Pacific salmon (Oncorhynchus spp.) support coastal and freshwater ecosystems, economies and cultures, but many populations have declined. We used priority threat management (PTM), a decision‐support ...framework for prioritizing conservation investments, to identify management strategies that could support thriving populations of wild salmon over 25 years. We evaluated the potential benefits of 14 strategies spanning fisheries, habitat, pollution, pathogens, hatcheries and predation management dimensions on 19 conservation units (CUs)—genetically and ecologically distinct populations—of the five Pacific salmon species in the lower Fraser River, British Columbia, Canada.
The PTM assessment indicated that under the current trajectory of ‘business as usual’, zero CUs were predicted to have >50% chance of thriving in 25 years. Implementation of all management strategies at an annual investment between 45 and 110 million CAD was, however, predicted to achieve >50% chance of thriving for most CUs (n = 16), with nearly half (seven CUs) having a > 60% chance, indicating there is a pathway towards recovery for most populations if we invest now. In fact, substantial gains could be made by investing in five combined habitat strategies, costing 20M CAD annually. These habitat strategies were estimated to bring 14 of 19 salmon CUs above this 50% threshold.
Co‐governance between First Nation and provincial and federal Canadian governments to manage salmon populations and harvest, and improved CU‐level monitoring emerged from the expert elicitation as critical ‘enabling’ strategies. By improving the feasibility of different management options, co‐governance brought an additional five CUs above the 60% threshold.
Synthesis and applications. Supporting wild salmon in the face of cumulative threats will require strategic investment in effective management strategies, as identified by this priority threat management (PTM) assessment. PTM uses the best available data to objectively assess the potential outcomes of management alternatives. With renewed commitments from provincial and federal Canadian governments to protect and restore salmon populations and their habitats, positive conservation outcomes following implementation of targeted management strategies may be within reach.
Supporting wild salmon in the face of cumulative threats will require strategic investment in effective management strategies, as identified by this priority threat management (PTM) assessment. PTM uses the best available data to objectively assess the potential outcomes of management alternatives. With renewed commitments from provincial and federal Canadian governments to protect and restore salmon populations and their habitats, positive conservation outcomes following implementation of targeted management strategies may be within reach.
Relationships between abundance--body size and trophic position--body size can reveal size structuring in food webs and test ecological theory. Although there is considerable evidence of size ...structuring in temperate aquatic food webs, little is known about the structure of tropical coral reef food webs. Here, we use underwater visual-census data and nitrogen stable isotope analysis to test if coral reef fish communities (i) are size structured and (ii) follow metabolic scaling rules. After examining individuals from over 160 species spanning four orders of magnitude in body size, we show that abundance scaled negatively with body size and, as predicted, individuals sharing energy through predation (carnivorous fishes) scaled more steeply than those individuals sharing a common energy source (herbivorous fishes). Estimated size spectra were, however, shallower than predicted by metabolic theory. Trophic position scaled positively with body size across species and across individuals, providing novel evidence of size structuring in a diverse tropical food web. Size-based approaches hold great promise for integrating the complexities of food webs into simple quantitative measures, thus providing new insights into the structure and function of aquatic ecosystems.
Variability in primary productivity and fishing pressure can shape the abundance, species composition, and diversity of marine life. Though parasites comprise nearly half of marine species, their ...responses to these important forces remain little explored. We quantified parasite assemblages at two spatial scales, across a gradient in productivity and fishing pressure that spans six coral islands of the Line Islands archipelago and within the largest Line Island, Kiritimati, which experiences a west-to-east gradient in fishing pressure and upwelling-driven productivity. In the across-islands data set, we found that increasing productivity was correlated with increased parasite abundance overall, but that the effects of productivity differed among parasite groups. Trophically transmitted parasites increased in abundance with increasing productivity, but directly transmitted parasites did not exhibit significant changes. This probably arises because productivity has stronger effects on the abundance of the planktonic crustaceans and herbivorous snails that serve as the intermediate hosts of trophically transmitted parasites than on the higher-trophic level fishes that are the sole hosts of directly transmitted parasites. We also found that specialist parasites increased in response to increasing productivity, while generalists did not, possibly because specialist parasites tend to be more strongly limited by host availability than are generalist parasites. After the effect of productivity was controlled for, fishing was correlated with decreases in the abundance of trophically transmitted parasites, while directly transmitted parasites appeared to track host density; we observed increases in the abundance of parasites using hosts that experienced fishing-driven compensatory increases in abundance. The within-island data set confirmed these patterns for the combined effects of productivity and fishing on parasite abundance, suggesting that our conclusions are robust across a span of spatial scales. Overall, these results indicate that there are strong and variable effects of anthropogenic and natural drivers on parasite abundance and taxonomic richness. These effects are likely to be mediated by parasite traits, particularly by parasite transmission strategies.
