Diet, energy storage, and reproductive condition in a bioindicator species across beaches with different levels of human disturbance

Abstract

Demographic shifts in populations of bioindicator species are widely used to gauge the extent of impacts of human disturbances on ecosystems. Yet, the mechanistic drivers of these demographic changes are often poorly understood. The Atlantic ghost crab, Ocypode quadrata is a bioindicator species of human disturbances on sandy shores, and experiences similar demographic changes as other bioindicator species in response to disturbance by reducing their population abundance and individual body sizes. Previous studies have focused on how human disturbances could cause these demographic changes through altering mortality rates or burrowing behavior. Here, we examine the potential for energetic impacts of human disturbance to cause these demographic shifts. Specifically, we investigate whether variation in habitat quality associated with the level of human disturbance results in reduced diet quality and therefore reduced physiological condition and reproductive effort of ghost crabs. We demonstrate an inverse relationship between diet quality and the level of human disturbance, with resulting reductions in the physiological and reproductive condition of ghost crabs with human disturbance. Our study shows that indirect human disturbance can explain existing variation in demographic characteristics of this bioindicator species, and highlights the importance of understanding bioenergetic relationships between species habitat use and human impacts.