Lower Trophic Levels Research Articles

Integrating ecosystem and contaminant models to predict the effects of ecosystem fluxes on contaminant dynamics

AbstractEnvironmental contamination is one of the major drivers of ecosystem change in the Anthropocene. Toxic chemicals are not constrained to their source of origin as they cross ecosystem boundaries via biotic (e.g., animal migration) and abiotic (e.g., water flow) vectors. Meta‐ecology has led to important insights on how spatial flows or subsidies of matter across ecosystem boundaries can have broad impacts on local and regional ecosystem dynamics but has not yet addressed the dynamics of pollutants in recipient ecosystems. Incorporating meta‐ecosystem processes (i.e., flux of materials across ecosystem boundaries) into contaminant dynamics can elucidate how contaminants may reverberate among local food chains. Here, we derive a modeling framework to predict how spatial ecosystem fluxes can influence contaminant dynamics and how this influence is dependent on the type of ecosystem flux (e.g., herbivore movement vs. abiotic chemical flows). We mix an analytical and numerical approach to analyze our integrative model which couples two subcomponents that have previously been studied independently of each other—an ecosystem model and a contaminant model. We observe an array of dynamics for how chemical concentrations change with increasing nutrient input and loss rate across trophic levels. When we tailor our range of chemical parameter values (e.g., environmental uptake of contaminant and assimilation efficiency of the contaminant) to specific organic chemicals, our results demonstrate that increasing nutrient input rates can lead to trophic dilution in pollutants such as polychlorinated biphenyls across trophic levels. However, increasing nutrient loss rate causes an increase in the concentrations of chemicals across all trophic levels. A sensitivity analysis demonstrates that nutrient recycling is an important ecosystem process impacting contaminant concentrations, generating predictions to be addressed by future empirical studies. Importantly, our model demonstrates the utility of our framework for identifying drivers of contaminant dynamics in connected ecosystems including the importance that (1) ecosystem processes and (2) movement, especially movement of lower trophic levels, have on contaminant concentrations.

Seasonal stratification leads to changes within the benthic food web of the Gulf of Lions (northwestern Mediterranean)

Due to its extensive continental shelf, the Gulf of Lions, situated in the northwestern Mediterranean Sea, plays a crucial role in providing ecological services amidst various natural and anthropogenic pressures. Exposed to the impacts of climate change and suitable for marine energy development projects, the conservation of marine biodiversity in this environment raises significant concerns. To detect any potential disturbances in the functioning of the terrigenous mud community on the continental shelf, we conducted stable carbon and nitrogen isotope analyses on suspended particulate organic matter, sediments, and benthic fauna. Since seasonality is a structuring factor for the functioning of such an oligotrophic ecosystem, we conducted two sampling campaigns in 2018 to capture contrasting scenarios of water column stratification — one in April during well-mixed conditions and high phytoplankton production, and another in September at the end of the summer thermal stratification period characterized by low primary productivity. Stable isotope analysis revealed changes in the structure of the benthic food web in response to seasonal stratification of the water column. While isotopic niches of taxa remained evenly distributed, the total niche space contracted between sampling dates, primarily affecting low trophic level consumers. The observed contraction aligns with that reported at the base of the pelagic food web. These results enhance our understanding of the functioning of the continental shelf of the Gulf of Lions. The intense trawling pressure on the study site affected sampling. In this context, this research contributes not only to the knowledge of seasonal trophic variations but also provides a reference state to understand the future of this Mediterranean continental shelf.

A diagnosis of the artisanal fishery landings in the Colombian Caribbean coast by means of indicators

Landings of the artisanal fishery in the Colombian Caribbean from 2013 to 2021 were characterized by means of two indicators: the trophic level and the vulnerability to fishery landings. Indicators showed a statistically significant decreasing trend in vulnerability and trophic level, suggesting that the fishery is increasingly targeting species of low vulnerability and trophic level, thus moving down the food web. The overall pattern of indicators was not uniform in space. Incidence interaction of gears and species landed explained the trajectory of indicators at the scale of Departments. Fishing gears targeted different levels in the food web, with gillnets responsible for the bulk of landings. Compared to a previous study, the group of fish species supporting most of landings has changed towards species with lower vulnerability, i.e. resistant to fishing mortality due to their evolved life-history but still of predatory habits in general. A notable exception is Mugil incilis, a species with a low trophic level that has become third in importance of landings in the database.

