Influence of calcium concentration on larval adhesion in a highly invasive fouling ascidian: From morphological changes to molecular mechanisms

Calcium ion (Ca²⁺) is involved in the protein-mediated larval adhesion of fouling ascidians, yet the effects of environmental Ca²⁺ on larval adhesion remain largely unexplored. Here, the larvae of fouling ascidian C. robusta were exposed to different concentrations of Ca²⁺. Exposures to low-concentration (0 mM and 5 mM) and high-concentration (20 mM and 40 mM) Ca²⁺ significantly decreased the adhesion rate of larvae, which was primarily attributed to the decreases in adhesive structure length and curvature. Changes in the expressions of genes encoding adhesion-, microvilli-, muscle contraction-, and collagen-related proteins provided a molecular-level explanation for adhesion rate reduction. Additionally, larvae likely prioritized their energy towards immunomodulation in response to Ca²⁺ stresses, ultimately leading to adhesion reduction. These findings advance our understanding of the influencing mechanisms of environmental Ca²⁺ on larval adhesion, which are expected to provide references for the development of precise antifouling strategies against ascidians and other fouling species.