Abstract The mixotrophic ciliate Mesodinium rubrum is a species of significant ecological importance and is known for forming massive, nontoxic blooms. While the presence of prey cryptophytes and favorable temperatures is recognized as key factors in bloom formation, the dynamics of life stage transitions in response to changing environments remain poorly understood. In this study, the stage-specific size spectra of M. rubrum were obtained through an integrated field-laboratory approach using an Imaging FlowCytobot (IFCB). The results show that temperature strongly modulated size-class rhythms and biovolume-based division rates of M. rubrum. At high temperature (25°C), the cell cycle was extended (24 h vs. 18 h at 17°C), promoting somatic growth (increase in cell biovolume) rather than immediate reproductive division. The prolonged cycle allowed greater resource accumulation per division, resulting in larger cell sizes and pronounced biovolume oscillations (2.7 to 3.3 times greater amplitude). The estimated division rate was 0.365 d−1 at 25°C, compared to 0.141 d−1 at 17°C. Prey availability had only minor effects on size-class proportions within a 24 h window, across predator: prey ratios between 2000:1000 and 2000:8000, suggesting both tested prey concentrations were near-saturating. In field samples, a distinct “medusa form” morphotype appeared exclusively during daylight hours, particularly within the first 6 h after sunrise. Together, these findings reveal the capacity of M. rubrum to modulate cell cycle dynamics in response to short-term temperature changes, with ecological implications for the growth of this cosmopolitan species across its broad thermal range. The integrated field—laboratory approaches demonstrated that the temperature-dependent biovolume rhythms represent a physiological acclimation mechanism that shifts life stages, thereby optimizing the fitness of M. rubrum in a fluctuating, warming environment.
Microzooplankton ecology was transformed by the dilution method, which made grazing measurable in natural plankton communities and established protistan grazers as major consumers of marine primary production. Four decades later, the field faces a different challenge. Automated imaging, metabarcoding, meta-omics and machine-learning tools increasingly resolve plankton identity, diversity and spatial structure, but grazer-resolved rates of ingestion, growth, prey selectivity, mortality and carbon transfer remain much harder to measure. This creates an identity-rate gap: community structure is becoming easier to describe than ecological function. The gap should not be reduced to a contrast between one classical method and modern identity tools; it reflects a broader difficulty of pairing organisms, prey, rates and environmental context within the same inference framework. Dilution experiments and related rate approaches remain indispensable, but their interpretation depends on assumptions about prey growth, grazer responses, nutrient limitation, mixoplankton behavior and bottle effects. Preserved samples also remain central to biomass estimates, although fixation and storage distort protists in taxon-specific ways. I argue that the next phase of microzooplankton ecology should not abandon classical incubations, but make them identity-aware, preservation-aware and model-facing through tiered datasets that separate bulk prey mortality, prey-resolved rates, targeted grazer-prey links and model-facing trait constraints.
ABSTRACT We examined the possible influence of the anticyclonic Ulleung Warm Eddy (UWE) on copepod community production, fecal pellet production (FPP), and suspended fecal pellet (SFP) biomass in the Ulleung Basin. Copepod biomass and production appeared to show spatial variability across the UWE, with relatively higher values observed at the eddy ring and outside the eddy compared to the eddy core. Large copepods, particularly Neocalanus, contributed substantially at the eddy ring and outside the eddy, whereas medium-sized copepods were more prevalent in the eddy core. FPP of the copepod community and SFP biomass also appeared to show a similar elevated trend at the eddy ring. Furthermore, SFP exhibited distinct diel variability at the eddy ring, reaching maxima at 100 m during the day and at 10–30 m at night, whereas little diel variation occurred at the eddy core. These results suggest that the UWE influences copepod size structure, production, and fecal pellet dynamics, highlighting potential implications for upper-ocean biogeochemical cycling and carbon export efficiency. Rather than relying on a statistically replicated regional survey, this study provides a process-oriented observational assessment of copepod community responses across the UWE.
