Use of Invasive <i>Rugulopteryx okamurae</i> Beach Wrack as Habitat and Food by <scp> <i>Talitrus saltator</i> </scp>

ABSTRACT The introduction of non‐native algae into coastal waters has increased worldwide, causing a range of ecological and socio‐economic impacts. However, when stranded on beaches as wrack, these invasive algae can provide refuge and food for supralittoral organisms, potentially benefiting local fauna communities and beach functioning. In this study, we analysed the population structure of the sandhopper Talitrus saltator on three beaches in southwestern Spain subjected to massive strandings of the invasive macroalga Rugulopteryx okamurae , to assess its potential effects on supralittoral communities. Additionally, laboratory feeding experiments were conducted to determine whether these wrack deposits are also used as food resources by talitrid amphipods. We found that R. okamurae wrack deposits harboured abundant (> 1000 individuals/m 2 ) and well‐structured populations of T. saltator , particularly in fresh driftlines. Variations in sandhopper populations were associated with beach characteristics and management practices; notably, sandhoppers were absent from the beach with high tourist activity and where mechanical grooming is typically applied. Feeding experiments showed that T. saltator can consume R. okamurae , although at lower rates compared to the native green alga. Our results highlight the role of invasive algal wrack as both habitat and food for the talitrid amphipod. However, further studies are needed to assess temporal variability and evaluate the potential long‐term effects of ingesting species‐specific chemical compounds, including toxic components, present in this invasive alga on sandhopper populations.