Higher Trophic Levels Research Articles

Preliminary assessment of blood mercury contamination in four African crocodile species

Heavy metal contamination in the environment is an increasingly pervasive threat to the long-term persistence of wildlife. As high trophic level consumers, crocodylians are at substantial risk from bioaccumulation of mercury (Hg). Despite that they are generally well-studied and the focal species of many conservation efforts around the world, little is known about Hg contamination levels in most crocodylians. Here we preliminarily evaluate blood Hg contamination in four African species – Central African slender-snouted crocodile (Mecistops leptorhynchus), African dwarf crocodile (Osteolaemus tetraspis), West African crocodile (Crocodylus suchus), and Nile crocodile (Crocodylus niloticus) – from a diversity of sites and habitats across 5 different countries representing varying degrees of environmental pollution. All of our sampled crocodiles were Hg contaminated and, worryingly, these African crocodiles generally showed the highest levels of Hg contamination of any crocodylian species examined to date. Of most concern was that Hg concentrations were not only highest in M. leptorhynchus, the most threatened amongst our study species, but also in individuals sampled in what are believed to be some of the most remote and pristine natural areas left in Africa – Gabon’s national parks. Our results underscore the need to better understand the impact of longstanding petroleum, mining, forestry, and agricultural industries on the entire aquatic food chain throughout much of Africa, including on the threatened species in these habitats and the human populations that depend on them for their subsistence and livelihoods.

Feeding specialization shapes the bottom‐up effect of arbuscular mycorrhizal fungi across a plant–aphid–parasitoid system

Societal Impact StatementArbuscular mycorrhizal fungi (AMF) impact the relationships between plants, aphids (insects that feed on plant phloem), and their natural enemies (insects that prey on or parasitize aphids). The presence of AMF influences the growth and population of different aphid species and affects the development of aphid‐killing wasps and their attraction to plants. This research has been conducted also considering the insects' feeding strategy and their feeding specialization. This study provides novel perspectives on how these fungi shape interactions in the natural world, offering potential insights for the development of sustainable pest management strategies in agriculture.Summary Arbuscular mycorrhizal fungi (AMF) are major root symbionts regulating plant physiology. Their presence affects the performance of aboveground insect herbivores in relation to their feeding strategy and their feeding specialization. For example, the effect of the arbuscular mycorrhizal (AM) symbiosis on chewing insects, positive for specialists and negative for generalists, has been previously demonstrated. Conversely, the impact of AMF on phloem‐suckers with relatively different levels of specialization remains unexplored. We tested the influence of the AM Funneliformis mosseae on the fitness of the specialist aphid Acyrthosiphon pisum and the generalist aphid Myzus persicae on Vicia faba plants. Further, we investigated the effects of AMF on the higher trophic level, the aphid parasitoids Aphidius ervi (specialist) and Aphidius colemani (generalist), by evaluating plant attractiveness and parasitoid fitness. To support the results of behavioral and biological bioassays we characterized the photosynthetic parameters, the volatilome and the transcriptome of tested plants. Mycorrhizal plants proved unsuitable for the generalist M. persicae but enhanced the fitness of the specialist A. pisum. The AM symbiosis had no effects on the behavioral response of A. colemani and enhanced the attraction and fitness of A. ervi. Volatilome and transcriptome profiling corroborated the results of bioassay highlighting a bottom‐up effect of the AMF across a plant–aphid–parasitoid system.

The impact of fungi on soil protist communities in European cereal croplands.

Protists, a crucial part of the soil food web, are increasingly acknowledged as significant influencers of nutrient cycling and plant performance in farmlands. While topographical and climatic factors are often considered to drive microbial communities on a continental scale, higher trophic levels like heterotrophic protists also rely on their food sources. In this context, bacterivores have received more attention than fungivores. Our study explored the connection between the community composition of protists (specifically Rhizaria and Cercozoa) and fungi across 156 cereal fields in Europe, spanning a latitudinal gradient of 3000 km. We employed a machine-learning approach to measure the significance of fungal communities in comparison to bacterial communities, soil abiotic factors, and climate as determinants of the Cercozoa community composition. Our findings indicate that climatic variables and fungal communities are the primary drivers of cercozoan communities, accounting for 70% of their community composition. Structural equation modelling (SEM) unveiled indirect climatic effects on the cercozoan communities through a change in the composition of the fungal communities. Our data also imply that fungivory might be more prevalent among protists than generally believed. This study uncovers a hidden facet of the soil food web, suggesting that the benefits of microbial diversity could be more effectively integrated into sustainable agriculture practices.

