ZOOGEOGRAPHIC CONSIDERATIONS 



Though the original title implied a local list, 

 the handbook included an assemblage that is quite 

 widespread. Hay and Shore justly termed it a 

 virtual descriptive list of decapod crustaceans of 

 the Middle Atlantic coast, in large measure tilling 

 but continuing in part from northwestern Florida 

 the gap between various lists of New England, 

 New York, and New Jersey crustaceans, and the 

 Puerto Rican list (Rathbun, 1901). The assem- 

 blage treated, both by Hay and Shore (in the 

 original) and this revised version, has a lati- 

 tudinal range extending primarily from Cape 

 Hatteras, N.C., to northeastern Florida (tig. 1), 

 to Texas; it is encompassed in a more generalized 

 assemblage sometimes recognized as the Caro- 

 linian province (Hedgpeth, 1953). Primarily 

 Antillean in its affinities, the Carolinian province 

 is distinct from the Virginian province to the 

 north and this fact has been emphasized by numer- 

 ous authors. 



Bathymetric limits included in this revised 

 handbook are altered somewhat from the original. 

 Species which occur from the heads of estuaries 

 to the 100-fathom contour are included. Fresh- 

 water decapods, included in the original, have 

 been excluded because they never occur in the 

 marine environment. Species that occur only 

 beyond the 100-fathom line more properly belong 

 to a deep-sea fauna that ranges far beyond the 

 Carolinian province, and are not included. 



Arbitrary limits are difficult to establish. Judg- 

 ments undoubtedly will differ as to what is extra- 

 limital and what is not. For some species with 

 uncertain distributional limits, a list of extra- 

 limital species has been included. 



An analysis of the decapod crustacean element 

 in the Carolinian fauna is given by family in 

 table 1. Here, categories chosen for limits in geo- 

 graphic range are used broadly, especially at their 

 southern extremities. For economy of space, the 

 term "South America" can mean either the north- 

 ern or southern Atlantic shores of the continent, 

 but details are given in the species accounts. Our 

 interest here centers primarily on the eastern coast 

 of North America, and on natural boundaries or 

 barriers that exist on this stretch of coast. 



It is apparent that a small number (6.8 percent) 

 of Carolinian decapods are northern in affinity, 

 extending to southern Florida in one case (Cancer 



borealis). To this group, Cape Cod is no barrier, 

 but to another group (12.7 percent) it is a barrier 

 to northward extension into upper New England 

 and the Maritime Provinces of Canada. 



Totals are given for species extending north- 

 ward to the Middle Atlantic States (9.1 percent). 

 Many of these records are for accidental or sea- 

 sonal occurrence; i.e., species whose northern 

 limits of range might well be set at Cape Hatteras. 

 But there are other species in the group which 

 must be permanent residents in those latitudes 

 and are not dependent on annual repopulation 

 from breeding stock to the south. 



Cape Hatteras is a barrier to northward dis- 

 tribution of shallow-water forms. Here, warm 

 water of the Gulf Stream meets the cold Labrador 

 Current to be deflected seaward (Hutchins, 1947), 

 and 27.7 percent of the decapods are apparently 

 unable to bridge the narrow transition zone to 

 colder water. 



Cape Lookout, surprisingly, seems to be a 

 greater barrier to northward extension of range 

 among Antillean species (31.4 percent) than Cape 

 Hatteras. This barrier may be real, or it may 

 be that fauna] limits fluctuate between these capes 

 as a consequence of natural events. More likely is 

 the fact that far more collecting has been done 

 near Cape Lookout than at Cape Hatteras because 

 of the nearness of marine laboratories to the 

 former. 



Species showing distributions reaching north- 

 ward only to Charleston, S.C., (4.5 percent) are 

 probably southern species with accidental records 

 at that latitude, for there is no apparent barrier 

 to dispersal in that area. Eastern and western 

 Atlantic forms are equally small in number (4.5 

 percent) . 



Cosmopolitan species (1.8 percent) are few, as 

 are endemic species (1.4 percent). 



Aside from the above patterns of distribution, 

 a number of species ranging along the Atlantic 

 coast and the Gulf coast to Texas have a disjunct 

 distribution in peninsular Florida. The number 

 of these species is conservatively estimated, from 

 literature records, at 10 percent of the total. This 

 type of distribution, discussed at length by Hedg- 

 peth (1953), shows a fairly recent separation of 

 Gulf elements from the Atlantic portion of the 

 species by emergence of peninsular Florida, but 

 with the two areas being climatically equivalent 



MARINE DECAPOD CRUSTACEANS OF THE CAROLINAS 



