William F. Loftus¹ and M. Cristina Bruno^2
1U.S. Geological Survey, Florida Integrated Science Center, Homestead, FL, USA
²Department of Environmental Science, Tuscia University, Viterbo, Italy

Florida is a global hotspot for subterranean crayfish because of the habitat provided by extensive, porous limestone aquifers that lie beneath its surface. Most of the stygobitic crayfishes occur in northern and central Florida; only one species has been described from extreme southern Florida, Procambarus (Leconticambarus) milleri Hobbs 1971. Since its description in 1971, few specimens have been collected. Our objectives were to update its distributional range and provide information on biology, size-structure, coloration, fecundity, and life history. We studied a captive population at a Homestead fish farm monthly during 2000-03, and also sampled groundwater wells in Everglades National Park (ENP) and the Atlantic Coastal Ridge to document distribution. We used bottle traps, substrate traps, pumping, and baited vials to collect crayfish in wells.

We did not find this rare crayfish in 34 wells in or near ENP; however, we found it at 13 new locations on the Atlantic Coastal Ridge. Most collections were from wells in the Fort Thompson limestone formation between seven to eleven-meters deep, although one collection was made at three meters. We measured 2,451 crayfishes in captivity: 1,023 females, 832 males, and 596 juveniles. Mean sizes of males and females did not differ significantly (t = 1.808, p = 0.071), unlike in most crayfishes. The majority (82% of 2,451 crayfish) had normal dark orange coloration with a red stripe on the dorsum of the abdomen; the remainder were light orange, beige, or albino. The largest, wild Form I (reproductive) male had a carapace length (CL) of 27.4 mm and the smallest, 16.2 mm. Of the 1,023 females, 80 had eggs; the mean CL (±1 s.d.) of eggbearing females was 22.3 (2.6) mm, and the smallest was 16.0 mm CL. Females with eggs were present every month, but were most abundant during January-March. Eggs were black, with a mean diameter (±1 s.d.) of 1.86 (0.38) mm (n = 37 females). Compared to the closely related Everglades crayfish (P. alleni), the Miami cave crayfish produced fewer and larger eggs-diameters ranged from 1.1-1.7 mm. This agrees with life-history theory, which predicts that the Miami cave crayfish, living in food-resource-limited subterranean waters, should produce larger and fewer ova than congeners inhabiting surface waters.

The origin of P. milleri as a subterranean organism is recent. In fact, it has not yet acquired all the morphological traits, such as blindness and lack of pigmentation, of truly subterranean organisms. Our data indicate that this rare crayfish is endemic to southern and central Miami-Dade County. As documented here, its small population and limited range make it vulnerable to human activities that affect groundwater, including pumping of water from the aquifer, degradation of water quality, and limestone removal.

Contact Information: William F. Loftus, U.S. Geological Survey-Florida Integrated Science Center, 40001 State Road 9336, Homestead, FL 33034 USA, Phone: 305-242-7835, Fax: 305-242-7836, Email: bill_loftus@usgs.gov

(This abstract is from the 2006 Greater Everglades Ecosystem Restoration Conference.)

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