Search

Disease is one of the major bottlenecks for aquaculture development, costing the industry in excess of US $6 billion each year. The increase in pressure to phase out some traditional approaches to disease control (e.g. antibiotics) is pushing farmers to search for alternatives to treat and prevent disease outbreaks, which do not have detrimental consequences (e.g. antibiotic resistance). We tested the effects of eleven seaweed species and four established fish immunostimulants on the innate immune response (cellular and humoral immunity) of the rabbitfish Siganus fuscescens. All supplements including different seaweeds from the three groups (Chlorophyta, Phaeophyta and Rhodophyta) were included in the fish pellet at 3% (by weight) and had variably positive effects across the four innate immune parameters we measured compared to control fish. Diets supplemented with the red seaweed Asparagopsis taxiformis and the brown seaweed Dictyota intermedia led to the largest boosts in humoral and cellular innate immune defences, including particularly significant increases in haemolytic activity. Diets supplemented with Ulva fasciata also led to promising positive effects on the fish innate immune responses. We conclude that dietary seaweed supplements can boost the immune response of S. fuscescens and thus the top three species highlighted in this study should be further investigated for this emerging aquaculture species and other fish species.

Targeted ‘omics’ research for seaweeds, utilizing various computational and informatics frameworks, has the potential to rapidly develop our understanding of biological processes at the molecular level and contribute to solutions for the most pressing environmental and social issues of our time. Here, a systematic review into the current status of seaweed omics research was undertaken to evaluate the biological diversity of seaweed species investigated (red, green and brown phyla), the levels to which the work was undertaken (from full genome to transcripts, proteins or metabolites) and the field of research to which it has contributed. We report that from 1994 to 2021 the majority of seaweed omics research has been performed on the red seaweeds (45% of total studies), with more than half of these studies based upon two genera Pyropia and Gracilaria. A smaller number of studies examined brown seaweed (key genera Saccharina and Sargassum) and green seaweed (primarily Ulva). Overall, seaweed omics research is most highly associated with the field of evolution (46% of total studies), followed by the fields of ecology, natural products and their biosynthesis, omics methodology and seaweed–microbe interactions. Synthesis and specific outcomes derived from omics studies in the red seaweeds are provided. Together, these studies have provided a broad-scale interrogation of seaweeds, facilitating our ability to answer fundamental queries and develop applied outcomes. Crucial to the next steps will be establishing analytical tools and databases that can be more broadly utilized by practitioners and researchers across the globe because of their shared interest in the key seaweed genera.

Aim: Spatial compositional turnover varies considerably among co-occurring assemblages of organisms, presumably shaped by common processes related to species traits. We investigated patterns of spatial turnover in a diverse set of marine assemblages using zeta diversity, which extends traditional pairwise measures of turnover to capture the roles of both rare and common species in shaping assemblage turnover. We tested the generality of hypothesized patterns related to ecological traits and provide insights into mechanisms of biodiversity change. Location: Temperate pelagic and benthic marine assemblages of micro- and macroorganisms along south-eastern Australia (30–36° S latitude). Time period: 2008–2021. Major taxa studied: Bacteria, phytoplankton, zooplankton, fish, and macrobenthic groups. Methods: Six marine datasets spanning bacteria to fishes were collated for measures of “species” occurrence, with a 1° latitude grain. For each assemblage, ecological traits of body size, habitat and trophic level were analysed for the form and rate of decline in zeta diversity and for the species retention rate. Results: Species at higher trophic levels showed two to three times the rate of zeta diversity decline compared with lower trophic levels, indicating an increase in turnover from phytoplankton to carnivorous fishes. Body size showed the hypothesized unimodal relationship with rates of turnover for macroorganisms. Patterns of bacterial turnover contrasted with those found for macroorganisms, with the highest levels of turnover in pelagic habitats compared with benthic (kelp-associated) habitats. The shape of retention rate curves showed the importance of both rare and common species in driving turnover; a finding that would not have been observable using pairwise (beta diversity) measures of turnover. Main conclusions: Our results support theoretical predictions for phytoplankton and macroorganisms, showing an increase in turnover rate with trophic level, but these predictions did not hold for bacteria. Such deviations from theory need to be investigated further to identify underlying processes that govern microbial assemblage dynamics.

Globally, critical habitats are in decline, threatening ecological, economic and social values and prompting calls for "future proofing" efforts that enhance resilience to climate change. Such efforts rely on predicting how neutral and adaptive genomic patterns across a species' distribution will change under future climate scenarios, but data is scant for most species of conservation concern. Here, we use seascape genomics to characterize genetic diversity, structure and gene-environmental associations in a dominant forest-forming seaweed, Phyllospora comosa, along its entire latitudinal (12° latitude), and thermal (~14°C) range. Phyllospora showed high connectivity throughout its central range, with evidence of genetic structure and potential selection associated with sea surface temperatures at its rear and leading edges. Rear and leading-edge populations harboured only half the genetic diversity of central populations. By modelling genetic turnover as a function of sea surface temperature, we assessed the genomic vulnerability across Phyllospora's distributional range under climate change scenarios. Despite low diversity, range-edge populations were predicted to harbour beneficial adaptations to marginal conditions and overall adaptability of the species may be compromised by their loss. Assisted gene flow from range edge populations may be required to enhance adaptation and increase resilience of central and leading-edge populations under warming oceans. Understanding genomic vulnerability can inform proactive restoration and future-proofing strategies for underwater forests and ensure their persistence in changing oceans.

