THE MUD CRAB, PANOPEUS HERBSTII, S.L. 

 PARTITION INTO SIX SPECIES (DECAPODA: XANTHIDAE) 



Austin B. Williams 1 



ABSTRACT 



The "forms" of the mud crab, Panupeus herbstii, s.L, recognized by M. J. Rathbun are rediagnosed as four full 

 species: P. herbstii, s.s., from oyster beds of the eastern United States; P. simpsoni from that habitat in the 

 Gulf of Mexico; P. obexus associated with salt marshes in the Carolinian Province of the southeastern and 

 southern United States; and P. lacustris from the intertidal and shallow littoral of the tropical west Atlantic. 

 Panopeus austrobesus is newly diagnosed from south of Cabo Frio, Brazil, andP. meridionalis from Uruguay. 

 Distinction of these six species is based on morphometry supplemented by color pattern and electrophoretic 

 analysis of hemocyanins. A key for identification is given. 



The xanthid crab, Panopeus herbstii H. Milne 

 Edwards, s.L (sensu lato), is recognized as an impor- 

 tant member of the American oyster, Crassostrea 

 uirginica (Gmelin), community. It has been charac- 

 terized as a selective feeder preferring small oysters 

 over barnacles and large oysters (McDermott and 

 Flower 1952), predatory on oysters and barnacles 

 and potentially the most destructive of mud crabs 

 occurring on New Jersey oyster beds (McDermott 

 1960), fifth in percent of total biomass on intertidal 

 oyster reefs (Bahr 1976), and the most commonly 

 captured decapod crustacean on Delaware oyster 

 reefs (Maurer and Watling 1973). Menzel and Hop- 

 kins (1956) stated that P. herbstii, s.L, is a significant 

 oyster predator in Louisiana and that along with 

 Menippe mercenaria (Say) it is large enough to kill 

 significant numbers of adult oysters in Florida (Men- 

 zel and Nichy 1 958). It has also been determined as a 

 consumer of Cliona celata Grant, the boring sponge 

 parasitic in oysters (Guida 1976), a detritovore cap- 

 able of feeding on barnacles and oyster spat (Ken- 

 dall 2 ), and, though an abundant associate on oyster 

 reefs of Alabama, a commensal and scavenger rather 

 than predator (May 1974). Whetstone and Eversole 

 (1978) found P. herbstii to be a predator on hard 

 clams, Mercenaria mercenaria (Linne), and Seed 

 (1980) found that both this crab and the blue crab, 

 Callinectes sapidus Rathbun, are significant pre- 

 dators on the Atlantic ribbed mussel, Geukensia (= 

 Modiolus) demissa (Dillwyn). McDonald (1982) con- 

 trasted the life history pattern of predatory P. herbstii 

 with that of the smaller, more omnivorous Eury- 



1 National Marine Fisheries Service, Systematics Laboratory, 

 National Museum of Natural History, Washington, DC 20560. 



' Kendall, D. R. 1974. The ecology of the macrobenthos ot a tidal 

 creek, St. Simons Island, Georgia. UnpubL M.S. Thesis, 212 

 p. Emory Univ., Atlanta, GA 30322. 



Manuscript accepted March 1 983. 



FISHERY BULLETIN: VOL. 81. NO. 4. 198.!. 



panopeus depressus (Smith) in South Carolina. Dame 

 and Vernberg (1982) evaluated the suggestion of 

 Dame and Patten (1981) that mud crabs (e.g., P. 

 herbstii) are one of the major controlling components 

 in an oyster reef system, even though the amount of 

 energy flowing through such predators is low in com- 

 parison with that moving through other elements of 

 this system, and calculated the energetics of a pop- 

 ulation of P. herbstii in a South Carolina oyster reef on 

 the basis of population density, size structure, stand- 

 ing crop, respiration, and production. The chelae of 

 this and similar species of the family Xanthidae are 

 strikingly adapted for cracking shelled prey, but the 

 exact ecological roles of Panopeus species that occur 

 in marine mollusk communities of the eastern and 

 southern United States have been obscured because 

 of imprecise identifications. 



Panopeus herbstii has been a species complex from 

 its initial misidentification and illustration as Cancer 

 panope by Say (1817-18), through its later descrip- 

 tion as new in the new genus Panopeus by H. Milne 

 Edwards (1834-40), and in a succession of specific 

 and varietal treatments summarized by Rathbun 

 (1930), Williams (1965), Holthuis (1979), and Man- 

 ning and Holthuis (1981). Rathbun (1930) recog- 

 nized four primary forms (typica, obesa, crassa, and 

 simpsoni) which she believed represented extremes 

 or perhaps environmental types connected by 

 intergrades, but which were not subspecies, although 

 there was a geographic component in her evaluation 

 of material studied. The geographic range of the 

 forms was listed as: form typica, Massachusetts to 

 Cedar Keys, Fla.; form obesa, South Carolina to 

 southern Brazil; form crassa, west Florida to central 

 Brazil; form simpsoni, primarily Gulf of Mexico but 

 also South Carolina where it was considered to 

 intergrade with form typica. 



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