Influence of Microstructure of Substrate Surface on the Attachment of Juvenile Mussels

The morphological characteristics and surface roughness of substrata can significantly affect the settlement behaviour of planktonic larvae and the post-settlement survival of benthic organisms, such as mussels. Despite widespread recognition of these effects on ecological and aquaculture processes, species-specific complexities and limited research hinder a comprehensive understanding of the phenomenon and the potential to harness its application. In this study, the settlement of juvenile green-lipped mussels (Perna canaliculus; 0.32–3.59 mm shell length) on 42 different custom-designed artificial substrata with varied branch widths and surface microstructures were compared. Mussels smaller than 0.99 mm in shell length exhibited a clear preference for substrates with a thinner branch width (1.6 mm), wider roughness width (3.2 mm), and shorter roughness height (0.4 mm) on both V-shaped and squared-shaped surface microstructures. In contrast, for mussels larger than 1 mm, only the branch width of artificial substrata significantly influenced mussel attachment, while millimetre-scale surface features had no measurable effect. These findings indicate that, at the millimetre scale, the attachment of mussels > 1 mm does not conform to the surface contact theory, which proposes that settling organisms prefer substrates with microstructures that maximize their surface contact. Overall, a thinner branch width consistently yielded higher attachment densities, underscoring its dominant role. Our results reveal significant opportunities for optimizing the design of artificial substrata in mussel aquaculture, such as spat catching and nursery ropes, potentially improving seed collection efficiency and reducing the subsequent loss of seed mussels during their culture on mussel farms.