Bait box survey of aquatic cave invertebrates for four caves in Glacier National Park, Montana

Bodenhamer, Hans; Bigfork High School Cave Club

Non-collecting survey of aquatic invertebrates in 4 park caves (2009-2010): Poia Lake, Algal, Heavy Runner, and Zoo caves. A non collecting, bait box study of aquatic cave invertebrates was conducted in 4 caves in Glacier National Park. Boxes were left submerged for 24 hrs, and then baited invertebrates were counted and returned to the pool. In addition to counting baited invertebrates, numbers of non baited invertebrates were estimated, pool dimensions were drawn on a map of the cave, and water temperature and chemistry were measured at each sampling site. In Algal Cave planarians were baited and isopods numbers were estimated. Numbers of planarians and isopods increased in the cave during early spring run off and decreased in late fall. What is believed to be a caddis fly larva was the only other aquatic invertebrate observed in Algal Cave. In Poia Lake Cave both planarians and amphipods were baited. Numbers of planarians and amphipods remained relatively constant from the fall of 2009 to the spring of 2010, but planarian numbers decreased in the fall of 2010. In addition to the decrease in planarians, the distribution of amphipods shifted closer to the entrance in the fall of 2010. Springtails and mites were also observed in the cave. No aquatic invertebrates were observed or baited in Heavy Runner or Zoo Cave. These speculations are made based on findings: 1) The number of aquatic cave invertebrate in both Algal and Poia Lake Cave likely depends on the amount and timing of water input into the cave. Planarian, isopod, and amphipod numbers are probably greater during spring run off and less in late fall. 2) The distribution of aquatic cave invertebrate species in Algal and Poia Lake Cave is probably related to the source of ground water flowing into the cave. Planarians appear to be associated with shallow groundwater that enters the cave along a shorter path passing through soils directly over the cave. Whereas, isopods and amphipods appear to be associated with deeper groundwater that enters the cave along a longer flow path and spends more time in contact with bedrock. 3) Isopod and amphipod populations in Algal Cave may be decreasing and planarians populations increasing. In contrasting the results of our study with a similar study conducted by Paul Hendricks (2000), isopod numbers decreased by a factor of 6 or more, planarians increased by a factor of 4 or more, and amphipods disappeared from the cave.