Large-scale impacts of sea star wasting disease (SSWD) on intertidal sea stars and implications for recovery

Impacts of marine heatwaves in coastal ecosystems depend on local environmental conditions

Marine heatwaves (MHWs), increasing in duration and intensity because of climate change, are now a major threat to marine life and can have lasting effects on the structure and function of ecosystems. However, the responses of marine taxa and ecosystems to MHWs can be highly variable, making predicting and interpreting biological outcomes a challenge. Here, we review how biological responses to MHWs, from individuals to ecosystems, are mediated by fine-scale spatial variability in the coastal marine environment (hereafter, local gradients). Viewing observed responses through a lens of ecological theory, we present a simple framework of three 'resilience processes' (RPs) by which local gradients can influence the responses of marine taxa to MHWs. Local gradients (1) influence the amount of stress directly experienced by individuals, (2) facilitate local adaptation and acclimatization of individuals and populations, and (3) shape community composition which then influences responses to MHWs. We then synthesize known examples of fine-scale gradients that have affected responses of benthic foundation species to MHWs, including kelp forests, coral reefs, and seagrass meadows and link these varying responses to the RPs. We present a series of case studies from various marine ecosystems to illustrate the differential impacts of MHWs mediated by gradients in both temperature and other co-occurring drivers. In many cases, these gradients had large effect sizes with several examples of local gradients causing a 10-fold difference in impacts or more (e.g., survival, coverage). This review highlights the need for high-resolution environmental data to accurately predict and manage the consequences of MHWs in the context of ongoing climate change. While current tools may capture some of these gradients already, we advocate for enhanced monitoring and finer scale integration of local environmental heterogeneity into climate models. This will be essential for developing effective conservation strategies and mitigating future marine biodiversity loss.

Source-Sink Dynamics in a Two-Patch SI Epidemic Model with Life Stages and No Recovery from Infection

This study presents a comprehensive analysis of a two-patch, two-life stage SI model without recovery from infection, focusing on the dynamics of disease spread and host population viability in natural populations. The model, inspired by real-world ecological crises like the decline of amphibian populations due to chytridiomycosis and sea star populations due to Sea Star Wasting Disease, aims to understand the conditions under which a sink host population can present ecological rescue from a healthier, source population. Mathematical and numerical analyses reveal the critical roles of the basic reproductive numbers of the source and sink populations, the maturation rate, and the dispersal rate of juveniles in determining population outcomes. The study identifies basic reproduction numbers R 0 for each of the patches, and conditions for the basic reproduction numbers to produce a receiving patch under which its population. These findings provide insights into managing natural populations affected by disease, with implications for conservation strategies, such as the importance of maintaining reproductively viable refuge populations and considering the effects of dispersal and maturation rates on population recovery. The research underscores the complexity of host-pathogen dynamics in spatially structured environments and highlights the need for multi-faceted approaches to biodiversity conservation in the face of emerging diseases.

Regime shifts in rocky intertidal communities associated with a marine heatwave and disease outbreak

Long-term, large-scale experimental studies provide critical information about how global change influences communities. When environmental changes are severe, they can trigger abrupt transitions from one community type to another leading to a regime shift. From 2014 to 2016, rocky intertidal habitats in the northeast Pacific Ocean experienced extreme temperatures during a multi-year marine heatwave (MHW) and sharp population declines of the keystone predator Pisaster ochraceus due to sea star wasting disease (SSWD). Here we measured the community structure before, during and after the MHW onset and SSWD outbreak in a 15-year succession experiment conducted in a rocky intertidal meta-ecosystem spanning 13 sites on four capes in Oregon and northern California, United States. Kelp abundance declined during the MHW due to extreme temperatures, while gooseneck barnacle and mussel abundances increased due to reduced predation pressure after the loss of Pisaster from SSWD. Using several methods, we detected regime shifts from substrate- or algae-dominated to invertebrate-dominated alternative states at two capes. After water temperatures cooled and Pisaster population densities recovered, community structure differed from pre-disturbance conditions, suggesting low resilience. Consequently, thermal stress and predator loss can result in regime shifts that fundamentally alter community structure even after restoration of baseline conditions.

Resistance of rocky intertidal communities to oceanic climate fluctuations

A powerful way to predict how ecological communities will respond to future climate change is to test how they have responded to the climate of the past. We used climate oscillations including the Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation, and El Niño Southern Oscillation (ENSO) and variation in upwelling, air temperature, and sea temperatures to test the sensitivity of nearshore rocky intertidal communities to climate variability. Prior research shows that multiple ecological processes of key taxa (growth, recruitment, and physiology) were sensitive to environmental variation during this time frame. We also investigated the effect of the concurrent sea star wasting disease outbreak in 2013-2014. We surveyed nearly 150 taxa from 11 rocky intertidal sites in Oregon and northern California annually for up to 14-years (2006-2020) to test if community structure (i.e., the abundance of functional groups) and diversity were sensitive to past environmental variation. We found little to no evidence that these communities were sensitive to annual variation in any of the environmental measures, and that each metric was associated with < 8.6% of yearly variation in community structure. Only the years elapsed since the outbreak of sea star wasting disease had a substantial effect on community structure, but in the mid-zone only where spatially dominant mussels are a main prey of the keystone predator sea star, Pisaster ochraceus. We conclude that the established sensitivity of multiple ecological processes to annual fluctuations in climate has not yet scaled up to influence community structure. Hence, the rocky intertidal system along this coastline appears resistant to the range of oceanic climate fluctuations that occurred during the study. However, given ongoing intensification of climate change and increasing frequencies of extreme events, future responses to climate change seem likely.

Examining the reproductive success of bull kelp (Nereocystis luetkeana, Phaeophyceae, Laminariales) in climate change conditions

Climate change is affecting marine ecosystems in many ways, including raising temperatures and leading to ocean acidification. From 2014 to 2016, an extensive marine heat wave extended along the west coast of North America and had devastating effects on numerous species, including bull kelp (Nereocystis luetkeana). Bull kelp is an important foundation species in coastal ecosystems and can be affected by marine heat waves and ocean acidification; however, the impacts have not been investigated on sensitive early life stages. To determine the effects of changing temperatures and carbonate levels on Northern California's bull kelp populations, we collected sporophylls from mature bull kelp individuals in Point Arena, CA. At the Bodega Marine Laboratory, we released spores from field-collected bull kelp, and cultured microscopic gametophytes in a common garden experiment with a fully factorial design crossing modern conditions (11.63 ± 0.54°C and pH 7.93 ± 0.26) with observed extreme climate conditions (15.56 ± 0.83°C and 7.64 ± 0.32 pH). Our results indicated that both increased temperature and decreased pH influenced growth and egg production of bull kelp microscopic stages. Increased temperature resulted in decreased gametophyte survival and offspring production. In contrast, decreased pH had less of an effect but resulted in increased gametophyte survival and offspring production. Additionally, increased temperature significantly impacted reproductive timing by causing female gametophytes to produce offspring earlier than under ambient temperature conditions. Our findings can inform better predictions of the impacts of climate change on coastal ecosystems and provide key insights into environmental dynamics regulating the bull kelp lifecycle.

Sea star wasting syndrome reaches the high Antarctic: Two recent outbreaks in McMurdo Sound

Sea star wasting syndrome (SSWS) can cause widespread mortality in starfish populations as well as long-lasting changes to benthic community structure and dynamics. SSWS symptoms have been documented in numerous species and locations around the world, but to date there is only one record of SSWS from the Antarctic and this outbreak was associated with volcanically-driven high temperature anomalies. Here we report outbreaks of SSWS-like symptoms that affected ~30% of individuals of Odontaster validus at two different sites in McMurdo Sound, Antarctica in 2019 and 2022. Unlike many SSWS events in other parts of the world, these outbreaks were not associated with anomalously warm temperatures. Instead, we suggest they may have been triggered by high nutrient input events on a local scale. Although the exact cause of these outbreaks is not known, these findings are of great concern because of the keystone role of O. validus and the slow recovery rate of Antarctic benthic ecosystems to environmental stressors.

