Multiscale ecological and evolutionary drivers of marine amphipod diversity

Abstract

Invisible to the naked eye, amphipods constitute one of the most diverse and ecologically significant groups of malacostracan crustaceans in marine ecosystems. Their remarkable ecological versatility enables them to exploit a wide range of habitats, while their diverse feeding strategies make them key secondary producers and essential connectors within benthic food webs. The intimate relationship between amphipods and habitat structure makes them ideal models for exploring how environmental variability shapes biodiversity patterns, community composition and evolutionary processes. This thesis employs a spatial and temporal approach to capture the natural dynamics of amphipod communities associated with key marine ecosystem engineers in the Canary Archipelago, integrating taxonomic, functional and molecular perspectives. By examining seagrass meadows of Cymodocea nodosa, rhodolith seabeds and black coral forests of Antipathella wollastoni, the research demonstrated that structural habitat complexity, rather than climatic variables, is the primary driver of species richness, abundance and community organization. Subtropical C. nodosa meadows were more stable habitats than temperate ones, leading to higher temporal β-diversity driven by turnover, while temperate meadows showed increased nestedness due to higher instability. In rhodolith seabeds, secondary habitats provided by epiphytic algae enhanced amphipod diversity, with bathymetric segregation concentrating juveniles and ovigerous females in shallow to intermediate depths. Black coral forests hosted communities dominated by amphipods, with larger colonies supporting higher abundance and richness. In these habitats, functional traits varied along an east–west gradient across the Canary Archipelago, reflecting adaptations in feeding strategies as well as in gnathopod and body morphology. Additionally, a new genus and species, Wollastenothoe minuta, was described associated with these forests, resulting in a global taxonomic key for the Stenothoidae family. Finally, molecular analyses across islands and habitats revealed that actual species richness is twice that detected by traditional taxonomy, with Molecular Operational Taxonomic Units (MOTUs) exhibiting complex evolutionary patterns, including highly diverse intraspecific and island-specific lineages alongside with high levels of connectivity. In summary, these findings underscore the central role of habitat heterogeneity, structural complexity and island-specific dynamics in shaping amphipod biodiversity and evolution, providing key insights for the conservation of Macaronesian marine ecosystems.