Role of β‐glucan on finfish and shellfish health and well‐being: A systematic review and meta‐analysis

AbstractThis study aimed to conduct a systematic review and meta‐analysis evaluating the inclusion of β‐glucan in aquaculture animal diets and its impact on their health outcomes. Relevant studies were identified from Scopus and Web of Science databases. A total of 82 primary studies published between 1996 and 2024 were reviewed, of which 70 were included in the meta‐analysis. The results revealed that the application of β‐glucan to aquaculture animal's diets significantly enhanced specific growth rate (SGR; mean effect, g = 2.71; p < 0.001), feed conversion ratio (FCR; g = −3.88; p < 0.0001) and lowered mortality after exposure to pathogens. Likewise, β‐glucan had a positive influence (p < 0.0001) on innate immune parameters (lysozyme and phagocyte activity, NBT, ACH50, and IgM). The study found that the effects of β‐glucans varied among marine and freshwater fish where freshwater fishes (g = 2.05–6.57) exhibit better performance. This study also found a negative correlation between fish's innate immune response and trophic level, suggesting that fish with higher trophic levels may be less efficient at absorbing this bio‐stimulant. Even though there were high heterogeneity (I2 = 73%–97%, p < 0.05) due to the diversity of tested organisms and publication bias, our model and findings are valid. The findings suggest that the dietary application of β‐glucans can have beneficial effects on growth and immune responses especially for freshwater species. The validity of these observations needs to be confirmed by further prospective studies.

Impact of summer hypoxia on macrobenthic communities in a semi-enclosed bay: A long-term observation in the North Yellow sea of China

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Despite this situation, the responses of macrobenthos under hypoxic conditions remain poorly understood. In this study, we conducted a long-term observation (2015–2022) to investigate the intricate impact of summer hypoxia on macrobenthic communities in a semi-enclosed bay of the North Yellow Sea. Comparative analyses revealed higher macrobenthos abundance (1956.8 ± 1507.5 ind./m2 vs. 871.8 ± 636.9 ind./m2) and biomass (8.2 ± 4.1 g/m2 vs. 5.6 ± 3.2 g/m2) at hypoxic sites compared to normoxic sites during hypoxic years. Notably, polychaete species demonstrated remarkable adaptability, dominating hypoxic sites, and shaping community structure. The decline in biodiversity underscored the vulnerability and diminished resilience of macrobenthic communities to hypoxic stressors. Stable isotope analysis provided valuable insights into food web structures. The average trophic level of macrobenthos measured 2.84 ± 0.70 at hypoxic sites, contrasting with the higher value of 3.14 ± 0.74 observed at normoxic sites, indicating the absence of predators at high trophic levels under hypoxic conditions. Moreover, trophic interactions were significantly altered, resulting in a simplified and more vulnerable macrobenthic trophic structure. The findings underscored the importance of comprehensive research to understand the complex responses of macrobenthic communities to hypoxia, thereby informing future conservation efforts in impacted ecosystems.

Anthropogenic CO2, air–sea CO2 fluxes, and acidification in the Southern Ocean: results from a time-series analysis at station OISO-KERFIX (51° S–68° E)

