Meeting Abstract
Many marine organisms and life stages lack specialized respiratory structures, like gills, and rely instead on cutaneous respiration, which they facilitate by having very thin integuments. This respiratory mode may limit body size, especially if the integument also functions in structural support or locomotion. Sea spiders, or pycnogonids, are a basal group of marine arthropods that lack gills and rely on cutaneous respiration but still grow to large sizes. Sea spider cuticle is not solid but has many pores that cross the cuticle, which may play a role in gas exchange. Here, we tested two hypotheses for gas exchange in sea spiders: 1) oxygen diffuses directly across the cuticle, a common mechanism in aquatic insects, or 2) oxygen diffuses across pores in the cuticle, a common mechanism in vertebrate egg shells. We tested these hypotheses by modeling diffusive oxygen fluxes across all pores in the body of sea spiders, and then asking whether those total fluxes were significantly different from our separately measured metabolic rates. We estimated fluxes across pores using Fick’s law incorporating measurements of pore morphology and oxygen gradients. Finally, we measured the scaling of size (length and diameter) and density of pores to test for effects of total pore area upon the animal’s rate of flux. Flux across the pores scaled similarly to that of oxygen consumption, which strongly supports the second hypothesis. Larger species, therefore, need greater total pore area to facilitate greater diffusive oxygen flux across their cuticle. This likely presents a functional trade-off between gas exchange and structural support in large species, where the cuticle must be thick enough to prevent buckling due to external forces but porous enough to allow sufficient gas exchange. NSF PLR-1341485.
