Climate?driven substitution of foundation species causes breakdown of a facilitation cascade with potential implications for higher trophic levels

Climate change can alter ecological communities both directly, by driving shifts in species distributions and abundances, indirectly influencing the strength direction of interactions. Within benthic marine ecosystems, foundation such as canopy-forming macro-algae often underpin important cascades facilitative We examined wider impacts climate-driven relative abundances within a temperate reef system, with particular focus on habitat cascade whereby kelp facilitate epiphytic algae that, turn, mobile invertebrates. Specifically, we tested whether warm-water Laminaria ochroleuca, which has proliferated response to recent warming trends, facilitated secondary habitat-former (epiphytic stipes) associated invertebrates, same degree cold-water hyperborea. The interaction between stipe-associated was dramatically weaker for species, leading breakdown impoverished faunal assemblages. On average, supported >250 times less (by biomass) >50 fewer invertebrates abundance) than kelp. Moreover, comparing regions pre- post-range expansion L. found that warming-impacted forests around half biomass one-fifth abundance per unit area, compared unimpacted forests. suggest disruption this facilitation potential impact upon higher trophic levels, specifically forest fishes, through lower prey availability. Synthesis. Climate-driven species' organisms will restructure interactions, consequences ecosystem functioning. show substitutions seemingly similar local biodiversity processes ecosystems.