Two decades of change in sea star abundance at a subtidal site in Puget Sound, Washington

Long-term datasets can reveal otherwise undetectable ecological trends, illuminating the historical context of contemporary ecosystem states. We used two decades (1997-2019) of scientific trawling data from a subtidal, benthic site in Puget Sound, Washington, USA to test for gradual trends and sudden shifts in total sea star abundance across 11 species. We specifically assessed whether this community responded to the sea star wasting disease (SSWD) epizootic, which began in 2013. We sampled at depths of 10, 25, 50 and 70 m near Port Madison, WA, and obtained long-term water temperature data. To account for species-level differences in SSWD susceptibility, we divided our sea star abundance data into two categories, depending on the extent to which the species is susceptible to SSWD, then conducted parallel analyses for high-susceptibility and moderate-susceptibility species. The abundance of high-susceptibility sea stars declined in 2014 across depths. In contrast, the abundance of moderate-susceptibility species trended downward throughout the years at the deepest depths- 50 and 70 m-and suddenly declined in 2006 across depths. Water temperature was positively correlated with the abundance of moderate-susceptibility species, and uncorrelated with high-susceptibility sea star abundance. The reported emergence of SSWD in Washington State in the summer of 2014 provides a plausible explanation for the subsequent decline in abundance of high-susceptibility species. However, no long-term stressors or mortality events affecting sea stars were reported in Washington State prior to these years, leaving the declines we observed in moderate-susceptibility species preceding the 2013-2015 SSWD epizootic unexplained. These results suggest that the subtidal sea star community in Port Madison is dynamic, and emphasizes the value of long-term datasets for evaluating patterns of change.

A Decade of Death and Other Dynamics: Deepening Perspectives on the Diversity and Distribution of Sea Stars and Wasting

AbstractMass mortality events provide valuable insight into biological extremes and also ecological interactions more generally. The sea star wasting epidemic that began in 2013 catalyzed study of the microbiome, genetics, population dynamics, and community ecology of several high-profile species inhabiting the northeastern Pacific but exposed a dearth of information on the diversity, distributions, and impacts of sea star wasting for many lesser-known sea stars and a need for integration across scales. Here, we combine datasets from single-site to coast-wide studies, across time lines from weeks to decades, for 65 species. We evaluated the impacts of abiotic characteristics hypothetically associated with sea star wasting (sea surface temperature, pelagic primary productivity, upwelling wind forcing, wave exposure, freshwater runoff) and species characteristics (depth distribution, developmental mode, diet, habitat, reproductive period). We find that the 2010s sea star wasting outbreak clearly affected a little over a dozen species, primarily intertidal and shallow subtidal taxa, causing instantaneous wasting prevalence rates of 5%-80%. Despite the collapse of some populations within weeks, environmental and species variation protracted the outbreak, which lasted 2-3 years from onset until declining to chronic background rates of ∼2% sea star wasting prevalence. Recruitment began immediately in many species, and in general, sea star assemblages trended toward recovery; however, recovery was heterogeneous, and a marine heatwave in 2019 raised concerns of a second decline. The abiotic stressors most associated with the 2010s sea star wasting outbreak were elevated sea surface temperature and low wave exposure, as well as freshwater discharge in the north. However, detailed data speaking directly to the biological, ecological, and environmental cause(s) and consequences of the sea star wasting outbreak remain limited in scope, unavoidably retrospective, and perhaps always indeterminate. Redressing this shortfall for the future will require a broad spectrum of monitoring studies not less than the taxonomically broad cross-scale framework we have modeled in this synthesis.

Heatwave restructures marine intertidal communities across a stress gradient

Significant questions remain about how ecosystems that are structured by abiotic stress will be affected by climate change. Warmer temperatures are hypothesized to shift species along abiotic gradients such that distributions track changing environments where physical conditions allow. However, community-scale impacts of extreme warming in heterogeneous landscapes are likely to be more complex. We investigated the impacts of a multiyear marine heatwave on intertidal community dynamics and zonation on a wave-swept rocky coastline along the Central Coast of British Columbia, Canada. Leveraging an 8-year time series with high seaweed taxonomic resolution (116 taxa) that was established 3 years prior to the heatwave, we document major shifts in zonation and abundance of populations that led to substantial reorganization at the community level. The heatwave was associated with shifts in primary production away from upper elevations through declines in seaweed cover and partial replacement by invertebrates. At low elevations, seaweed cover remained stable or recovered rapidly following decline, being balanced by increases in some species and decreases in others. These results illustrate that, rather than shifting community zonation uniformly along abiotic stress gradients, intense and lasting warming events may restructure patterns of ecological dominance and reduce total habitability of ecosystems, especially at extreme ends of pre-existing abiotic gradients.

Lethal and sublethal implications of low temperature exposure for three intertidal predators

Benthic invertebrate predators play a key role in top-down trophic regulation in intertidal ecosystems. While the physiological and ecological consequences of predator exposure to high temperatures during summer low tides are increasingly well-studied, the effects of cold exposure during winter low tides remain poorly understood. To address this knowledge gap, we measured the supercooling points, survival, and feeding rates of three intertidal predator species in British Columbia, Canada - the sea stars Pisaster ochraceus and Evasterias troschelii and the dogwhelk Nucella lamellosa - in response to exposure to sub-zero air temperatures. Overall, we found that all three predators exhibited evidence of internal freezing at relatively mild sub-zero temperatures, with sea stars exhibiting an average supercooling point of -2.50 °C, and the dogwhelk averaging approximately -3.99 °C. None of the tested species are strongly freeze tolerant, as evidenced by moderate-to-low survival rates after exposure to -8 °C air. All three predators exhibited significantly reduced feeding rates over a two-week period following a single 3-h sublethal (-0.5 °C) exposure event. We also quantified variation in predator body temperature among thermal microhabitats during winter low tides. Predators that were found at the base of large boulders, on the sediment, and within crevices had higher body temperatures during winter low tides, as compared to those situated in other microhabitats. However, we did not find evidence of behavioural thermoregulation via selective microhabitat use during cold weather. Since these intertidal predators are less freeze tolerant than their preferred prey, winter low temperature exposures can have important implications for organism survival and predator-prey dynamics across thermal gradients at both local (habitat-driven) and geographic (climate-driven) scales.

Identifying the core microbiome of the sea star Pisaster ochraceus in the context of sea star wasting disease

Sea stars are keystone species and their mass die-offs due to sea star wasting disease (SSWD) impact marine communities and have fueled recent interest in the microbiome of sea stars. We assessed the host specificity of the microbiome associated with three body regions of the sea star Pisaster ochraceus using 16S rRNA gene amplicon surveys of the bacterial communities living on and in Pisaster, their environment, and sympatric marine hosts across three populations in British Columbia, Canada. Overall, the bacterial communities on Pisaster are distinct from their environment and differ by both body region and geography. We identified core bacteria specifically associated with Pisaster across populations and nearly absent in other hosts and the environment. We then investigated the distribution of these core bacteria on SSWD-affected Pisaster from one BC site and by reanalyzing a study of SSWD on Pisaster from California. We find no differences in the distribution of core bacteria in early disease at either site and two core taxa differ in relative abundance in advanced disease in California. Using phylogenetic analyses, we find that most core bacteria have close relatives on other sea stars and marine animals, suggesting these clades have evolutionary adaptions to an animal-associated lifestyle.

