Cost-benefit analysis of ecosystem modeling to support fisheries management.

Mathematical and statistical models underlie many of the world's most important fisheries management decisions. Since the 19th century, difficulty calibrating and fitting such models has been used to justify the selection of simple, stationary, single-species models to aid tactical fisheries management decisions. Whereas these justifications are reasonable, it is imperative that we quantify the value of different levels of model complexity for supporting fisheries management, especially given a changing climate, where old methodologies may no longer perform as well as in the past. Here we argue that cost-benefit analysis is an ideal lens to assess the value of model complexity in fisheries management. While some studies have reported the benefits of model complexity in fisheries, modeling costs are rarely considered. In the absence of cost data in the literature, we report, as a starting point, relative costs of single-species stock assessment and marine ecosystem models from two Australian organizations. We found that costs varied by two orders of magnitude, and that ecosystem model costs increased with model complexity. Using these costs, we walk through a hypothetical example of cost-benefit analysis. The demonstration is intended to catalyze the reporting of modeling costs and benefits.

Evaluating ecological benefits of oceanic protected areas.

Oceans beyond the continental shelf represent the largest yet least protected environments. The new agreement to increase protection targets to 30% by 2030 and the recent United Nations (UN) High Seas Treaty try to address this gap, and an increase in the declaration of oceanic Marine Protected Areas (oMPAs) in waters beyond 200 m in depth is likely. Here we find that there is contradictory evidence concerning the benefits of oMPAs in terms of protecting pelagic habitats, providing refuge for highly mobile species, and potential fisheries benefits. We discover a mismatch between oMPA management objectives focusing on protection of pelagic habitats and biodiversity, and scientific research focusing on fisheries benefits. We suggest that the solution is to harness emerging technologies to monitor inside and outside oMPAs.

Improving the biological realism of predator-prey size relationships in food web models alters ecosystem dynamics.

Body-size relationships between predators and prey exhibit remarkable diversity. However, the assumption that predators typically consume proportionally smaller prey often underlies size-dependent predation in ecosystem models. In reality, some animals can consume larger prey or exhibit limited changes in prey size as they grow larger themselves. These distinct predator-prey size relationships challenge the conventional assumptions of traditional size-based models. Cephalopods, with their diverse feeding behaviours and life histories, offer an excellent case study to investigate the impact of greater biological realism in predator-prey size relationships on energy flow within a size-structured ecosystem model. By categorizing cephalopods into high and low-activity groups, in line with empirically derived, distinct predator-prey size relationships, we found that incorporating greater biological realism in size-based feeding reduced ecosystem biomass and production, while simultaneously increasing biomass stability and turnover. Our results have broad implications for ecosystem modelling, since distinct predator-prey size relationships extend beyond cephalopods, encompassing a wide array of major taxonomic groups from filter-feeding fishes to baleen whales. Incorporating a diversity of size-based feeding in food web models can enhance their ecological and predictive accuracy when studying ecosystem dynamics.

Priority areas to protect mangroves and maximise ecosystem services.

Anthropogenic activities threaten global biodiversity and ecosystem services. Yet, area-based conservation efforts typically target biodiversity protection whilst minimising conflict with economic activities, failing to consider ecosystem services. Here we identify priority areas that maximise both the protection of mangrove biodiversity and their ecosystem services. We reveal that despite 13.5% of the mangrove distribution being currently strictly protected, all mangrove species are not adequately represented and many areas that provide disproportionally large ecosystem services are missed. Optimising the placement of future conservation efforts to protect 30% of global mangroves potentially safeguards an additional 16.3 billion USD of coastal property value, 6.1 million people, 1173.1 Tg C, and 50.7 million fisher days yr-1. Our findings suggest that there is a pressing need for including ecosystem services in protected area design and that strategic prioritisation and coordination of mangrove conservation could provide substantial benefits to human wellbeing.

Gelatinous larvacean zooplankton can enhance trophic transfer and carbon sequestration.

Larvaceans are gelatinous zooplankton abundant throughout the ocean. Larvaceans have been overlooked in research because they are difficult to collect and are perceived as being unimportant in biogeochemical cycles and food-webs. We synthesise evidence that their unique biology enables larvaceans to transfer more carbon to higher trophic levels and deeper into the ocean than is commonly appreciated. Larvaceans could become even more important in the Anthropocene because they eat small phytoplankton that are predicted to become more prevalent under climate change, thus moderating projected future declines in ocean productivity and fisheries. We identify critical knowledge gaps and argue that larvaceans should be incorporated into ecosystem assessments and biogeochemical models to improve predictions of the future ocean.

