The role of substrata width and millimeter scale surface micro-structure in the attachment of juvenile mussels

The global mussel aquaculture industry is constrained by the unreliable supply of wild seed mussels and high losses of seed mussels shortly after they are seeded onto coastal farms. The success in the collection of the settling larvae of mussel in the wild and the subsequent on-growing of early seed mussels in aquaculture are largely determined by the settlement and attachment behaviour of the larval and juvenile mussels, which is strongly influenced by the physical structure of their attachment substrata, especially filamentous substrata. This study aimed to identify an ideal set of morphological characteristics of filamentous substrata that would promote the improved attachment of early mussels and contribute to reducing the shortage of seed mussels in the New Zealand green-lipped mussel ( Perna canaliculus ) aquaculture industry. Artificial filamentous substrata with varying branch width and textured surfaces were tested for their ability to promote the attachment of wild juvenile mussels. The attachment of early juvenile mussels to 1.6 mm wide filamentous substrate was six times higher than their wider counterparts (i.e., 3.7, 5.6, 7.4, and 9.5 mm). There was also a higher proportion of small-size mussels (<0.99 mm shell length) on the 1.6 mm substrata. Furthermore, the filamentous substrata with regularly ridged surface contours (1 mm spacings) tended to attract more juvenile mussels. However, this preference was not consistent for small-size mussels on filaments of thinner width (i.e., 0.4, 0.8, 1.6, and 3.7 mm). Overall, the dimensions of filamentous substrates identified through this study will be valuable for improving the design of artificial substrata used in mussel aquaculture for improving its effectiveness for the attachment of seed mussels. • Juvenile mussels prefer to attach to narrower filamentous substrata (0.4–2.4 mm). • Higher fraction of small mussels (<0.99 mm) on 1.6 mm narrow filamentous substrata. • 1 mm ridge on 5.6 mm wide branch significantly increased juvenile mussel attachment. • Study results can help improve design of catching material for juvenile mussels.