Assessing the resilience of hermit crabs to extrinsic and intrinsic environmental change

Abstract

The resilience of communities to environmental change depends on the interplay between extrinsic and intrinsic factors that may have contrasting outcomes for constituent species. We investigated the resilience of two co-occurring species of hermit crab (Clibanarius spp.) to different levels of environmental disturbance (i.e., burial depth and sediment type as extrinsic factors) and resource quality (i.e., shell encrustation and adequacy as intrinsic factors), which may interact to affect survival outcomes in intertidal environments. Results showed that for both species, the ability to emerge from mud was dramatically less than sand, suggesting that human activities which increase the deposition of fine sediments may be detrimental for entire populations. Secondly, deeper burial events had a negative effect on emergence, although this was more profound for C. antillensis than the more abundant species C. vittatus. To explore the interplay between extrinsic factors and intrinsic characteristics, we expanded our comparisons to include shell quality (clean vs. encrusted gastropod shells) and a continuous variable describing shell adequacy (i.e., shell fit for a given size of crab). This analysis was done using Generalized Linear Mixed Models (GLMM's), with results indicating that the factors governing the emergence of C. antillensis were mostly extrinsic, while those for C. vittatus were more complex and modulated by aspects of shell quality. Overall, our models highlight the interplay between extrinsic and intrinsic factors in response to environmental variability which may affect species in unpredictable ways that can undermine the resilience of entire communities.