Heat stress does not induce wasting symptoms in the giant California sea cucumber (Apostichopus californicus)

Oceanic heatwaves have significant impacts on disease dynamics in marine ecosystems. Following an extreme heatwave in Nanoose Bay, British Columbia, Canada, a severe sea cucumber wasting event occurred that resulted in the mass mortality of Apostichopus californicus. Here, we sought to determine if heat stress in isolation could trigger wasting symptoms in A. californicus. We exposed sea cucumbers to (i) a simulated marine heatwave (22 °C), (ii) an elevated temperature treatment (17 °C), or (iii) control conditions (12 °C). We measured the presence of skin lesions, mortality, posture maintenance, antipredator defences, spawning, and organ evisceration during the 79-hour thermal exposure, as well as 7-days post-exposure. Both the 22 °C and 17 °C treatments elicited stress responses where individuals exhibited a reduced ability to maintain posture and an increase in stress spawning. The 22 °C heatwave was particularly stressful, as it was the only treatment where mortality was observed. However, none of the treatments induced wasting symptoms as observed in the Nanoose Bay event. This study provides evidence that sea cucumber wasting may not be triggered by heat stress in isolation, leaving the cause of the mass mortality event observed in Nanoose unknown.

Minor Genetic Consequences of a Major Mass Mortality: Short-Term Effects in Pisaster ochraceus

AbstractMass mortality events are increasing globally in frequency and magnitude, largely as a result of human-induced change. The effects of these mass mortality events, in both the long and short term, are of imminent concern because of their ecosystem impacts. Genomic data can be used to reveal some of the population-level changes associated with mass mortality events. Here, we use reduced-representation sequencing to identify potential short-term genetic impacts of a mass mortality event associated with a sea star wasting outbreak. We tested for changes in the population for genetic differentiation, diversity, and effective population size between pre-sea star wasting and post-sea star wasting populations of Pisaster ochraceus-a species that suffered high sea star wasting-associated mortality (75%-100% at 80% of sites). We detected no significant population-based genetic differentiation over the spatial scale sampled; however, the post-sea star wasting population tended toward more differentiation across sites than the pre-sea star wasting population. Genetic estimates of effective population size did not detectably change, consistent with theoretical expectations; however, rare alleles were lost. While we were unable to detect significant population-based genetic differentiation or changes in effective population size over this short time period, the genetic burden of this mass mortality event may be borne by future generations, unless widespread recruitment mitigates the population decline. Prior results from P. ochraceus indicated that natural selection played a role in altering allele frequencies following this mass mortality event. In addition to the role of selection found in a previous study on the genomic impacts of sea star wasting on P. ochraceus, our current study highlights the potential role the stochastic loss of many individuals plays in altering how genetic variation is structured across the landscape. Future genetic monitoring is needed to determine long-term genetic impacts in this long-lived species. Given the increased frequency of mass mortality events, it is important to implement demographic and genetic monitoring strategies that capture baselines and background dynamics to better contextualize species' responses to large perturbations.

Is It in the Stars? Exploring the Relationships between Species' Traits and Sea Star Wasting Disease

AbstractAn explanation for variation in impacts of sea star wasting disease across asteroid species remains elusive. Although various traits have been suggested to play a potential role in sea star wasting susceptibility, currently we lack a thorough comparison that explores how life-history and natural history traits shape responses to mass mortality across diverse asteroid taxa. To explore how asteroid traits may relate to sea star wasting, using available data and recognizing the potential for biological correlations to be driven by phylogeny, we generated a supertree, tested traits for phylogenetic association, and evaluated associations between traits and sea star wasting impact. Our analyses show no evidence for a phylogenetic association with sea star wasting impact, but there does appear to be phylogenetic association for a subset of asteroid life-history traits, including diet, substrate, and reproductive season. We found no relationship between sea star wasting and developmental mode, diet, pelagic larval duration, or substrate but did find a relationship with minimum depth, reproductive season, and rugosity (or surface complexity). Species with the greatest sea star wasting impacts tend to have shallower minimum depth distributions, they tend to have their median reproductive period 1.5 months earlier, and they tend to have higher rugosities relative to species less affected by sea star wasting. Fully understanding sea star wasting remains challenging, in part because dramatic gaps still exist in our understanding of the basic biology and phylogeny of asteroids. Future studies would benefit from a more robust phylogenetic understanding of sea stars, as well as leveraging intra- and interspecific comparative transcriptomics and genomics to elucidate the molecular pathways responding to sea star wasting.

Species' attributes predict the relative magnitude of ecological and genetic recovery following mass mortality

Theoretically, species' characteristics should allow estimation of dispersal potential and, in turn, explain levels of population genetic differentiation. However, a mismatch between traits and genetic patterns is often reported for marine species, and interpreted as evidence that life-history traits do not influence dispersal. Here, we couple ecological and genomic methods to test the hypothesis that species with attributes favouring greater dispersal potential-e.g., longer pelagic duration, higher fecundity and larger population size-have greater realized dispersal overall. We used a natural experiment created by a large-scale and multispecies mortality event which created a "clean slate" on which to study recruitment dynamics, thus simplifying a usually complex problem. We surveyed four species of differing dispersal potential to quantify the abundance and distribution of recruits and to genetically assign these recruits to probable parental sources. Species with higher dispersal potential recolonized a broader extent of the impacted range, did so more quickly and recovered more genetic diversity than species with lower dispersal potential. Moreover, populations of taxa with higher dispersal potential exhibited more immigration (71%-92% of recruits) than taxa with lower dispersal potential (17%-44% of recruits). By linking ecological with genomic perspectives, we demonstrate that a suite of interacting life-history and demographic attributes do influence species' realized dispersal and genetic neighbourhoods. To better understand species' resilience and recovery in this time of global change, integrative eco-evolutionary approaches are needed to more rigorously evaluate the effect of dispersal-linked attributes on realized dispersal and population genetic differentiation.

A Review of Asteroid Biology in the Context of Sea Star Wasting: Possible Causes and Consequences

AbstractSea star wasting-marked in a variety of sea star species as varying degrees of skin lesions followed by disintegration-recently caused one of the largest marine die-offs ever recorded on the west coast of North America, killing billions of sea stars. Despite the important ramifications this mortality had for coastal benthic ecosystems, such as increased abundance of prey, little is known about the causes of the disease or the mechanisms of its progression. Although there have been studies indicating a range of causal mechanisms, including viruses and environmental effects, the broad spatial and depth range of affected populations leaves many questions remaining about either infectious or non-infectious mechanisms. Wasting appears to start with degradation of mutable connective tissue in the body wall, leading to disintegration of the epidermis. Here, we briefly review basic sea star biology in the context of sea star wasting and present our current knowledge and hypotheses related to the symptoms, the microbiome, the viruses, and the associated environmental stressors. We also highlight throughout the article knowledge gaps and the data needed to better understand sea star wasting mechanistically, its causes, and potential management.

The first records of sea star wasting disease in Crossaster papposus in Europe

Sea star wasting disease (SSWD) refers to a suite of gross pathological signs observed in Asteroidea species. It presents to varying degrees as abnormal posture, epidermal ulceration, arm autotomy and eversion of viscera. We report observations of SSWD in the sunstar Crossaster papposus, the first observations of its kind in Europe. While the exact cause of SSWD remains unknown, studies have proposed pathogenic and environmental-stress pathways for disease outbreaks. Although the present observations do not support a precise aetiology, the presence of SSWD in a keystone predator may have wide reaching ecological and management implications.

Toward an atlas of Salish Sea biodiversity: the flora and fauna of Galiano Island, British Columbia, Canada. Part I. Marine zoology

Background

Based on records dating from 1859 to 2021, we provide an overview of the marine animal diversity reported for Galiano Island, British Columbia, Canada. More than 650 taxa are represented by 20,000 species occurrence records in this curated dataset, which includes dive records documented through the Pacific Marine Life Surveys, museum voucher specimens, ecological data and crowd-sourced observations from the BC Cetacean Sightings Network and iNaturalist.

