Plasticity of marine ecosystem dynamics as a condition for its stability: modeling seasonal and vertical dynamics of the Arctic shelf ecosystem.

Algal blooms in shallow lakes have attracting increasing attention owing to their high frequency and severe ecological harm. Previous studies, which primarily focused on single influencing factors such as nutrient input or toxins released by phytoplankton, have demonstrated that excessive nutrient input can increase the incidence of algal blooms, while high toxin levels exert an inhibitory effect. This study proposes a general analytical framework for exploring zooplankton grazing responses to phytoplankton-derived toxins and nutrient uptake, with a focus on zooplankton immunity to such toxins. A novel nutrient-phytoplankton-zooplankton model is adopted to investigate the combined impacts of nutrient input and phytoplankton-derived toxins on algal blooms, considering zooplankton immunity. We conduct analyses on the existence, stability, and bifurcations of the model to explore its complex dynamic behaviors, including Hopf bifurcation and Bogdanov-Takens bifurcation of codimension 2 and a degenerate case with a nilpotent cusp of codimension at least 3. Specific forms of nutrient uptake and zooplankton grazing functions are employed to validate the relevant theoretical results and perform numerical simulations. Beyond existing findings, this study reveals that oscillation periods tend to lengthen under lower toxin levels or higher nutrient input when oscillations occur.

Ciliate Uronema marinum feeding influences the production of dimethyl sulfur compounds.

Climate change and plankton dynamics: A fractional-order model-based investigation

The region off northwestern Australia in the eastern Indian Ocean is an oligotrophic open-ocean ecosystem characterized by low nutrients and high stratification, and is the only known spawning ground for Southern Bluefin Tuna (SBT). We conducted four multi-day Lagrangian experiments (cycles) and transect sampling to investigate plankton trophic flows during the peak SBT spawning season (Jan-Feb 2022). These cycles were carried out after recent storm mixing and subsequent warming and stratification of the water column. We quantified mesozooplankton size-fractionated biomass and grazing, targeting processes that coincide with SBT larval habitat (upper 30 m) and the full euphotic zone (150 m). Higher grazing occurred in the upper 30 m at the start of our study, coinciding with the deeper mixed layer. Euphotic-zone integrated grazing peaked later, coinciding with higher stratification and increased abundance of diatoms at depth. Mesozooplankton grazing impact averaged 0.11 ± 0.01 d -1 for the region, equivalent to 21.2% of phytoplankton growth, Combined with microzooplankton grazing removals, phytoplankton growth and total zooplankton grazing losses were approximately in balance for the euphotic zone. While direct consumption of phytoplankton only supported respiratory needs of a portion of the assemblage in two of the four experimental cycles, respiratory and production needs were largely met by including the consumption of microzooplankton production. Thus, the production of mesozooplankton prey required to sustain SBT larvae in this nutrient-poor environment was obtained by both high grazing and efficient trophic coupling. This study highlights the role of metazoan zooplankton in warm oligotrophic waters of the eastern tropical Indian Ocean and indicates that efficient ecosystem transfer can be achieved even under conditions assumed to severely limit production and biomass accumulation.

