Sandy beach ecology in the Anthropocene: Ghost shrimp (Crustacea: Callianassidae) as a study model

Abstract

The close relationship between biotic systems and physical conditions determines the classic ecological hypotheses and theories of sandy beaches. Accordingly, the Habitat Harshness Hypothesis (HHH) predicts that macroinvertebrates inhabiting beaches with less hydrodynamic severity have larger body size, higher fecundity and thrive more abundant populations than harsher beaches. The current omnipresence of human impacts on beaches demands that ecological studies take on a holistic approach, including the interaction between physical factors and variables that represent these disturbances as regulators in diversity patterns. Here we tested the classic HHH, using the ghost shrimp Callichirus major (Crustacea: Callianassidae) as a study model. Considering this species as a habitat specialist, we predicted that the ghost shrimp would respond mainly to sedimentological changes, used as a proxy for the physical harshness of the habitat. Eleven sectors were sampled along two extensive beach arcs in southeastern Brazil, including counting burrows to estimate abundance metrics and collecting individuals to measure individual attributes, such as body size and fecundity. Abundance and body size were greater in beaches with smaller sediment particles size and well-sorted sediments, confirming the typical predictions of HHH. Moreover, larger individuals were found in beaches that were closer to major rivers, probably due to greater trophic subsidies. The urbanization indicator imposed negative effects on body size and fecundity, though with lower predictive power than sediment features and distance to rivers. Our results are useful for modelling coastal impacts, guiding monitoring, conservation and restoration planning, and offer a better understanding of the ecology of ghost shrimp.