New information

We describe Galiano Island's marine animal diversity in relation to the Salish Sea's overall biodiversity and quantify the proportional contributions of different types of sampling effort to our current local knowledge. Overviews are provided for each taxonomic group in a format intended to be accessible to amateur naturalists interested in furthering research into the region's marine biodiversity. In summary, we find that the Pacific Marine Life Surveys, a regional community science diving initiative, account for 60% of novel records reported for Galiano Island. Voucher specimens account for 19% and crowd-sourced biodiversity data 18% of novel records, respectively, with the remaining 3% of reports coming from other sources. These findings shed light on the complementarity of different types of sampling effort and demonstrate the potential for community science to contribute to the global biodiversity research community. We present a biodiversity informatics framework that is designed to enable these practices by supporting collaboration among researchers and communities in the collection, curation and dissemination of biodiversity data.

Identification of infectious agents in early marine Chinook and Coho salmon associated with cohort survival

Recent decades have seen an increased appreciation for the role infectious diseases can play in mass mortality events across a diversity of marine taxa. At the same time many Pacific salmon populations have declined in abundance as a result of reduced marine survival. However, few studies have explicitly considered the potential role pathogens could play in these declines. Using a multi-year dataset spanning 59 pathogen taxa in Chinook and Coho salmon sampled along the British Columbia coast, we carried out an exploratory analysis to quantify evidence for associations between pathogen prevalence and cohort survival and between pathogen load and body condition. While a variety of pathogens had moderate to strong negative correlations with body condition or survival for one host species in one season, we found that Tenacibaculum maritimum and Piscine orthoreovirus had consistently negative associations with body condition in both host species and seasons and were negatively associated with survival for Chinook salmon collected in the fall and winter. Our analyses, which offer the most comprehensive examination of associations between pathogen prevalence and Pacific salmon survival to date, suggest that pathogens in Pacific salmon warrant further attention, especially those whose distribution and abundance may be influenced by anthropogenic stressors.

Transmission studies and the composition of prokaryotic communities associated with healthy and diseased Aplysina cauliformis sponges suggest that Aplysina Red Band Syndrome is a prokaryotic polymicrobial disease

Aplysina cauliformis, the Caribbean purple rope sponge, is commonly affected by Aplysina Red Band Syndrome. This transmissible disease manifests as circular lesions with red margins and results in bare spongin fibers. Leptolyngbya spp. appear to be responsible for the characteristic red coloration but transmission studies with a sponge-derived isolate failed to establish disease, leaving the etiology of ARBS unknown. To investigate the cause of ARBS, contact transmission experiments were performed between healthy and diseased sponges separated by filters with varying pore sizes. Transmission occurred when sponges were separated by filters with pore sizes ≥2.5 μm, suggesting a prokaryotic pathogen(s) but not completely eliminating eukaryotic pathogen(s). Using 16S rRNA gene sequencing methods, thirty-eight prokaryotic taxa were significantly enriched in diseased sponges, including Leptolyngbya, whereas seven taxa were only found in some, but not all, of the ARBS-affected sponges. These results do not implicate a single taxon, but rather a suite of taxa that changed in relative abundance with disease, suggesting a polymicrobial etiology as well as dysbiosis. As a better understanding of dysbiosis is gained, changes in the composition of associated prokaryotic communities may have increasing importance for evaluating and maintaining the health of individuals and imperiled coral reef ecosystems.

Cloning and Selfing Affect Population Genetic Variation in Simulations of Outcrossing, Sexual Sea Stars

AbstractMany sea stars are well known for facultative or obligate asexual reproduction in both the adult and larval life-cycle stages. Some species and lineages are also capable of facultative or obligate hermaphroditic reproduction with self-fertilization. However, models of population genetic variation and empirical analyses of genetic data typically assume only sexual reproduction and outcrossing. A recent reanalysis of previously published empirical data (microsatellite genotypes) from two studies of one of the most well-known sea star species (the crown-of-thorns sea star; Acanthaster sp.) concluded that cloning and self-fertilization in that species are rare and contribute little to patterns of population genetic variation. Here we reconsider that conclusion by simulating the contribution of cloning and selfing to genetic variation in a series of models of sea star demography. Simulated variation in two simple models (analogous to previous analyses of empirical data) was consistent with high rates of cloning or selfing or both. More realistic scenarios that characterize population flux in sea stars of ecological significance, including outbreaks of crown-of-thorns sea stars that devastate coral reefs, invasions by Asterias amurensis, and epizootics of sea star wasting disease that kill Pisaster ochraceus, also showed significant but smaller effects of cloning and selfing on variation within subpopulations and differentiation between subpopulations. Future models or analyses of genetic variation in similar study systems might benefit from simulation modeling to characterize possible contributions of cloning or selfing to genetic variation in population samples or to understand the limits on inferring the effects of cloning or selfing in nature.

Little evidence for genetic variation associated with susceptibility to sea star wasting syndrome in the keystone species Pisaster ochraceus

The keystone species Pisaster ochraceus suffered mass mortalities along the northeast Pacific Ocean from Sea Star Wasting Syndrome (SSWS) outbreaks in 2013-2016. SSWS causation remains of debate, leading to concerns as to whether outbreaks will continue to impact this species. Considering the apparent link between ocean temperature and SSWS, the future of this species and intertidal communities remains uncertain. Surveys of co-occurring apparently normal and wasting P. ochraceus along the central Oregon coast in 2016 allowed us to address whether variation in disease status showed genetic variation that may be associated with differences in susceptibility to SSWS. We performed restriction site-associated DNA sequencing (2bRAD-seq) to genotype ~72,000 single nucleotide polymorphism (SNP) loci across apparently normal and wasting sea stars. Locus-specific analyses of differentiation (F_ST ) between disease-status groups revealed no signal of genetic differences separating the two groups. Using a multivariate approach, we observed weak separation between the groups, but identified 18 SNP loci showing highest discriminatory power between the groups and scanned the genome annotation for linked genes. A total of 34 protein-coding genes were found to be located within 15 kb (measured by linkage disequilibrium decay) of at least one of the 18 SNPs, and 30 of these genes had homologies to annotated protein databases. Our results suggest that the likelihood of developing SSWS symptoms does not have a strong genetic basis. The few genomic regions highlighted had only modest levels of differentiation, but the genes associated with these regions may form the basis for functional studies aiming to understand disease progression.

Disease-driven mass mortality event leads to widespread extirpation and variable recovery potential of a marine predator across the eastern Pacific

The prevalence of disease-driven mass mortality events is increasing, but our understanding of spatial variation in their magnitude, timing and triggers are often poorly resolved. Here, we use a novel range-wide dataset comprised 48 810 surveys to quantify how sea star wasting disease affected Pycnopodia helianthoides, the sunflower sea star, across its range from Baja California, Mexico to the Aleutian Islands, USA. We found that the outbreak occurred more rapidly, killed a greater percentage of the population and left fewer survivors in the southern half of the species's range. Pycnopodia now appears to be functionally extinct (greater than 99.2% declines) from Baja California, Mexico to Cape Flattery, Washington, USA and exhibited severe declines (greater than 87.8%) from the Salish Sea to the Gulf of Alaska. The importance of temperature in predicting Pycnopodia distribution rose more than fourfold after the outbreak, suggesting latitudinal variation in outbreak severity may stem from an interaction between disease severity and warmer waters. We found no evidence of population recovery in the years since the outbreak. Natural recovery in the southern half of the range is unlikely over the short term. Thus, assisted recovery will probably be required to restore the functional role of this predator on ecologically relevant time scales.