Harmful cyanobacterial blooms pose increasing threats to aquatic ecosystems and human health; yet, the role of zooplankton grazing in regulating blooms remains understudied. We investigated the seasonal feeding behaviour and fitness consequences of feeding preferences in natural zooplankton communities for toxic (microcystin-producing) versus non-toxic cyanobacteria across temperature gradients in eutrophic Lake Greifen, Switzerland. We conducted monthly experiments from April to October 2023 to test the grazing behaviour of four zooplankton groups (daphnids, calanoid copepods, cyclopoid copepods, and microzooplankton) exposed to mixed diets of green algae and either toxic or non-toxic Microcystis strains at 15 °C and 25 °C. Contrary to expectations of cyanobacteria avoidance, zooplankton exhibited predominantly non-selective grazing throughout the seasonal succession, consuming both toxic and non-toxic cyanobacteria at similar rates, regardless of temperature. Notably, during the peaks of phytoplankton abundance (April and September), mesozooplankton demonstrated a selective preference for cyanobacteria over green algae, particularly non-toxic strains. Temperature effects were subtle but revealed metabolic constraints: elevated temperatures occasionally triggered selective consumption of cyanobacteria in copepods, while fitness costs (survival) from exposure to toxic species were mostly restricted to transitional bloom periods and high-temperature conditions. These findings suggest that toxic cyanobacteria may not always evade grazing pressure through secondary metabolite deterrent effects. Our results suggest that zooplankton communities can adapt and graze on cyanobacteria regardless of toxicity under the tested conditions, even during bloom conditions. These observations highlight the potential for zooplankton to interact with cyanobacterial populations, which may have implications for bloom prediction and management strategies, particularly under climate warming scenarios.

Photosynthetic microorganisms are responsible for primary production at the base of the marine food web and influence global biogeochemistry. Their growth is balanced by mortality processes, including zooplankton grazing and viral lysis. These predators coexist despite competing for the same microorganisms. Here, we develop a community model of photosynthetic microorganisms, grazers and viruses that incorporates elemental quotas and is suitable for ocean ecosystem models. We evaluate the extent to which coexistence is facilitated by: (i) explicit infected phytoplankton; (ii) heterogeneity in susceptibility to viral infection; and (iii) higher-order mortality for the predators. We show a trade-off between the virus latent period and virulence in facilitating coexistence. The latent period generates oscillations that reduce the growth rate of the free virus, promoting coexistence. Heterogeneity in susceptibility supports coexistence through resource partitioning, while higher-order mortality widens the coexistence regime. The model outcomes are sensitive to viral life history traits, including the percentage of infected cells and the balance between virally- and zooplankton-induced mortality. Leveraging algebraic model equilibria, we identify parameter combinations that yield realistic ecological properties in simplified epipelagic environments. Our models suggest that efforts to embed virus dynamics in ocean ecosystem models should include moderate to strong resistance to viral infection.

Polycyclic aromatic hydrocarbons and chlorophenols are common aquatic pollutants from industrial and agricultural runoff that have adverse effects on living organisms and aquatic ecosystems in general. While aquatic wildlife is often exposed to these contaminants simultaneously, little is known about their combined effects. To fill this gap, we tested whether and how exposure to relevant concentrations of phenanthrene (Phe), 2,4-dichlorophenol (2,4-DCP), or a mixture of both altered key behaviors in brine shrimp (Artemia parthenogenetica), an emerging model in behavioral ecotoxicology. We exposed newborns to one of four treatments until adulthood: control, Phe (400 ng/L), 2,4-DCP (400 ng/L), and the combination of both Phe and 2,4-DCP (400 ng/L each). We repeatedly measured individual activity levels at adulthood in both the x-y plane (distance moved) and in three dimensions (mobility), as suggested for planktonic animals. We found that Phe, but not 2,4-DCP, significantly reduced average activity levels that were better captured by looking at activity in three than two dimensions. When combined, the pollutants appeared to exhibit an antagonistic interaction, with 2,4-DCP mitigating phenanthrene's negative impact on average mobility levels. Moving beyond average effects, we tested whether effects also appeared at the individual level. Our analysis revealed that within-individual variation (behavioral plasticity) in mobility decreased substantially in all exposure treatments compared to unexposed animals, whereas between-individual variation (behavioral individuality) did not vary. Our findings highlight the importance of considering interactive and individual-level effects of pollutants in ecological risk assessment, as effects may differ from predictions based on single contaminants and average responses alone.