Ecological differentiation between strains of bacterial species is shaped by genomic and metabolic variability. However, connecting genotypes to ecological niches remains a major challenge. Here, we linked bacterial geno- and phenotypes by contextualizing pangenomic, exometabolomic and physiological evidence in twelve strains of the marine bacterium Alteromonas macleodii, illuminating adaptive strategies of carbon metabolism, microbial interactions, cellular communication and iron acquisition. In A. macleodii strain MIT1002, secretion of amino acids and the unique capacity for phenol degradation may promote associations with Prochlorococcus cyanobacteria. Strain 83-1 and three novel Pacific isolates, featuring clonal genomes despite originating from distant locations, have profound abilities for algal polysaccharide utilization but without detrimental implications for Ecklonia macroalgae. Degradation of toluene and xylene, mediated via a plasmid syntenic to terrestrial Pseudomonas, was unique to strain EZ55. Benzoate degradation by strain EC673 related to a chromosomal gene cluster shared with the plasmid of A. mediterranea EC615, underlining that mobile genetic elements drive adaptations. Furthermore, we revealed strain-specific production of siderophores and homoserine lactones, with implications for nutrient acquisition and cellular communication. Phenotypic variability corresponded to different competitiveness in co-culture and geographic distribution, indicating linkages between intraspecific diversity, microbial interactions and biogeography. The finding of “ecological microdiversity” helps understanding the widespread occurrence of A. macleodii and contributes to the interpretation of bacterial niche specialization, population ecology and biogeochemical roles. Published version

Infectious diseases affecting habitat-forming species can have significant impacts on population dynamics and alter the structure and functioning of marine ecosystems. Recently, a fungal infection was described as the causative agent of necrotic lesions on the stipe of the forest-forming macroalga Phyllospora comosa, a disease named "stipe rot" (SR). Here, we developed a quantitative PCR (qPCR) method for rapid detection and quantification of this pathogen, which was applied to evaluate the level of SR infection in eight P. comosa populations spanning the entire latitudinal distribution of this species along southeastern Australia. We also investigated the relationship between the abundance and prevalence of Stipe Rot Fungus (SRF) and potential host chemical defenses as well as its relationship with morphological and ecophysiological traits of P. comosa. qPCR estimates of SRF abundance reflected the levels of infection estimated by visual assessment, with higher numbers of SRF copies being observed in individuals showing high or intermediate levels of visual symptoms of SR. Concordance of conventional PCR and visual assessments was 92 and 94%, respectively, compared to qPCR detection. SRF prevalence was positively related to fucoxanthin content and herbivory, but not significant related to other traits measured (phlorotannin content, total length, thallus diameter, stipe width, number of branches, frond width, fouling, bleaching, gender, and photosynthetic efficiency). These results provide confidence for previous reports of this disease based upon visual assessments only, contribute to the development of monitoring and conservation strategies for safeguarding P. comosa forests, and generate insights into potential factors influencing host-pathogen interactions in this system.

BackgroundWe know very little about natural variation in microbiomes of marine herbivorous fish in the wild or in captivity (aquaculture). Understanding how the consumption of seaweed influences intestinal microbial communities will shed light on how such phytobiotics could enhance the health and productivity of farmed fish. Here we screened the effects of supplementing the diets of mottled rabbitfish (Siganus fuscescens), a candidate species for international aquaculture development, with 15 different species of seaweeds and functional supplements currently used in aquaculture, on the bacterial communities that colonised their hindguts. ResultsRemarkably, the second most abundant phylum and the majority (53%) of the bacterial genera were not assigned, highlighting a significant knowledge gap for the field of animal microbiomes. Dietary supplementation increased alpha diversity by up to 23% relative to the control fish. Furthermore, most supplements significantly increased the relative abundance of Firmicutes, with similar trends for Proteobacteria and consistent decreases in Bacteroides. Seaweed supplementation also had important effects at the genus level, including significant increases in Fusobacterium sp. in fish fed seaweed - especially the green Caulerpa taxifolia – and overall trends for reduced levels of Arcobacter sp., a genus that includes fish and human pathogens. When we compared microbiomes in our fish to those from two recently published studies of conspecific populations sampled many thousands of kilometres away, the populations were clearly distinct, however there were 55 ASVs that were shared across the three fish populations, of which 35 were present in 50% of all fish sampled.ConclusionThe identification of a core microbiome suggests that a host organism relies on certain microbes for key functions and our findings suggest that this candidate aquaculture species has a core microbiome in its hindgut which is robust to dietary manipulations and broad geographical and temporal variation. This insight will help guide future work investigating the functional and mechanistic bases of these relationships, as will improvements in microbial taxonomic resolution. Supplementation with seaweeds did have subtle influences on bacteria in the hindgut of Siganus fuscescens which could have important impacts on fish health and should be considered as aquaculture systems are developed for this species.