Abstract Etymological classifications of species epithets provide insight into how taxonomists encode morphology, ecology and culture in scientific names, but such classifications are rarely available for large clades. We benchmarked a large language model (LLM) against expert labels for the etymology of species epithets in 989 zooplankton species (rotifers and microcrustaceans). The LLM assigned each epithet to one of five categories (Morphology, Ecology & Behavior, Geography, People, Culture), and we evaluated its predictions using a confusion matrix, overall accuracy, Cohen’s kappa, per-class precision, recall and F1-scores, and generalized additive models (GAMs) fitted to yearly and decadal frequencies. Overall accuracy was 0.84, with Cohen’s kappa of 0.74. F1-scores were very high for Morphology and People and high for Geography, but moderate for Ecology & Behavior and low for Culture. GAMs showed that LLM-based labels broadly reproduced long-term temporal trends in epithet usage, with clear discrepancies only for Culture-related names. These results indicate that LLMs can provide reliable first-pass etymology labels and support macro-scale analyses of naming practices, while culturally nuanced and context-dependent epithets remain under expert curation. We recommend using LLM-based classification as a complementary, human-in-the-loop tool for building and maintaining large etymology databases.
The Amazon River plume generates strong hydrographic gradients that shape pelagic ecosystem functioning in the tropical Atlantic. We quantify the relative influence of key environmental drivers on copepod biomass and diversity and identify indicator taxa across contrasting plume regions. Using data from the AMAZOMIX expedition, we sampled three hydrographic zones, the coastal plume [Shelf Amazon River Plume (SARP)], oceanic plume (Ocean Amazon River Plume) and oligotrophic ocean (Non-Amazon River Plume). Twenty-five copepod families were recorded, reflecting high biodiversity across plume-influenced and oceanic environments. Hierarchical Bayesian models were used to assess environmental effects and to derive a Latent Ecosystem Functioning Index (LIFE), defined as a shared ecological state integrating biomass and diversity along environmental gradients. Copepod biomass peaked in the plume-influenced SARP (mean = 1 585 mu g C m-3) and was positively associated with fluorescence (beta = 392) and salinity (beta = 257), indicating strong bottom-up control. In contrast, diversity showed weak environmental responses, suggesting stronger dependence on habitat heterogeneity than on productivity. LIFE was strongly correlated with biomass (r = 0.93) but not with diversity (r = 0.03), revealing a spatial decoupling between productivity and community structure. These findings emphasize key environmental drivers of copepod biomass and propose a latent ecosystem functioning index as an integrative tool for plume-affected ecosystems.
Zooplankton is a key component of marine food webs, yet its short-term variability in submarine canyons remains poorly resolved. Here, high-frequency changes in mesozooplankton abundance, hydrography, acoustic backscatter, and Acoustic Doppler Current Profiler (ADCP)-derived velocity structure were examined during a 24 h fixed-station study at the head of the Biob & iacute;o Canyon, central Chile, an area influenced by the Biob & iacute;o River plume. Integrated WP2 net tows were collected every 3 h, and environmental variability was characterized with a MIDAS CTD and a 300 kHz RDI Workhorse ADCP. Copepods and amphipods dominated the zooplankton assemblage. Acoustic backscatter revealed a clear diel vertical migration signal, while rotated depth-mean-removed along-canyon velocities, harmonic diagnostics, phase composites, and echo-anomaly gradients indicated vertically heterogeneous near semidiurnal baroclinic modulation. Amphipods were most closely associated with a diurnal cycle, whereas several other groups, especially gelatinous taxa, were more consistent with near semidiurnal variability. These results indicate that internal-tide-like baroclinic forcing co-occurred with strong biological diurnal behavior, jointly shaping zooplankton dynamics at the canyon head.
ABSTRACT Urbanization is one of the main drivers of environmental degradation in continental aquatic ecosystems. Although numerous studies have examined links between urbanization and the structure of aquatic communities, conclusive generalizations about its effects on planktonic communities remain elusive. Drawing on a meta-analysis of 38 studies in urban lakes, we evaluated (i) whether the impacts of urbanization on plankton community attributes (density, biomass, richness, and diversity) are consistent across independent studies (i.e. show a common direction and limited between-study heterogeneity) and (ii) where variation occurs, to identify moderators (e.g. surrounding land use) that may account for between-study differences. We quantified pooled effect sizes using Hedges’ g, meta-regression and subgroup analyses to test moderators, including sampling extent, response descriptors, urbanization measures, and taxonomic group. Between-study heterogeneity was quantified with T2 and I2. The overall effect size did not differ significantly from zero, and heterogeneity was high, indicating context-dependent responses. Among urbanization measures, land use and urban density showed detectable effects, whereas other measures showed no consistent pattern. We call for methodological standardization (particularly in urbanization metrics and spatial extent, plankton response descriptors, and reporting of summary statistics and metadata) to enable generalizations about the biodiversity consequences of urbanization in aquatic ecosystems.