This special issue honours Rob Peters’ outstanding contributions to the field of aquatic ecology. It focuses on the size spectrum approach — in which individual organisms, rather than species, are ...the most basic biological unit — and highlights applications of this approach to fisheries management. The 21 papers in this issue cover three subject areas: (i) the use of size spectra to characterize variation in community structure, (ii) the development of size-based models of ecosystem dynamics to address fisheries questions, and (iii) applications of size-based theory to examine the consequences of variation in predator–prey size relationships, body size – trophic level relationships, and body size – life history relationships. The empirical studies herein demonstrate the utility of size spectra as indicators of population or community structure and for detecting impacts associated with environmental change. Future research focused on refining size-based sampling methods, standardizing metrics and analytical methods, understanding model sensitivity to the underlying assumptions, and comparative studies across ecosystems will enhance our ability to reliably interpret changes in size spectrum characteristics, thus facilitating their use as indicators of ecological change.
Many indices have been proposed to measure functional diversity and its four distinct dimensions: functional richness, evenness, divergence and redundancy. Identifying indices that reliably measure ...the functional diversity dimension(s) of interest requires careful testing of how each index responds to species' traits and abundance distributions. In the absence of a convenient simulation tool, tests with artificial data have to date explored only a limited number of scenarios or have altered trait and abundance distributions only indirectly based on principles of evolution and community assembly.
We provide simul.comms, an R function that allows users to test the efficacy of functional diversity indices by easily creating artificial species communities with user‐specified abundance and trait distributions for continuous, ordinal and categorical traits. To illustrate the function's utility, we examine the performance of R, a recently published abundance‐sensitive index for functional redundancy. We use two approaches to designing simulation tests for this example analysis. The first uses simul.comms to create six separate sets of artificial communities to qualitatively assess how R responds to predictable changes in functional redundancy. The second uses simul.comms to independently alter seven community composition parameters, whose influence on R is then examined quantitatively via effect sizes in linear regression.
Our analyses indicate that R broadly mirrors expected changes in functional redundancy and predictably responds to changes in community composition parameters. R appears, however, to primarily reflect trait distributions, responding minimally to variance in abundance and counter‐intuitively to abundance range. Further refinement of tools to measure functional redundancy may therefore be desirable.
The R tool we provide should assist with refining functional diversity measures, a critical step towards improving our ability to understand and mitigate the impacts of biodiversity loss on ecosystem functioning. Because simul.comms simply produces two linked matrices, a species‐by‐traits matrix and a site‐by‐species abundance matrix, it may be equally valuable in exploring questions and analytical approaches in other areas of community ecology.
Quantification and mapping of surficial seabed sediment organic carbon have wide-scale relevance for marine ecology, geology and environmental resource management, with carbon densities and ...accumulation rates being a major indicator of geological history, ecological function and ecosystem service provisioning, including the potential to contribute to nature-based climate change mitigation. While global analyses can appear to provide a definitive understanding of the spatial distribution of sediment carbon, regional maps may be constructed at finer resolutions and can utilise targeted data syntheses and refined spatial data products and therefore have the potential to improve these estimates. Here, we report a national systematic review of data on organic carbon content in seabed sediments across Canada and combine this with a synthesis and unification of the best available data on sediment composition, seafloor morphology, hydrology, chemistry and geographic settings within a machine learning mapping framework. Predictive quantitative maps of mud content, dry bulk density, organic carbon content and organic carbon density were produced along with cell-specific estimates of their uncertainty at 200 m resolution across 4 489 235 km2 of the Canadian continental margin (92.6 % of the seafloor area above 2500 m) (https://doi.org/10.5683/SP3/ICHVVA, Epstein et al., 2024). Fine-scale variation in carbon stocks was identified across the Canadian continental margin, particularly in the Pacific Ocean and Atlantic Ocean regions. Overall, we estimate the standing stock of organic carbon in the top 30 cm of surficial seabed sediments across the Canadian shelf and slope to be 10.9 Gt (7.0–16.0 Gt). Increased empirical sediment data collection and higher precision in spatial environmental data layers could significantly reduce uncertainty and increase accuracy in these products over time.
