Rapid collapse of extensive kelp forests and a regime shift to tropicalized temperate reefs followed extreme heatwaves and decades of gradual warming. Abstract:Ecosystem reconfigurations arising from climate driven changes in species distributions are expected to have profound ecological, social and economic implications. Here, we reveal a rapid climate driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. Following decades of ocean warming, extreme marine heatwaves forced a 100 km range contraction of extensive kelp forests, and saw temperate species replaced by seaweeds, invertebrates, corals and fishes characteristic of subtropical and tropical waters. This community wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests. Main Text:Broad scale losses of species which provide the foundations for habitats cause dramatic shifts in ecosystem structure because they support core ecological processes (1-3). Such habitat loss can lead to a regime shift where reinforcing feedback mechanisms intensify to provide resilience to an alternate community configuration, often with profound ecological, social and economic consequences (4-6). Benthic marine regime shifts have been associated with the erosion of ecological resilience through overfishing or eutrophication, altering the balance between consumers and resources, rendering ecosystems vulnerable to major disturbances (1, 2,6,7). Now, climate change is also contributing to the erosion of resilience (8,9), where increasing temperatures are modifying key physiological, demographic and community scale processes (8, 10), driving species redistribution at a global scale and rapidly breaking down long-standing biogeographic boundaries (11,12). These processes culminate in novel ecosystems where tropical and temperate species interact with unknown implications (13). Here we document how a marine heatwave caused the loss of kelp forests across ~2,300 km 2 of Australia's Great Southern Reef, forcing a regime shift to seaweed turfs. We demonstrate a rapid 100 km rangecontraction of kelp forests and a community-wide shift toward tropical species with ecological processes suppressing kelp forest recovery.To document ecosystem changes we surveyed kelp forests, seaweeds, fish, mobile invertebrates and corals at 65 reefs across a ~2,000 km tropical to temperate transition zone in western Australia (14). Surveys were conducted between 2001 to 2015, covering the years before and after an extreme marine heatwave impacted the region.The Indian Ocean adjacent to western Australia is a 'hotspot' where the rate of ocean warming is in the top 10% globally (15), and isotherms are shifting poleward at a rate of 20 -50 km per decade (16). Until recently, kelp forests were dominant along >800 km of the west coast (8), covering 2,266 km 2 of rocky reefs between 0 -30 m depth south of 27.7°S (Fig. 1). Kelp forests along the midwest section of this ...

Species' ranges are shifting globally in response to climate warming, with substantial variability among taxa, even within regions. Relationships between range dynamics and intrinsic species traits may be particularly apparent in the ocean, where temperature more directly shapes species' distributions. Here, we test for a role of species traits and climate velocity in driving range extensions in the ocean-warming hotspot of southeast Australia. Climate velocity explained some variation in range shifts, however, including species traits more than doubled the variation explained. Swimming ability, omnivory and latitudinal range size all had positive relationships with range extension rate, supporting hypotheses that increased dispersal capacity and ecological generalism promote extensions. We find independent support for the hypothesis that species with narrow latitudinal ranges are limited by factors other than climate. Our findings suggest that small-ranging species are in double jeopardy, with limited ability to escape warming and greater intrinsic vulnerability to stochastic disturbances.

No abstract

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.

