MEPS 756:1-17 (2025)  -  DOI: https://doi.org/10.3354/meps14798

ABSTRACT: Intraspecific trait variation, whether phenotypic or due to genotypic differences, can influence ecosystem functioning, especially in the case of ecosystem engineering species. Here, we investigated a coastal ecosystem dominated by 2 distinct genetic lineages of the native brown mussel Perna perna in 2 biogeographical regions along the South African coastline. Both euendolithic corrosion and genetically based behavioural differences have been shown to improve the microclimate of mussel beds and thus reduce abiotic stress for associated macrofauna. We therefore hypothesized that euendolithic corrosion of mussel shells, and its interactions with known genotypic variation, would affect the bioengineering capabilities of mussels on the rocky shores. Two manipulative field experiments revealed that macrofaunal communities differed significantly between experimental sites, reflecting the effects of biogeography and regional patterns in species distribution. Unexpectedly, neither euendolithic corrosion nor its interaction with P. perna genetic lineages influenced macrofaunal community structure. In marine bioengineered habitats, the associated macrofauna respond differently to intraspecific trait variations in the engineer depending on their own sensitivity to environmental stressors. In addition, this influence is limited to the spatio-temporal context in which trait variations have an effect. Although intraspecific trait variation was previously demonstrated to influence ecosystem processes in mussel beds, regional/biogeographic effects were more important in determining the composition of the associated macrofauna. Identifying the relative influence of genotypic and phenotypic intraspecific trait variation versus biogeography and large-scale processes on both ecosystem engineers and their associated communities is required to predict their ecosystem-level consequences for coastal communities under the effects of global climate change.

KEY WORDS: Photoautotrophic euendoliths · Perna perna · Genetic lineages · Ecosystem functioning · Conditional mutualism · Conditionally helpful parasites · Phenotypic variation