Infrequent Fluctuations in Temperature and Salinity May Enhance Feeding in Pisaster ochraceus (Asteroidea) but Not in Dendraster excentricus (Echinoidea) Larvae

AbstractIn recent years, low-salinity events characterized by high temperatures (18-23 °C) and low-salinity waters (20‰-22‰) have increased during late spring and summer, when many marine invertebrate larvae are developing. The present study examines the effects of low-salinity events on particle ingestion for larvae of two echinoderm species, the sea star Pisaster ochraceus and the sand dollar Dendraster excentricus. Larvae were exposed to high temperatures and low salinities for 24 hours, followed by feeding on the alga Isochrysis galbana in high or low salinity for another 10 minutes. Exposing Pisaster larvae to high temperatures and low salinities, followed by feeding in low salinity, did not impair ingestion rates. In fact, these larvae ingested particles at similar and sometimes higher rates than those in the controls. In sharp contrast, a 24-hour exposure to a high temperature and low salinity, followed by continued exposure to low salinity to feed, led to a decrease in the number of particles ingested by 8-arm Dendraster larvae. Larvae of both species captured very few particles when returned to 30‰ after a low-salinity event, indicating that continuous interruption of larval feeding by low-salinity events during development could be deleterious. Sand dollar larvae may have responded negatively to low-salinity events in our experiments because they are found in protected bays, where they may seldom experience these events.

Expansion of intertidal mussel beds following disease-driven reduction of a keystone predator

Disease shapes community composition by removing species with strong interactions. To test whether the absence of keystone predation due to disease produced changes to the species composition of rocky intertidal communities, we leverage a natural experiment involving mass mortality of the keystone predator Pisaster ochraceus from Sea Star Wasting Syndrome. Over four years, we measured dimensions of mussel beds, sizes of Mytilus californianus, mussel recruitment, and species composition on vertical rock walls at six rocky intertidal sites on the central California coast. We also assessed the relationship between changes in mussel cover and changes in sea star density across 33 sites along the North American Pacific coast using data from long-term monitoring. After four years, the lower boundary of the central California mussel beds shifted downward toward the water 18.7 ± 15.8 cm (SD) on the rock and 11.7 ± 11.0 cm in elevation, while the upper boundary remained unchanged. In central California, downward expansion and total area of the mussel bed were positively correlated with mussel recruitment but were not correlated with pre-disease sea star density or biomass. At a multi-region scale, changes in mussel percent cover were positively correlated with pre-disease sea star densities but not change in densities. Species composition of primary substrate holders and epibionts below the mussel bed remained similar across years. Extirpation of the community below the bed did not occur. Instead, this community became limited to a smaller spatial extent while the mussel bed expanded.

Sea star wasting disease pathology in Pisaster ochraceus shows a basal-to-surface process affecting color phenotypes differently

Sea star wasting disease (SSWD) refers to a suite of poorly described non-specific clinical signs including abnormal posture, epidermal ulceration, and limb autotomy (sloughing) causing mortalities of over 20 species of sea stars and subsequent ecological shifts throughout the northeastern Pacific. While SSWD is widely assumed to be infectious, with environmental conditions facilitating disease progression, few data exist on cellular changes associated with the disease. This is unfortunate, because such observations could inform mechanisms of disease pathogenesis and host susceptibility. Here, we replicated SSWD by exposing captive Pisaster ochraceus to a suite of non-infectious organic substances and show that development of gross lesions is a basal-to-surface process involving inflammation (e.g. infiltration of coelomocytes) of ossicles and mutable collagenous tissue, leading to epidermal ulceration. Affected sea stars also manifest increases in a heretofore undocumented coelomocyte type, spindle cells, that might be a useful marker of inflammation in this species. Finally, compared to purple morphs, orange P. ochraceus developed more severe lesions but survived longer. Longer-lived, and presumably more visible, severely-lesioned orange sea stars could have important demographic implications in terms of detectability of lesioned animals in the wild and measures of apparent prevalence of disease.

Microbial dysbiosis reflects disease resistance in diverse coral species

Disease outbreaks have caused significant declines of keystone coral species. While forecasting disease outbreaks based on environmental factors has progressed, we still lack a comparative understanding of susceptibility among coral species that would help predict disease impacts on coral communities. The present study compared the phenotypic and microbial responses of seven Caribbean coral species with diverse life-history strategies after exposure to white plague disease. Disease incidence and lesion progression rates were evaluated over a seven-day exposure. Coral microbiomes were sampled after lesion appearance or at the end of the experiment if no disease signs appeared. A spectrum of disease susceptibility was observed among the coral species that corresponded to microbial dysbiosis. This dysbiosis promotes greater disease susceptiblity in coral perhaps through different tolerant thresholds for change in the microbiome. The different disease susceptibility can affect coral’s ecological function and ultimately shape reef ecosystems.

MacKnight et al. compared the phenotypic and microbial responses of seven Caribbean coral species with diverse life-history strategies after exposure to white plague disease. The different species exhibited a spectrum of disease susceptibility and associated mortality that corresponded with their tolerances to microbial change, indicating that coral disease and microbial dysbiosis may ultimately shape reef ecosystems.

Latitudinal variation in long-term stability of North American rocky intertidal communities

Although long‐term ecological stability is often discussed as a community attribute, it is typically investigated at the species level (e.g. density, biomass), or as a univariate metric (e.g. species diversity). To provide a more comprehensive assessment of long‐term community stability, we used a multivariate similarity approach that included all species and their relative abundances.

We used data from 74 sites sampled annually from 2006 to 2017 to examine broad temporal and spatial patterns of change within rocky intertidal communities along the west coast of North America. We explored relationships between community change (inverse of stability) and the following potential drivers of change/stability: (a) marine heatwave events; (b) three attributes of biodiversity: richness, diversity and evenness and (c) presence of the mussel, Mytilus californianus, a dominant space holder and foundation species in this system.

At a broad scale, we found an inverse relationship between community stability and elevated water temperatures. In addition, we found substantial differences in stability among regions, with lower stability in the south, which may provide a glimpse into the patterns expected with a changing climate. At the site level, community stability was linked to high species richness and, perhaps counterintuitively, to low evenness, which could be a consequence of the dominance of mussels in this system.

Synthesis. Assessments of long‐term stability at the whole‐community level are rarely done but are key to a comprehensive understanding of the impacts of climate change. In communities structured around a spatially dominant species, long‐term stability can be linked to the stability of this ‘foundation species’, as well as to traditional predictors, such as species richness.

Bootstrap methods can help evaluate monitoring program performance to inform restoration as part of an adaptive management program

The objective of many fish and wildlife restoration programs is to utilize management actions to change the state of a system. Because restoration programs are often expensive, iteratively assessing whether the restoration is having the desired outcome is a critical aspect of learning how to inform ongoing and sampling designs to evaluate proposed restoration programs. We provide an example of how we are using data resampling as part of an adaptive restoration process to test the effectiveness of a restoration action and associated monitoring program to restore the degraded Lone Cabbage oyster reef in Suwannee Sound, Florida in the northeast Gulf of Mexico. We use a resampling framework through simulations to inform the progress of the restoration efforts by examining the direction and magnitude of the differences in live oyster counts between restored and unrestored (wild) reefs over time. In addition, we evaluated the effort (number of sites sampled) needed to determine the effect of restoration to understand how many surveys should be conducted in subsequent sampling seasons. These efforts allow us to provide timely insight into the effectiveness of both our monitoring efforts and restoration strategy which is of critical importance not only to the restoration of Lone Cabbage Reef but to larger restoration efforts within the Gulf of Mexico as part of the consolidated Deepwater Horizon settlements and funded restoration efforts.

Temporal and spatial variation in population structure among brooding sea stars in the genus Leptasterias

Temporal genetic studies of low-dispersing organisms are rare. Marine invertebrates lacking a planktonic larval stage are expected to have lower dispersal, low gene flow, and a higher potential for local adaptation than organisms with planktonic dispersal. Leptasterias is a genus of brooding sea stars containing several cryptic species complexes. Population genetic methods were used to resolve patterns of fine-scale population structure in central California Leptasterias species using three loci from nuclear and mitochondrial genomes. Historic samples (collected between 1897 and 1998) were compared to contemporary samples (collected between 2008 and 2014) to delineate changes in species distributions in space and time. Phylogenetic analysis of contemporary samples confirmed the presence of a bay-localized clade and revealed the presence of an additional bay-localized and previously undescribed clade of Leptasterias. Analysis of contemporary and historic samples indicates two clades are experiencing a constriction in their southern range limit and suggests a decrease in clade-specific abundance at sites at which they were once prevalent. Historic sampling revealed a dramatically different distribution of diversity along the California coastline compared to contemporary sampling and illustrates the importance of temporal genetic sampling in phylogeographic studies. These samples were collected prior to significant impacts of Sea Star Wasting Disease (SSWD) and represent an in-depth analysis of genetic structure over 117 years prior to the SSWD-associated mass die-off of Leptasterias.

