| Abstract |
Uca pugnaxand U. pugilator are common fiddler crabs in salt marshes on the Atlantic
coast of the United States. As adults, U. pugnaxfrequent muddier, vegetated (typically Spartina alter-
niflora)substrate while U. pugilatorusually occupy sandier, open habitats. It is unclear where juve-
nile U. pugnaxand U. pugilatorreside because the early crab stages of these species are difficult to
identify by simple gross morphology. Using a novel restriction fragment length polymorphism (RFLP)
protocol to distinguish postlarval U. pugnaxand U. pugilator, we studied their distribution along a
horizontal gradient in the North Inlet Estuary, South Carolina. We collected juvenile crabs along tran-
sects at 3 different sites that spanned S. alterniflora-covered mud and open sand habitats with adult
populations of U. pugnaxand U. pugilator, respectively. Over 75% of the juveniles collected were
U.pugnax, showing greater recruitment by this species. U. pugnaxjuveniles of all sizes preferred the
same muddy habitat occupied by adults, but habitat preferences of juvenile U. pugilatorvaried by
site. Generally, U. pugilatordisplayed a shift in distribution from S. alternifloracover to sandier habi-
tat during early juvenile stages. The younger stages may prefer S. alterniflora-covered, muddier
habitat because it provides better cover from predators, or so that they can avoid displacement by
currents during high tides; alternatively, they may be able to feed better on muddy sediment. U. pugi-
latordevelops specialized mouthparts to scrape organic matter from larger sand grains, but these are
not present in early juveniles nor in U. pugnaxjuveniles. Although young juvenile U. pugnax
strongly favored S. alternifloracover, older juveniles (those large enough to dig burrows for protec-
tion) were occasionally found in sandier habitat with U. pugilator.
KEY WORDS: Uca pugnax· U. pugilator · Postlarval settlement · Restriction fragment length
polymorphism · RFLP |