Mapping breeding birds in a re-naturalized historical fortress: composition, structure and considerations about abundance vs. biomass comparisons

Using the mapping method, I obtained data about a rich, even and diversified breeding bird assemblage inhabiting an abandoned and re-naturalized historical military fortress (Rome, central Italy). Fortress and the surrounding parks host a large number of edge-mosaic, forest and synanthropic species (often localized at urban scale as Dendrocopos minor and Columba palumbus) due to a large availability of many sub-habitats and related niches (walls, cavities, tree holes, mature trees, mowed meadows, hedgerows, and deep moats). In this regard, this historical site may be considered a “key-stone structure” at the landscape scale (i.e., a mature forest/rocky patch embedded in an agromosaic suburban mosaic). The application of the Abundance/Biomass Comparison (ABC) evidenced a dominant role of large body mass species. The underlying logic behind this approach assumes that, generally, in less disturbed environments species with higher trophic level (and higher body mass) dominate: the increase in frequency of these larger species induce early cumulating biomass curves. However, in our anthropized case study, this assumption seems not valid since many large body mass species (as Columba livia dom., Psittacula krameri and Corvus cornix) show a low trophic level (e.g. granivorous or homnivorous): i.e. body mass is not an indicator of trophic level. Therefore, the pattern reported by ABC curves evidence only a dominance of large body mass species without implications on the trophic level and, consequently, on the disturbance acting on the assemblage. In this regard, assumptions linked to the ABC curves are probably not universal but only limited to specific taxa and contexts.

Astaxanthin: a powerful antioxidant used in aquaculture for coloration with aquatic animal health implications

Astaxanthin is a xanthophyll with unique properties that make it a potent antioxidant and photoreceptor. It is synthesized in lower trophic level organisms, such as microalgae, yeast, and some other microbes. It is also synthetically manufactured. The use of astaxanthin for pigmentation in aquaculture is well documented, as are the numerous benefits for humans from the consumption of astaxanthin. However, little research has been conducted on its potential health benefits to aquatic species. Astaxanthin has recently been identified as a semi-essential nutrient for some common aquaculture species, such as crustaceans and salmonids, but its effectiveness as a health supplement in aquatic species is unclear. This review aims to summarize the varied current uses of astaxanthin in aquaculture, as well as the potential effects of astaxanthin on the aquatic animal species which receive it.

Trophic downgrading of an adaptable carnivore in an urbanising landscape

Urbanisation critically alters wildlife habitat and resource distribution, leading to shifts in trophic dynamics. The loss of apex predators in human-transformed landscapes can result in changes in the ecological roles of the remaining mesocarnivores. Decreased top–down control together with increased bottom–up forcing through greater availability of anthropogenic foods can result in a predation paradox. Understanding these changes is important for conserving ecological function and biodiversity in rapidly urbanising systems. Here, we use stable isotope analysis to provide insight into longer term changes in trophic position, niche width and overlap of an elusive, medium-sized urban adapter, the caracal (Caracal caracal) in and around the city of Cape Town, South Africa. Using fur samples (n = 168) from individuals along a gradient of urbanisation we find that overall caracals have a broad isotopic dietary niche that reflects their large variation in resource use. When accounting for underlying environmental differences, the intensity of anthropogenic pressure, measured using the Human Footprint Index (HFI), explained variation in both food subsidy use (δ13C values) and trophic status (δ15N values). The significantly higher δ13C values (P < 0.01) and lower δ15N values (P < 0.001) of caracals in more urbanised areas suggest that predator subsidy consumption occurs via predictable, anthropogenic resource subsidies to synanthropic prey. These prey species are predominantly primary consumers, resulting in shifts in diet composition towards lower trophic levels. Further, caracals using areas with higher HFI had narrower isotope niches than those in less impacted areas, likely due to their hyperfocus on a few lower trophic level prey species. This pattern of niche contraction in urban areas is retained when accounting for caracal demographics, including sex and age. The removal of apex predators in human-transformed landscapes together with reliable resource availability, including abundant prey, may paradoxically limit the ecological influence of the remaining predators, and bring about a degree of predator trophic downgrading. The dampening of top–down control, and thus ecosystem regulation, likely points to widespread disruption of trophic dynamics in rapidly developing areas globally.