BackgroundGlobally, coral bleaching has been responsible for a significant decline in both coral cover and diversity over the past two decades. During the summer of 2010–11, anomalous large-scale ocean warming induced unprecedented levels of coral bleaching accompanied by substantial storminess across more than 12° of latitude and 1200 kilometers of coastline in Western Australia (WA).Methodology/Principal FindingsExtreme La-Niña conditions caused extensive warming of waters and drove considerable storminess and cyclonic activity across WA from October 2010 to May 2011. Satellite-derived sea surface temperature measurements recorded anomalies of up to 5°C above long-term averages. Benthic surveys quantified the extent of bleaching at 10 locations across four regions from tropical to temperate waters. Bleaching was recorded in all locations across regions and ranged between 17% (±5.5) in the temperate Perth region, to 95% (±3.5) in the Exmouth Gulf of the tropical Ningaloo region. Coincident with high levels of bleaching, three cyclones passed in close proximity to study locations around the time of peak temperatures. Follow-up surveys revealed spatial heterogeneity in coral cover change with four of ten locations recording significant loss of coral cover. Relative decreases ranged between 22%–83.9% of total coral cover, with the greatest losses in the Exmouth Gulf.Conclusions/SignificanceThe anomalous thermal stress of 2010–11 induced mass bleaching of corals along central and southern WA coral reefs. Significant coral bleaching was observed at multiple locations across the tropical-temperate divide spanning more than 1200 km of coastline. Resultant spatially patchy loss of coral cover under widespread and high levels of bleaching and cyclonic activity, suggests a degree of resilience for WA coral communities. However, the spatial extent of bleaching casts some doubt over hypotheses suggesting that future impacts to coral reefs under forecast warming regimes may in part be mitigated by southern thermal refugia.

Tropical reefs have been subjected to a range of anthropogenic pressures such as global climate change, overfishing and eutrophication that have raised questions about the prominence of macroalgae on tropical reefs, whether they pose a threat to biodiversity, and how they may influence the function of tropical marine ecosystems. We synthesise current understanding of the structure and function of tropical macroalgal reefs and how they may support various ecosystem goods and services. We then forecast how key stressors may alter the role of macroalgal reefs in tropical seascapes of the Anthropocene. High levels of primary productivity from tropical canopy macroalgae, which rivals that of other key producers (e.g., corals and turf algae), can be widely dispersed across tropical seascapes to provide a boost of secondary productivity in a range of biomes that include coral reefs, and support periodic harvests of macroalgal biomass for industrial and agricultural uses. Complex macroalgal reefs that comprise a mixture of canopy and understorey taxa can also provide key habitats for a diverse community of epifauna, as well as juvenile and adult fishes that are the basis for important tropical fisheries. Key macroalgal taxa (e.g., Sargassum) that form complex macroalgal reefs are likely to be sensitive to future climate change. Increases in maximum sea temperature, in particular, could depress biomass production and/or drive phenological shifts in canopy formation that will affect their capacity to support tropical marine ecosystems. Macroalgal reefs can support a suite of tropical marine ecosystem functions when embedded within an interconnected mosaic of habitat types. Habitat connectivity is, therefore, essential if we are to maintain tropical marine biodiversity alongside key ecosystem goods and services. Consequently, complex macroalgal reefs should be treated as a key ecological asset in strategies for the conservation and management of diverse tropical seascapes. A plain language summary is available for this article.

Tropical coral reefs are highly diverse and globally threatened. Management to ensure their persistence requires sound biological knowledge in regions where coral reef biodiversity and/or the threats to it are greatest. This paper uses a novel text analysis approach and Google Maps TM to examine the spatial coverage of scientific papers on coral reefs listed in Web of Science R . Results show that research is highly clumped spatially, positively related to per capita gross domestic product, negatively related to coral species richness, and unrelated to threats to coral reefs globally; indicating a serious mismatch between conservation needs and the knowledge required for effective management. Greater research effort alone cannot guarantee better conservation outcomes, but given some regions of the world (e.g., Central Indo-Pacific) remain severely understudied, priority allocation of resources to fill such knowledge gaps should support greater adaptive management capacity through the development of an improved knowledge base for reef managers.

1. Baited remote underwater stereo-video systems (stereo-BRUVs) are a popular tool to sample demersal fish assemblages and gather data on their relative abundance and body size structure in a robust, cost-effective and non-invasive manner. Given the rapid uptake of the method, subtle differences have emerged in the way stereo-BRUVs are deployed and how the resulting imagery is annotated. These disparities limit the interoperability of datasets obtained across studies, preventing broadscale insights into the dynamics of ecological systems. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.