Our understanding of diseases has been transformed by the realisation that people are holobionts, comprised of a host and its associated microbiome(s). Disease can also have devastating effects on populations of marine organisms, including dominant habitat formers such as seaweed holobionts. However, we know very little about how interactions between microorganisms within microbiomes - of humans or marine organisms – affect host health and there is no underpinning theoretical framework for exploring this. We applied ecological models of succession to bacterial communities to understand how interactions within a seaweed microbiome affect the host. We observed succession of surface microbiomes on the red seaweed Delisea pulchra in situ, following a disturbance, with communities ‘recovering’ to resemble undisturbed states after only 12 days. Further, if this recovery was perturbed, a bleaching disease previously described for this seaweed developed. Early successional strains of bacteria protected the host from colonisation by a pathogenic, later successional strain. Host chemical defences also prevented disease, such that within-microbiome interactions were most important when the host’s chemical defences were inhibited. This is the first experimental evidence that interactions within microbiomes have important implications for host health and disease in a dominant marine habitat-forming organism.

Salmonids represent US$23 billion of global aquaculture value, yet Atlantic salmon farms lose approximately 10% of their production to diseases and parasites every year. New approaches to minimise such losses are urgently needed because current treatments (e.g. antibiotics) have environmental and human health impacts with increasing sea temperatures predicted to further exacerbate the impacts of disease. Immunostimulants that boost fish resistance to disease without negative environmental or human health impacts are currently being assessed. Seaweeds and their extracts are used as immunostimulants for land animals and are increasingly being investigated for use in finfish aquaculture, including for Atlantic salmon. Here we show that when the red seaweed Asparagopsis taxiformis and its extract were incorporated in Atlantic salmon feed, fish growth rates were enhanced up to 33%, feed intake was enhanced up to 13%, FCR were reduced, and innate immune responses were enhanced up to 58% compared to fish fed unsupplemented control diets over 4 weeks. Overall, fish fed the methanolic extract of A. taxiformis (at an inclusion of ~1% on a dry weight basis, D:D of feed) had the best combination of enhanced growth rate, feed intake and immune response. Fish fed the immunostimulant lipopolysaccharide (LPS) derived from Escherichia coli had the highest innate immune response in our trial, however LPS had no enhanced effect on growth or feed intake. Additionally, we provide evidence that the seaweed and LPS supplements modulated the expression of immune and stress-related genes in both the liver and head kidneys. More specifically, the fish fed the supplemented diets showed increased expression of the HSP70 gene in both their liver and head kidney after 2 weeks of treatment. At 4 weeks high HSP70 and lysozyme gene expression was observed in the fish fed the two seaweed methanolic extract diets. The seaweed diets also enhanced the diversity of bacterial communities within the hindgut of Atlantic salmon while the LPS treatment appeared to have the opposite effect. Whole A. taxiformis or its methanolic extracts could therefore be used as functional feed ingredients that boost the immune response and enhance the growth rate of Atlantic salmon without affecting feed efficiencies.

Incidence, or compositional, matrices are generated for a broad range of research applications in biology. Zeta diversity provides a common currency and conceptual framework that links incidence-based metrics with multiple patterns of interest in biology, ecology, and biodiversity science. It quantifies the variation in species (or OTU) composition of multiple assemblages (or cases) in space or time, to capture the contribution of the full suite of narrow, intermediate, and wide-ranging species to biotic heterogeneity. Here we provide a conceptual framework for the application and interpretation of patterns of continuous change in compositional diversity using zeta diversity. This includes consideration of the survey design context, and the multiple ways in which zeta diversity decline and decay can be used to examine and test turnover in the identity of elements across space and time. We introduce the zeta ratio-based retention rate curve to quantify rates of compositional change. We illustrate these applications using 11 empirical data sets from a broad range of taxa, scales, and levels of biological organization-from DNA molecules and microbes to communities and interaction networks-including one of the original data sets used to express compositional change and distance decay in ecology. We show (1) how different sample selection schemes used during the calculation of compositional change are appropriate for different data types and questions, (2) how higher orders of zeta may in some cases better detect shifts and transitions, and (3) the relative roles of rare vs. common species in driving patterns of compositional change. By exploring the application of zeta diversity decline and decay, including the retention rate, across this broad range of contexts, we demonstrate its application for understanding continuous turnover in biological systems.

Climate change is driving global declines of marine habitat-forming species through physiological effects and through changes to ecological interactions, with projected trajectories for ocean warming and acidification likely to exacerbate such impacts in coming decades. Interactions between habitat-formers and their microbiomes are fundamental for host functioning and resilience, but how such relationships will change in future conditions is largely unknown. We investigated independent and interactive effects of warming and acidification on a large brown seaweed, the kelp Ecklonia radiata , and its associated microbiome in experimental mesocosms. Microbial communities were affected by warming and, during the first week, by acidification. During the second week, kelp developed disease-like symptoms previously observed in the field. The tissue of some kelp blistered, bleached and eventually degraded, particularly under the acidification treatments, affecting photosynthetic efficiency. Microbial communities differed between blistered and healthy kelp for all treatments, except for those under future conditions of warming and acidification, which after two weeks resembled assemblages associated with healthy hosts. This indicates that changes in the microbiome were not easily predictable as the severity of future climate scenarios increased. Future ocean conditions can change kelp microbiomes and may lead to host disease, with potentially cascading impacts on associated ecosystems.

