Abstract
Ghost crabs have been widely used as a bio-indicator species of human impacts on sandy beaches to obtain reliable biological data for management and conservation purposes. Ghost crab population densities and individual sizes decline dramatically under human pressure. However, distribution within a beach and the factors that determine this distribution of ghost crabs is still an open question. These factors may provide valuable information for understanding human impacts on sandy beaches. Here we examine ghost crab burrows on 20 sandy beaches of South Carolina, USA under various levels of human impacts to understand the response in terms of spatial distribution of this species to human impacts. We also examine the burrow characteristics and environmental properties of the burrows to determine whether these factors alter burrow characteristics. We show that crabs on heavily impacted beaches altered their spatial distribution to mostly occupy the edges of impacted beaches. Further, this change in spatial distribution was influenced by the size distribution of the population on a beach (i.e. larger individuals occupy upper parts on the beaches). We also found that ghost crabs altered the morphology of their burrows on heavily impacted beaches. Ghost crabs create deeper, steeper and smaller burrows under human impacts. These patterns were also influenced by physical characteristics of the beach. Our results suggest that human impacts can directly influence the spatial distribution of ghost crab populations within a beach and therefore sampling at upper parts of the beaches overestimates the population density and individual sizes. Our results support the use of ghost crabs as indicator species in effective beach management, but suggest that assessments would benefit from examining the morphology and distribution of burrows as opposed to simply using burrow counts to assess the health of sandy shores.
Highlights
Human impacts have become the major force shaping ecosystems globally over the past century
We have shown that the distribution of the O. quadarata burrows on sandy beaches vary among the sites that are under influence of various levels and the types of human disturbance
We have further demonstrated that O. quadrata populations responds strongly to various human impact types by declining in both size and density, and burrowing characteristics and burrow dimensions vary based on human impacts on sandy beaches
Summary
Human impacts have become the major force shaping ecosystems globally over the past century. The strength of these impacts in different regions are largely correlated with human. Coastal ecosystems are highly preferred regions due to their valuable services [2,3] such as recreation and tourism [2,4]. While recreation and tourism provide a socio-economic boost [5,6,7], they cause important ecological issues [4] such as alteration in natural habitats, declines in biodiversity and increase in pollution [8], which can cause either reversible or irreversible damage in coastal ecosystems [3, 9]
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