Shifting Relationships Between Crayfish and Symbiotic Worms in Surface Water and Subterranean Environments

Abstract

Branchiobdellidans are small annelids (Clitellata) that have neutral, positive, and negative effects on stream crayfishes. Host effects are context dependent, with positive effects (increased survivorship and growth) observed under high fouling pressure. Branchiobdellidans may be particularly beneficial to burrowing crayfishes in subterranean water, which is characterized by reduced water quality relative to surface water. The red swamp crayfish (Procambarus clarkii) is an ideal organism for testing this model as this species spends significant portions of its life in both open water and burrows, and can host large numbers of branchiobdellidans (100+ worms per adult). I tested for effects of the branchiobdellidan Cambarincola spp. on survivorship, growth, and ecosystem-level processing of P. clarkii in subterranean burrows and surface water environments in laboratory experiments. I also evaluated survivorship of Cambarincola spp. in natural surface water and burrow environments and utilized acute (48 hr) dose response assays to test effects of pH and ammonia on worm mortality. Results from laboratory studies showed worms thrived and significantly increased the growth of P. clarkii in surface waters but not in underground burrows. Worms had significant impacts on some ecosystem-level processing in surface waters but not in burrows. Field study results supported the finding of poor worm survivorship in laboratory burrows, but showed variable worm survivorship in ponds. Dose response assays showed worms were tolerant of a broad range in ammonia (0-40 mg/L) and pH (6.5-9.5). My results suggest the symbiotic relationship between C. spp. and P. clarkii is context-dependent: mutualistic in open waters, and commensal to non-existent in subterranean burrows. The mechanisms behind differential survivorship of worms in burrows and among ponds remain unclear. Further investigation into the shift in outcomes between habitats requires a better understanding of the specific environmental factors limiting worm survivorship in burrow and pond environments.