Demystifying global climate models for use in the life sciences.

For each assessment cycle of the Intergovernmental Panel on Climate Change (IPCC), researchers in the life sciences are called upon to provide evidence to policymakers planning for a changing future. This research increasingly relies on highly technical and complex outputs from climate models. The strengths and weaknesses of these data may not be fully appreciated beyond the climate modelling community; therefore, uninformed use of raw or preprocessed climate data could lead to overconfident or spurious conclusions. We provide an accessible introduction to climate model outputs that is intended to empower the life science community to robustly address questions about human and natural systems in a changing world.

A metric-based framework for climate-smart conservation planning.

Climate change is already having profound effects on biodiversity, but climate change adaptation has yet to be fully incorporated into area-based management tools used to conserve biodiversity, such as protected areas. One main obstacle is the lack of consensus regarding how impacts of climate change can be included in spatial conservation plans. We propose a climate-smart framework that prioritizes the protection of climate refugia-areas of low climate exposure and high biodiversity retention-using climate metrics. We explore four aspects of climate-smart conservation planning: (1) climate model ensembles; (2) multiple emission scenarios; (3) climate metrics; and (4) approaches to identifying climate refugia. We illustrate this framework in the Western Pacific Ocean, but it is equally applicable to terrestrial systems. We found that all aspects of climate-smart conservation planning considered affected the configuration of spatial plans. The choice of climate metrics and approaches to identifying refugia have large effects in the resulting climate-smart spatial plans, whereas the choice of climate models and emission scenarios have smaller effects. As the configuration of spatial plans depended on climate metrics used, a spatial plan based on a single measure of climate change (e.g., warming) will not necessarily be robust against other measures of climate change (e.g., ocean acidification). We therefore recommend using climate metrics most relevant for the biodiversity and region considered based on a single or multiple climate drivers. To include the uncertainty associated with different climate futures, we recommend using multiple climate models (i.e., an ensemble) and emission scenarios. Finally, we show that the approaches we used to identify climate refugia feature trade-offs between: (1) the degree to which they are climate-smart, and (2) their efficiency in meeting conservation targets. Hence, the choice of approach will depend on the relative value that stakeholders place on climate adaptation. By using this framework, protected areas can be designed with improved longevity and thus safeguard biodiversity against current and future climate change. We hope that the proposed climate-smart framework helps transition conservation planning toward climate-smart approaches.

Monitoring and modelling marine zooplankton in a changing climate.

Zooplankton are major consumers of phytoplankton primary production in marine ecosystems. As such, they represent a critical link for energy and matter transfer between phytoplankton and bacterioplankton to higher trophic levels and play an important role in global biogeochemical cycles. In this Review, we discuss key responses of zooplankton to ocean warming, including shifts in phenology, range, and body size, and assess the implications to the biological carbon pump and interactions with higher trophic levels. Our synthesis highlights key knowledge gaps and geographic gaps in monitoring coverage that need to be urgently addressed. We also discuss an integrated sampling approach that combines traditional and novel techniques to improve zooplankton observation for the benefit of monitoring zooplankton populations and modelling future scenarios under global changes.

Marked shifts of harmful algal blooms in the Bohai Sea linked with combined impacts of environmental changes.

The Bohai Sea, a semi-enclosed inland sea in China and an important mariculture region, has experienced extensive harmful algal blooms (HABs) and their negative impacts for several decades. To investigate the changes of HABs and their potential drivers over time and space, a dataset of 230 HAB events (1952-2017), along with corresponding environmental data (1990-2017) was compiled. The frequency of HAB events in the Bohai Sea has increased over time but plateaued in the last decade, and our analysis showed that history of HABs in the Bohai Sea could be categorized into three periods based on their frequency, scale, and HAB-forming species. The seasonal window of HAB events has started earlier and lasted longer, and the main hotspot has moved from Bohai Bay to coastal waters of Qinhuangdao over time. There were marked shifts in the representative HAB-forming microalgae, from dinoflagellates in the first period (before 2000) to haptophytes in the second period (2000-2009), and pelagophytes in the third period (2009 onwards). These community changes are accompanied by a trend toward diversification of HAB-forming microalgae, decrease in cell-size, and increase in negative impacts. Statistical analyses indicate that long-term changes in HABs in the Bohai Sea are linked with the combined effects of climate change, eutrophication and mariculture development. The results of the present study require to refine future monitoring programs, develop adaptive management strategies and predictive models for HABs in the Bohai Sea.

