The Hine’s emerald dragonfly (HED, Somatachlora hineana), is an endangered species whose larvae have a complex relationship with the devil crayfish (Cambarus diogenes). They live within crayfish burrow-systems for 8-9 months a year over the four to five years that larvae take to develop from hatching to emergence. HED larvae have a somewhat dysfunctional relationship with C. diogenes since although they benefit from the refuge that the burrow provides from drought and winter conditions, they also are preyed upon by the crayfish. Understanding the interactions that occur within burrow systems is thus essential for understanding this complex dynamic. Polysaccharide gelling compounds such gellan gum (Gelzan®) has been frequently used as a transparent media for study of the development of root systems of plants. This material has much wider potential for the visualization of many other processes that occur in soils. This is especially true for burrowing organisms that live in aquatic and semiaquatic habitats. We attempt to use Gelzan® as a transparent soil substitute that allows crayfish to create semi-natural burrow systems, that can be used for viewing interactions between the HED larvae and devil crayfish.
Results/Conclusions
Devil crayfish will readily burrow into the gellan gum matrix, in a way that is apparently similar to the way they would into the muddy wetland soils that they live within. In less than 24 hours crayfish constructed simple burrow systems with a single chamber. Over the period of a week most crayfish had added significantly to the complexity of their burrows by constructing additional chambers and passages. The gellan gum matrix is able to retain burrow structure without collapsing for several weeks. The Gelzan® media allowed both physical and recorded observations of the burrow-systems. The material, stained with food coloring to decrease transparency, allowed for viewing of the burrow-systems from all angles and was transparent to near infrared light allowing for observation of HED larval and crayfish interactions in what they should perceive to be total darkness. These results indicate that the use of Gelzan® in studies of burrowing freshwater and marine species could provide many new insights into how these species and other species that use their burrows interact and coexist. It can potentially provide us new insights into the ecology of underground worlds previously inaccessible except through intrusive methodologies.