Is the ghost crab’s feeding behavior a good early indicator of human pressure in sandy beaches?

Abstract

Phenotypic plasticity is a trait found among organisms that dwell in dynamic ecosystems such as sandy beaches. One of the main model of ecological studies in this ecosystem are ghost crabs (Crustacea: Ocypodidae), which present trophic plasticity and are considered ecological-disturbance indicator species. Their reactions to these impacts can manifest as sublethal responses, including behavioral aspects. We aimed to evaluate possible effects of urbanization on the feeding behavior of the ghost crab Ocypode quadrata (Fabricius, 1787). The study was conducted in a beach arc categorized into three urbanization levels located in the northern Rio de Janeiro state, Brazil. Each sector was sampled twice during high and low tourist seasons. The crabs’ diet was described by inspecting their digestive tracts with a stereomicroscope. Food preference (the choice of food items by each individual) and behavioral aspects (i.e., time of emergence from burrows, look-out time, number of choices, and handling time of the resource provided) were observed through in situ experiments, where food items were placed around burrows. The behavioral aspects were not affected by urbanization level. The diet mainly consisted of insects and macroalgae, though during experiments the species selected the most caloric items (fish and the bivalve Donax hanleyanus), regardless of the urbanization level. Local human disturbances seemed neither to change the availability of local resources nor to select individuals by feeding behavior. Therefore, there was no evidence that the feeding behavior of ghost crabs can be considered as a potential early indicator of human disturbance.