A global horizon scan of issues impacting marine and coastal biodiversity conservation.

The biodiversity of marine and coastal habitats is experiencing unprecedented change. While there are well-known drivers of these changes, such as overexploitation, climate change and pollution, there are also relatively unknown emerging issues that are poorly understood or recognized that have potentially positive or negative impacts on marine and coastal ecosystems. In this inaugural Marine and Coastal Horizon Scan, we brought together 30 scientists, policymakers and practitioners with transdisciplinary expertise in marine and coastal systems to identify new issues that are likely to have a significant impact on the functioning and conservation of marine and coastal biodiversity over the next 5-10 years. Based on a modified Delphi voting process, the final 15 issues presented were distilled from a list of 75 submitted by participants at the start of the process. These issues are grouped into three categories: ecosystem impacts, for example the impact of wildfires and the effect of poleward migration on equatorial biodiversity; resource exploitation, including an increase in the trade of fish swim bladders and increased exploitation of marine collagens; and new technologies, such as soft robotics and new biodegradable products. Our early identification of these issues and their potential impacts on marine and coastal biodiversity will support scientists, conservationists, resource managers and policymakers to address the challenges facing marine ecosystems.

A global, historical database of tuna, billfish, and saury larval distributions.

Knowing the distribution of fish larvae can inform fisheries science and resource management in several ways, by: 1) providing information on spawning areas; 2) identifying key areas to manage and conserve; and 3) helping to understand how fish populations are affected by anthropogenic pressures, such as overfishing and climate change. With the expansion of industrial fishing activity after 1945, there was increased sampling of fish larvae to help better understand variation in fish stocks. However, large-scale larval records are rare and often unavailable. Here we digitize data from Nishikawa et al. (1985), which were collected from 1956-1981 and are near-global (50°N-50°S), seasonal distribution maps of fish larvae of 18 mainly commercial pelagic taxa of the families Scombridae, Xiphiidae, Istiophoridae, Scombrolabracidae, and Scomberesocidae. Data were collected from the Pacific, Atlantic, and Indian Oceans. We present four seasonal 1° × 1° resolution maps per taxa representing larval abundance per grid cell and highlight some of the main patterns. Data are made available as delimited text, raster, and vector files.

Global collision-risk hotspots of marine traffic and the world's largest fish, the whale shark.

Marine traffic is increasing globally yet collisions with endangered megafauna such as whales, sea turtles, and planktivorous sharks go largely undetected or unreported. Collisions leading to mortality can have population-level consequences for endangered species. Hence, identifying simultaneous space use of megafauna and shipping throughout ranges may reveal as-yet-unknown spatial targets requiring conservation. However, global studies tracking megafauna and shipping occurrences are lacking. Here we combine satellite-tracked movements of the whale shark, Rhincodon typus, and vessel activity to show that 92% of sharks' horizontal space use and nearly 50% of vertical space use overlap with persistent large vessel (>300 gross tons) traffic. Collision-risk estimates correlated with reported whale shark mortality from ship strikes, indicating higher mortality in areas with greatest overlap. Hotspots of potential collision risk were evident in all major oceans, predominantly from overlap with cargo and tanker vessels, and were concentrated in gulf regions, where dense traffic co-occurred with seasonal shark movements. Nearly a third of whale shark hotspots overlapped with the highest collision-risk areas, with the last known locations of tracked sharks coinciding with busier shipping routes more often than expected. Depth-recording tags provided evidence for sinking, likely dead, whale sharks, suggesting substantial "cryptic" lethal ship strikes are possible, which could explain why whale shark population declines continue despite international protection and low fishing-induced mortality. Mitigation measures to reduce ship-strike risk should be considered to conserve this species and other ocean giants that are likely experiencing similar impacts from growing global vessel traffic.

Flexibility for fuelling reproduction in a pelagic ray (Mobula eregoodoo) suggested by bioenergetic modelling.