Declines of habitat-forming organisms in terrestrial and marine systems can lead to changes in community-wide biodiversity. The dominant habitat-forming macroalga Phyllospora comosa (Fucales) went locally extinct along the metropolitan coastline of Sydney in the 1980s. However, the consequences of that disappearance to the associated faunal diversity in these habitats, and whether Phyllospora is ecologically redundant with respect to the biodiversity it supports, are not known. Efforts are underway to restore Phyllospora, and the capacity to enhance local biodiversity is an important component of the rationale for restoration. We compared epifaunal diversity (abundances and composition) between Phyllospora and two other co-occurring habitat-forming algae, the kelp Ecklonia radiata and the fucoid Sargassum vestitum, and determined whether Phyllospora transplanted to Sydney developed different epifaunal communities than undisturbed thalli and controls. Where the 3 species naturally co-occurred, Phyllospora supported different abundances of taxa than Ecklonia and Sargassum, as well as different composition at finer scales, which suggests that this species is not completely redundant and that its disappearance may have affected local biodiversity. Similarly, assemblages on transplanted Phyllospora differed from those on Ecklonia and Sargassum at restored sites, but did not always resemble assemblages from extant natural Phyllospora populations, even 18 months after transplantation. These experiments indicate that restoration of key habitat-forming seaweeds not only recovers the algal species but also reduces risks of losing habitat diversity for epifauna and their consumers. However, restoration of all the original biodiversity associated with these seaweeds can be a difficult, complex, and long-term process. © 2016 Society for Ecological Restoration.

Summary Interactions between hosts and associated microbial communities can fundamentally shape the development and ecology of ‘holobionts’, from humans to marine habitat-forming organisms such as seaweeds. In marine systems, planktonic microbial community structure is mainly driven by geography and related environmental factors, but the large-scale drivers of host-associated microbial communities are largely unknown. Using 16S-rRNA gene sequencing, we characterized 260 seaweed-associated bacterial and archaeal communities on the kelp Ecklonia radiata from three biogeographical provinces spanning 10° of latitude and 35° of longitude across the Australian continent. These phylogenetically and taxonomically diverse communities were more strongly and consistently associated with host condition than geographical location or environmental variables, and a ‘core’ microbial community characteristic of healthy kelps appears to be lost when hosts become stressed. Microbial communities on stressed individuals were more similar to each other among locations than those on healthy hosts. In contrast to biogeographical patterns of planktonic marine microbial communities, host traits emerge as critical determinants of associated microbial community structure of these holobionts, even at a continental scale.

Zeta diversity provides the average number of shared species acrossnsites (or shared operational taxonomic units (OTUs) acrossncases). It quantifies the variation in species composition of multiple assemblages in space and time to capture the contribution of the full suite of narrow, intermediate and wide-ranging species to biotic heterogeneity. Zeta diversity was proposed for measuring compositional turnover in plant and animal assemblages, but is equally relevant for application to any biological system that can be characterised by a row by column incidence matrix. Here we illustrate the application of zeta diversity to explore compositional change in empirical data, and how observed patterns may be interpreted. We use 10 datasets from a broad range of scales and levels of biological organisation – from DNA molecules to microbes, plants and birds – including one of the original data sets used by R.H. Whittaker in the 1960’s to express compositional change and distance decay using beta diversity. The applications show (i) how different sampling schemes used during the calculation of zeta diversity may be appropriate for different data types and ecological questions, (ii) how higher orders of zeta may in some cases better detect shifts, transitions or periodicity, and importantly (iii) the relative roles of rare versus common species in driving patterns of compositional change. By exploring the application of zeta diversity across this broad range of contexts, our goal is to demonstrate its value as a tool for understanding continuous biodiversity turnover and as a metric for filling the empirical gap that exists on spatial or temporal change in compositional diversity.

Degradation and loss of natural habitats due to human activities is a main cause of global biodiversity loss. In temperate systems, seaweeds are a main habitat former and support extremely diverse communities, including many economically important species. Coastal urbanisation is, however, causing significant declines of key habitat-forming seaweeds. To develop successful management strategies such as seaweed habitat restoration, it is necessary to first determine what additional ecosystem values are likely to be added through restoration and to provide baseline data against which goals can be established and success can be measured. The habitat-forming fucoid Phyllospora comosa was once common on shallow subtidal reefs around Sydney, Australia’s largest city, but disappeared in the 1980s, coincident with heavy sewage outfall discharges. To provide the baseline data necessary for restoring and managing Phyllospora in areas from where it has disappeared, we quantified the community composition and abundance of fish and large invertebrates (abalone and sea urchins) in healthy Phyllospora habitats and compared them to those in Ecklonia radiata (the other major habitat-forming kelp in the region) as well as other common shallow subtidal habitats. Fish assemblage structure was similar between Phyllospora vs Ecklonia beds, but Phyllospora supported much greater numbers of abalone and urchins than any other habitat. This suggests that, in terms of some components of the biodiversity it supports, Phyllospora is functionally unique and not a redundant species. Restoring this seaweed will, therefore, also contribute to biodiversity rehabilitation by restoring unique faunal assemblages that are supported by Phyllospora, including economically important species.

