Life history of the endangered dwarf wedgemussel, Alasmidonta heterodon (Lea 1829) (Pelecypoda: Unionidae), in the Tar River, North Carolina and Aquia Creek, Virginia

Abstract

The reproductive cycle, population dynamics, and habitat use of the dwarf wedgemussel (Alasmidonta heterodon) were studied in populations from the Tar River, North Carolina and Aquia Creek, Virginia during 1991 and 1992. This mussel is a long-term brooder, spawning in late summer and becoming gravid in September with glochidia maturing in November. Drift net sampling at sites with this species in both rivers during spring and fall of 1991 and spring of 1992 yielded no A. heterodon glochidia, indicating poor or no reproduction at both sites in 1991.

Laboratory infestation experiments testing 15 fish species found three hosts for A. heterodon. The tessellated darter (Etheostoma olmstedi), the Johnny darter (EE. nigrum), and the mottled sculpin (Cottus bairdi) all supported glochidial development to the juvenile phase. Six species of sunfishes, four minnows, one sucker, and one catfish species tested in the laboratory did not serve as hosts. Because of seemingly poor reproductive success in 1991, natural infestations of fishes with glochidia were not documented.

Age and growth characteristics were calculated using a thin-sectioning technique on valves collected from the Tar River, Aquia Creek, and the Neversink River, New York. As computed by the von Bertalanffy equation, the dwarf wedgemussel reaches a maximum length of 38.70 mm, 45.26 mm, and 45.84 mm in the Tar River, Aquia Creek, and Neversink River, respectively. There were significant differences among the growth curves of A. heterodon from the Tar River and Aquia Creek, and between those of the Neversink River and Aquia Creek. There was no significant difference between the growth curves of dwarf wedge mussels from the Tar and Neversink rivers.

Microhabitat parameters including depth, roughness, velocity, turbulence, distance from shore, distance from obstructions, canopy cover, presence or absence of macrophytes, and substratum size were collected for dwarf wedge mussels at the Tar River and Aquia Creek. Microhabitat use differed between the sites, most significantly described by the following variables: distance from shore; turbulence; and velocity. Laboratory preference studies designed to determine preferred substratum size and water velocity were conducted. Dwarf wedge mussels always preferred the finer substratum offered; little preference was exhibited by the mussels for lotic versus lentic flow regimes in the laboratory.