This study investigated the measurements of energy density and bioenergetic modelling for a pelagic ray, Mobula eregoodoo, to estimate its relative allocation to various bodily processes and especially reproduction. The data revealed M. eregoodoo uses up to 21.0% and 2.5% of its annual energy budget on growth and reproduction, respectively. During pregnancy, females depleted energy reserves in the liver, which, along with their biennial reproductive cycle, aligns with general theory that ectotherms are capital breeders and thus build energy reserves before reproduction. Nonetheless, the reduction in energy reserves did not account for all reproductive costs, and therefore, gravid females supplement reproductive costs through energy derived from the diet, according to an income-breeding strategy. These characteristics imply that M. eregoodoo exhibits some flexibility in fuelling reproduction depending on energy availability throughout the reproductive cycle, which may be prevalent in other elasmobranchs. The data represent the first estimates of both the metabolic costs of gestation in elasmobranchs and the relative cost of reproduction in rays. Energy costs and plasticity associated with highly variable reproductive strategies in elasmobranchs may influence long-term population viability under a rapidly changing environment.

Next-generation ensemble projections reveal higher climate risks for marine ecosystems.

Projections of climate change impacts on marine ecosystems have revealed long-term declines in global marine animal biomass and unevenly distributed impacts on fisheries. Here we apply an enhanced suite of global marine ecosystem models from the Fisheries and Marine Ecosystem Model Intercomparison Project (Fish-MIP), forced by new-generation Earth system model outputs from Phase 6 of the Coupled Model Intercomparison Project (CMIP6), to provide insights into how projected climate change will affect future ocean ecosystems. Compared with the previous generation CMIP5-forced Fish-MIP ensemble, the new ensemble ecosystem simulations show a greater decline in mean global ocean animal biomass under both strong-mitigation and high-emissions scenarios due to elevated warming, despite greater uncertainty in net primary production in the high-emissions scenario. Regional shifts in the direction of biomass changes highlight the continued and urgent need to reduce uncertainty in the projected responses of marine ecosystems to climate change to help support adaptation planning.

Reef manta rays forage on tidally driven, high density zooplankton patches in Hanifaru Bay, Maldives.

Manta rays forage for zooplankton in tropical and subtropical marine environments, which are generally nutrient-poor. Feeding often occurs at predictable locations where these large, mobile cartilaginous fishes congregate to exploit ephemeral productivity hotspots. Investigating the zooplankton dynamics that lead to such feeding aggregations remains a key question for understanding their movement ecology. The aim of this study is to investigate the feeding environment at the largest known aggregation for reef manta rays Mobula alfredi in the world. We sampled zooplankton throughout the tidal cycle, and recorded M. alfredi activity and behaviour, alongside environmental variables at Hanifaru Bay, Maldives. We constructed generalised linear models to investigate possible relationships between zooplankton dynamics, environmental parameters, and how they influenced M. alfredi abundance, behaviour, and foraging strategies. Zooplankton biomass changed rapidly throughout the tidal cycle, and M. alfredi feeding events were significantly related to high zooplankton biomass. Mobula alfredi switched from non-feeding to feeding behaviour at a prey density threshold of 53.7 mg dry mass m-3; more than double the calculated density estimates needed to theoretically meet their metabolic requirements. The highest numbers of M. alfredi observed in Hanifaru Bay corresponded to when they were engaged in feeding behaviour. The community composition of zooplankton was different when M. alfredi was feeding (dominated by copepods and crustaceans) compared to when present but not feeding (more gelatinous species present than in feeding samples). The dominant zooplankton species recorded was Undinula vulgaris. This is a large-bodied calanoid copepod species that blooms in oceanic waters, suggesting offshore influences at the site. Here, we have characterised aspects of the feeding environment for M. alfredi in Hanifaru Bay and identified some of the conditions that may result in large aggregations of this threatened planktivore, and this information can help inform management of this economically important marine protected area.

Mutualism promotes site selection in a large marine planktivore.