Abstract. The temporal variation of the carbonate system, air–sea CO2 fluxes, and pH is analyzed in the southern Indian Ocean, south of the polar front, based on in situ data obtained from 1985 to 2021 at a fixed station (50°40′ S–68°25′ E) and results from a neural network model that reconstructs the fugacity of CO2 (fCO2) and fluxes at monthly scale. Anthropogenic CO2 (Cant) is estimated in the water column and is detected down to the bottom (1600 m) in 1985, resulting in an aragonite saturation horizon at 600 m that migrated up to 400 m in 2021 due to the accumulation of Cant. At the subsurface, the trend of Cant is estimated at +0.53±0.01 µmol kg−1 yr−1 with a detectable increase in the trend in recent years. At the surface during austral winter the oceanic fCO2 increased at a rate close to or slightly lower than in the atmosphere. To the contrary, in summer, we observed contrasting fCO2 and dissolved inorganic carbon (CT) trends depending on the decade and emphasizing the role of biological drivers on air–sea CO2 fluxes and pH inter-annual variability. The regional air–sea CO2 fluxes evolved from an annual source to the atmosphere of 0.8 molC m−2 yr−1 in 1985 to a sink of −0.5 molC m−2 yr−1 in 2020. Over 1985–2020, the annual pH trend in surface waters of -0.0165±0.0040 per decade was mainly controlled by the accumulation of anthropogenic CO2, but the summer pH trends were modulated by natural processes that reduced the acidification rate in the last decade. Using historical data from November 1962, we estimated the long-term trend for fCO2, CT, and pH, confirming that the progressive acidification was driven by the atmospheric CO2 increase. In 59 years this led to a diminution of 11 % for both aragonite and calcite saturation state. As atmospheric CO2 is expected to increase in the future, the pH and carbonate saturation state will decrease at a faster rate than observed in recent years. A projection of future CT concentrations for a high emission scenario (SSP5-8.5) indicates that the surface pH in 2100 would decrease to 7.32 in winter. This is up to −0.86 lower than pre-industrial pH and −0.71 lower than pH observed in 2020. The aragonite undersaturation in surface waters would be reached as soon as 2050 (scenario SSP5-8.5) and 20 years later for a stabilization scenario (SSP2-4.5) with potential impacts on phytoplankton species and higher trophic levels in the rich ecosystems of the Kerguelen Islands area.

Spatial, Temporal, and Interspecific Differences in Composition of Stable Isotopes in Fishes in Maryland Coastal Bays

Carbon (δ13C) and nitrogen (δ15N) isotopes were used to evaluate spatial, temporal, and interspecific differences in trophic relationships of four fish species (Paralichthys dentatus, Anchoa mitchilli, Leiostomus xanthurus, and Bairdiella chrysoura) in Maryland’s coastal bays. The δ13C values for all species were more enriched in 2017 than in 2018, a year of higher-than-average rainfall that likely caused higher amounts of terrestrial carbon to enter the estuary. There were significant differences among species in the δ13C values, with L. xanthurus being the least depleted (−17.2‰ in 2017; −18.8‰ in 2018). Spatially, the δ13C values of the species, particularly P. dentatus and B. chrysoura, were more depleted in the northern bays, which have a higher nutrient content and receive more freshwater inflow directly from tributaries, than the southern bays. The observed δ13C values (−19.5 ± 0.2‰ to –17.2 ± 0.3‰), however, indicate that marine phytoplankton was the primary carbon source of the fishes. Overall, A. mitchilli was the most enriched in δ15N (13.0‰), and L. xanthurus was the most depleted (10.2‰). δ15N was more enriched in fish from the more human-impacted northern bays than in fish from the southern bays, though this might also have stemmed from the differences in the diet composition of the species in the northern and southern bays. A. mitchilli had the highest trophic level, while L. xanthurus and P. dentatus had the lowest trophic levels. Niche breadth was widest in L. xanthurus compared to the other fish species, suggesting a higher variability in diets among L. xanthurus individuals, leading to specialized diets. There was a high niche overlap between B. chrysoura, A. mitchilli, and L. xanthurus, which indicates they fed on similar prey resources.

Habitat loss and simplification lower arthropod richness but not diversity

AbstractHabitat loss is rarely truly random and often occurs selectively with respect to the plant species comprising the habitat. Such selective habitat removal that decreases plant species diversity, that is, habitat simplification or homogenization, may have two negative effects on other species. First, the reduction in plant community size (number of individuals) represents habitat loss for species at higher trophic levels who use plants as habitat. Second, when plants are removed selectively, the resulting habitat simplification decreases the diversity of resources available to species at higher trophic levels. It follows that habitat loss combined with simplification will reduce biodiversity more than habitat loss without simplification. To test this, we experimentally implemented two types of habitat loss at the plant community level and compared biodiversity of resident arthropods between habitat loss types. In the first type of habitat loss, we reduced habitats by 50% nonselectively, maintaining original relative abundance and diversity of plant species and therefore habitat and resource diversity for arthropods. In the second type of habitat loss, we reduced habitats by 50% selectively, removing all but one common plant species, dramatically simplifying habitat and resources for arthropods. We replicated this experiment across three common plant species: Asclepias tuberosa, Solidago altissima, and Baptisia alba. While habitat loss with simplification reduced arthropod species richness compared with habitat loss without simplification, neither type of habitat loss affected diversity, measured as effective number of species (ENS), or species evenness as compared with controls. Instead, differences in ENS and evenness were explained by the identity of the common plant species. Our results indicate that the quality of remaining habitat, in our case plant species identity, may be more important for multi‐trophic diversity than habitat diversity per se.

