Ala Moana Regional Park visitors may be looking forward to the wider, softer shoreline after a $10 million sand replenishment project scheduled for next year.

But the benefits to beachgoers won’t come without sacrifice. The small creatures that live in the sand – such as worms, crabs and shrimp – are facing likely death, according to researchers from the University of California San Diego.

“It’s not a desert,” said Joshua R. Kohn, a professor of ecology, behavior and evolution. “There are things that live there, they’re all invertebrates, and piling sand on top of them tends to kill them.”

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This potential downside was not addressed in the city’s environmental impact statement, but Kohn and another scientist who studied beach replenishment in California – and found the practice to be lethal to some organisms – said their findings would likely hold true for Hawaii.

Their conclusions are supported by several other studies, including one in Australia in which researchers observed “samples collected two days after the conclusion of nourishment were entirely devoid of all invertebrate life.”

Beach replenishment, also called sand nourishment, involves loading sand onto eroded beaches. It’s considered a more eco-friendly alternative to other solutions like sea walls that can exacerbate erosion, but it can have some undesired consequences, Kohn’s 2016 study states.

Kohn and his colleagues studied eight beaches in San Diego County. Each had sections that were replenished and areas that were not, creating a unique opportunity for a well-designed controlled experiment.

Beach replenishment hit invertebrates hard, according to their study. Even 15 months after the sand nourishment project was complete, the number of invertebrates was still down by about half, Kohn said.

Even if humans don’t notice the losses, they can affect the larger ecosystem, said Brock Wooldridge, a Kailua native and Punahou School graduate who studied San Diego’s beaches with Kohn.

“They’re an important food item for the birds walking in the sand poking their beaks in, and when the tide rises, little fish are also eating these creatures,” said Wooldridge, who is pursuing a Ph.D at Harvard University. “If they don’t have their food, it could potentially have cascading effects. You could see a general decline in the health of the ecosystem starting from the ground up.”

Bouncing back from sand replenishment

At Ala Moana, the plan is to dredge an estimated 70,000 cubic yards of sand from an offshore site 2,000 feet makai of the closest surf break, according to the city parks and recreation department. With enough sand to fill 21 Olympic swimmings pools, it will be one of the largest beach nourishment projects in Hawaii history, according to data collected by the American Shore and Beach Preservation Association.

According to Wooldridge, there is no question organisms at Ala Moana will die.

“The part where there’s uncertainty is the time and scale of recovery,” he said. “Without a doubt, immediately after this renourishment project, anything living in the sand there is going to be in a tough place.”

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The final environmental impact statement for Ala Moana park improvements, which includes the sand nourishment project, was released on Friday. It makes no mention of invertebrates being buried in the sand or how their population loss would impact the ecosystem.

The report states the water is home to “copious amounts of Hawaiian seagrass” and swimmers like damselfish, whitespotted puffer, long-spine porcupinefish, spotted boxfish, Chinese trumpetfish, triggerfish and the Moorish idol – the kinds of fish that delight snorkelers. During a survey by project consultants, several threatened green sea turtles were spotted in the area. Endangered species like the humpback whale and Hawaiian monk seal are known to live in Hawaiian waters, the EIS states, but they were not observed during an Ala Moana survey.

The EIS did not indicate these animals would be threatened by the sand replenishment project other than saying new sand will cover some coral on the shoreline, “resulting in a loss of habitat for juvenile fish.” The report outlines several recommendations to minimize potential impacts. If “proper management and mitigation practices” are employed, a survey included in the EIS concluded that the project “should have little or no potential for significant permanent effects to the existing marine environment.”

The city decided the rewards outweighed the risks.

“We understand there will be some effect, but we believe it’s on such a minimal level it’s acceptable for the benefit,” said Robert Kroning, director of the department of design and construction.

Already Impacted

In Hawaii, environmental concerns aren’t the only consideration when planning a beach replenishment project, said Sam Lemmo, administrator of the Hawaii Office of Conservation and Coastal Lands.

“People recognize Hawaii for its beaches. It’s an important amenity for us, for people who live here and our visitor industry,” said Lemmo, whose office is part of the Department of Land and Natural Resources. “It’s something we need to invest in on a continual basis to keep ourselves competitive.”

Beach restoration projects should be considered on a case-by-case basis, Lemmo said. Ala Moana was a good candidate, he said. Like Waikiki, it was already an “artificial beach.”

“If you said there is a beautiful, pristine coral reef, I’m talking about a valuable coral ecosystem, and this beach restoration project is going to cover this, that could be problematic,” he said. “Or if you wanted to do something in a prime monk seal pup area or turtle habitat. You can get into situations where you have issues authorizing projects like that.”

But Ala Moana is already “highly impacted” by human activity, he said. In other words, there’s not much to lose.

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“The system is not exactly a pristine natural system,” he said. “You’re looking at, basically, what’s in the sand and what’s in the immediate near-shore area in the channel. Frankly, there is probably not that much going on.”

Asked about the findings in San Diego, Lemmo said: “I don’t agree with the scientist on that one.”

“When you do the renourishment, that whole thing equilibrates very quickly,” Lemmo said. “All the organisms will adjust to that environment. It’s not that big of a deal.”

A Waikiki nourishment project by DLNR added 24,000 cubic yards of sand to the beach in 2012. In a survey done afterward, researchers did not find statistically significant differences in counts of corals, sea urchins, sea cucumbers or invertebrates, according to a report provided by Lemmo. However, total species diversity “significantly decreased” in the impacted area when compared to a control area.

“When they say that diversity decreased, I don’t think they are saying that it decreased because of the project,” he said in an email. “There was just less diversity there.”

Since Ala Moana is a man-made shoreline with no natural way of replenishing, it will need repeated sand imports, according to the parks department. With sea level rise and the continuation of extreme climate conditions, parks department spokesman Nathan Serota said it’s difficult to say when the next replenishment will be. Estimates range from 20 to 30 years.

Kohn said more research is needed to learn about how these projects impact ecosystems in the long run.

“Replenishment doesn’t usually last very long, but they have to replenish again in a few years,” he said. “What we really don’t know is the long term effects, particularly with repeated replenishment.”