Adults and small juveniles were first identified in Possum Kingdom Reservoir, Palo Pinto County, Texas in the summer of 1998. Since that time, we have confirmed the presence of this species in eight additional Texas impoundments including: Trading House Creek Reservoir, Lake Colorado City, Lake E.V. Spence, Lake Granbury, Lake Balmorhea, Lake Whitney, Squaw Creek Reservoir in Glen Rose and Lake Texoma. Mud crabs have also been reported from Braunig Lake in San Antonio but we have not conformed this finding.
The salinities at Possum Kingdom and Lake Granbury usually range between 1 and 2 ppt, and Trading House Creek Reservoir generally ranges between 0.4 and 0.5 ppt. These salinities are below the minimum that has been demonstrated for larval survival yet there is strong evidence that these crabs have established permanent breeding populations.These are the first known occurrences of this species in inland freshwater lakes. Exactly how this crab was introduced into the reservoirs is questionable though fish-stocking programs are suspected. Evidence that the crab has established breeding populations at all seven impoundments is demonstrated by the extreme abundance of crabs with size variation from 1.5 mm to 23 mm, the occurrence of gravid females, and the presence of zoea larvae in the plankton. Eggs from gravid females have been hatched in our lab at salinities from 0.5 to 15 ppt with no significant difference in the percent of eggs that hatched (average about 85%)
The crabs have caused fouling problems at Possum Kingdom by clogging
PVC inlets to lakeshore homes, and have been found on the intake screens at the
power generating plant at Glen Rose. There is also some evidence that they
may be disrupting natural community structure by replacing the crayfish that
naturally occur in these freshwater habitats. Because of these concerns,
it is important to understand how the crab has managed to adapt and reproduce in
its new habitat. Our research is attempting to establish the potential for this
species to reproduce and spread to other freshwater bodies, and determine the
degree of genetic alteration from their coastal relatives. This is being
accomplished by attempting to establish the lowest salinities that larvae can
survive to the juvenile crab stage, and making DNA comparisons between the lake
and estuarine populations. DNA comparisons are also being conducted to determine
variations that occur in populations of different lakes.