Mutualism is a form of symbiosis whereby both parties benefit from the relationship. An example is cleaning symbiosis, which has been observed in terrestrial and marine environments. The most recognized form of marine cleaning symbiosis is that of cleaner fishes and their clients.Cleaner species set up cleaning stations on the reef, and other species seek out their services. However, it is not well understood how the presence of cleaning stations influence movements of large highly mobile species. We examined the role of cleaning stations as a driver of movement and habitat use in a mobile client species.Here, we used a combination of passive acoustic telemetry and in-water surveys to investigate cleaning station attendance by the reef manta ray Mobula alfredi. We employed a novel approach in the form of a fine-scale acoustic receiver array set up around a known cleaning area and tagged 42 rays. Within the array, we mapped structural features, surveyed the distribution of cleaner wrasse, and observed the habitat use of the rays.We found manta ray space use was significantly associated with blue-streak cleaner wrasse Labroides dimidiatus distribution and hard coral substrate. Cleaning interactions dominated their habitat use at this site, taking precedence over other life history traits such as feeding and courtship.This study has demonstrated that cleaning symbiosis is a driver for highly mobile, and otherwise pelagic, species to visit inshore reef environments. We suggest that targeted and long-term use of specific cleaning stations reflects manta rays having a long-term memory and cognitive map of some shallow reef environments where quality cleaning is provided. We hypothesize that animals prefer cleaning sites in proximity to productive foraging regions.

Movement ecology of black marlin Istiompax indica in the Western Indian Ocean.

The black marlin Istiompax indica is an apex marine predator and is susceptible to overfishing. The movement ecology of the species remains poorly known, particularly within the Indian Ocean, which has hampered assessment of their conservation status and fisheries management requirements. Here, we used pop-up archival satellite tags to track I. indica movement and examine their dispersal. Forty-nine tags were deployed off Kenya during both the north-east (November-April) and south-west (August-September) monsoon seasons, providing locations from every month of the year. Individual I. indica were highly mobile and track distance correlated with the duration of tag attachment. Mean track duration was 38 days and mean track distance was >1800 km. Individuals dispersed in several directions: north-east into Somalian waters and up to northern Oman, east towards the Seychelles, and south into the Mozambique Channel. Their core habitat shifted seasonally and overlapped with areas of high productivity off Kenya, Somalia and Oman during the first half of the year. A second annual aggregation off the Kenyan coast, during August and September, did not coincide with high chlorophyll-a (chl-a) concentrations or thermal fronts, and the drivers of the species' presence and movement from this second aggregation was unclear. We tested their habitat preferences by comparing environmental conditions at track locations to the conditions at locations along simulated tracks based on the empirical data. Observed I. indica preferred cooler water with higher chl-a concentrations and stayed closer to the coast than simulated tracks. The rapid and extensive dispersal of I. indica from Kenya suggests that there is likely a single stock in the Western Indian Ocean, with individuals swimming between areas of high commercial catches off northern Somalia and Oman, and artisanal and recreational fisheries catches throughout East Africa and Mozambique.

Global warming is causing a more pronounced dip in marine species richness around the equator.

The latitudinal gradient in species richness, with more species in the tropics and richness declining with latitude, is widely known and has been assumed to be stable over recent centuries. We analyzed data on 48,661 marine animal species since 1955, accounting for sampling variation, to assess whether the global latitudinal gradient in species richness is being impacted by climate change. We confirm recent studies that show a slight dip in species richness at the equator. Moreover, richness across latitudinal bands was sensitive to temperature, reaching a plateau or declining above a mean annual sea surface temperature of 20 °C for most taxa. In response, since the 1970s, species richness has declined at the equator relative to an increase at midlatitudes and has shifted north in the northern hemisphere, particularly among pelagic species. This pattern is consistent with the hypothesis that climate change is impacting the latitudinal gradient in marine biodiversity at a global scale. The intensification of the dip in species richness at the equator, especially for pelagic species, suggests that it is already too warm there for some species to survive.

A database of zooplankton biomass in Australian marine waters.

Zooplankton biomass data have been collected in Australian waters since the 1930s, yet most datasets have been unavailable to the research community. We have searched archives, scanned the primary and grey literature, and contacted researchers, to collate 49187 records of marine zooplankton biomass from waters around Australia (0-60°S, 110-160°E). Many of these datasets are relatively small, but when combined, they provide >85 years of zooplankton biomass data for Australian waters from 1932 to the present. Data have been standardised and all available metadata included. We have lodged this dataset with the Australian Ocean Data Network, allowing full public access. The Australian Zooplankton Biomass Database will be valuable for global change studies, research assessing trophic linkages, and for initialising and assessing biogeochemical and ecosystem models of lower trophic levels.