Adding crushed shells to beach sand could help protect shell-making animals from the harmful effects of ocean acidification, according to new research from the University of California, Davis. The study found that crushed shells, also known as shell hash, can change the chemistry of water trapped between sediment particles, making it less acidic and creating more favourable conditions for shell growth.
The researchers found that clams raised in sediment containing crushed shells developed larger shells on average. Their genetic responses to acidification were also substantially reduced when shell hash was present.
“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 and a 2024 PhD graduate in earth and planetary sciences from UC Davis. “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 provide local protection against ocean acidification and support the growth of marine organisms that depend on calcium-based shells.
Why Ocean Acidification Threatens Shell-Making Animals
Ocean acidification occurs when seawater absorbs excess carbon dioxide from the atmosphere. As acidity increases, shell-making organisms face greater difficulty building and maintaining their shells. More acidic conditions can make shell formation energetically costly and can even dissolve existing shells.
Young organisms, particularly larvae and juveniles, are considered especially vulnerable to these effects.
To investigate how crushed shells might reduce this impact, the researchers raised young Pacific littleneck clams under four different conditions: normal seawater with sediment, acidified seawater with sediment, normal seawater with sediment and shell hash, and acidified seawater with sediment and shell hash.
Over the 90-day experiment, the team sampled the water three times a week, measuring acidity, salinity, temperature and dissolved oxygen. They also monitored shell growth and collected mantle tissue from the clams at the end of the experiment for genetic sequencing.
Clams raised in sediments containing shell hash were larger on average. Furthermore, the gene expression profiles of clams exposed to acidified water in the presence of shell hash were largely indistinguishable from those raised in non-acidified water.
“Adding crushed shells removed the negative genetic changes that occur when young clams are raised in acidified water,” said corresponding author David Gold, an associate professor of earth and planetary sciences at UC Davis.
Gold noted that this was the first time researchers had investigated the question from a genetic perspective.
Indigenous Ecological Knowledge Offers Lessons for Coastal Protection
The research also highlights the value of Indigenous knowledge in understanding and protecting coastal ecosystems. Indigenous communities have long incorporated shell hash into coastal sediments to support the health of shellfish habitats.
Study co-author Tsim Schneider, an associate professor of anthropology at the University of California, Santa Cruz, pointed to traditional ecological practices in the Pacific Northwest. Some Indigenous communities have created large-scale structures that expand intertidal spaces, encouraging habitats for invertebrates and other marine organisms.
Schneider said the findings could create opportunities for researchers to work more closely with Indigenous communities and support their established environmental practices.
“For me, one of the interesting aspects of this research is the potential to engage more fully with tribes on designing projects that promote their long-standing expertise and Indigenous science,” said Schneider, who is also affiliated with the National Science Foundation’s Center for Braiding Indigenous Knowledges and Science. “If there’s a history of adding shell hash to clam beds in California, for example, western science might be able to better support communities interested in reawakening dormant cultural knowledge and coastal stewardship practices.”
Read More :