Seasonal variation in microplankton communities in Suttsu, Hokkaido, northern Japan, from 2020 to 2022

Southwestern Hokkaido faces intricate physiological and chemical changes. Subsequently, changes in lower trophic levels are of concern, but fully understanding the relationship between microplankton and hydrography in this region is required. To examine the relationship between the microplankton community (diatoms, dinoflagellates, ciliates, and euglenoids) and environmental factors in Suttsu, Hokkaido, water samples were collected at 4–15-day intervals from August 2020 to August 2022 at Yokoma Port. Diatoms were dominant in the study area, with an apparent seasonal change in species composition. Lower phytoplankton cell density was observed in the second year than in the first year during autumn and winter because of low temperatures and light intensity in the second year. A significant decrease in the number of attached diatoms (Navicula spp.) was observed during the winter of the second year, possibly due to calm conditions (low tide and wind speed), which prevent the detachment of weakly attached species. Large blooms of euglenoids (Eutreptiella gymnastica and E. marina) in April and May were caused by the exclusive use of nutrients from the inflow of river water during the snowmelt season. Warm-water species sporadically occurred, suggesting their transportation by the Tsushima Warm Current. Temperature, nutrients, and light intensity primarily control microplankton communities, which vary seasonally. These findings led to the prediction of lower trophic levels due to the impact of warm water inflow.

Morphological Variability and Function of Labial Cartilages in Sharks (Chondrichthyes, Elasmobranchii).

(1) Background: Labial cartilages (LCs), as their name suggests, lie in the folds of the connective tissue, the lips, framing the gape of elasmobranch chondrichthyans. As such, these cartilages lie laterally to the jaws and marginal teeth. They are considered to influence the ability of creating suction during the feeding process. As past studies have shown, LCs in sharks are as diverse as their varied feeding techniques and differ between species in number, size, shape, and position. This allows establishing parameters for inferring the feeding and hunting behaviors in these ecologically important fishes. (2) Methods: We present a study of LCs based on the CT scans of more than 100 extant shark species and, therefore, represent at least one member of every living family within the Euselachii, excluding batoids. (3) Results: Accordingly, sharks without labial cartilages or that have only small remnants are ram feeders or use pure biting and mainly occupy higher trophic levels (tertiary and quaternary consumers), whereas suction-feeding sharks have higher numbers (up to five pairs) of well-developed LCs and occupy slightly lower trophic levels (mainly secondary consumers). Species with unique feeding strategies, like the cookie-cutter shark (Isistius brasiliensis, an ectoparasite), display distinct shapes of LCs, while generalist species, conversely, exhibit a simpler arrangement of LCs. (4) Conclusions: We propose a dichotomous identification key to classify single LCs into different morphotypes and propose combinations of morphotypes that result in suction feeding differing in strength and, therefore, different hunting and feeding strategies. The conclusions of this study allow to infer information about feeding strategies not only in extant less-known sharks but also extinct sharks.

Contrasting management regimes indicative of mesopredator release in temperate coastal fish assemblages.

The absence of functional top predators has been proposed as a mechanism acting to shape fish assemblages in temperate marine ecosystems, with cascading effects on lower trophic levels. We explore this scenario by comparing the trophic and functional status of fish assemblages in Norwegian marine national parks, open to fishing, to a nearby coastal seascape that harbors a system of marine protected areas (MPAs) including a no-take zone. Demersal fish assemblages were sampled using fyke nets over three consecutive seasons. Atlantic cod (Gadus morhua) is potentially a dominant top predator in this ecosystem, and historically, this and other gadids have been targeted by the full range of former and present fisheries. In the present study, we find that average body size of the Atlantic cod was significantly larger in the zoned seascape compared to the unprotected areas (mean ± SD: 36.6 cm ± 14.38 vs. 23.4 ± 7.50; p < .001) and that the unprotected seascape was characterized by a higher abundance of mesopredator fish species. These observations are consistent with the hypothesis that the protection of top predators within MPAs aids to control the mesopredator populations and provides empirical support to the notion that the present state of many coastal fish assemblages is driven by mesopredator release linked to functional depletion of large top predators.

