Observations on the biology of the endangered stygobiotic shrimp Palaemonias alabamae, with notes on P. ganteri (Decapoda: Atyidae)

Abstract

Palaemonias alabamae is endemic to subterranean waters in northern Alabama. Its type locality is Shelta Cave, Madison County, and ostensibly conspecifi c shrimps have been found in Bobcat and two other caves. Pollution and other factors may have extirpated the shrimp from the type locality. In Shelta Cave the species is smaller than the shrimp in Bobcat Cave and P. ganteri in Mammoth Cave, Kentucky. Adult female P. alabamae (s.s.) and P. ganteri are larger than males. Female P. alabamae with visible oocytes or, rarely, attached ova, were observed from July through January in Shelta Cave. Each female there produces 8 to 12 large ova, whereas females of the population in Bobcat Cave produce 20 to 24 ova, and P. ganteri produces 14 to 33 ova. Plankton samples taken in Shelta and Mammoth caves yielded nothing identifi able as zoea or postlarvae. Palaemonias alabamae and P. ganteri usually feed by fi ltering bottom sediments through their mouthparts, but both sometimes feed upside down at the water’s surface. Although there is some overlap, the compositions of the aquatic communities in Shelta and Mammoth caves differ, and there are some major differences among the Alabama shrimp caves. The stygobiotic fi sh, Typhlichthys subterraneus, is a known predator on P. alabamae in Shelta Cave.