Evidence That Microorganisms at the Animal-Water Interface Drive Sea Star Wasting Disease

Sea star wasting (SSW) disease describes a condition affecting asteroids that resulted in significant Northeastern Pacific population decline following a mass mortality event in 2013. The etiology of SSW is unresolved. We hypothesized that SSW is a sequela of microbial organic matter remineralization near respiratory surfaces, one consequence of which may be limited O₂ availability at the animal-water interface. Microbial assemblages inhabiting tissues and at the asteroid-water interface bore signatures of copiotroph proliferation before SSW onset, followed by the appearance of putatively facultative and strictly anaerobic taxa at the time of lesion genesis and as animals died. SSW lesions were induced in Pisaster ochraceus by enrichment with a variety of organic matter (OM) sources. These results together illustrate that depleted O₂ conditions at the animal-water interface may be established by heterotrophic microbial activity in response to organic matter loading. SSW was also induced by modestly (∼39%) depleted O₂ conditions in aquaria, suggesting that small perturbations in dissolved O₂ may exacerbate the condition. SSW susceptibility between species was significantly and positively correlated with surface rugosity, a key determinant of diffusive boundary layer thickness. Tissues of SSW-affected individuals collected in 2013–2014 bore δ¹⁵N signatures reflecting anaerobic processes, which suggests that this phenomenon may have affected asteroids during mass mortality at the time. The impacts of enhanced microbial activity and subsequent O₂ diffusion limitation may be more pronounced under higher temperatures due to lower O₂ solubility, in more rugose asteroid species due to restricted hydrodynamic flow, and in larger specimens due to their lower surface area to volume ratios which affects diffusive respiratory potential.

Diversity of Sea Star-Associated Densoviruses and Transcribed Endogenous Viral Elements of Densovirus Origin

The primary interest in sea star densoviruses, specifically SSaDV, has been their association with sea star wasting syndrome (SSWS), a disease that has decimated sea star populations across the West Coast of the United States since 2013. The association of SSaDV with SSWS was originally drawn from metagenomic analysis, which was further studied through field surveys using quantitative PCR (qPCR), with the conclusion that it was the most likely viral candidate in the metagenomic data based on its representation in symptomatic sea stars compared to asymptomatic sea stars. We reexamined the original metagenomic data with additional genomic data sets and found that SSaDV was 1 of 10 densoviruses present in the original data set and was no more represented in symptomatic sea stars than in asymptomatic sea stars. Instead, SSaDV appears to be a widespread, generalist virus that exists among a large diversity of densoviruses present in sea star populations.

A viral etiology of sea star wasting syndrome (SSWS) was originally explored with virus-sized material challenge experiments, field surveys, and metagenomics, leading to the conclusion that a densovirus is the predominant DNA virus associated with this syndrome and, thus, the most promising viral candidate pathogen. Single-stranded DNA viruses are, however, highly diverse and pervasive among eukaryotic organisms, which we hypothesize may confound the association between densoviruses and SSWS. To test this hypothesis and assess the association of densoviruses with SSWS, we compiled past metagenomic data with new metagenomic-derived viral genomes from sea stars collected from Antarctica, California, Washington, and Alaska. We used 179 publicly available sea star transcriptomes to complement our approaches for densovirus discovery. Lastly, we focus the study on sea star-associated densovirus (SSaDV), the first sea star densovirus discovered, by documenting its biogeography and putative tissue tropism. Transcriptomes contained only endogenized densovirus elements similar to the NS1 gene, while numerous extant densoviral genomes were recovered from viral metagenomes. SSaDV was associated with nearly all tested species from southern California to Alaska, and in contrast to previous work, we show that SSaDV is one genotype among a high diversity of densoviruses present in sea stars across the West Coast of the United States and globally that are commonly associated with grossly normal (i.e., healthy or asymptomatic) animals. The diversity and ubiquity of these viruses in sea stars confound the original hypothesis that one densovirus is the etiological agent of SSWS.

IMPORTANCE The primary interest in sea star densoviruses, specifically SSaDV, has been their association with sea star wasting syndrome (SSWS), a disease that has decimated sea star populations across the West Coast of the United States since 2013. The association of SSaDV with SSWS was originally drawn from metagenomic analysis, which was further studied through field surveys using quantitative PCR (qPCR), with the conclusion that it was the most likely viral candidate in the metagenomic data based on its representation in symptomatic sea stars compared to asymptomatic sea stars. We reexamined the original metagenomic data with additional genomic data sets and found that SSaDV was 1 of 10 densoviruses present in the original data set and was no more represented in symptomatic sea stars than in asymptomatic sea stars. Instead, SSaDV appears to be a widespread, generalist virus that exists among a large diversity of densoviruses present in sea star populations.

Perception and Conflict in Conservation: The Rashomon Effect

Conflict is a common feature in conservation and resource management. Environmental conflicts are frequently attributed to differences in values; however, variability in the perception of facts, rooted in social and cultural differences also underlies conflicts. Such differences in perception have been termed the Rashomon effect after the Kurosawa film. In the present article, we explore a conservation Rashomon effect—a phenomenon that results from a combination of differences in perspective, plausible alternative perspectives of a conservation issue, and the absence of evidence to elevate one perspective above others. As a remedy to the Rashomon effect, policy-makers have turned to scientists as honest brokers who share a common environmental reality. We evaluate this supposition and suggest that scientists, themselves, display Rashomon effects. We suggest that Rashomon effects can be reduced by acknowledging the plurality of reality, embracing epistemic pluralism, and prioritizing an inclusive process of resource management.

Models with environmental drivers offer a plausible mechanism for the rapid spread of infectious disease outbreaks in marine organisms

The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 along the entire North American Pacific coast. Disease dynamics did not manifest as the typical travelling wave of reaction-diffusion epidemiological model, suggesting that other environmental factors might have played some role. To help explore how external factors might trigger disease, we built a coupled oceanographic-epidemiological model and contrasted three hypotheses on the influence of temperature on disease transmission and pathogenicity. Models that linked mortality to sea surface temperature gave patterns more consistent with observed data on sea star wasting disease, which suggests that environmental stress could explain why some marine diseases seem to spread so fast and have region-wide impacts on host populations.

An initial comparative genomic autopsy of wasting disease in sea stars

Beginning in 2013, sea stars throughout the Eastern North Pacific were decimated by wasting disease, also known as "asteroid idiopathic wasting syndrome" (AIWS) due to its elusive aetiology. The geographic extent and taxonomic scale of AIWS meant events leading up to the outbreak were heterogeneous, multifaceted, and oftentimes unobserved; progression from morbidity to death was rapid, leaving few tell-tale symptoms. Here, we take a forensic genomic approach to discover candidate genes that may help explain sea star wasting syndrome. We report the first genome and annotation for Pisaster ochraceus, along with differential gene expression (DGE) analyses in four size classes, three tissue types, and in symptomatic and asymptomatic individuals. We integrate nucleotide polymorphisms associated with survivors of the wasting disease outbreak, DGE associated with temperature treatments in P. ochraceus, and DGE associated with wasting in another asteroid Pycnopodia helianthoides. In P. ochraceus, we found DGE across all tissues, among size classes, and between asymptomatic and symptomatic individuals; the strongest wasting-associated DGE signal was in pyloric caecum. We also found previously identified outlier loci co-occur with differentially expressed genes. In cross-species comparisons of symptomatic and asymptomatic individuals, consistent responses distinguish genes associated with invertebrate innate immunity and chemical defence, consistent with context-dependent stress responses, defensive apoptosis, and tissue degradation. Our analyses thus highlight genomic constituents that may link suspected environmental drivers (elevated temperature) with intrinsic differences among individuals (age/size, alleles associated with susceptibility) that elicit organismal responses (e.g., coelomocyte proliferation) and manifest as sea star wasting mass mortality.