Use of stable isotope ratio analysis to investigate the biology and clinical significance of seal parasites.

Stranded seals are often infected with a broad range of parasites, although whether they are the cause of significant morbidity or an incidental finding is usually unclear. In this study we used stable isotope ratio analysis, a method frequently used to investigate food webs, to explore the extent to which common seal parasites feed directly on host tissue and fluids or absorb host-derived metabolites, which in turn may give an indication of their potential impact on the host's health. The trophic discrimination factor Δ15N for the nasal mite, Halarachne halichoeri, was mostly positive, ranging between −0.015 and 3.2‰ (n = 6), while for the Acanthocephalan worm, Corynosoma strumosum and the anisakid nematode, Pseudoterranova decipiens, Δ15N ranged between −4.2 and −2.0‰ (n = 7), and between −6.7 and −0.8‰ (n = 5) respectively. In the case of the lungworm, Otostrongylus circumlitus, Δ15N measured between −5.6 and 0‰ for worms collected in the stomach (n = 5), between −1.1 and 0.2‰ for worms collected from the heart (n = 3), between −0.7 and 1.9‰ for worms situated in the lungs (n = 4). Based on Δ15N, parasites could be clearly divided into those that were on a higher trophic level than their host suggesting a predator–prey-like relationship, and those that were not. It is hypothesized that Δ15N may be indicative of the clinical significance of parasite–host associations.

Does the microplastics ingestion patterns and polymer composition vary across the oceanic zones? A case study from the Indian coast

This study explores microplastic (MP) presence in the gastrointestinal tracts of deep-sea fish from the Central Indian Ocean, off the Indian coast. Among the 27 species examined, 19 showed MP contamination, averaging 2.68 ± 0.30 (±SE) MPs per individual. Polymer analysis via FTIR and micro-Raman identified several types, including polyethylene terephthalate (PET), polyvinyl alcohol (PVA), polypropelene (PP), polyvinyl acetate (PVC), polyurethane (PU), polytetrafluoroethylene (PTFE), polyaniline (PANI), polymethyl methacrylate (PMMA), and polyethersulfone (PES), with PET being the most prevalent (33.33 %). MP ingestion was higher in benthopelagic fish and those at higher trophic levels, as indicated by comparisons across oceanic zones. Niche partitioning analysis suggests feeding behaviour as a primary influencer of MP ingestion in deep-sea fish rather than habitat or trophic level. The study proposes the potential use of deep-sea fish as indicators for assessing microplastic pollution across oceanic zones and deep-sea regions through bycatch monitoring.

Using passive acoustic monitoring to assess the overlap between endemic endangered Hector's dolphin (Cephalorhynchus hectori hectori) and mussel farms in the Banks Peninsula Marine Mammal Sanctuary, New Zealand

Abstract Aquaculture has maintained a sustained growth trend over the last 50 years, worldwide and in Aotearoa New Zealand. This industry is known to have environmental consequences, such as impacts on benthos, water column and higher trophic levels. Some of these impacts have been thoroughly studied, while others, such as the effects on cetaceans, are not well understood. This study used passive acoustic monitoring (PAM) to assess, for the first time, the overlap between kūtai—New Zealand greenlipped mussel (Perna canaliculus)—farms and habitat use by endemic endangered Hector's dolphins (Cephalorhynchus hectori hectori) within the Banks Peninsula Marine Mammal Sanctuary. T‐PODs were deployed in six bays, three with mussel farms and three without, between 2018 and 2019. Occurrence of dolphins, expressed as ‘dolphin positive minutes per day’ (DPM/day), was modelled using generalized linear mixed models. Results showed a strong interaction between farm (presence/absence) and season (summer/winter), with fewer acoustic detections of dolphins in winter if farms were present. Furthermore, in bays with mussel farms, there were significantly more click train detections on the opposite side of the bay, compared to the side by the mussel farm. Considering that results from this study suggest potential displacement of the dolphins due to the mussel farms, the recommendation is a precautionary approach. Further expansion of aquaculture in Hector's dolphin habitat should be done carefully, taking into account their habitat use, and conducting intensive monitoring including a robust ‘before and after’ design prior to the establishment of new farms.

