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1. Climate change can alter ecological communities both directly, by driving shifts in species distributions and abundances, and indirectly by influencing the strength and direction of species interactions. Within benthic marine ecosystems, foundation species such as canopy -forming macro-algae often underpin important cascades of facilitative interactions. 2. We examined the wider impacts of climate-driven shifts in the relative abundances of foundation species within a temperate reef system, with particular focus on a habitat cascade whereby kelp facilitate epiphytic algae that in turn facilitate mobile invertebrates. Specifically we tested whether the warm water kelp Laminaria ochroleuca, which has proliferated in response to recent warming trends, facilitated a secondary habitat-former (epiphytic algae on stipes) and associated mobile invertebrates, to the same degree as the cold water kelp Laminaria hyperborea. 3. The facilitative interaction between kelp and stipe-associated epiphytic algae was dramatically weaker for the warm water foundation species, leading to breakdown of a habitat cascade and impoverished associated faunal assemblages. On average, the warm water kelp supported >250 times less epiphytic algae (by biomass) and >50 times fewer mobile invertebrates (by abundance) than the cold water kelp. Moreover, by comparing regions of pre and post range expansion by L. ochroleuca, we found that warming-impacted kelp forests supported around half the biomass of epiphytic algae and one-fifth of the abundance of mobile invertebrates, per unit area, compared with unimpacted forests. We suggest that disruption to this facilitation cascade has the potential to impact upon higher trophic levels, specifically kelp forest fishes, through lower prey availability. 5. Synthesis. Climate-driven shifts in species’ distributions and the relative abundances of foundation organisms will restructure communities and alter ecological interactions, with consequences for ecosy

Phylogenetic relationships and the timing of evolutionary events are essential for understanding evolution on longer time scales. Cheilostome bryozoans are a group of ubiquitous, species-rich, marine colonial organisms with an excellent fossil record but lack phylogenetic relationships inferred from molecular data. We present genome-skimmed data for 395 cheilostomes and combine these with 315 published sequences to infer relationships and the timing of key events among c. 500 cheilostome species. We find that named cheilostome genera and species are phylogenetically coherent, rendering fossil or contemporary specimens readily delimited using only skeletal morphology. Our phylogeny shows that parental care in the form of brooding evolved several times independently but was never lost in cheilostomes. Our fossil calibration, robust to varied assumptions, indicates that the cheilostome lineage and parental care therein could have Paleozoic origins, much older than the first known fossil record of cheilostomes in the Late Jurassic