An occurrence of epizooic chantransia on rusty crayfish

Tufts of red algal chantransia stage were found growing epizooically on rusty crayfish (Orconectes rusticus) in Hog Creek, a second order stream in the Till Plains of west-central Ohio.  This phenomenon shows a seasonal trend with the first macroscopic appearance of algae on the crayfish occurring in early September and diminishing in January.  The heaviest cover of chantransia was found on the crayfish antennae and antennules and at joints in the exoskeleton.  There was a strong correlation between the size of crayfish and algal coverage (r = 0.75) with larger individuals displaying a greater cover of chantransia.  A portion of the plastid rbcL gene for the chantransia was sequenced and unequivocally identified it as Thorea hispida (Thore) Desvaux.  This freshwater red alga is more typical of tropical/subtropical streams, but members of the genus have been infrequently recorded from temperate regions in North America.  It has not been reported growing epizooically, but tends to be on hard benthic surfaces. A 30 meter section of Hog Creek was surveyed for in-stream habitats, such as rocks and fallen logs.  These substrata were examined both macro- and microscopically, but no chantransia was observed.