Effect of Plastic Ocean Pollution on Marine Life and Human Health in Brazil

Purpose: The aim of the study was to examine effect of plastic ocean pollution on marine life and human health in Brazil. Methodology: This study adopted a desk methodology. A desk study research design is commonly known as secondary data collection. This is basically collecting data from existing resources preferably because of its low cost advantage as compared to a field research. Our current study looked into already published studies and reports as the data was easily accessed through online journals and libraries. Findings: The study found that pervasive presence of plastic debris in Brazil's coastal waters threatens marine ecosystems, leading to entanglement, ingestion, and suffocation of marine species such as seabirds, turtles, and marine mammals. Furthermore, microplastics, resulting from the breakdown of larger plastic items, pose insidious risks to marine life as they are ingested by plankton and subsequently enter the food chain, potentially accumulating in higher trophic levels, including fish consumed by humans. This not only disrupts marine biodiversity but also raises concerns about the safety and quality of seafood, impacting human health and food security in coastal communities. Unique Contribution to Theory, Practice and Policy: Ecological theory, health impact assessment (HIA) theory & environmental justice theory may be used to anchor future studies on Effect of Plastic Ocean Pollution on Marine Life and Human Health in Brazil. Develop and deploy technologies that efficiently remove microplastics and larger debris from marine environments. This includes advancements in filtration systems for water treatment facilities and specialized equipment for collecting debris from ocean surfaces and shorelines. Enforce regulations limiting the production of non-essential single-use plastics, promoting the use of sustainable materials. Policy-makers should consider lifecycle assessments in the approval process of new plastic products.

Surface currents shape protist community structure across the Indo-Pacific.

Biogeographic structure in marine protist communities is shaped by a combination of dispersal potential and environmental selection. High-throughput sequencing and global sampling efforts have helped better resolve the composition and functions of these communities in the world's oceans using both molecular and visual methods. However, molecular barcoding data are critically lacking across the Indo-Pacific, a region widely considered the epicenter of marine biodiversity. To fill this gap, we characterized protist communities in four sampling regions across Indonesia that represent the latitudinal, longitudinal, and human population gradients of the region: Lombok, Wakatobi, Misool, and Waigeo. We show high spatial structuring in marine protist communities across Indonesia, and biotic factors appear to play little role in driving this observed structure. Our results appear to be driven by abiotic factors linked to surface current patterns across the Indo-Pacific as a result of: (1) a choke point in circulation at the Indonesian Throughflow leading to low diatom diversity in Lombok, Wakatobi, and Misool; (2) an increase in nutrient availability at the edge of the Halmahera Eddy in Waigeo, leading to an increase in diatom diversity; and/or (3) seasonal variations in protist communities in line with shifts in velocity of the Indonesian Throughflow. Overall, our results highlight the importance of abiotic factors in shaping protist communities on broad geographic scales over biotic, top-down pressures, such as grazing from higher trophic levels.

Restoration of open ecosystems in the face of climate change

Open ecosystems occur all around the world in various forms including temperate and tropical grasslands, savannas, shrublands, heathlands, among others. They are home to unique biodiversity, provide key ecosystem services and sustain traditional livelihoods of nearly two billion people. In the face of ongoing climate change, practitioners aiming to restore open ecosystems need the support of the scientific community more than ever. The aim of this Special Issue (SI) is to provide an attention-grabbing collection of high-quality publications addressing the growing challenges of open ecosystems restoration. The SI contains 14 papers that fill various, often interdisciplinary knowledge gaps. Three papers deal with the challenges of identifying the right target states, including the genetic composition of constituting plant species, for restoration under changing environmental conditions and competing stakeholder interests. Five papers advance our understanding on the appropriate timing and methodological toolkit to actively ignite re-assembly of the target plant communities, while two papers focus on situations where spontaneous processes can still also be relied on. The interaction of open ecosystems health and recovery with higher trophic levels, particularly grazers, is also discussed in three papers. Finally, a review paper systematically identifies further knowledge gaps, such as the role of soil microbes in grassland recovery and makes clear guidelines how to fill them. Due to the variety of topics and the rigorous content, this SI provides strong support for open ecosystems restoration policy and practice under the UN Decade on Ecosystem Restoration and beyond.

