Crushed Shells Protect Against Ocean Acidification

A UC Davis experiment examined how crushed shells mixed into beach sediment, a practice used by Indigenous coastal communities, can protect shell-forming animals from ocean acidification. Researchers raised juvenile Pacific littleneck clams for 90 days in four conditions: ordinary or acidified seawater, each with sediment either containing or lacking shell fragments. They repeatedly measured the water chemistry and tracked clam shell growth, then analyzed gene activity in the clams’ mantle tissue.

Clams raised in sediment containing crushed shells grew larger shells on average. The shell fragments also reduced acidity in the water trapped between sand grains, creating conditions more favorable for shell formation. Most notably, juveniles exposed to acidified water alongside shell fragments had gene-expression patterns similar to clams raised in ordinary seawater; the genetic response associated with acidification was largely absent. The results explain a local buffering effect rather than a solution to ocean acidification itself. They also provide biological evidence for traditional ecological knowledge that shell additions can support coastal habitats. The researchers say the findings could inform collaboration with Indigenous communities seeking to renew cultural stewardship practices, including approaches that enhance intertidal areas and support clams and other marine life.