Phytoremediation by Guinea grass (Panicum maximum): A Focused Review

Environmental contamination from heavy metals has grown to be a significant problem on a global basis. Due to the mobilisation of heavy metals during ore extraction and subsequent processing for diverse applications, they have been dispersed into the environment. Utilising plants for pollutant extraction, degradation, or volatilization is possible. Using plants and the bacteria that live on them to clean up the environment is known as phytoremediation. &#x0D; The bioaccumulation of elements in the body tissues of hyperaccumulator plants is used in phytoextraction, phytofiltration, phytostabilization, phytovolatilization, phytodesalination, and phytomining processes. As they move from low trophic levels to high trophic levels, their concentrations rise (a process also named as biomagnification). Recent studies indicates ability of Panicum maximum to clean places that have been contaminated with diversifed heavy metals and other types of pollution.

The influence of dynamic resources and stable isotope incorporation rates on aquatic consumer trophic position estimation

AbstractA key assumption in trophic position (TP) estimation using stable isotope analysis is that consumers are in isotopic equilibrium with their resources. Here, we assess the degree to which time‐varying resource dynamics and isotope incorporation rates of consumers influence consumer TP estimates across multiple trophic levels and aquatic ecosystems. We constructed a first‐order kinetics model to explore consumer stable isotope incorporation rates and modeled the effect on TP calculations using bulk and compound‐specific stable isotope data from previous experimental and observational studies. We found TP estimates of higher trophic level consumers are less accurate than lower trophic level consumers when applying bulk stable isotope analysis (BSIA) and using particulate organic matter as the stable isotope baseline. The accuracy of TP estimates depended on the time‐varying dynamics of the stable isotope baseline. Tertiary consumers had the highest TP estimation error, and this error was not eliminated by sampling tissues with fast incorporation rates (i.e., blood) in the tertiary consumer. Compound‐specific stable isotope analysis (CSIA) of individual amino acids was more accurate in estimating TP for all consumers and ecosystems compared to BSIA. Our analysis confirms that consideration for the dynamic nature of stable isotope ratios is necessary for accurate TP estimates. Finally, we show how first‐order kinetics models can provide a useful framework for integrating prey and consumer incorporation rates in stable isotope studies to improve TP estimates.

Fish microplastic ingestion may induce tipping points of aquatic ecosystems.

Microplastics can be ingested by a wide range of aquatic animals. Extensive studies have demonstrated that microplastic ingestion-albeit often not lethal-can affect a range of species life-history traits. However, it remains unclear how the sublethal effects of microplastics on individual levels scale up to influence ecosystem-level dynamics through cascading trophic interactions. Here we employ a well-studied, empirically fed three-species trophic chain model, which was parameterized to mimic a common type of aquatic ecosystems to examine how microplastic ingestion by fish on an intermediate trophic level can produce cascading effects on the species at both upper and lower trophic levels. We show that gradually increasing microplastics in the ingested substances of planktivorous fish may cause population structure effects such as skewed size distributions (i.e. reduced average body length vs. increased maximal body size), and induce abrupt declines in fish biomass and reproduction. Our model analysis demonstrates that these abrupt changes correspond to an ecosystem-level tipping point, crossing which difficult-to-reverse ecosystem degradation can happen. Importantly, microplastic pollution may interact with other anthropogenic stressors to reduce safe operating space of aquatic ecosystems. Our work contributes to better understanding complex effects of microplastic pollution and anticipating tipping points of aquatic ecosystems in a changing world. It also calls attention to an emerging threat that novel microplastic contaminants may lead to unexpected and abrupt degradation of aquatic ecosystems, and invites systematic studies on the ecosystem-level consequences of microplastic exposure.

