included material from considerable depth. The 

 species found here might presumably be most 

 constant, since temperatures vary less than else- 

 where in our general territory except, perhaps, 

 in that part of the Gulf floor which is under 



