Biogeography of fish sounds across Europe’s Atlantic and Mediterranean coasts

In marine ecosystems, biodiversity, biological rhythms, and macrofaunal community behaviors are fundamental to assess the cumulative impact of environmental and human pressures but they remain understudied. Ecoacoustics offers a promising approach to fill these gaps: it analyzes biological (biophony), abiotic (geophony), and anthropogenic (anthrophony) sounds to provide high temporal-resolution insights. Marine forests (e.g., kelp, seagrass meadows) are essential habitats, that rank among the most productive and biodiversity-rich ecosystems and provide billions of dollars of essential ecosystem services to humanity. However, with less than 3% of ecoacoustics studies, they remain largely underrepresented. Despite the potential of ecoacoustics in acquiring information on the cryptic species of dense habitats, the biophonic component of European marine forests is currently poorly or not documented.
Here we describe the biogeography of fish acoustic communities of three different marine forests (kelp forest, zostera and posidonia seagrass meadow) at the European scale (Atlantic and Mediterranean coasts). During the European TREC expedition, continuous sound recordings were conducted over 48-72h at 17 sites across Europe.
Using a standardized sound classification method, this biogeographic study provides the first detailed description of fish acoustic communities in European marine forests. We analyzed the composition and parameters of acoustic communities (abundance, richness, biodiversity indices) and revealed inter-habitat, intra- and inter-site variability. Acoustic communities were significantly distinct between habitats, with greater site variability within Zostera meadows, compared to kelp forests, suggesting differences in connectivity in seagrass. Site characteristics and sampling periods were considered, and relationships between acoustic communities, taxonomic diversity, diel variation and environmental variables (e.g., light, temperature) were examined. Our findings offer an unprecedented large-scale view of fish acoustic community composition in underexplored European habitats. This work reveals that acoustic biodiversity can contribute to habitat biogeography and infer information on the invisible, hidden animal assemblages, their dynamics and responses to environmental changes.