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Survey results and feeding experiment data All fish and benthos (algae and invertebrate) survey data and results from feeding assays. All data collected in the field. data_Verges_Tomas_etalJEcol.xlsx, A striking example of climate-mediated range shifts in marine systems is the intrusion of tropical species into temperate areas worldwide, but we know very little about the ecological consequences of these range expansions. In the Mediterranean Sea, the range expansion of tropical rabbitfishes that first entered the basin via the Suez Canal provides a good example of how tropical herbivorous fish can impact the structure of rocky bottoms in temperate seas. Two species of rabbitfishes have now become a dominant component of total fish biomass in the southernmost part of the eastern Mediterranean. Experimental evidence shows these species can profoundly transform benthic communities, turning algal forests into ‘barrens’, but the specific mechanisms that facilitate this shift have not been established. We surveyed ~1000 km of coastline in the eastern Mediterranean and identified two clearly distinct areas, a warmer group of regions with abundant tropical rabbitfish and a colder group of regions where these consumers were absent/ extremely rare. In regions with abundant rabbitfish, canopy algae were 65% less abundant, there was a 60% reduction of overall benthic biomass (algae and invertebrates) and a 40% decrease in total species richness. Video-recorded feeding experiments showed that the extensive barrens characteristic of regions with abundant rabbitfish were not due to greater rates of herbivory by these tropical consumers, but rather by functional differences among the herbivores. Temperate herbivorous fish displayed the greatest macroalgae consumption rates overall, but they fed exclusively on established adult macroalgae. In contrast, in regions with abundant rabbitfishes, these consumers fed complementarily on both established macroalgae and on the epilithic algal matrix, which typically contains macroalgal recruits. Synthesis: Range-shifting tropical rabbitfish can severely reduce the biomass and biodiversity of temperate reefs at a scale of hundreds of kilometres. A shift from macroalgal dominance to barrens is mediated by the addition of functionally diverse herbivores that characterise tropical reefs. This work highlights the importance of assessing the functional traits of range-shifting species to determine potential mechanisms of impact on ecological communities., Peer reviewed

Linares et al_Data and Supplementary Material Data and supplementary material, Ocean acidification is one of the main stressors affecting marine ecosystems. Rare CO2 vents offer a unique opportunity to investigate the response of benthic ecosystems to acidification. However, the benthic habitats that have been investigated so far are mainly very shallow water (≤5 m depth) and, therefore, to habitats that are poorly representative of the broad range of habitats that occur on the continental shelf. Here, we show that a decrease from pH 8.1 to 7.9 observed in a CO2 vent system at 40 m depth leads to a dramatic shift in highly diverse and structurally complex habitats. Forests of the kelp Laminaria rodriguezii usually found at larger depths (>65 m) replace the dominant habitats (i.e. coralligenous outcrops and rhodolith beds), which are mainly characterized by calcifying organisms. Only the aragonite-calcifying algae are able to survive in acidified waters, while high-magnesium calcite organisms lack almost completely. Beyond significant changes at species level also reported in most of previous studies, our results demonstrate that moderate ocean acidification and pH levels expected to occur at the end of this century will entail outstanding changes in the distribution and dominance of key benthic ecosystems at regional scales, with far-reaching ecological and socio-economic implications., Peer reviewed