Coelomic Fluid Evaluation in Pisaster ochraceus Affected by Sea Star Wasting Syndrome: Evidence of Osmodysregulation, Calcium Homeostasis Derangement, and Coelomocyte Responses

Sea Star Wasting Syndrome (SSWS) is one of the largest marine wildlife die-offs ever recorded, killing millions of sea stars from more than 20 Asteroid species from Alaska to Mexico from 2013 to 2015 from yet undetermined cause(s). Coelomic fluid surrounds the sea star's organs, playing critical roles in numerous systemic processes, including nutrient transportation and immune functions. Coelomocytes, which are cellular components of coelomic fluid and considered functionally equivalent to vertebrate leukocytes, are responsible for innate cell-mediated immunity. The objectives of this study were to (1) evaluate changes in coelomic fluid chemistry, coelomocyte counts, and cytology from ochre sea stars (Pisaster ochraceus) (n = 55) with clinical signs consistent with SSWS at varying intensity (SSWS score 1: n = 4, score 2: n = 2, score 3: n = 3, score 4: n = 18, score 5: n = 26) in comparison to coelomic fluid from clinically normal sea stars (n = 26) and to (2) correlate SSWS score with cellular and biochemical analytes. SSWS-affected sea stars had wider ranges of all electrolytes, except calcium; statistically significantly higher chloride, osmolality, and total protein; lower calcium; and higher coelomocyte counts when compared to clinically normal sea stars maintained under identical environmental conditions. Free and/or phagocytized bacteria were noted in 29% (16 of 55) coelomic fluid samples from SSWS-affected sea stars but were absent in clinically normal sea stars. SSWS score correlated significantly with increasing chloride concentration, osmolality, and coelomocyte counts. These chemistry and cytological findings in coelomic fluid of SSWS-affected sea stars provide insight into the pathophysiology of SSWS as these results suggest osmo- and calcium dysregulation, coelomocyte responses, and presumptive opportunistic bacterial infection in SSWS-affected sea stars. This information provides potential future research applications for the development of treatment strategies for sea stars in managed care and for understanding the complexity of various biochemical and cellular pathophysiological mechanisms involved in sea star wasting.

Sea star wasting disease demography and etiology in the brooding sea star Leptasterias spp

Sea star wasting disease (SSWD) describes a suite of disease signs believed to have led to catastrophic die-offs in many asteroid species, beginning in 2013. While most studies have focused on large, easily visible sea stars with widely-dispersing larvae, less information is available on the effect of this disease outbreak on smaller sea star species, such as the six-armed sea star Leptasterias spp. Unlike many larger sea stars, Leptasterias brood non-feeding young instead of broadcast-spawning planktonic larvae. Limited dispersal and thus limited gene flow may make these sea stars more vulnerable to local selective pressures, such as disease outbreaks. Here, we examined Leptasterias populations at sites along the California coast and documented abundance changes coincident with recent Pacific coast SSWD in 2014. Detection of Leptasterias in central California declined, and Leptasterias were not detected at multiple sites clustered around the San Francisco Bay outflow in the most recent surveys. Additionally, we categorized disease signs in Leptasterias in the field and laboratory, which mirrored those seen in larger sea stars in both settings. Finally, we found that magnesium chloride (MgCl2) slowed the progression of physical deterioration related to SSWD when applied to sea stars in the laboratory, suggesting that MgCl2 may prolong the survival of diseased individuals.

Predator identity dominates non-consumptive effects in a disease-impacted rocky shore food web

Predicting the effects of predator diversity loss on food webs is challenging, because predators can both consume and induce behavioral responses in their prey (i.e., non-consumptive effects or NCEs). Studies manipulating predator diversity and investigating NCEs are rare, especially in marine systems. Recently, a severe outbreak of sea star wasting syndrome (SSWS) on the west coast of North America resulted in unprecedented declines of the sea star Pisaster ochraceus. We investigated the consequences of Pisaster loss on an abundant grazer, the black turban snail Tegula funebralis, through NCEs. We combined a laboratory experiment and field surveys to examine the importance of identity vs. diversity in a predator assemblage (Pisaster, crabs, and octopuses) on Tegula behavior, feeding, and growth. Laboratory and field results indicated that predator identity, not diversity, drives Tegula behavior and causes NCEs. Mesocosm treatments with Pisaster caused greater NCEs on Tegula than assemblages without Pisaster. Tegula's distribution in the field, which is driven primarily by anti-predator behavior, was strongly associated only with Pisaster abundance, and not with the abundance of crabs, octopuses, and other predatory sea stars (Leptasterias spp.). We conclude that Pisaster primarily drives Tegula vertical distribution and may be having strong NCEs on Tegula on northern California rocky shores. Furthermore, predator diversity in northern California does not provide functional redundancy, in terms of NCEs on Tegula, to buffer the system from Pisaster loss. Thus, predator-induced vertical distributions and grazing suppression may not be maintained in areas where Pisaster populations are reduced or slow to recover from SSWS.

Coelomic Fluid Evaluation in Clinically Normal Ochre Sea Stars Pisaster ochraceus: Cell Counts, Cytology, and Biochemistry Reference Intervals

Coelomic fluid sampling is a noninvasive technique that is used to access the body fluid of sea stars for diagnostics and research. Given recent mortality events including sea star wasting disease, which has killed millions of sea stars along the Pacific coast since 2013, there is a need for validated diagnostic tests to evaluate sea star health. The objectives of this study were to establish coelomic fluid reference intervals for clinically normal ochre sea stars Pisaster ochraceus in an open system aquarium, to describe the cytologic findings, and to compare the chemistries of coelomic fluid with open system tank water. Coelomic fluid from 26 clinically normal sea stars was sampled for coelomocyte counts, cytologic evaluation, and biochemical analysis including magnesium, sodium, potassium, chloride, calcium, and total protein. The number of coelomocytes and total protein did not fit normal distribution and were excluded from analyses. Reference intervals were established for other chemistry analytes. There was no statistical difference in biochemistries between sea star coelomic fluid and water from five open system tanks, which supports previous evidence that sea stars are osmoconformers. Very low numbers of coelomocytes were observed cytologically. These results provide a useful baseline and diagnostic tool for health assessments of sea stars.

Climate and fishing drive regime shifts in consumer-mediated nutrient cycling in kelp forests

Globally, anthropogenic pressures are reducing the abundances of marine species and altering ecosystems through modification of trophic interactions. Yet, consumer declines also disrupt important bottom-up processes, like nutrient recycling, which are critical for ecosystem functioning. Consumer-mediated nutrient dynamics (CND) is now considered a major biogeochemical component of most ecosystems, but lacking long-term studies, it is difficult to predict how CND will respond to accelerating disturbances in the wake of global change. To aid such predictions, we coupled empirical ammonium excretion rates with an 18-year time series of the standing biomass of common benthic macroinvertebrates in southern California kelp forests. This time series of excretion rates encompassed an extended period of extreme ocean warming, disease outbreaks, and the abolishment of fishing at two of our study sites, allowing us to assess kelp forest CND across a wide range of environmental conditions. At their peak, reef invertebrates supplied an average of 18.3 ± 3.0 µmol NH4 +  m-2  hr-1 to kelp forests when sea stars were regionally abundant, but dropped to 3.5 ± 1.0 µmol NH4 +  m-2  hr-1 following their mass mortality due to disease during a prolonged period of extreme warming. However, a coincident increase in the abundance of the California spiny lobster, Palinurus interupptus (Randall, 1840), likely in response to both reduced fishing and a warmer ocean, compensated for much of the recycled ammonium lost to sea star mortality. Both lobsters and sea stars are widely recognized as key predators that can profoundly influence community structure in benthic marine systems. Our study is the first to demonstrate their importance in nutrient cycling, thus expanding their roles in the ecosystem. Climate change is increasing the frequency and severity of warming events, and rising human populations are intensifying fishing pressure in coastal ecosystems worldwide. Our study documents how these projected global changes can drive regime shifts in CND and fundamentally alter a critical ecosystem function.