Most alpine-type lakes in the Tatra Mountains were stocked with salmonid fish during the 19th and 20th centuries, triggering profound ecological shifts. In the Five Lakes Valley, trout introductions into Przedni Staw Polski, Czarny Staw Polski and Wielki Staw Polski had contrasting effects on pelagic ecosystems. In the smaller and shallower Przedni Staw Polski and Czarny Staw Polski, fish introduction was associated with the loss of large-bodied zooplankton, increased trophic status and a rapid decline in water transparency—from 13–18 m to 5–7 m. Between 2021 and 2023, partial fish removal in Przedni Staw Polski resulted in a marked increase in water transparency (from 7 to 17 m), coinciding with reduced surface phytoplankton biomass. This improvement likely reflected decreased phosphorus input from fish excretion rather than enhanced zooplankton grazing. Large-bodied cladocerans did not recolonize the lake, although small-bodied taxa increased in abundance. In contrast, Czarny Staw Polski—where fish remain abundant—showed no signs of recovery: water transparency declined further and zooplankton community structure remained unchanged. Unlike the other stocked lakes, Wielki Staw Polski—the largest and deepest—retains high transparency and large-bodied zooplankton, likely due to low fish density or availability of predator-free refugia. While partial fish control in Przedni Staw Polski yielded rapid benefits, restoring natural ecosystem functioning in these fragile alpine ecosystems will require complete fish eradication.

One of the major subfields of chemical ecology is the study of toxins and how they mediate interactions between organisms. Toxins produced by harmful algae (phycotoxins) impact a wide variety of organisms connected to the marine food web. Significant research efforts have thus aimed to identify the ecological and evolutionary drivers behind harmful algal blooms (HABs) to facilitate their forecasting, mitigation, and management. Nutrient availability is a key factor controlling growth and toxin production. Additionally, recent evidence has shown that harmful algae can sense the presence of zooplankton grazers, primarily copepods, and respond by dramatically increasing toxin production. Phycotoxin production is consequently controlled by a combination of bottom-up and top-down drivers, but the relative importance of the two is not understood. We therefore conducted a meta-analysis of 113 control-treatment contrasts from 37 peer-reviewed experimental studies, comparing the effects of relative nitrogen enrichment (defined here as an increased nitrogen: phosphorus ratio relative to control) and elevated grazing risk (exposure to zooplankton grazers or their chemical cues) on phycotoxin induction. We focused on the two most studied marine HAB-forming genera, Alexandrium dinoflagellates and Pseudo-nitzschia diatoms. We show that phycotoxins are induced in response to both relative nitrogen enrichment and elevated grazing risk. Although both genera responded similarly to relative nitrogen enrichment, Pseudo-nitzschia toxins increased 10 times more than Alexandrium toxins in response to grazers. Grazing risk thus appears to rival, perhaps even supersede, the well-established phycotoxin-inducing effect of relative nitrogen enrichment in marine harmful algae. Although this analysis is limited to the two most-studied marine HAB genera, we conclude that future attempts to understand the evolution and variable production of phycotoxins require integration of bottom-up nutrient availability and top-down selective pressures to elucidate phycotoxin dynamics in marine HAB-forming species.

Abstract The carbon sequestration capacity of the biological carbon pump (BCP) is determined by surface ocean carbon fixation and the transportation of fixed carbon to the ocean interior, which is closely linked to the trophic structure of planktonic ecosystem. However, previous biogeochemical reconstructions focused mostly on primary productivity, overlooking changes in community structure (e.g., ratio of primary producers to consumers). In this study, we investigate the late Quaternary history of planktonic trophic structure in the western equatorial Pacific by generating sedimentary amino acid δ 15 N record of Site MD10‐3340. Our results demonstrate well‐preserved amino acid δ 15 N signatures. Using the δ 15 N gradients between trophic and source amino acids, we calculate the average sedimentary trophic position and design an idealized ecosystem model to quasi‐quantitively estimate changes in grazing proportion (the proportion of primary production consumed by zooplanktons). Notably, lower trophic position and smaller grazing proportion point to a decline of zooplankton grazing during precession maxima, which is primarily attributed to enhanced nutrient availability in the western equatorial Pacific during El Niño‐like mean‐states. Moreover, average grazing proportion is slightly lower during Interglacial warmth than the last glacial period, implying a secondary control of sea level change. Furthermore, our ocean‐biogeochemical simulations show that a halved grazing proportion could cause pronounced decrease in Pacific carbon storage and a remarkable increase in atmospheric p CO 2 , due to a shallower remineralization depth. We thus highlight the necessity to incorporate varying marine grazing proportions into future proxy reconstructions and model simulations to facilitate a more comprehensive understanding of the BCP.