6 páginas, 3 figuras., Some of the most profound effects of climate change on ecological communities are due to alterations in species interactions rather than direct physiological effects of changing environmental conditions. Empirical evidence of historical changes in species interactions within climate-impacted communities is, however, rare and difficult to obtain. Here, we demonstrate the recent disappearance of key habitat-forming kelp forests from a warming tropical–temperate transition zone in eastern Australia. Using a 10-y video dataset encompassing a 0.6 °C warming period, we show how herbivory increased as kelp gradually declined and then disappeared. Concurrently, fish communities from sites where kelp was originally abundant but subsequently disappeared became increasingly dominated by tropical herbivores. Feeding assays identified two key tropical/ subtropical herbivores that consumed transplanted kelp within hours at these sites. There was also a distinct increase in the abundance of fishes that consume epilithic algae, and much higher bite rates by this group at sites without kelp, suggesting a key role for these fishes in maintaining reefs in kelp-free states by removing kelp recruits. Changes in kelp abundance showed no direct relationship to seawater temperatures over the decade and were also unrelated to other measured abiotic factors (nutrients and storms). Our results show that warming-mediated increases in fish herbivory pose a significant threat to kelp-dominated ecosystems in Australia and, potentially, globally., This research was funded by a University of New South Wales (UNSW) Early Career Researcher Award and a New Opportunities Funding Initiative from the Evolution and Ecology Research Centre (UNSW) (to A.V.). This research was undertaken under Research Permit 2012/ 006 from the New South Wales Marine Parks Authority. This is contribution 192 from the Sydney Institute of Marine Science.

Coral cover on reefs is declining globally due to coastal development, overfishing and climate change. Reefs isolated from direct human influence can recover from natural acute disturbances, but little is known about long term recovery of reefs experiencing chronic human disturbances. Here we investigate responses to acute bleaching disturbances on turbid reefs off Singapore, at two depths over a period of 27 years. Coral cover declined and there were marked changes in coral and benthic community structure during the first decade of monitoring at both depths. At shallower reef crest sites (3–4 m), benthic community structure recovered towards pre-disturbance states within a decade. In contrast, there was a net decline in coral cover and continuing shifts in community structure at deeper reef slope sites (6–7 m). There was no evidence of phase shifts to macroalgal dominance but coral habitats at deeper sites were replaced by unstable substrata such as fine sediments and rubble. The persistence of coral dominance at chronically disturbed shallow sites is likely due to an abundance of coral taxa which are tolerant to environmental stress. In addition, high turbidity may interact antagonistically with other disturbances to reduce the impact of thermal stress and limit macroalgal growth rates.

Herbivores play a critical role in structuring benthic communities on tropical coral dominated reefs by removing macroalgae. Reducing herbivory has been implicated in promoting phase shifts from coral dominance to other ecosystem states following disturbances. Turbidity and sedimentation are key physical processes that also structure coral reef communities because they limit light penetration and interfere with biological processes such as heterotrophy. Singapore’s coral reefs have been heavily impacted by human activities for decades and experience very high levels of sedimentation and turbidity. As a result, coral and algal growth is restricted to shallow reef flats and upper reef slopes. While macroalgae, particularly Sargassum spp., are abundant on the reef flats (0-2 m depth), adjacent upper reef slopes (3-4 m depth) are dominated by diverse hard coral assemblages composed primarily of sediment tolerant taxa. To gain a better understanding of the role of herbivore biomass and herbivory rates in structuring these disturbed reefs, we examined the relationship between cover of corals, macroalgae, fish herbivore biomass and urchin abundance at eight representative sites among Singapore’s southern islands during two seasons. In addition we filmed herbivory assays on replicate experimental macroalgal stands (4 separate macroalgal species) and natural EAM patches at three of these sites to estimate species-specific rates of herbivory.Average coral cover at 3-4 m depth was surprisingly high (~40%), compared to current levels found on other Indo-Pacific reefs, although comparisons with historical data from these sites suggests ~15% decline in cover over the last three decades. The average biomass of herbivorous fishes (~4 g m-2), on the other hand, was more typical of degraded and heavily overfished reefs, while urchin abundances were within the range found at other Indo-Pacific sites. Herbivorous fish were not observed feeding on macroalgal assays, while fish bites recorded on EAM were mostly made by territorial damselfish. There was a significant but weak relationship between coral cover and fish herbivore biomass but none for macroalgae or between urchin abundance and benthic cover of corals and macroalgae. A possible explanation for the relatively low cover of macroalgae and low biomass of fish herbivores is that a disproportionate amount of the grazing is being carried out by one or a few fish species not captured by visual survey methods. In addition, the composition of the coral community, which is dominated by sediment tolerant taxa that are relatively resistant to thermal stress, has undoubtedly contributed to the ability of these shallow turbid reefs to persist in a coral dominated state. Furthermore, a combination of limited space for algal growth and low light levels at 3-4 m depth may limit algal growth rates so that only low levels of herbivory are necessary to prevent seaweeds outcompeting corals on these disturbed reefs.

Despite the importance of consumers in structuring communities, and the widespread assumption that consumption is strongest at low latitudes, empirical tests for global scale patterns in the magnitude of consumer impacts are limited. In marine systems, the long tradition of experimentally excluding herbivores in their natural environments allows consumer impacts to be quantified on global scales using consistent methodology. We present a quantitative synthesis of 613 marine herbivore exclusion experiments to test the influence of consumer traits, producer traits and the environment on the strength of herbivore impacts on benthic producers. Across the globe, marine herbivores profoundly reduced producer abundance (by 68% on average), with strongest effects in rocky intertidal habitats and the weakest effects on habitats dominated by vascular plants. Unexpectedly, we found little or no influence of latitude or mean annual water temperature. Instead, herbivore impacts differed most consistently among producer taxonomic and morphological groups. Our results show that grazing impacts on plant abundance are better predicted by producer traits than by large-scale variation in habitat or mean temperature, and that there is a previously unrecognised degree of phylogenetic conservatism in producer susceptibility to consumption.

