UC San Diego Study on Beach Replenishment

UC San Diego biologists who examined the biological impact of replenishing eroded beaches with offshore sand found that such beach replenishment efforts could have long-term negative impacts on coastal ecosystems.

The scientists, who studied the effects of beach replenishment efforts on the abundance of intertidal invertebrates at eight different beaches in San Diego County, discovered that the movement of sand onto those beaches resulted in a more than twofold reduction in the abundance of intertidal invertebrates after 15 months.

“We found rather long lasting declines in invertebrate abundances due to replenishment,” said Joshua Kohn, a professor of biology who headed the study, which was published this week in the journal Estuarine, Coastal and Shelf Science. “These invertebrates are what shorebirds eat when they poke their bills in the sand. They are also food for small inshore fish.”

While other researchers had previously looked at the impact of beach replenishment on certain taxa of invertebrates at specific beaches, the UC San Diego study is unusual in that it examined the impact on the total invertebrate community across eight different beaches in San Diego County from Oceanside south to Imperial Beach.

The UC San Diego biologists were also able compare their results at each beach where sand was pumped onshore to an untreated section of the beach, which served as a control.

The opportunity to conduct the study came about in the fall of 2012 when the San Diego Association of Governments, or SANDAG, and the U.S. Army Corps of Engineers embarked on an ambitious project to replenish eight beaches with a total of 1.76 million cubic meters of sand.

The eight beaches sampled from north to south were South Oceanside Beach, North Carlsbad Beach, South Carlsbad Beach, Batiquitos Beach, Moonlight Beach, Cardiff State Beach, Fletcher Cove and Imperial Beach.