Eutrophication remains a persistent challenge in the Romanian Black Sea coastal zone, driven by excess nutrient inputs from riverine and coastal sources and further intensified by climate change. This study assesses eutrophication dynamics and explores mitigation options using an integrated framework that combines in situ observations, satellite-derived chlorophyll a data, machine learning, and system dynamics modelling. Water samples collected during two field campaigns (2023–2024) were analyzed for nutrient concentrations and linked with chlorophyll a products from the Copernicus Marine Service. Random Forest analysis identified dissolved inorganic nitrogen, phosphate, salinity, and temperature as the most influential predictors of chlorophyll a distribution. A system dynamics model was subsequently used to explore relative ecosystem responses under multiple management scenarios, including nutrient reduction, enhanced zooplankton grazing, and combined interventions. Scenario-based simulations indicate that nutrient reduction alone produces a moderate decrease in chlorophyll a (45% relative to baseline conditions), while restoration of grazing pressure yields a comparable response. The strongest reduction is achieved under the combined scenario, which integrates nutrient reduction with biological control and lowers normalized chlorophyll a levels by approximately two thirds (71%) relative to baseline. In contrast, a bloom-favourable scenario results in a several-fold increase in chlorophyll a of 160%. Spatial analysis highlights persistent eutrophication hotspots near the Danube mouths and urban discharge areas. These results demonstrate that integrated strategies combining nutrient source control with ecological restoration are substantially more effective than single-measure interventions. The proposed framework provides a scenario-based decision-support tool for ecosystem-based management and supports progress toward achieving Good Environmental Status under the Marine Strategy Framework Directive.

Effects of micro- and nano-plastics on community assemblages and dimethylated sulfur compounds production.

The rapidly changing Arctic has led to evolving natural aerosol emissions, which have strong feedback effects on its climate system. Sea spray aerosol (SSA) particles are a main source of aerosols; they influence cloud formation and cloud properties. Ocean microbiota potentially have an impact on SSA production and flux, but our understanding of the mechanisms is still limited. The potential impact of ocean microbiota on SSA fluxes is still a matter of active research. In this multidisciplinary study conducted in the central Arctic during The Multidisciplinary Drifting Observatory for the Study of Arctic Climate expedition, air–sea interactions were measured by means of in situ bubble-bursting experiments. For the first time, we studied the effect of zooplankton grazing on aerosol production. We found that surface water subjected to zooplankton grazing had a 2-fold increase in SSA production relative to controls without zooplankton. Our biogeochemical results suggest that fresh organic material—possibly dissolved organic carbon and dissolved organic nitrogen from humic-like substances—influences aerosol production. We find a strong chemical-selective process affecting SSA production, with humic-like substances much enriched (40%–280%) relative to protein-like material in the aerosol relative to the water. Our results point to a complex relationship between specific low-concentration organic components in the water phase and its relative capability of being aerosolized, with strong chemically selective processes affecting SSA production. We provide evidence for the role of zooplankton, implying a complex microbial loop that may be regulating the organic component of the SSA production. This study underlines the role of zooplankton in biogeochemical cycles, due to their large biomass and transformation of organic matter during feeding and digestion. Similar processes may occur in other regions with high zooplankton grazing impact, for example, in productive parts of the Southern Ocean and in upwelling regions.

