Density and distribution in laboratory populations of midge larvae (Chironomidae: diptera)

The troglobitic amphipod crustacean Crangonyx antennatus occupies mud-bottom pools and small, gravel-bottom streams in caves in the southern Appalachians. One large, mud-bottom pool population in Lee Co., Virginia was observed periodically from 1967 to 1975. Amphipods in this population frequently burrowed into the soft mud substrate, where they were able to survive desiccation during periods when the pool dried up. Animals kept in the laboratory also burrowed and survived desiccation during an experiment which simulated drought conditions similar to those observed in caves. Amphipods collected from both pool and stream habitats burrowed, thereby indicating that stream-adapted populations of this species still retain sufficient flexibility to survive under variable environmental conditions that might be encountered in nature. It is concluded that burrowing provides a means of survival for C. antennatus when it is sometimes exposed to drought conditions in cave pool habitats and also provides protection from potential terrestrial predators under similar conditions. Burrowing also offers amphipods protection from aquatic predators (such as salamander larvae) during normal water levels and possibly allows juveniles a means of escaping cannibalism by adults.