The need for animals and plants to control microbial colonization is important in the marine environment with its high densities of microscopic propagules and seawater that provides an ideal medium for their dispersal. In contrast to the traditional emphasis on antagonistic interactions of marine organisms with microbes, emerging studies lend support to the notion that health and performance of many marine organisms are functionally regulated and assisted by associated microbes, an ecological concept defined as a holobiont. While antimicrobial activities of marine secondary metabolites have been studied in great depth ex-situ, we are beginning to understand how some of these compounds function in an ecological context to maintain the performance of marine holobionts. The present article reviews two decades of our research on the red seaweed Delisea pulchra by addressing: the defense chemistry of this seaweed; chemically-mediated interactions between the seaweed and its natural enemies; and the negative influence of elevated seawater temperature on these interactions. Our understanding of these defense compounds and the functional roles they play for D. pulchra extends from molecular interactions with bacterial cell signaling molecules, to ecosystem-scale consequences of chemically-controlled disease and herbivory. Delisea pulchra produces halogenated furanones that antagonize the same receptor as acylated homoserine lactones (AHL)-a group of widespread intercellular communication signals among bacteria. Halogenated furanones compete with and inhibit bacterial cell-to-cell communication, and thus interfere with important bacterial communication-regulated processes, such as biofilm formation. In a predictable pattern that occurs at the ecological level of entire populations, environmental stress interferes with the production of halogenated furanones, causing downstream processes that ultimately result in disease of the algal holobiont.

Disease is emerging as an important impact of global climate change, due to the effects of environmental change on host organisms and their pathogens. Climate-mediated disease can have severe consequences in natural systems, particularly when ecosystem engineers, such as habitat-formers or top predators are affected, as any impacts can cascade throughout entire food webs. In temperate marine ecosystems, seaweeds are the dominant habitat-formers on rocky reefs. We investigated a putative bleaching disease affecting Delisea pulchra, a chemically defended seaweed that occurs within a global warming 'hot-spot' and assessed how patterns of this phenomenon were influenced by ocean temperature, solar radiation, algal chemical defences and microbial pathogens. Warmer waters were consistently and positively correlated with higher frequencies of bleaching in seaweed populations, but patterns of bleaching were not consistently influenced by light levels. Bleached thalli had low levels of antibacterial chemical defences relative to healthy conspecifics and this was observed across entire thalli of partially bleached algae. Microbial communities associated with bleached algae were distinct from those on the surfaces of healthy seaweeds. Direct testing of the importance of algal chemical defences, done here for the first time in the field, demonstrated that they protected the seaweed from bleaching. Treatment of algal thalli with antibiotics reduced the severity of bleaching in experimental algae, especially at high water temperatures. These results indicate that bleaching in D. pulchra is the result of temperature-mediated bacterial infections and highlight the potential for warming to influence disease dynamics by stressing hosts. Understanding the complex ways in which global change may affect important organisms such as habitat-forming seaweeds, is essential for the management and conservation of natural resources. © 2011 Blackwell Publishing Ltd.

Anthropogenic activities have caused profound changes globally in biodiversity, species interactions and ecosystem functions and services. In terrestrial systems, restoration has emerged as a useful approach to mitigate these changes, and is increasingly recognised as a tool to fortify ecosystems against future disturbances. In marine systems, restoration is also gaining traction as a management tool, but it is still comparatively scant and underdeveloped relative to terrestrial environments. Key coastal habitats, such as seaweed forests and seagrass meadows are showing widespread patterns of decline around the world. As these important ecosystems increasingly become the target of emerging marine restoration campaigns, it is important not only to address current environmental degradation issues, but also to focus on the future. Given the rate at which marine and other environments are changing, and given predicted increases in the frequency and magnitude of multiple stressors, we argue for an urgent need for subtidal marine macrophyte restoration efforts that explicitly incorporate future-proofing in their goals. Here we highlight emerging scientific techniques that can help achieve this, and discuss changes to managerial, political and public frameworks that are needed to support scientific innovation and restoration applications at scale.

Host-pathogen interactions have been widely studied in humans and terrestrial plants, but are much less well explored in marine systems. Here we show that a marine macroalga, Delisea pulchra, utilizes a chemical defence - furanones - to inhibit colonization and infection by a novel bacterial pathogen, Ruegeria sp. R11, and that infection by R11 is temperature dependent. Ruegeria sp. R11 formed biofilms, invaded and bleached furanone-free, but not furanone-producing D. pulchra thalli, at high (24°C) but not low (19°C) temperatures. Bleaching is commonly observed in natural populations of D. pulchra near Sydney, Australia, during the austral summer when ocean temperatures are at their peak and the chemical defences of the alga are reduced. Furanones, produced by D. pulchra as a chemical defence, inhibit quorum sensing (QS) in bacteria, and this may play a role in furanone inhibition of R11 infection of furanone-free thalli as R11 produces QS signals. This interplay between temperature, an algal chemical defence mechanism and bacterial virulence demonstrates the complex impact environmental change can have on an ecosystem. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

