The Portuguese coast has overlapping distributions of species of both boreal and Lusitanian origins; a large number of cold-and warm-water species have their southern or northern distributional range edges here. A latitudinal gradient in ocean climate, particularly sea surface temperature (SST) and primary production, has been described along this coast. Here, we took advantage of this gradient in ocean climate to explore affinities in the biogenic landscape structure of subtidal shallow reefs (the abundance of habitat patches), as well as in the assemblage structure of macroalgae and associated fishes, between each of 3 regions: Viana do Castelo (41.5°N), Peniche (39.2°N) and Sines (37.8°N). Five reefs were sampled to determine the abundance of biogenic habitats and the assemblage structure of macroalgae and fishes in each region. The structure of the landscape, and of macroalgal and fish assemblages, differed between Viana do Castelo and Peniche and between Viana do Castelo and Sines, but not between Peniche and Sines. Viana do Castelo was the only region with conspicuous kelp forests, while Peniche and Sines were dominated by patches of foliose turf-forming and filamentous algae. Our study revealed an abrupt macroecological change from northern Portugal to central and southern Portugal, suggesting a possible biogeographical reconfiguration and recognition of a wider transitional area from the Atlantic into Mediterranean waters.KEY WORDS: Latitude · Macroecology · Habitat structure · Assemblage structure · Kelps · Fishes · Rocky reefs · Atlantic Ocean Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 466: [9][10][11][12][13][14][15][16][17][18][19] 2012 distribution, abundance and fitness of organisms may be relevant for predicting the effects of climate change, because shifts in distribution patterns along these gradients are among the principal detectable responses to climate change by both aquatic and terrestrial organisms (Southward et al. 1995, Walther et al. 2002, Parmesan & Yohe 2003, Poloczanska et al. 2007, Hawkins et al. 2009, Wernberg et al. 2011b.In the marine realm, biogeographic classifications are a crucial tool for reaching international agreements in marine conservation. Biogeographic units have been defined using sets of hierarchical criteria, within which the biogeographic affinities of biological entities and assemblages are a key component (Lüning 1990, Spalding et al. 2007. Considerable heterogeneity in the composition and abundance of biological communities may exist within any particular biogeographic level, mainly within large spatial units, and so a more detailed classification system is recommended (Spalding et al. 2007, Waters et al. 2010. This is particularly pertinent as shifts in the distributional ranges of several species are occurring in most oceans of the globe as a result of global change (e.g. Southward et al. 1995, Last et al. 2011, Philippart et al. 2011, Wernberg et al. 2012. In this context, it is crucial to tes...

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Anthropogenically induced global climate change has important implications for marine ecosystems with unprecedented ecological and economic consequences. Climate change will include the simultaneous increase of temperature and CO2 concentration in oceans. However, experimental manipulations of these factors at the community scale are rare. In this study, we used an experimental approach in mesocosms to analyse the combined effects of elevated CO2 and temperature on macroalgal assemblages from intertidal rock pools. Our model systems were synthetic assemblages of varying diversity and understory component and canopy species identity. We used assemblages invaded by the non‐indigenous canopy forming alga Sargassum muticum and assemblages with the native canopy species Cystoseira tamariscifolia. We examined the effects of both climate change factors on several ecosystem functioning variables (i.e. photosynthetic efficiency, productivity, respiration and biomass) and how these effects could be shaped by the diversity and species identity of assemblages. CO2 alone or in combination with temperature affected the performance of macroalgae at both individual and assemblage level. In particular, high CO2 and high temperature (20°C) drastically reduced the biomass of macroalgal assemblages and affected their productivity and respiration rates. The identity of canopy species also played an important role in shaping assemblage responses, whereas species richness did not seem to affect such responses. Species belonging to the same functional effect group responded differently to the same environmental conditions. Data suggested that assemblages invaded with S. muticum might be more resistant in a future scenario of climate change. Thus, in a future scenario of increasing temperature and CO2 concentration, macroalgal assemblages invaded with canopy‐forming species sharing response traits similar to those of S. muticum could be favoured.