|MAKING WAVES, June 2004 issue: Table of Contents|
|A Feast Interrupted Ed note: This is the second installment of a five-part series on beach ecology.|
By Hal Hughes
Every few days in some places as often as twice a day tractors roll along a hundred miles or so of sandy beaches in Southern California, scooping up not only trash but also seaweed that’s washed ashore, along with the myriad small creatures that shelter in it. This mechanical “beach grooming” practiced for decades helps keep up the classic sand-and-surf image that draws millions of people to the region’s beaches, but it also sweeps away a resource that provides vital nourishment for shorebirds.
“Grooming sandy beaches changes rich coastal habitats into barren plains of unstable sand,” says Jenifer Dugan of the Marine Science Institute at the University of California, Santa Barbara, whose team has surveyed over 40 beaches, both those that are regularly groomed and beaches where beach wrack kelps and seagrasses brought ashore by waves and tides is left in place. Their ongoing studies since 1995, funded by California Sea Grant, California State Parks, Minerals Management Service, and the National Science Foundation, have found far fewer creatures and far lower diversity of life on beaches that are regularly cleaned by “sanitizer” tractors.
On beaches where wrack was left undisturbed, “Our surveys have found a very high abundance and diversity of intertidal life compared to similar beaches in other parts of the world,” Dugan says. “The abundant life of natural beaches provides food for large numbers of wintering shorebirds of many species, and for nesting western snowy plovers.” In contrast, the upper intertidal zone of many beaches where wrack is removed is populated only by a few flies, leaving little for shorebirds to eat. Her studies show that without the nutrients supplied by kelp and other organic matter that washes ashore, beaches are not hospitable to many animals, including shorebirds.
Beach wrack accumulates at the top of the intertidal zone, where it becomes home for tiny creatures like beach hoppers that feed on it and help to break it down. Other animals feed on the beach hoppers, and an intricate food web and succession of life develops in piles of decomposing wrack. These little critters in turn become food for shorebirds. Undisturbed beach wrack establishes a rich, dynamic zone of life that links marine and terrestrial habitats. Waves and wind constantly shift this zone, so the creatures that rely on this moveable feast are adapted to living and eating on the run.
Dugan and her colleagues have found that the wrack piles also catch and hold beach sand, which helps to form hummocks and larger dunes. This gives dune plants a foothold and needed nutrients, and increases the stability of the beach. On groomed beaches, fine sand is washed or blown away more readily, leaving coarser grains behind.
Focused on abundance and diversity, Dugan’s research found beach hoppers (Megalorchestia spp.) to be among the most abundant macrofauna (animals that are large enough to be seen with the naked eye) on natural California beaches. These tiny crustaceans stay hidden under the sand and wrack during the day. After dark, beach hoppers emerge and go to work on the kelp, rapidly devouring the lighter portions and hastening the breakdown of the rest. These and other animals that thrive in or under beach wrack beetles, flies, isopods, and other insects and crustaceans are delectable treats for shorebirds like plovers, sanderlings, godwits, and sandpipers. The wrack line also attracts mammals and birds from inland. She has seen foxes, feral pigs, flycatchers, even endangered Belding’s savannah sparrows come to feed there.
The results of Dugan’s research have encouraged some beach managers to reexamine the practice of mechanical beach grooming. On a few formerly groomed beaches, wrack is now being left in place. At San Buenaventura State Beach, in Ventura County, where one stretch directly in front of the lifeguard station has been left ungroomed, “dune plant recovery has been dramatic,” said Dugan. “For natural beaches, wherever beach wrack is left undisturbed, animal colonization is very rapid a matter of hours.”
Meanwhile, in San Diego, Sea Grant-supported studies are investigating whether grooming damages the eggs that grunion lay on beaches during high tides between March and August. This research has already led to revised grooming practices.
“The more we study beach wrack,” says Dugan, “the more we learn how important this resource is to coastal ecology.” The dominant species on California beaches is, of course, Homo sapiens, which uses sandy shores for recreation. Some people don’t like decaying seaweed, others don’t like flies or other little critters to disturb their sunbathing. (Mechanical grooming is unknown on the cooler beaches of Northern California.)
Dugan hopes there’s room for compromise to restore beach life after years of grooming. “It might be possible to designate some zones to be left ungroomed,” she said. “If the wrack were left year-round, the communities of plants and animals could recover. Then they’d process much of the wrack naturally.”