Summary 1 Herbivory is particularly intense in marine environments, with a higher proportion of primary productivity removed than in terrestrial habitats. Experimental manipulation of large herbivores (fish, urchins) has clearly documented their grazing impacts on algal and seagrass beds. Grazing impacts of mesograzers (small invertebrates such as amphipods and isopods) are, however, less understood due to the practical difficulties in manipulating their abundance in field conditions. 2 We developed a novel technique that successfully manipulated the abundance of herbivorous amphipods on macroalgae without the potential artefacts associated with exclusion cages or mesocosms. We then used this technique to test the effects of reduced amphipod grazing over extended periods on the structure of a temperate algal assemblage. We tested grazer effects on growth rates and epiphyte cover of the brown alga Sargassum linearifolium, and on developing assemblages on bare substrates. 3 Large reductions in the abundance of herbivorous amphipods affected neither the growth rates of S. linearifolium, the cover of its epiphytes, nor the structure of algal assemblages. This result contrasts strongly to previous studies in mesocosms documenting strong impacts of mesograzers on community structure, and we discuss differences in the experimental approaches and biology of the systems that could give rise to the observed differences in grazer impacts. 4 Synthesis. Marine macroalgae and seagrasses support very high densities of small herbivores whose ecological role in these habitats is poorly understood. We have provided the first, replicated experiment that directly manipulates their density in situ to quantify grazer impacts without caging artefacts. Our results indicate that strong impacts are not likely with the naturally occurring amphipod densities in the temperate algal bed studied. Further such experimental tests in field conditions are required to understand the properties of grazer and plant communities that can predict grazer impacts.

Rear (warm) edge populations are often considered more susceptible to warming than central (cool) populations because of the warmer ambient temperatures they experience, but this overlooks the potential for local variation in thermal tolerances. Here we provide conceptual models illustrating how sensitivity to warming is affected throughout a species' geographical range for locally adapted and non-adapted populations. We test these models for a range-contracting seaweed using observations from a marine heatwave and a 12-month experiment, translocating seaweeds among central, present and historic range edge locations. Growth, reproductive development and survivorship display different temperature thresholds among central and rear-edge populations, but share a 2.5 °C anomaly threshold. Range contraction, therefore, reflects variation in local anomalies rather than differences in absolute temperatures. This demonstrates that warming sensitivity can be similar throughout a species geographical range and highlights the importance of incorporating local adaptation and acclimatization into climate change vulnerability assessments., Low latitude populations are often thought to be more vulnerable to climate change due to warmer ambient conditions. Here, Bennett et al. show that populations of seaweed from different areas of their range have distinct thermal-tolerance thresholds, but share remarkably similar thermal safety margins to warming.

Interactions between hosts and associated microbial communities can fundamentally shape the development and ecology of 'holobionts', from humans to marine habitat-forming organisms such as seaweeds. In marine systems, planktonic microbial community structure is mainly driven by geography and related environmental factors, but the large-scale drivers of host-associated microbial communities are largely unknown. Using 16S-rRNA gene sequencing, we characterized 260 seaweed-associated bacterial and archaeal communities on the kelp Ecklonia radiata from three biogeographical provinces spanning 10° of latitude and 35° of longitude across the Australian continent. These phylogenetically and taxonomically diverse communities were more strongly and consistently associated with host condition than geographical location or environmental variables, and a 'core' microbial community characteristic of healthy kelps appears to be lost when hosts become stressed. Microbial communities on stressed individuals were more similar to each other among locations than those on healthy hosts. In contrast to biogeographical patterns of planktonic marine microbial communities, host traits emerge as critical determinants of associated microbial community structure of these holobionts, even at a continental scale.

In many temperate regions, brown macroalgae fulfil essential ecosystem services such as the provision of structure, the fixation of nutrients and carbon, and the production of biomass and oxygen. Their populations in many regions around the globe have declined and/or spatially shifted in recent decades. In this review we highlight the potential global and regional drives of these changes, describe the status of regionally particularly important brown macroalgal species, and describe the capacity of interactions among abiotic and biotic factors to amplify or buffer environmental pressure on brown macroalgae. We conclude with a consideration of possible management and restoration measures.

Adriana Vergés et al., Climate-driven changes in biotic interactions can profoundly alter ecological communities, particularly when they impact foundation species. In marine systems, changes in herbivory and the consequent loss of dominant habitat forming species can result in dramatic community phase shifts, such as from coral to macroalgal dominance when tropical fish herbivory decreases, and from algal forests to 'barrens' when temperate urchin grazing increases. Here, we propose a novel phase-shift away from macroalgal dominance caused by tropical herbivores extending their range into temperate regions. We argue that this phase shift is facilitated by poleward-flowing boundary currents that are creating ocean warming hotspots around the globe, enabling the range expansion of tropical species and increasing their grazing rates in temperate areas. Overgrazing of temperate macroalgae by tropical herbivorous fishes has already occurred in Japan and the Mediterranean. Emerging evidence suggests similar phenomena are occurring in other temperate regions, with increasing occurrence of tropical fishes on temperate reefs. © 2014 The Author(s) Published by the Royal Society. All rights reserved., We thank the Evolution and Ecology Research Centre (UNSW) for funding the workshop on the tropicalization of temperate marine ecosystems that resulted in this review. This study resulted from a workshop convened by A.V., P.D.S. and A.G.P. entitled ‘Shifting species interactions and the tropicalization of temperate marine ecosystems’, held at the Sydney Institute of Marine Science (Australia) in November 2011

