Search

AIM: Understanding the relative importance of climatic and non‐climatic distribution drivers for co‐occurring, functionally similar species is required to assess potential consequences of climate change. This understanding is, however, lacking for most ecosystems. We address this knowledge gap and forecast changes in distribution for habitat‐forming seaweeds in one of the world's most species‐rich temperate reef ecosystems. LOCATION: The Great Southern Reef. The full extent of Australia's temperate coastline. METHODS: We assessed relationships between climatic and non‐climatic environmental data known to influence seaweed, and the presence of 15 habitat‐forming seaweeds. Distributional data (herbarium records) were analysed with MAXENT and generalized linear and additive models, to construct species distribution models at 0.2° spatial resolution, and project possible distribution shifts under the RCP 6.0 (medium) and 2.6 (conservative) emissions scenarios of ocean warming for 2100. RESULTS: Summer temperatures, and to a lesser extent winter temperatures, were the strongest distribution predictors for temperate habitat‐forming seaweeds in Australia. Projections for 2100 predicted major poleward shifts for 13 of the 15 species, on average losing 78% (range: 36%–100%) of their current distributions under RCP 6.0 and 62% (range: 27%–100%) under RCP 2.6. The giant kelp (Macrocystis pyrifera) and three prominent fucoids (Durvillaea potatorum, Xiphophora chondrophylla and Phyllospora comosa) were predicted to become extinct from Australia under RCP 6.0. Many species currently distributed up the west and east coasts, including the dominant kelp Ecklonia radiata (71% and 49% estimated loss for RPC 6.0 and 2.6, respectively), were predicted to become restricted to the south coast. MAIN CONCLUSIONS: In close accordance with emerging observations in Australia and globally, our study predicted major range contractions of temperate seaweeds in coming decades. These changes will likely have significant impacts on marine biodiversity and ecosystem functioning because large seaweeds are foundation species for 100s of habitat‐associated plants and animals, many of which are socio‐economically important and endemic to southern Australia.

Aim We used modelled environmental data to identify important drivers of bioregional patterns of demersal fish assemblages characterized by a high proportion of endemic species. Location Of 1,600 km of coastal marine environment in south-western Australia. Methods We compiled data from 1090 stereo-BRUVs samples; a total of ~55,000 individuals belonging to 219 demersal fish species. Multivariate Regression Trees and Distance-based Linear Models distinguished which biological and/or environmental variables, amongst an initial set of 49, were most correlated to observed patterns of demersal fish assemblage structure. Indicator species analysis identified fish species most representative of the assemblage types. Results The most parsimonious model (constrained by five benthic variables and one spatial variable) explained 42% of the variation in spatial patterns of fish community structure. Canopy-forming seaweeds were the major benthic drivers, and, when found on structurally complex hard habitat, supported the highest diversity of species after sites dominated by hard coral cover. Indicator species analysis revealed that 28 of 35 significant species for this habitat type were endemics with fish assemblages associated with these habitats often spatially restricted to tens of kilometres. Main conclusions Demersal fish assemblage composition and biogeographical ranges in south-western Australia are strongly influenced by the presence of canopy-forming macroalgae. Canopy-dominated habitats have already been subject to catastrophic temperature-related die-offs in the northern part of this study, indicating its vulnerability to temperature-driven climate change. These results highlight not only the crucial role of this habitat in supporting endemic fish communities in the region, and the tenuous nature of their existence, but also the challenges facing marine managers who, unable to manipulate the influence of climate change variables, can only focus on alleviating stresses operating on local scales.