Warming alters the top–down effect of a common mesopredator in an aquatic food web

Global warming is altering the composition and functioning of both terrestrial and aquatic ecosystems. Most research has focussed on direct effects of warming on species and their population dynamics, while less is known about indirect effects through species interactions. Trophic cascades are especially likely to influence the effects of warming given that trophic levels differ in their response to warming because of differences in metabolism and vital rates such as growth and reproduction. We investigated if the top–down effect of a common mesopredator, the threespine stickleback, alters the impact of warming on a Baltic Sea food web. We manipulated both temperature and the presence of stickleback in mesocosms, and found the stickleback to alter the impact of warming on lower trophic levels. This was through increased consumption of herbivores that exceeded the rate at which the herbivore population could grow under higher temperature, which in turn increased algae biomass compared to a scenario without stickleback, but not compared to conditions under normal temperature. Thus, the mesopredator increased the transfer of biomass to higher trophic levels of the food web when temperature was increased. This stresses the importance of considering the impact of warming on multiple trophic levels and their interactions. Failing to consider differences in responses among trophic levels and the impact this has on their interactions can result in faulty conclusions about the impact of warming on ecosystems.

Effects of proximity to humans on neophilia, foraging ecology and population structure of kea

ABSTRACT Neophilic tendencies in scavenging species living near humans may have adverse consequences for these animals. New Zealand’s kea (Nestor notabilis), an endangered parrot, potentially faces exacerbated mortality risk associated with proximity to humans. Hazards include lead building materials, introduced mammalian predators, and poison baits used to control these predators. How kea respond to these hazards can affect life expectancy. We modelled the effects of (1) proximity to humans, (2) age, (3) presence of conspecifics, and (4) blood lead levels, on the time taken to approach and contact a novel object. We also compared dietary trophic level between populations adjacent to and remote from humans using stable isotopes, and compared the age structure of these populations. Adjacent kea contacted the object faster than remote kea, as did younger individuals and those with elevated blood lead concentration, but conspecific presence did not affect approach latency. We conclude that adjacent kea exhibit enhanced neophilia, which may translate to reduced life expectancy due to interacting with anthropogenic hazards. Kea adjacent to humans were younger and foraged at a lower trophic level than remote kea, with a possible consequence of reduced productivity. Our results should be considered when setting management policy for kea habitat.

Seasonal and regional variability of model-based zooplankton biomass in the Salish Sea and evaluation against observations

We used a three-dimensional coupled biophysical model to examine zooplankton dynamics in the Salish Sea, NE Pacific. First, we evaluated the two zooplankton classes of the SalishSeaCast model using a transboundary zooplankton dataset comprised of observation data from the Canadian and United States waters of the Salish Sea from 2015 to 2019. Model zooplankton classes correspond to micro- and meso-zooplankton whose biomass is tightly coupled to phytoplankton through modelled food web dynamics (Z1) and mesozooplankton with life cycle-based seasonal grazing impacts (Z2). Overall, the model effectively captured seasonal patterns in observed biomass, although with slightly higher biomass estimates for both Z1 and Z2 (Bias = 0.10 and 0.08 g C m−2, respectively). Model fit varied regionally, with a weaker model fit being observed in nearshore regions. In addition, an autumn peak in Z2 was observed in the model, but not in the observations, suggesting some seasonal variations in model fit. Following the model evaluation, we used the model to determine seasonal and regional patterns of zooplankton grazing. Seasonally, the main peak in modelled zooplankton biomass increased in April or May in most of the regions defined within the Salish Sea and was driven by grazing on diatoms. Regionally, depth-integrated zooplankton biomass was consistently highest in areas adjacent to regions of strong tidal mixing. In addition, model-based zooplankton grazing was highest in the tidally mixed regions where phytoplankton biomass was high due to advection into the region despite low primary productivity. Our model-based results provide an opportunity to examine bottom-up food web processes at spatio-temporal scales not achievable with in situ sampling and help to elucidate key drivers of lower trophic level dynamics within the Salish Sea.