Diseases affecting natural ecosystems are increasing in frequency and severity, but unless obviously catastrophic, the consequences of disease outbreaks are often overlooked, relative to other ecological processes (e.g., predation, competition). Disease can have profound effects on individuals and can also strongly influence interactions between infected hosts and their natural enemies. We investigated whether a novel bleaching disease affected the survival or performance of a habitat‐forming red seaweed, Delisea pulchra. In addition, we investigated bidirectional, multipartite interactions between this seaweed host, its pathogens, and consumers. Although we found no negative impacts of disease on survival of D. pulchra, bleaching had substantial, negative consequences for affected individuals, including a dramatic drop in fecundity and a significant decrease in size. In the first direct demonstration of bacterial disease‐mediated herbivory of seaweeds, herbivores generally preferred to consume bleached tissue in feeding trials, and we also found higher densities of herbivores on bleached than co‐occurring, healthy algae at sites where herbivores were abundant. In a conceptually reciprocal test of the effects of herbivores on infection, we showed that simulated herbivory increased susceptibility to bleaching when algae were also exposed to cultures of a bacterial pathogen. Given the high proportions of D. pulchra affected by bleaching during peak periods, the impacts of this disease are likely to have important implications at the population level. This work highlights complex interactions between habitat‐forming organisms and their natural enemies and further emphasizes the need to consider disease in ecological research. Published version

As global climates change, the incidence and severity of diseases in natural ecosystems also appears to be increasing. This has been linked to increasingly stressful conditions, which can lead to more susceptible hosts and environmental effects on pathogen abundance and virulence. Recently, environmentally-mediated diseases have affected a diverse range of both terrestrial and marine organisms. The ecological impacts of diseases are likely to be more severe when they affect habitat-forming organisms like trees, corals and seaweeds, as any impacts could cascade throughout entire communities. In marine environments, organisms are exposed to persistently high densities of potentially pathogenic microorganisms, which can affect habitat-formers like corals and seagrasses. On temperate rocky reefs, the dominant habitat-formers are seaweeds. Here we review recent work on a chemically defended seaweed, and a bleaching phenomenon common in natural populations near Sydney, Australia. The prevalence of bleaching is positively correlated with water temperature and negatively correlated with concentrations of secondary metabolites in the alga, which are known to inhibit bacteria. Bleaching is associated with a shift in the composition of microbial communities on algal surfaces and can be induced via exposure to ambient seawater microbes and cultures of putative pathogens. Direct consequences of bleaching include reductions in algal growth and fecundity. Bleaching also has indirect ecological effects on the alga, with bleached individuals attracting higher densities of herbivores and preferential consumption of bleached tissues. This environmentally-mediated bleaching phenomenon appears to be the result of complex interactions between increasing ocean temperatures, host defences and pathogen virulence and has significant implications for this habitat-forming organism and the community it supports.

The sensory capacity of bacteria and macroalgae (seaweeds) is limited with respect to many modalities (visual, auditory) common in "higher" organisms such as animals. Thus, we expect that other modalities, such as chemical signaling and sensing, would play particularly important roles in their sensory ecology. Here, we discuss two examples of chemical signaling in bacteria and seaweeds: (1) the role of chemical defenses and quorum-sensing (QS) regulatory systems in bacterial colonization and infection of the red alga Delisea pulchra and their ecological consequences, and (2) the regulation of dispersal and differentiation by nitric oxide (NO) in bacterial biofilms. Consistent with the goals of neuroecology, in both cases, we investigate the links between specific signal-mediated molecular mechanisms, and ecological outcomes, for populations or assemblages of bacteria or seaweeds. We conclude by suggesting that because of the fundamental role played by chemical signaling in bacteria, bacterial systems, either by themselves or in interactions with other organisms, have much to offer for understanding general issues in neuroecology. Thus, further integration of microbiology with the biology of eukaryotes would seem warranted and is likely to prove illuminating. © The Author 2011. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved.

World production of sea urchins peaked in 1995, when 120 306 t were landed. Chile dominates world production, producing more than half the world's total landings of 90 257 t in 1998. Other important fisheries are found in Japan, Maine, British Columbia, California, South Korea, New Brunswick, Russia, Mexico, Alaska, Nova Scotia, and in a number of countries that produced less than 1000 t in 1998. Aside from the Chilean fishery for Loxechinus albus, most harvest is of Strongylocentrotus spp., particularly S. intermedius, S. franciscanus, and S. droebachiensis. Only a small minority of fisheries have been formally assessed and in the absence of such assessments it is difficult to determine whether fisheries are overfished or whether the large declines observed in many represent the "fish down" of accumulated biomass. Nevertheless, those in Chile, Japan, Maine, California and Washington and a number of smaller fisheries, have declined considerably since their peaks and are likely to be overfished. Fisheries in Japan, South Korea and the Philippines have been enhanced by reseeding hatchery-reared juveniles and by modifying reefs to increase their structural complexity and to promote the growth of algae. Sea urchin fisheries have potentially large ecological effects, usually mediated through increases in the abundance and biomass of large brown algae. Although such effects may have important consequences for management of these and related fisheries, only in Nova Scotia, South Korea and Japan is ecological knowledge incorporated into management.