Sticking down calcium’s role in underwater adhesion

Many aquatic organisms rely on protein-mediated underwater adhesion to attach to submerged surfaces. Studying this process can help researchers create underwater adhesives and develop strategies to prevent biofouling. While calcium ions are suspected to play a role in this adhesion, it is unclear exactly how, especially in representative species like ascidians.

Li et al. investigated calcium’s involvement in the underwater adhesion of ascidian adhesive protein 1 (AAP1) from Ciona robusta, a widespread marine invertebrate. With in vitro experiments, they examined AAP1’s aggregation, cohesion, and interfacial adhesion under varying concentrations of calcium ranging from 0 to 25 millimolars.

The authors found that calcium ions induce AAP1 aggregation in a concentration-dependent manner, with denser aggregation at higher concentrations. The cohesion and interfacial adhesion of AAP1 also depended on the calcium concentration: Peak cohesion energy occurred at 25 millimolars, while interfacial adhesion energy peaked at 10 millimolars, which is the natural concentration of seawater.

“Unlike previous computational predictions, we used surface force apparatus measurements and microscopy to quantitatively demonstrate calcium-dependent adhesion mechanisms under physiologically relevant conditions,” said author Shiguo Li. “This work bridges a critical gap between theoretical predictions and experimental validation in marine bioadhesion research. It clarifies how calcium ions regulate underwater adhesion in a key fouling organism, offering mechanistic insights that can inform antifouling strategies and inspire the design of bioadhesives for wet environments.”

The authors suggest that disrupting calcium-ion binding could be a novel antifouling strategy. Next, they plan to gather more information relevant to antifouling, including testing AAP1 adhesion in seawater, investigating the synergistic effects of other ions, and mapping calcium binding sites and changes in protein shape.

Source: “Calcium is involved in protein cohesion and interfacial adhesion in a marine invasive fouling ascidian,” by Shiguo Li, Ying Zhang, Dan He, Miaolian Zhang, and Aibin Zhan, Biointerphases (2025). The article can be accessed at https://doi.org/10.1116/6.0004889 .

This paper is part of the Biointerfaces in China 2025 Collection, learn more here .