Multi-decade ocean monitoring of plankton is important to distinguish between short-term variability due to environmental drivers and longer-term changes due to climate stressors. Traditional methods for plankton enumeration are time consuming, have long lag times, and preservation may result in cell shrinkage. Fluorometric measurements of Chlorophyll-a concentrations exclude pigment separation, which is required to identify and quantify major taxonomic groups. To address these challenges, flow imaging microscopy (FIM) and high-performance liquid chromatography (HPLC) pigment analysis were combined to optimize the detection of plankton biomass seasonal patterns and their environmental drivers in the Bedford Basin, Nova Scotia, Canada. Eleven plankton sub-groups were detected, three of which overlapped between methods (pigmented dinoflagellates, diatoms and euglenoids). The HPLC was able to detect small cells (e.g. nano-diatoms), while FIM added higher taxonomic resolution and detection of non-pigmented cells, including two of the highest biomass groups, ciliates and non-pigmented dinoflagellates. Hierarchical clustering of the composite community dataset revealed four communities: C1-diatom/cryptophytes, C2-ciliates/chlorophytes, C3-dinoflagellates/haptophytes and C4-diverse community, which were influenced by seasonal cycles associated with nutrient replenishment and stratification. The complementary approaches increased monitoring efficiency of plankton population dynamics, which is essential for understanding the marine ecosystem and potential impacts of anthropogenic climate change.
The Guinea Current Large Marine Ecosystem (GCLME), located in the Eastern Equatorial Atlantic, is highly productive and supports important coastal livelihoods and fisheries across West Africa. Mesozooplankton and hydrographic sampling were conducted across an extended area of the GCLME, from Guinea-Bissau to Ghana, during two consecutive surveys between July and September 2017. The sampling coincided with the West African Monsoon and the major upwelling period in the central GCLME (C-GCLME: Côte d'Ivoire, Ghana), while the western GCLME (W-GCLME: Guinea-Bissau to Liberia) experienced its main rainy season. Contrasting hydrographic regimes between the two subsystems were reflected in the zooplankton community structure and distribution patterns. The cooler upwelled waters of the C-GCLME supported significantly higher mesozooplankton stock and a copepod assemblage characterized by opportunistic, or upwelling-associated species (i.e. Calanoides natalis, Centropages chierchiae), most prominently along the Ivorian and eastern Ghanaian coasts. In contrast, the W-GCLME was characterized by thermally stratified, low-salinity waters influenced by riverine inputs, supporting thermophilic, as well as opportunistic species, particularly along the Guinea-Sierra Leone Plateau. These results highlight clear ecological differences between the two subsystems and provide baseline information on zooplankton biomass and biodiversity, relevant to local food web dynamics and ecosystem-based management efforts.
Understanding how early life stages of Calanus finmarchicus respond to warming is crucial for predicting the resilience of North Atlantic ecosystems under climate change. We experimentally investigated the effects of heat stress on resting metabolic rate and key life-history traits, including hatching success, developmental time, body size and mortality, as well as the combined effects of temperature and food availability on naupliar survival. Increasing temperature (10°C-24°C) accelerated hatching and development but reduced hatching success, with no hatching observed at 23°C and 24°C. Nauplii developed faster at 15°C than at 10°C but were smaller, indicating a trade-off between growth and developmental rate. Mortality increased with temperature (10°C vs 15°C), although food availability partially mitigated this effect, suggesting that energetic input can buffer, but not fully compensate for thermal stress. Egg metabolic rate remained stable across temperatures, while naupliar metabolic rate followed a thermal performance curve, peaking at 15°C and declining at higher temperatures. These findings reveal strong, stage-specific thermal sensitivities and highlight physiological trade-offs between metabolic demand, growth and survival. As marine heatwaves become more frequent, such responses could lead to smaller, less viable individuals and reduced prey quality, ultimately affecting trophic transfer and marine population productivity.
Artificial intelligence is already reshaping the production of scientific text, literature synthesis, coding and image-based biological analysis. In plankton research, where automated imaging, molecular surveys and large ecological datasets are expanding rapidly, the critical bottleneck will increasingly be empirical validation: knowing organisms, recognizing artefacts, maintaining cultures, designing biologically meaningful experiments and judging whether automated outputs remain faithful to living plankton. Yet these are precisely the skills that many evaluation systems have allowed to erode. Taxonomy, fieldwork, experimental manipulation, natural history and specimen curation have lost institutional status in a culture that rewards speed, scale and publication volume. The rise of AI makes this loss urgent rather than merely unfortunate. This Horizons article argues that AI will not eliminate the need for plankton experts; it will expose how dangerous it is to lose them. Journals, funders and training programs should therefore revalue empirical expertise, not out of nostalgia, but because taxonomic, experimental and organismal judgment will soon become the bottleneck on which the credibility of AI-assisted plankton science depends.
