"The effect of traffic on the beaches is significant," said Jacqueline Steinback of East Falmouth, Mass., who studied the creatures living in and around the wrack -- the vegetation that accumulates at the high tide line -- on the beaches of the Cape Cod National Seashore.
"Scientists originally thought that driving on beaches wouldn't have much impact since beaches are constantly changing and the species are already surviving waves, winds and extreme temperatures. But traffic is still having an effect on certain species," she added.
Funded by the National Park Service, Steinback's research compared the composition and abundance of beach invertebrates living in and around the wrack on beaches with and without vehicular traffic. She took core samples, set pitfall traps, and collected wrack samples on three beaches at the Cape Cod National Seashore -- Race Point North, Race Point South, and Coast Guard Beach in North Truro.
On beaches where traffic was permitted, the number of animals tallied was from 30 to 50 percent lower than on beaches where traffic was prohibited.
"The wrack line is where a lot of insects and crustaceans congregate and live," she said. "Birds and other scavengers pick through it. It's an important part of beach ecosystems."
The wrack is used in many different ways by different animals. For instance, many creatures use it as both food and cover from predators and extreme temperatures; several species of flies use it as a site to lay their eggs; and wolf spiders migrate back and forth from the beach grass to the wrack to feed on small crustaceans called amphipods.
"Some species, like beach hoppers, are very susceptible to drying out in immature stages, so they hang out and feed under the wrack," Steinback said. But when vehicles drive over the wrack, their tires break up the vegetation, which makes it dry out. "That changes the abundance and diversity of species on the beach."
Steinback noted that the beach ecosystem is very variable because environmental conditions change from day to day. As a result, species composition changes daily as well.
"The important thing is that the Park Service is doing a good job of protecting most of the species diversity by limiting where people can drive and encouraging them to stay away from the wrack. If you protect the wrack, you protect many of the species, especially those that spend part of their life burrowed in the bare sand behind the wrack where vehicles are instructed to drive," she said.
Steinback suggests that one step the Park Service might take to further protect beach fauna is to close beaches to traffic on an alternating schedule, rather than close some beaches for the entire season and open others.
"Maybe by alternating closures at various beaches, there wouldn't be such a consistent negative impact on the beaches where traffic is allowed," she said. "The species are flexible and move around a great deal, so by regularly opening and closing the beaches to traffic, the impact may not be as great.
"This is an environment that few people study, so there are still lots of questions," she concluded. "Off-road vehicles are having a tremendous impact on many natural communities, but on these beaches they haven't yet caused long-term damage that can't be remedied."