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 ...

Lionfish (Pterois volitans and P. miles) have become a major concern in the western Atlantic and Caribbean since their introduction in the 1980s. Invasive lionfish can reach very high population densities on coral reefs in their invaded range, yet there are few data from their native range in the Indo-Pacific for comparison. We compiled data on the geographical distribution and density of Indo-Pacific lionfishes in their native ranges from published and unpublished underwater visual censuses and field collections. We found that lionfish in their native Indo-Pacific range are unevenly distributed, with higher densities in the Indian Ocean than in the Pacific. Lionfish densities increase significantly with increasing latitude, and are significantly higher in continental areas than around islands. In the Indo-Pacific, lionfishes are found not only on reefs but also on soft bottoms and in nearshore habitats such as seagrass beds and mangroves, and near estuaries. Native lionfish can be found at depths greater than 75 m. Because lionfish can be cryptic and secretive, we estimate that only ~1/8 of Indo-Pacific lionfishes are detected during general underwater visual censuses. In the Pacific Ocean, the relative abundance of lionfish in the catch of reef-fish larvae is of the same order of magnitude as the relative abundance of adult lionfish within reef fish assemblages. Overall the observed densities of lionfishes in the Indo-Pacific are much lower (max. 26.3 fish ha -1 ) than the densities reported in their invaded Atlantic range (max. 400 fish ha -1 ). We found no effects of fishing or pollution on the densities of lionfishes.

Pacific red lionfish Pterois volitans have invaded Atlantic reefs and reached much greater population densities than on native reefs. We hypothesized that lionfish on invaded reefs would (1) experience higher kill rates and thus spend less time hunting, given the naïveté of Atlantic prey, (2) consume a greater variety of prey, given the lack of native prey defenses, and (3) display less pronounced crepuscular patterns of hunting, given the ease of capturing Atlantic prey. Comparative behavioral observations were conducted in 2 native regions (Philippines and Guam) and 2 invaded regions (Cayman Islands and Bahamas) to assess lionfish time budgets and diurnal activity patterns and to explore correlations between environmental variables and lionfish behavior. Contrary to our first hypothesis, total time allocated to hunting and kill rates showed no difference between native and invaded reefs, despite considerable regional variation. However, Atlantic prey of lionfish were twice as large as Pacific prey, suggesting that despite similar hunting behavior, invasive lionfish ingest greater daily rations of prey biomass. Furthermore, consistent with our second hypothesis, lionfish on invaded reefs had broader diets, and also relied less on 'blowing' behavior for prey capture, pointing to substantial prey naïveté in the invaded range. Importantly, only in the invaded range did we observe lionfish consuming parrotfishes, the decline of which could have indirect effects on interactions between seaweeds and corals. Finally, lionfish overall tended to exhibit a crepuscular pattern in behavior whereby hunting peaked at sunrise and/or sunset, with no differences attributable to native vs. invasive status. KEY WORDS: Native vs. invasive behavior · Diurnal hunting pattern · Crepuscular hunting · Time budget Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 467: [181][182][183][184][185][186][187][188][189][190][191][192] 2012 (Albins & Hixon 2008, Green et al. 2012. Invasive lionfish can also negatively affect native piscivorous predators through both predation on juveniles and competition with adults (Albins 2012). Thus, lionfish may ultimately cause drastic changes in Atlantic coral-reef ecosystems (Albins & Hixon 2011).Lionfish are likely protected from predators by their cryptic coloration and numerous venomous spines (Allen & Eschmeyer 1973). Predators rarely target adult lionfish at either native or invaded locations, despite anecdotal evidence of occasional predation (Bernadsky & Goulet 1991, Maljković & Van Leeuwen 2008. Because natural controls have not been definitively identified in either the native Pacific or invaded Atlantic, direct removals of lionfish by humans have to date been the only effective way to reduce invasive populations; however invasive lionfish are widespread geographically and occur far deeper than usual SCUBA depths (Whitfield et al. 2007, Lesser & Slattery 2011, so complete eradication is unlikely.Before the invasion, little was known abo...

Red lionfish were transported outside their native Pacific range to supply aquaria, subsequently escaped or were released, and have established breeding populations in Atlantic reefs. This invasion has negatively affected coral reef fishes, reducing recruitment success through predation. To provide insight into the factors explaining invasion success, we examined the distribution and abundance of native lionfish in 2 regions of the Western Pacific (Marianas and Philippines). Densities of lionfish and other predatory coral reef fishes were evaluated via stratified surveys targeting habitat preferred by lionfish. There were considerable regional differences in species composition of lionfishes in general and density of Pterois volitans in particular. Red lionfish were uncommon on Guam (3.5 fish ha −1 ) but 6 times more abundant in the Philippines (21.9 fish ha −1 ). Densities in both regions were an order of magnitude less than reported in the invaded Atlantic. There was no relationship between density of lionfish and that of other reef predators, including groupers. Both native populations of P. volitans were more common on reefassociated habitats (sandy slopes, reef channels, and artificial reefs) than on coral reefs. On Guam, P. volitans was more abundant in areas of low water visibility (reef channels and river mouths) compared to reefs with high water clarity. Lionfish in their native range are habitat generalists that occupy various environments, including areas with low salinity and high sediment loads. This plasticity in habitat use helps explain invasive success, given that ecological generalization is recognized as a major factor accounting for the successful establishment of invasive species.