Predator specific chemicals cues (so-called kairomones) are essential in shaping aquatic predator–prey interactions. While past research has largely focused on identifying these predator related kairomones, the broader question of whether predator kairomones function as universal signals (detected by many prey taxa) or as highly specific cues (recognized only by certain taxa) has received little attention. This distinction is crucial for understanding evolutionary ecology, and the response of food webs to environmental change. Universal predator kairomones can be widely emitted by predator taxa and are recognized by various prey taxa, offering a generalized warning system in dynamic ecological contexts. However, this general responsiveness of the prey may increase the risk of false alarms and unnecessary defensive responses. In contrast, specific predator kairomones are unique compounds, allowing for tailored defensive strategies in prey species but limiting adaptability to novel threats. This article integrates current knowledge of predator kairomone chemistry with the evolution of sensory detection pathways. We hypothesize that chemical communication is a mosaic of universal and specific predator kairomones and may be shaped by the phylogenetic background of the prey species. Understanding this balance is one key to predicting food web stability and adaptation under changing conditions.
Abstract Plankton community respiration (PCR) plays a central role in aquatic ecosystems, driving the breakdown of organic matter and influencing global carbon cycling through its contribution to the production and consumption of carbon and oxygen. Coastal areas are regarded as metabolic hotspots in the oceans, due to their intense biological and biogeochemical activities. This review synthesizes experimental evidence to explore how environmental constraints and climate drivers affect PCR in European coastal waters. In total, 46 studies were found in which PCR was measured during experiments testing the effects of one or multiple global climate change drivers in European coastal waters. Among them, the majority of experiments focused on changes in temperature, nutrient concentrations and stoichiometry, and/or pH, while other stressors were less studied. In addition to this qualitative synthesis, a quantitative meta-analysis was conducted on warming and acidification experiments, the only drivers for which comparable experimental designs were available. This analysis, based on 19 warming and 6 acidification studies, was used to perform a standardized comparison of effect sizes across studied areas and experimental set-ups. This review highlights critical knowledge gaps, notably regarding non- and understudied areas and understudied interactions between stressors that occurs jointly in ecosystems.
Salps are pelagic tunicates capable of rapid growth, impacting marine ecosystems. Salp blooms may result from the effect of environmental factors on its biology or physical aggregation caused by hydrodynamics. Understanding salp distributions requires a regional perspective, but most studies in the northwestern Mediterranean have been local. We (i) analyse how mesoscale spatial patterns are structured by local physical and biological conditions and (ii) characterize life-stage distributions of Salpa fusiformis and Thalia democratica. Using generalized additive models, we analysed spatial patterns across 80 stations along transects off the Catalan coast. Results showed that S. fusiformis concentrated along the shelf break and slope, following the Northern Current, with occurrences shaped by transport, passive accumulation at the shelf-slope front and intrusions around anticyclonic eddies. In stations with high S. fusiformis abundance, populations were characterized by a higher proportion of mature oozoids and blastozoid buds, suggesting active asexual reproduction. Thalia democratica was restricted to warm stratified coastal waters and absent from colder, less stratified northern areas influenced by slope water intrusions. Its population was dominated by blastozoids with a visible embryo, suggesting limited growth. This study shows that mesoscale hydrodynamics are important in shaping salp distribution, while indirectly influencing population demography in the northwestern Mediterranean.
Global warming threatens zooplankton across generations, yet quantifying transgenerational thermal responses remains labor-intensive. We developed and validated a U-Net-based morphometric model pipeline integrated with non-linear growth models to quantify body-size dynamics of Mesocyclops woutersi across temperatures and generations. Trained on 1786 annotated images, the model achieved high segmentation accuracy (R2 = 0.99, IoU = 0.90, Dice = 0.94) and strong agreement with manual measurements (R2 = 0.974, MAE = 0.02, RMSE = 0.044; n = 300), substantially reducing processing time. Body length and volume were fitted to four growth models under 24, 28 and 32 degrees C across three generations. The Hernandez-Llamas & Ratkowsky model best described length dynamics (R2 = 0.91-0.94, competitive AIC, narrow confidence intervals). Copepods at 28 degrees C developed faster and reached larger sizes than at 24 degrees C, indicating optimal conditions. In contrast, the third generation at 32 degrees C showed delayed development without significant changes in size or growth coefficients, suggesting thermal stress primarily altered developmental timing. Integrating machine learning-based morphometrics with growth modeling framework provides a scalable, objective approach for transgenerational copepod research under climate warming.
