Locations of green-lipped mussel attachment within macroalgal substrates on a mussel reef in New Zealand

The goal of this study was to develop and test a tool that has the potential to aid restoration practitioners in the selection of suitable natural substrates for overcoming substrate limitation at mussel reef restoration sites in New Zealand and potentially elsewhere across the globe. One of the objectives of this study was to compare the relative performance of various macroalgae species with differing morphology as attachment substrates for three size classes of juvenile green-lipped mussels or Perna canaliculus on two remnant mussel reefs. To aid an understanding of why certain morphological characteristics of macroalgae support the presence of juvenile P. canaliculus at different ontogenic stages, the location of attachment within each macroalga species was characterised for each mussel size class. This data details the presence of three different size classes of juvenile green-lipped mussels or Perna canaliculus (<10 mm, 10 - <20 mm, and 20 - <30 mm in shell length) attached to different locations within macroalgae that were sampled on two remnant intertidal mussel reefs in northeastern New Zealand (Waipu Cove and Pakiri Beach). The six possible locations of mussel attachment on different macroalgae species were; the holdfast, stipe, lower branches, lower branch nodes, upper branches, and upper branch nodes. The presence of juvenile mussels in each size class attached to each location within each macroalga species is reported binomially (i.e., present: 1, absent: 0) in the "Juvenile Mussel Presence" column.
For smaller juvenile mussels <10 mm, attachments to the branches and branch nodes of macroalgae were far more common than for juveniles ≥10 mm, suggesting that juvenile mussel attachment is more likely to be influenced by the branching morphology of macroalgae earlier in juvenile development. For juveniles <10 mm SL, attachments to the upper branches and nodes of macroalgae were more common at Waipū Cove than at Pākiri Beach, where smaller juveniles were more often attached to the lower portion of macroalgae. Lastly, macroalgal holdfasts were the most common location of attachment in this study for juvenile mussels ≥10 mm, and for juveniles smaller than 10 mm, it was as common of an attachment location as the branch nodes of macroalgae. These results suggest that juvenile mussels attached to macroalgae are likely to be influenced by a macroalga’s holdfast morphology throughout all stages of development but especially in later development.