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: New research from the University of California, Davis, reveals why adding crushed shells to beach sand helps protect shell-making animals—such as clams, oysters and mussels—from the detrimental effects of ocean acidification. In a study appearing in Biogeosciences, the researchers designed an experiment at the UC Davis Bodega Marine Laboratory in which they mixed crushed shells, or shell hash, into sand where baby Pacific littleneck clams burrowed and grew.
They then monitored the clams' growth and the water's chemistry over a 90-day period. Adding shell hash, the researchers found, altered the chemistry of the water that fills the tiny spaces between sand particles, decreasing its overall acidity and creating a better environment for shell growth. "We found that, on average, clams grew larger shells when shell hash was present in their treatment," said study first author Hannah Kempf, an environmental scientist at the California State Water Board who graduated from UC Davis with a Ph.D. in earth and planetary sciences in 2024.
"Interestingly, we also found that, on a genetic level, the 'acidification' signal was dramatically minimized when shell hash was present." The findings suggest that shell hash can buffer, on a very local level, the impacts of acidification and promote clam growth. Indigenous communities have long added shell hash to sands to keep coastal ecosystems healthy. The research illuminates the biology underlying why this method is effective.
"This was the first time the question was studied from a genetic perspective," said study corresponding author David Gold, an associate professor of earth and planetary sciences at UC Davis. Ocean acidification occurs when seawater absorbs excess carbon dioxide from the atmosphere. As the water becomes more acidic, Kempf said, it becomes more energetically costly and difficult for shell-making animals to build their shells.
Acidic seawater can even dissolve shells. Larvae and juveniles are thought to be especially vulnerable to its negative effects. To understand why adding shell hash acts as a buffer against ocean acidification, the researchers raised baby Pacific littleneck clams in four different conditions: seawater with sediment, acidified seawater with sediment, control seawater with sediment plus shell hash, and acidified seawater with sediment plus shell hash.
Over 90 days, the researchers sampled the seawater three times a week, monitoring acidity, salinity, temperature and dissolved oxygen. They also tracked the clams' shell growth, and after 90 days, they sampled the clams' mantle tissue for follow-up gene sequencing. Not only were the clams raised in shell hash–rich sediments larger on average, but the gene expression profiles of those raised in acidified seawater with shell hash were largely indistinguishable from those raised in nonacidified waters.
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