Developmental transitions from nauplii to copepodites are critical in ocean ecology, yet behavioral and kinematic changes across stages remain understudied, especially in cruise-feeding copepods. Using high-speed microscale imaging, this study quantified morphology, swimming and appendage beating in nauplii and copepodites of the copepod Clausocalanus furcatus. Nauplii swam in a looping swim-and-sink pattern at prosome-length-specific speeds of 38.4 +/- 12.4 L s(-1) with appendage beat frequencies of 99.4 +/- 21.7 Hz, whereas copepodites mainly cruised at 14.8 +/- 4.2 L s(-1) and 103.1 +/- 12.1 Hz. Despite major differences in morphology, size and kinematics, both stages achieved similar body-volume-specific maximal clearance rates (similar to 10(6) body volumes d(-1)), sufficient for survival in nutritionally dilute oceans. Although beat frequencies varied little across stages, the nondimensional beat number decreased from > 1 in nauplii to < 1 in copepodites, suggesting a shift toward energetically inexpensive, unsteady viscous vortical flows that may also reduce hydrodynamic predation risk. Copepodites captured prey through direct interception aided by coordinated appendage movements and through active maneuvering, with short mean reaction distance (similar to 0.5 body widths) and reaction-to-capture time (similar to 30 ms), indicating non-contact detection. These results demonstrate how C. furcatus maintains clearance rates through ontogenetic shifts in kinematics, highlighting behavioral and sensory adaptations that enable cruise-feeding copepods to thrive in oligotrophic oceans.
Despite the pivotal role of fungi in regulating algal blooms and ecosystem health, community-level fungal dynamics in natural cyanobacterial bloom events, and their correlation with changes in algal communities, remain poorly understood. Through a year-long survey in eutrophic Lake Chaohu, China, we analyzed the planktonic fungal and phytoplankton community changes. The results showed that Chytridiomycota dominated the fungal community throughout the year, whereas Ascomycota and Basidiomycota increased markedly during late-bloom and post-bloom periods, suggesting a functional shift from potential parasitism to saprotrophy. Algal and fungal communities showed significant concordance at the community level, as indicated by the positive relationship between their Bray-Curtis distances (P < 0.001). Separate fitting of dominant algal taxa onto the fungal ordination space showed that Microcystis was primarily associated with the bloom-period fungal assemblage, whereas Chlorella and others were more closely associated with non-bloom fungal community variation. The strength of algal-fungal associations also increased significantly with the relative dominance of algal taxa (P < 0.05), supporting a dominance-dependent interaction pattern. Together, these results indicate that planktonic fungal communities were closely associated with algal community dynamics through both host-abundance- and host-dominance-related patterns, and highlight the importance of considering fungal processes in ecological frameworks for understanding phytoplankton succession and cyanobacterial bloom dynamics.
Even though ecologically complementary, contrasting phyto- and zooplankton responses to anthropogenic pressures are scarcely applied to tropical coastal lagoons. We hypothesize that anthropogenic pressure acts as a local environmental filter, promoting biotic homogenization of plankton communities across tropical coastal lagoons. Coastal lagoons under different conservation statuses were sampled (wet and dry periods) to measure photosynthetic pigments, nutrient concentrations, salinity, oxidation-reduction potential, dissolved oxygen (DO) and phyto- and zooplankton communities. Linear regression was applied, controlling for geographical distance, to identify the main factors affecting plankton beta-diversity components. Sampled stations were classified based on trophic conditions and clustered based on environmental variables for further analysis of the plankton assemblages associated with each cluster. Distance-based linear model analysis (DistLM) was used to examine the relationship between biotic and abiotic variables. Supereutrophic and hypereutrophic lagoons had significantly lower beta-diversity values, with turnover dominance over nestedness. DistLM revealed inorganic carbon, DO, chlorophyll pigments and salinity as key environmental drivers of plankton community structure. Environmental variables structured phyto- and zooplankton composition across the lagoons, acting as environmental filters and supporting the hypothesis of an ongoing biotic homogenization process in hypereutrophic lagoons. Our findings highlight the importance of eutrophication control for preventing biodiversity loss in coastal lagoons.