Elevation-associated pathways mediate aquatic biodiversity at multi-trophic levels along a plateau inland river

Aquatic biodiversity plays a significant role in maintaining the ecological balance and the overall health of riverine ecosystems. Elevation is an important factor influencing biodiversity patterns. However, it is still unclear through which pathway elevation influences riverine biodiversity at different trophic levels. In this study, the elevation-associated pathways affecting aquatic biodiversity at different trophic levels were explored using structural equation modeling (SEM) and taking the Bayin River, China as the case. The results showed that the elevational patterns were different among aquatic organisms at different trophic levels. For macroinvertebrates and bacteria, the pattern was hump-shaped; while for phytoplankton and zooplankton, it was U-shaped. Building upon these observed elevational patterns, our investigation delved into the direct and indirect pathways through which elevation influences aquatic biodiversity. We found that elevation exerts an impact on aquatic biodiversity via indirect pathways. For all aquatic organisms investigated, the major pathway through which elevation influences biodiversity is mediated by water temperature and water quality. For aquatic organisms at higher trophic levels, like macroinvertebrates and zooplankton, the crucial pathway is also mediated by the landscape. The results of this study contributed to understanding the effects of elevation on aquatic organisms at different trophic levels and provided an important basis for the assessment of riverine biodiversity at large scales.

Does This Look Infected? Hidden Host Plant Infection by the Pathogen Botrytis cinerea Alters Interactions between Plants, Aphids and Their Natural Enemies in the Field.

Few studies have considered whether hidden (asymptomatic) plant pathogen infection alters ecological interactions at the higher trophic levels, even though such infection still affects plant physiology. We explored this question in two field experiments, where two varieties of lettuce (Little Gem, Tom Thumb) infected with Botrytis cinerea were either (1) naturally colonised by aphids or (2) placed in the field with an established aphid colony. We then recorded plant traits and the numbers and species of aphids, their predators, parasitoids and hyperparasitoids. Infection significantly affected plant quality. In the first experiment, symptomatically infected plants had the fewest aphids and natural enemies of aphids. The diversity and abundance of aphids did not differ between asymptomatically infected and uninfected Little Gem plants, but infection affected the aphid assemblage for Tom Thumb plants. Aphids on asymptomatically infected plants were less attractive to predators and parasitoids than those on uninfected plants, while hyperparasitoids were not affected. In the second experiment, when we excluded natural enemies, aphid numbers were lower on asymptomatically and symptomatically infected plants, but when aphid natural enemies were present, this difference was removed, most likely because aphids on uninfected plants attracted more insect natural enemies. This suggests that hidden pathogen infection may have important consequences for multitrophic interactions.

Comparative analysis of the molecular starvation response of Southern Ocean copepods.

Large lipid-storing copepods dominate mesozooplankton biomass in the polar oceans and form a critical link between primary production and higher trophic levels. The ecological success of these species depends on their ability to survive periods of food deprivation in a highly seasonal environment, but the molecular changes that mediate starvation tolerance in these taxa are unknown. We conducted starvation experiments for two dominant Southern Ocean copepods, Calanoides acutus and Calanus propinquus, allowing us to compare the molecular starvation response between species. These species differ in life history, diet and metabolic traits, and expressed overlapping but distinct transcriptomic responses to starvation. Most starvation-response genes were species-specific, but we identified a conserved core set of starvation-response genes related to RNA and protein metabolism. We used phylotranscriptomics to place these results in the context of copepod evolution and found that starvation-response genes are under strong purifying selection at the sequence level and stabilizing selection at the expression level, consistent with their role in mediating essential biological functions. Selection on starvation-response genes was especially strong in our focal lipid-storing lineage relative to other copepod taxa, underscoring the significance of starvation tolerance for these species. We also found that certain key lipid enzymes (elongases and desaturases) have experienced diversification and positive selection in lipid-storing lineages, reflecting the unique lipid storage needs of these animals. Our results shed light on the molecular adaptations of high-latitude zooplankton to variable food conditions and suggest that starvation-response genes are under particularly strong sequence and expression constraints.

Combining mesocosms with models reveals effects of global warming and ocean acidification on a temperate marine ecosystem.

