Overwintering capacity of water boatmen (Hemiptera: Corixidae) and other invertebrates encased in the ice of shallow prairie wetlands

Abstract

Overwintering in shallow habitats presents a serious obstacle for aquatic invertebrates. Here we investigated the little-known ability of water boatmen (Hemiptera: Corixidae), an aquatic insect, to survive the winter encased in air pockets within the ice of shallow wetlands. We extracted and experimentally thawed large blocks of ice from prairie wetlands in Saskatchewan, Canada, from which we examined the species composition and revival of corixids. While multiple corixid species were present in wetlands prior to freeze-up, a single species, Cymatia americana Hussey, 1920, comprised the vast majority of corixids that were found within the ice later in winter. Only 4%–9% of corixids, all Cymatia americana, revived after ice thawing over both study years. Being encased within an air pocket appeared to be necessary for the survival of corixids in the ice, with up to 300 individuals grouped together. Other invertebrate taxa also revived after thawing, including Haliplidae and Dytiscidae (Coleoptera) encased within air pockets both alongside corixids and on their own, as well as Coenagrionidae (Odonata), Phryganeidae and Leptoceridae (Trichoptera), Chironomidae (Diptera), and Physidae and Planorbidae (Basommatophora), which appeared to be encased in solid ice. The ability to overwinter inside ice represents a little understood survival mechanism of aquatic invertebrates in shallow wetlands, which could confer energetic and reproductive advantages to those that endure until spring.