Zooplankton or animal plankton, is an organism that is generally small in size whose life is swayed by currents in the free ocean. Banda Sakti District, Lhokseumawe City is a coastal area with potential for the study of its coastal waters, which have not been extensively explored. The purpose of this study was to assess the zooplankton community structure—including abundance, diversity, uniformity, and dominance in the coastal waters of Banda Sakti District, and to evaluate water quality conditions in relation to their suitability for supporting zooplankton life. The research was conducted in December 2021 in the coastal waters of Banda Sakti District, Lhokseumawe City, using a purposive sampling method. A total of 50 zooplankton species representing 10 phyla were identified. The total abundance of zooplankton in this study ranged from 105.55 – 140.27 ind/L. In this study, the diversity index value ranged from 22.14 to 2.77, the uniformity index ranged from 0.65 to 0.79, and the dominance index ranged from 0.04 to 0.05. Overall, water quality parameters indicated that the coastal waters of Banda Sakti District remain within suitable conditions to sustain zooplankton communities according to established environmental standards.

Speciation and leachability of radiocesium in the soil, sediment, and aquatic organisms surrounding Lake Onuma at Mt. Akagi.

Seasonal dynamics at low trophic level and ecological interactions of microbial and plankton communities during harmful algal blooms.

Size-Dependent grazing and trophic cascades shape Zooplankton-phytoplankton interactions in Eutrophic Lake.

In the Elbe estuary, a sharp decline in phytoplankton concentration is observed as the river reaches the deep shipping channels of the Port of Hamburg. This collapse significantly impacts the estuarine food web and carbon cycle, shifting the ecosystem from autotrophic to heterotrophic. Previous studies hypothesized that this decline is primarily due to zooplankton grazing. We propose an alternative hypothesis focused on the role of phytoplankton aggregation with inorganic suspended sediments. We present a novel individual-based Lagrangian model of the Elbe estuary. This model couples hydrodynamic, sediment transport, and biogeochemical processes to investigate the influence of aggregation on phytoplankton mortality. By explicitly accounting for the effect of aggregation-induced sinking, our model suggests that over 80% of phytoplankton larger than 50 µm may be lost to light-limitation-induced mortality. Furthermore, the mortality pattern predicted by our model aligns with areas of intense organic matter remineralization in the estuary. These findings underscore the need for estuarine-specific ecosystem models that can capture the complex interplay between physical and biogeochemical processes in these dynamic environments, while demonstrating the potential of Lagrangian methods to provide new insights into the mechanisms shaping estuarine ecosystems.

ABSTRACT Understanding mechanisms governing phytoplankton succession under nutrient fluctuations is essential for algal bloom prevention. Using the Qiantang River Basin as a model system encompassing mesotrophic to mid-eutrophic conditions, we investigated phytoplankton assemblage shifts, bloom-forming traits, and main regulatory mechanisms behind nutrient-driven phytoplankton dynamics. We identified 268 phytoplankton with abundance and biomass ranging from 2.71 × 104 to 9.42 × 106 ind L−1 and 0.025–4.49 mg L− 1, respectively. Phytoplankton diversity and biomass increased with nutrient levels, and eutrophication caused taxonomic shifts: Cyanophyta abundance increased significantly while Bacillariophyta declined. Network analysis revealed that nutrient-rich waters supported stronger phytoplankton–zooplankton interactions, highlighting a zooplankton-mediated top-down regulatory mechanism that could constrain phytoplankton biomass accumulation through intensified grazing pressure. Specific nutrient forms (e.g., ammonium [NH4-N], nitrite [NO2-N], phosphate [PO4-P], and dissolved total phosphorus) were primary environmental drivers shaping phytoplankton composition, accounting for 56% of community variation, while zooplankton contributed 25.6%. Mid-eutrophic sites supported more bloom-forming taxa with motility (37.1–73.6%), toxicity (11.4–43.0%), and nitrogen fixation (7.8–24.6%) traits. Mechanistically, bottom-up nutrient supply and top-down zooplankton grazing were both significant regulators of phytoplankton dynamics. These results emphasize the importance of nutrient species, ecological feedback, and functional trait dynamics in modulating algal bloom risks under eutrophication.