Burrow density does not predict burrowing crab abundance across space or time in a New Jersey salt marsh

Burrowing crabs are salt marsh ecosystem engineers that can exert strong trophic and non-trophic (e.g., burrowing) effects on their environments, with the potential to alter biotic conditions and biogeochemical processes. While burrowing crabs are a model organism, predicting where and to what degree they will influence their environments remains challenging. This inability to develop robust hypotheses may be attributed to the widespread use of crab burrow density as a proxy for burrowing crab density, which is problematic as burrowing crabs (e.g., Minuca spp.) burrow and forage in distinct habitats. Here, we conducted a survey of crab burrow density and burrowing crab density, relative to a suite of abiotic and biotic factors, across spatial and temporal scales in a Mid-Atlantic salt marsh. We found no relationship between crab burrow density and burrowing crab density across space or time, with abiotic factors and biotic factors impacting crab burrow density and burrowing crab density differently across spatial scales. This suggests that crab burrow density is not always a functional proxy for burrowing crab density and we implore future studies to quantify burrowing crab density, in addition to crab burrow density, to more rigorously evaluate burrowing crab trophic and non-trophic effects.