Public participation in science: How citizen science initiatives in healthcare and the environment are opening up new directions in research

Public participation in science is opening up new research avenues. Recognising the potential of citizen science in fields such as health care could help science to better meet societal needs.

Reciprocal abundance shifts of the intertidal sea stars, Evasterias troschelii and Pisaster ochraceus, following sea star wasting disease

Disease emergence occurs within the context of ecological communities, and disease driven declines in host populations can lead to complex direct and indirect ecological effects. Varying effects of a single disease among multiple susceptible hosts could benefit relatively resistant species. Beginning in 2013, an outbreak of sea star wasting disease (SSWD) led to population declines of many sea star species along the west coast of North America. Through field surveys and laboratory experiments, we investigated how and why the relative abundances of two co-occurring sea star species, Evasterias troschelii and Pisaster ochraceus, shifted during the ongoing wasting epidemic in Burrard Inlet, British Columbia, Canada. We hypothesized that Evasterias is competitively inferior to Pisaster but more resistant to SSWD. Thus, we predicted that SSWD-induced declines of Pisaster could mitigate the negative effects of SSWD on Evasterias, as the latter would experience competitive release. We document shifts in sea star abundance from 2008-2017: Pisaster abundance and mean size declined during the outbreak, while Evasterias abundance increased from relatively rare to numerically dominant within the intertidal. When exposed to symptomatic sea stars, Pisaster and Evasterias both showed signs of SSWD, but transmission and susceptibility was lower in Evasterias. Despite diet overlap documented in our field surveys, Evasterias was not outcompeted by Pisaster in laboratory trails conducted with the relatively small Pisaster available after the outbreak. Interference competition with larger Pisaster, or prey exploitation by Pisaster during the summer when Evasterias is primarily subtidal, may explain the rarity of Evasterias prior to Pisaster declines. Our results suggest that indirect effects mediated by competition can mask some of the direct effects of disease outbreaks, and the combination of direct and indirect effects will determine the restructuring of a community after disturbance.

Heat Waves, the New Normal: Summertime Temperature Extremes Will Impact Animals, Ecosystems, and Human Communities

A consequence of climate change is the increased frequency and severity of extreme heat waves. This is occurring now as most of the warmest summers and most intense heat waves ever recorded have been during the past decade. In this review, I describe the ways in which animals and human populations are likely to respond to increased extreme heat, suggest how to study those responses, and reflect on the importance of those studies for countering the devastating impacts of climate change.

Disease epidemic and a marine heat wave are associated with the continental-scale collapse of a pivotal predator (Pycnopodia helianthoides)

Multihost infectious disease outbreaks have endangered wildlife, causing extinction of frogs and endemic birds, and widespread declines of bats, corals, and abalone. Since 2013, a sea star wasting disease has affected >20 sea star species from Mexico to Alaska. The common, predatory sunflower star (Pycnopodia helianthoides), shown to be highly susceptible to sea star wasting disease, has been extirpated across most of its range. Diver surveys conducted in shallow nearshore waters (n = 10,956; 2006-2017) from California to Alaska and deep offshore (55 to 1280 m) trawl surveys from California to Washington (n = 8968; 2004-2016) reveal 80 to 100% declines across a ~3000-km range. Furthermore, timing of peak declines in nearshore waters coincided with anomalously warm sea surface temperatures. The rapid, widespread decline of this pivotal subtidal predator threatens its persistence and may have large ecosystem-level consequences.

Microbiome shifts with onset and progression of Sea Star Wasting Disease revealed through time course sampling

The recent outbreak of Sea Star Wasting Disease (SSWD) is one of the largest marine epizootics in history, but the host-associated microbial community changes specific to disease progression have not been characterized. Here, we sampled the microbiomes of ochre sea stars, Pisaster ochraceus, through time as animals stayed healthy or became sick and died with SSWD. We found community-wide differences in the microbiomes of sick and healthy sea stars, changes in microbial community composition through disease progression, and a decrease in species richness of the microbiome in late stages of SSWD. Known beneficial taxa (Pseudoalteromonas spp.) decreased in abundance at symptom onset and through disease progression, while known pathogenic (Tenacibaculum spp.) and putatively opportunistic bacteria (Polaribacter spp. and Phaeobacter spp.) increased in abundance in early and late disease stages. Functional profiling revealed microbes more abundant in healthy animals performed functions that inhibit growth of other microbes, including pathogen detection, biosynthesis of secondary metabolites, and degradation of xenobiotics. Changes in microbial composition with disease onset and progression suggest that a microbial imbalance of the host could lead to SSWD or be a consequence of infection by another pathogen. This work highlights the importance of the microbiome in SSWD and also suggests that a healthy microbiome may help confer resistance to SSWD.

Exploring the pathology of an epidermal disease affecting a circum-Antarctic sea star

Over the past decade, unusual mortality outbreaks have decimated echinoderm populations over broad geographic regions, raising awareness globally of the importance of investigating such events. Echinoderms are key components of marine benthos for top-down and bottom-up regulations of plants and animals; population declines of these individuals can have significant ecosystem-wide effects. Here we describe the first case study of an outbreak affecting Antarctic echinoderms and consisting of an ulcerative epidermal disease affecting ~10% of the population of the keystone asteroid predator Odontaster validus at Deception Island, Antarctica. This event was first detected in the Austral summer 2012–2013, coinciding with unprecedented high seawater temperatures and increased seismicity. Histological analyses revealed epidermal ulceration, inflammation, and necrosis in diseased animals. Bacterial and fungal alpha diversity was consistently lower and of different composition in lesioned versus unaffected tissues (32.87% and 16.94% shared bacterial and fungal operational taxonomic units OTUs respectively). The microbiome of healthy stars was more consistent across individuals than in diseased specimens suggesting microbial dysbiosis, especially in the lesion fronts. Because these microbes were not associated with tissue damage at the microscopic level, their contribution to the development of epidermal lesions remains unclear. Our study reveals that disease events are reaching echinoderms as far as the polar regions thereby highlighting the need to develop a greater understanding of the microbiology and physiology of marine diseases and ecosystems health, especially in the era of global warming.

Decimation by sea star wasting disease and rapid genetic change in a keystone species, Pisaster ochraceus

Standing genetic variation enables or restricts a population's capacity to respond to changing conditions, including the extreme disturbances expected to increase in frequency and intensity with continuing anthropogenic climate change. However, we know little about how populations might respond to extreme events with rapid genetic shifts, or how population dynamics may influence and be influenced by population genomic change. We use a range-wide epizootic, sea star wasting disease, that onset in mid-2013 and caused mass mortality in Pisaster ochraceus to explore how a keystone marine species responded to an extreme perturbation. We integrated field surveys with restriction site-associated DNA sequencing data to (i) describe the population dynamics of mortality and recovery, and (ii) compare allele frequencies in mature P. ochraceus before the disease outbreak with allele frequencies in adults and new juveniles after the outbreak, to identify whether selection may have occurred. We found P. ochraceus suffered 81% mortality in the study region between 2012 and 2015, and experienced a concurrent 74-fold increase in recruitment beginning in late 2013. Comparison of pre- and postoutbreak adults revealed significant allele frequency changes at three loci, which showed consistent changes across the large majority of locations. Allele frequency shifts in juvenile P. ochraceus (spawned from premortality adults) were consistent with those seen in adult survivors. Such parallel shifts suggest detectable signals of selection and highlight the potential for persistence of this change in subsequent generations, which may influence the resilience of this keystone species to future outbreaks.