This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Stand on the damp sand on a California beach and chances are you're standing on top of an active earthworks site. Sand hoppers (Megalorchestia spp.), the tiny, shrimp-like creatures commonly found eating away at kelp on the shore, have been found to move massive amounts of sand, excavating up to 50 kg (110 pounds) of sand per meter (3.3 feet) of shoreline per day.
"They have one of the highest rates of bioturbation of anything on the planet," said UC Santa Barbara marine scientist David Hubbard, referring to the process of sediment displacement by living organisms. The sheer volume of sediment moved by these crustaceans, according to Hubbard and fellow coastal researchers, puts these amphipods on par with coastal longshore processes and some major Southern California rivers. Their findings, published in the Journal of Geophysical Research: Earth Surface, put new perspectives on the roles of these and other sand-dwelling creatures in the physical processes that shape the coast.
Though they may look stationary, sandy beaches act like rivers of sediment, constantly moving sand transported by waves, winds and currents along the coast. The beach is but one part of a bigger system called a littoral cell that cycles sediment from its sources, such as cliffs and dunes that back some beaches, rivers and streams that carry sediment from coastal watersheds, or onshore processes that push sand from nearshore to the beach. Beaches serve as reservoirs for sand as it continues its way along the coast.
While coastal sediment transport processes are well known, the impact of the animals that live in this highly dynamic environment is less understood. It became an intriguing question for Tim Baxter, a physical geographer interested in interactions between wildlife and their physical environment in the coastal zone. When he moved from the U.K. to UCSB a few years ago to complete his postdoctoral work with geography professor Ian Walker, Baxter found in marine scientists Hubbard, Kyle Emery and Jenny Dugan a complementary curiosity about sand hoppers.
These tiny crustaceans burrow 10–30 cm (4–12 inches) into the sand or hide under washed-up seaweed, emerging after dark to feed on kelp wrack. "We combined our interests and started thinking about the abundance of sand hoppers around UCSB, but also across California," said Baxter, who is now a research fellow at the University of Oxford. "That got us asking, how much are they digging?
What are they contributing to the sediment system and sediment transport on these beaches?" To find out, they devised a simple field experiment at Isla Vista Beach, a bluff-backed stretch of shore adjacent to the UCSB campus. After high tide on a summer night, when the waves had smoothed the sand and the tide had begun to recede, they sectioned off an array of sampling plots with metal frames in the sand hoppers' preferred burrowing zone. "They don't like saturated sand that's like liquid—their burrows collapse immediately," Hubbard explained.
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