Seasonal changes in diet, immune function, and oxidative stress in three passerines inhabiting a Mediterranean climate.

Oxidative status and immune function are energy-demanding traits closely linked to diet composition, particularly resource availability and nutritional value. In seasonal environments, nutrient availability and diet quality fluctuate, potentially influencing these traits. However, limited evidence exists regarding these dietary effects on immune function in seasonal environments. In this study, we employed stable isotope analysis to assess the impact of seasonal changes in niche width and trophic level (i.e., δ15N) on two immune variables (hemolysis and hemagglutination scores) and two oxidative status parameters (lipid peroxidation and total antioxidant capacity) in three passerine species: Zonotrichia capensis (omnivorous), Troglodytes aedon (insectivorous), and Spinus barbatus (granivorous). We found that hemolysis scores varied seasonally in Z. capensis, with higher values in winter compared to summer. Total antioxidant capacity (TAC) also increased during the winter in Z. capensis and S. barbatus. The isotopic niche width for Z. capensis and S. barbatus was smaller in winter than in summer, with the omnivorous species exhibiting a decrease in δ15N. Despite the seasonal shifts in ecological and physiological traits in Z. capensis, we identified no correlation between immune response and TAC with trophic level. In contrast, in the granivorous S. barbatus, the lower trophic level resulted in an increase in TAC without affecting immunity. Our findings revealed that dietary shifts do not uniformly impact oxidative status and immune function across bird species, highlighting species-specific responses to seasonal changes. This underscores the importance of integrating ecological and evolutionary perspectives when examining how diet shapes avian immunity and oxidative balance.

Parental exposure to heat waves improves offspring reproductive investment in Tetranychus urticae (Acari: Tetranychidae), but not in its predator, Phytoseiulus persimilis (Acari: Phytoseiidae).

The more frequent and intense occurrence of heat waves is a challenge for arthropods because their unpredictable incidence requires fast adaptations by the exposed individuals. Phenotypic plasticity within and across generations might be a solution to cope with the detrimental effects of heat waves, especially for fast-developing, small arthropods with limited dispersal abilities. Therefore, we studied whether severe heat may affect the reproduction of a pest species, the spider mite Tetranychus urticae, and its counterpart, the predatory mite Phytoseiulus persimilis. Single offspring females with different parental thermal origins (reared under mild or extreme heat waves) of both species were exposed to mild or extreme heat waves on bean leaves over 10 days, and the oviposition, egg sizes, survival, and escape behavior of the females were evaluated daily. The total losses of predators mainly via escapers were very high compared to prey, which makes a separation between selective and plastic effects on shifted reproductive traits impossible. Predator females laid smaller eggs, while their consumption and oviposition rates were unaffected during extreme heat waves. In comparison, larger prey females fed more and produced more, but smaller, eggs due to within- and trans-generational effects. These advantages for the prey in comparison to its predator when exposed to extreme heat waves during the reproductive phase support the trophic sensitivity hypothesis: higher trophic levels (i.e., the predator) are more sensitive to thermal stress than lower trophic levels (i.e., the prey). Furthermore, the species-specific responses may reflect their lifestyles. The proactive and mobile predator should be selected for behavioral thermoregulation under heat waves via spatiotemporal avoidance of heat-exposed locations rather than relying on physiological adaptations in contrast to the more sessile prey. Whether these findings also influence predator-prey interactions and their population dynamics under heat waves remains an open question.

Comparative stable isotope analyses of green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) in the San Francisco estuary.

