First Report of Freshwater Jellyfish in Montana

Abstract

The first known sample of freshwater jellyfish [(Craspedacusta sowerbyi ) Lankester, 1880 (Cnidaria: Limnomedusae: Olindiidae)] in Montana came from an artificial pond on an abandoned golf course in Cascade County near the town of Great Falls in 2009. The pond is located ~600 m from the Missouri River and is part of a four pond network connected by a dry artificial stream.The initial collection occurred on 25 August 2009. Hydromedusa were observed swimming near the surface, collected with a dip net. Mean diameter of the jellyfish measured 29 mm. A second visit occurred on 3 September 2009 to make museum collections and record habitat conditions. Surface water temperature was 18.1 degrees C. The substrate of the pond was primarily coarse sand with a few piles of rock 12-25 cm in diameter. No vegetation was present in the water or along the shoreline. Two plankton tows were made from a small raft with a 30-cm diameter 80-micron Wisconsin net at the deepest part of the pond. Plankton collected were Bosmina spp., Cyclops spp., Nauplii of Cyclops and trace amounts of rotifers Kellicotia spp., Conochilius spp., and Asplanchna spp. The location of this population raises concern about possible expansion into the Missouri River. Given the ability of this organism to select for specific plankton and affect their reduction, the ecological impacts of this species could be far reaching if it becomes established in the Missouri River reservoirs.