Ocean warming and species exploitation have already caused large-scale reorganization of biological communities across the world. Accurate projections of future biodiversity change require a comprehensive understanding of how entire communities respond to global change. We combined a time-dynamic integrated food web modeling approach (Ecosim) with previous data from community-level mesocosm experiments to determine the independent and combined effects of ocean warming, ocean acidification and fisheries exploitation on a well-managed temperate coastal ecosystem. The mesocosm parameters enabled important physiological and behavioral responses to climate stressors to be projected for trophic levels ranging from primary producers to top predators, including sharks. Through model simulations, we show that under sustainable rates of fisheries exploitation, near-future warming or ocean acidification in isolation could benefit species biomass at higher trophic levels (e.g., mammals, birds, and demersal finfish) in their current climate ranges, with the exception of small pelagic fishes. However, under warming and acidification combined, biomass increases at higher trophic levels will be lower or absent, while in the longer term reduced productivity of prey species is unlikely to support the increased biomass at the top of the food web. We also show that increases in exploitation will suppress any positive effects of human-driven climate change, causing individual species biomass to decrease at higher trophic levels. Nevertheless, total future potential biomass of some fisheries species in temperate areas might remain high, particularly under acidification, because unharvested opportunistic species will likely benefit from decreased competition and show an increase in biomass. Ecological indicators of species composition such as the Shannon diversity index decline under all climate change scenarios, suggesting a trade-off between biomass gain and functional diversity. By coupling parameters from multilevel mesocosm food web experiments with dynamic food web models, we were able to simulate the generative mechanisms that drive complex responses of temperate marine ecosystems to global change. This approach, which blends theory with experimental data, provides new prospects for forecasting climate-driven biodiversity change and its effects on ecosystem processes.

Clustering evaluation of water quality for various classes of in-flow rivers in connected brackish lakes.

Brackish waters and estuaries at the lower reaches of rivers accumulate organic matter and nutrients from various sources in the watershed. Sufficient light and shallow water depth stimulate phytoplankton growth, resulting in a more diversified ecosystem with higher trophic levels. For effective watershed management, it is crucial to characterize the water quality of all rivers, including small and medium-sized ones. Our field survey assessed water quality parameters in 26 inflow rivers surrounding Lakes Shinji and Nakaumi, two consolidated brackish lakes in Japan. The parameters included water temperature, salinity, chlorophyll-a, and nutrients. The study used hierarchical clustering. The Silhouette Index was used to assess clustering outcomes and identify any difficulties in dispersion across clusters. The 26 rivers surrounding Lakes Shinji and Nakaumi were classified into six groups based on their water quality characteristics. This classification distinguishes itself from earlier subjective methods that relied on geographical factors. The new approach identifies a need for improved management of river water quality. The results of the cluster analysis provide valuable insights for future management initiatives. It is important to consider these findings alongside established watershed criteria.

Trophic position determines the persistence of neotropical understory birds after forest disturbance.

Habitat loss and degradation are key drivers of the current biodiversity crisis. Most research focuses on the question of which traits allow species to persist in degraded habitats. We asked whether a species' trophic position or niche width influences the resilience of species in degraded habitats and to what extent habitat degradation affects trophic interactions between species. We used nitrogen isotope ratios (15N:14N, expressed as δ15N value) to quantify and compare trophic positions and niche widths of understory birds inhabiting old-growth and young secondary forests in the Pacific lowlands of Costa Rica. We found that a species' trophic position rather than its trophic niche width determined its persistence in secondary forests. Species feeding at lower trophic levels in old-growth forests were less likely to persist in secondary forests than those occupying a higher trophic position in old-growth forests. This pattern is likely induced by the occurrence of relatively large-bodied habitat specialists with a flexible and high-trophic level diet in secondary forests. These habitat specialists likely caused generalist bird species to lower their trophic position relative to conspecifics in old-growth forests. Regarding trophic niche widths, species in secondary forests tend to have larger niche widths than old-growth forest species. However, as old-growth forest specialists and generalists did not differ in their niche widths, no systematic effect of trophic niche width on species persistence after forest disturbance was found. This is the first study that shows a systematic effect of trophic position on the persistence of a wide range of bird species in a disturbed forest ecosystem. It therefore provides important insights into species' responses to habitat degradation and the conservation value of secondary forests. To improve habitat quality for old-growth forest birds and facilitate avian seed dispersal, the creation of large contiguous forest patches should be prioritised when implementing reforestation measures.