Green sturgeon (Acipenser medirostris) and white sturgeon (A. transmontanus) are closely related, sympatric species that inhabit the San Francisco estuary. Green sturgeon have a more marine life history but both species spawn in the Sacramento River and reside for some duration in San Francisco Bay. These sturgeons are of conservation concern, yet little is known about their dietary competition when they overlap in space and time. To examine evidence of dietary differentiation, we collected whole blood and blood plasma from 26 green sturgeon and 35 white sturgeon in San Francisco Bay. Using carbon and nitrogen stable isotope analyses, we compared their relative trophic levels and foraging locations along the freshwater to marine gradient. Sampling blood plasma and whole blood allowed comparison of dietary integration over shorter and longer time scales, respectively. Plasma and whole blood δ13 C values confirmed green sturgeon had more marine dietary sources than white sturgeon. Plasma δ15 N values revealed white sturgeon fed at lower trophic levels than green sturgeon recently, however, whole blood δ15 N values demonstrated the two species fed at the same trophic level over longer time scales. Larger individuals of both species had higher δ13 C values than smaller individuals, reflecting more marine food sources in adulthood. Length did not affect δ15 N values of either species. Isotope analyses supported the more marine life history of green than white sturgeon and potentially highlight a temporary trophic differentiation of diet between species during and preceding the overlapping life stage in San Francisco Bay.

Synergistic and additive effects of microplastic, nickel and pyrene on survival, reproduction, and egestion of a tropical copepod

Coastal tropical ecosystems provide livelihood for millions of people but are at the same time exposed to an increasing intensity of diverse anthropogenic stressors, including pollution. Nevertheless, the combined effects of pollutants on marine ecosystems are poorly understood, particularly regarding lower trophic levels (plankton) and tropical ocean. We exposed the tropical copepod Centropages velificatus to 4–5 concentrations of a heavy metal (nickel), an oil compound (pyrene) and microplastic (PET), either alone or in combination, and measured their egestion, reproduction, and mortality rates. Microplastic alone did not have any effect on pellet or egg production of copepods, whereas nickel reduced egg production rate at concentrations ≥1 µg L−1 and pyrene reduced both egg and pellet production rates at concentrations ≥1 nM. The addition of nickel and pyrene to PET - microplastic resulted in a reduction similar to one caused by nickel or pyrene alone, suggesting an additive effect. In contrast, a combination of nickel and pyrene had a synergistic effect, with a strong reduction in survival, egg and pellet production. Our results suggest that combinations of contaminants that are commonly found in tropical coastal waters have detrimental effects on copepods—the crucial link in the pelagic food web—at lower concentrations than suggested by single stressor studies. This can have an influence on the food web productivity - the basis of fisheries that local communities rely on.

Differential gene expression and developmental pathologies associated with persistent organic pollutants in sentinel fish in Troutman Lake, Sivuqaq, Alaska

Persistent organic pollutants (POPs) are lipophilic compounds that bioaccumulate in animals and biomagnify within food webs. Many POPs are endocrine disrupting compounds that impact vertebrate development. POPs accumulate in the Arctic via global distillation and thereby impact high trophic level vertebrates as well as people who live a subsistence lifestyle. The Arctic also contains thousands of point sources of pollution, such as formerly used defense (FUD) sites. Sivuqaq (St. Lawrence Island), Alaska was used by the U.S. military during the Cold War and FUD sites on the island remain point sources of POP contamination. We examined the effects of POP exposure on ninespine stickleback (Pungitius pungitius) collected from Troutman Lake in the village of Gambell as a model for human exposure and disease. During the Cold War, Troutman Lake was used as a dump site by the U.S. military. We found that PCB concentrations in stickleback exceeded the U.S. Environmental Protection Agency's guideline for unlimited consumption despite these fish being low trophic level organisms. We examined effects at three levels of biological organization: gene expression, endocrinology, and histomorphology. We found that ninespine stickleback from Troutman Lake exhibited suppressed gonadal development compared to threespine stickleback (Gasterosteus aculeatus) studied elsewhere. Troutman Lake stickleback also displayed two distinct hepatic phenotypes, one with lipid accumulation and one with glycogen-type vacuolation. We compared the transcriptomic profiles of these liver phenotypes using RNA sequencing and found significant upregulation of genes involved in ribosomal and metabolic pathways in the lipid accumulation group. Additionally, stickleback displaying liver lipid accumulation had significantly fewer thyroid follicles than the vacuolated phenotype. Our study and previous work highlight health concerns for people and wildlife due to pollution hotspots in the Arctic, and the need for health-protective remediation.