COS 6-4 - Functional traits and habitat characteristics predict the effects of bioturbation on sediment properties and functions.

Abstract: Burrowing animals can profoundly affect the biological structure and ecosystem functions of their environments. For instance, burrowing crabs can increase sediment deposition and facilitate sediment homogenization and turnover, with consequences for sediment biogeochemistry. However, the relative importance of burrowing animals on sediments are challenging to predict and are expected to be affected by animal functional traits (e.g., diet and burrow morphology) and habitat conditions (e.g., vegetation presence). To develop a predictive framework for the impacts of burrowing animals on ecosystem functions, we conducted a systematic meta-analysis focusing on the effects of burrowing crab communities on sediment properties and biogeochemical functions in soft-sediment coastal ecosystems (e.g., salt marshes, mangrove forests, tidal flats). We also explored the roles of crab functional traits (e.g., diet and burrow morphology) and habitat characteristics (i.e., vegetation) in shaping burrowing crab effects on coastal sediment conditions and functions, such as redox potential and CO₂ flux.

Burrowing crabs increased sediment erosion, oxygenation, and rates of nutrient cycling (i.e., nitrification and CO₂ flux). However, the magnitude and direction of these effects depended on the structure of the burrowing crab community and the presence of vegetation. For example, burrowing crabs in the Superfamily Ocypodoidea (e.g., fiddler crabs) had greater effects on sediment conditions and functions than burrowing crabs in the Superfamily Grapsoidea (e.g., Sesarma sp.), likely due to their detritivorous diets and deeper burrows. Additionally, the presence of vegetation reduced the magnitude of burrowing crab effects on sediment C cycling (e.g., organic C and sediment organic matter). Overall, our findings suggest that burrowing crab communities have predictable impacts on sediments in coastal environments, with the magnitude of those effects being mediated by crab functional traits and habitat characteristics. Evaluating how burrowing animals, like crabs, influence sediments is a critical step in assessing the drivers of ecosystem functions in threatened soft-sediment coastal environments.