Our ability to understand natural constraints on coral reef benthic communities requires quantitative assessment of the relative strengths of abiotic and biotic processes across large spatial scales. ...Here, we combine underwater images, visual censuses and remote sensing data for 1566 sites across 34 islands spanning the central-western Pacific Ocean, to empirically assess the relative roles of abiotic and grazing processes in determining the prevalence of calcifying organisms and fleshy algae on coral reefs. We used regression trees to identify the major predictors of benthic composition and to test whether anthropogenic stress at inhabited islands decouples natural relationships. We show that sea surface temperature, wave energy, oceanic productivity and aragonite saturation strongly influence benthic community composition; overlooking these factors may bias expectations of calcified reef states. Maintenance of grazing biomass above a relatively low threshold (~ 10–20 kg ha
−1
) may also prevent transitions to algal-dominated states, providing a tangible management target for rebuilding overexploited herbivore populations. Biophysical relationships did not decouple at inhabited islands, indicating that abiotic influences remain important macroscale processes, even at chronically disturbed reefs. However, spatial autocorrelation among inhabited reefs was substantial and exceeded abiotic and grazing influences, suggesting that natural constraints on reef benthos were superseded by unmeasured anthropogenic impacts. Evidence of strong abiotic influences on reef benthic communities underscores their importance in specifying quantitative targets for coral reef management and restoration that are realistic within the context of local conditions.
Climate change-amplified marine heatwaves can drive extensive mortality in foundation species. However, a paucity of longitudinal genomic datasets has impeded understanding of how these rapid ...selection events alter cryptic genetic structure. Heatwave impacts may be exacerbated in species that engage in obligate symbioses, where the genetics of multiple coevolving taxa may be affected. Here, we tracked the symbiotic associations of reef-building corals for 6 years through a prolonged heatwave, including known survivorship for 79 of 315 colonies. Coral genetics strongly predicted survival of the ubiquitous coral,
(massive growth form), with variable survival (15 to 61%) across three morphologically indistinguishable-but genetically distinct-lineages. The heatwave also disrupted strong associations between these coral lineages and their algal symbionts (family Symbiodiniaceae), with symbiotic turnover in some colonies, resulting in reduced specificity across lineages. These results highlight how heatwaves can threaten cryptic genotypes and decouple otherwise tightly coevolved relationships between hosts and symbionts.
Climate change–amplified marine heatwaves can drive extensive mortality in foundation species. However, a paucity of longitudinal genomic datasets has impeded understanding of how these rapid ...selection events alter cryptic genetic structure. Heatwave impacts may be exacerbated in species that engage in obligate symbioses, where the genetics of multiple coevolving taxa may be affected. Here, we tracked the symbiotic associations of reef-building corals for 6 years through a prolonged heatwave, including known survivorship for 79 of 315 colonies. Coral genetics strongly predicted survival of the ubiquitous coral,
Porites
(massive growth form), with variable survival (15 to 61%) across three morphologically indistinguishable—but genetically distinct—lineages. The heatwave also disrupted strong associations between these coral lineages and their algal symbionts (family Symbiodiniaceae), with symbiotic turnover in some colonies, resulting in reduced specificity across lineages. These results highlight how heatwaves can threaten cryptic genotypes and decouple otherwise tightly coevolved relationships between hosts and symbionts.
Marine heatwaves differentially impact cryptic coral lineages and decouple tight relationships between host and symbiont.
Corals are imminently threatened by climate change-amplified marine heatwaves. However, how to conserve coral reefs remains unclear, since those without local anthropogenic disturbances often seem ...equally or more susceptible to thermal stress as impacted ones. We disentangle this apparent paradox, revealing that the relationship between reef disturbance and heatwave impacts depends upon the scale of biological organization. We show that a tropical heatwave of globally unprecedented duration (~1 year) culminated in an 89% loss of hard coral cover. At the community level, losses depended on pre-heatwave community structure, with undisturbed sites, which were dominated by competitive corals, undergoing the greatest losses. In contrast, at the species level, survivorship of individual corals typically declined as local disturbance intensified. Our study reveals both that prolonged heatwaves projected under climate change will still have winners and losers and that local disturbance can impair survival of coral species even under such extreme conditions.
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