The impact of off-road vehicles on beach-dwelling wildlife

Common ghost crab (Ocypode cordimanus) in New South Wales, Australia. Driving off-road vehicles on beaches is a popular recreational activity on many coastlines around the world. However a new study in the journal Environmental Management finds that off-road vehicles can impact beach-dwelling wildlife.

At beaches along the eastern coast of Australia, Serena Lucrezi and Thomas Schlacher conducted surveys of ghost crab burrows and measured characteristics such as the entrance diameter and elevation.
In an unusual attempt to see what the burrows looked like underground, they poured plaster into 305 burrows and dug out the casts, which extended as deep as 1.5 meters.  

Beaches open to traffic had smaller crabs and narrower crab burrows, and the crabs living on these beaches tunneled deeper than those on beaches closed to vehicles.

The deeper tunneling was especially noticeable after the Christmas and New Year holidays, when off-road vehicle traffic hit its peak. Digging deeper burrows may leave the crabs with less energy for reproduction and less time for foraging.

The findings indicate that crabs are affected negatively by off-road vehicles even when not crushed and killed outright.

Ghost crabs in the genus Ocypode live on tropical and subtropical beaches and dunes worldwide. The crabs dig burrows into the sand to gain shelter from predators, hot weather, and other threats, and they emerge to feed at night.

Because they are major predators as well as an important prey for birds, ghost crabs represent a critical link in the beach ecosystem.  

Travel by off-road vehicles on beaches and dunes has a range of well-known environmental impacts: damage to dune vegetation, harm to nesting birds and turtles, and reductions in abundance and diversity of invertebrates.

However, little is known about sublethal effects on beach-dwelling species such as ghost crabs, which may survive the traffic but change their behavior.  

Given the study findings and the ecological importance of ghost crabs, Lucrezi and Schlacher suggest that resource managers could use crab burrows as an indicator of vehicle impacts on the ecosystem.

This indicator could reveal important impacts before they become evident through declines in the numbers of crabs and other beach species. The authors write,  

"Managers of beaches and dunes...require measures of ecological condition and indicators of change that span more than one attribute of the biota...to strengthen assessments and evaluate the efficacies of interventions; to this end, burrow architecture of ghost crabs could make a useful contribution."

by Peter Taylor

Lucrezi, S., & Schlacher, T. (2010). Impacts of Off-Road Vehicles (ORVs) on Burrow Architecture of Ghost Crabs (Genus Ocypode) on Sandy Beaches Environmental Management DOI: 10.1007/s00267-010-9491-5