Plankton Groups Research Articles

CASCADE: Dataset of extant coccolithophore size, carbon content and global distribution

Coccolithophores are marine calcifying phytoplankton important to the carbon cycle and a model organism for studying diversity. Here, we present CASCADE (Coccolithophore Abundance, Size, Carbon And Distribution Estimates), a new global dataset for 139 extant coccolithophore taxonomic units. CASCADE includes a trait database (size and cellular organic and inorganic carbon contents) and taxonomic-unit-specific global spatiotemporal distributions (Latitude/Longitude/Depth/Month/Year) of coccolithophore abundance and organic and inorganic carbon stocks. CASCADE covers all ocean basins over the upper 275 meters, spans the years 1964-2019 and includes 33,119 gridded taxonomic-unit-specific abundance observations. Within CASCADE, we characterise the underlying uncertainties due to measurement errors by propagating error estimates between the different studies. This error propagation pipeline is statistically robust and could be applied to other plankton groups. CASCADE can contribute to (observational or modelling) studies that focus on coccolithophore distribution and diversity and the impacts of anthropogenic pressures on historical populations. Additionally, our new taxonomic-unit-specific cellular carbon content estimates provide essential conversions to quantify the role of coccolithophores on ecosystem functioning and global biogeochemistry.

Size normalizing planktonic Foraminifera abundance in the water column

AbstractPlanktonic Foraminifera have been collected from the water column with different plankton sampling devices equipped with nets of various mesh sizes, which impedes direct comparison of observed quantifications. Here, we use data on the community size structure of planktonic Foraminifera to assess the impact of mesh size on the measured abundance (ind m−3) of planktonic Foraminifera. We use data from the FORCIS database (Chaabane et al., 2023, Scientific Data 10: 354) on the global ocean at different sampling depths over the past century. We find a global cumulative increase in abundance with size, which is best described using a Michaelis–Menten function. This function yields multiplication factors by which one size fraction can be normalized to any other size fraction equal to or larger than 100 μm. The resulting size normalization model is calibrated over a range of different depth intervals, and validated with an independent dataset from various depth ranges. The comparison to Berger's (1969, Deep. Res. Oceanogr. Abstr. 16: 1–24) equivalent catch approach shows a significant increase in the predictive skill of the model. The new size normalization scheme enables comparison of Foraminifera abundance data sampled with plankton nets of different mesh sizes, such as compiled in the FORCIS database. The correction methodology may be effectively employed for various other plankton groups such as diatoms and dinoflagellates.

Organismal trade-offs and the pace of planktonic life.

No one is perfect, and organisms that perform well in some habitat or with respect to some tasks, do so at the cost of performance in others: there are inescapable trade-offs. Organismal trade-offs govern the structure and function of ecosystems and attempts to demonstrate and quantify trade-offs have therefore been an important goal for ecologists. In addition, trade-offs are a key component in trait-based ecosystem models. Here, I synthesise evidence of trade-offs in plankton organisms, from bacteria to zooplankton, and show how a slow-fast gradient in life histories emerges. I focus on trade-offs related to the main components of an organism's Darwinian fitness, that is resource acquisition, survival, and propagation. All consumers need to balance the need to eat without being eaten, and diurnal vertical migration, where zooplankton hide at depth during the day to avoid visual predators but at the cost of missed feeding opportunities in the productive surface layer, is probably the best documented result of this trade-off. However, there are many other more subtle but equally important behaviours that similarly are the result of an optimisation of these trade-offs. Most plankton groups have also developed more explicit defence mechanisms, such as toxin production or evasive behaviours that are harnessed in the presence of their predators; the costs of these have often proved difficult to quantify or even demonstrate, partly because they only materialise under natural conditions. Finally, all multicellular organisms must allocate time and resources among growth, reproduction, and maintenance (e.g. protein turnover and DNA repair), and mate finding may compromise both survival and feeding. The combined effects of all these trade-offs is the emergence of a slow-fast gradient in the pace-of-life, likely the most fundamental principle for the organisation of organismal life histories. This crystallisation of trade-offs may offer a path to further simplification of trait-based models of marine ecosystems.

Hydrodynamic and biochemical impacts on the development of hypoxia in the Louisiana–Texas shelf – Part 1: roles of nutrient limitation and plankton community

Abstract. A three-dimensional coupled hydrodynamic–biogeochemical model with multiple nutrient and plankton functional groups was developed and adapted to the Gulf of Mexico to investigate the role of nutrients and the complexity of plankton community in dissolved oxygen (DO) dynamics. A 15-year hindcast was achieved covering the period of 2006–2020. Extensive model validation against in situ data demonstrates that the model was capable of reproducing vertical distributions of DO and spatial distributions of bottom DO concentration, as well as their interannual variations. The study demonstrates that bottom DO dynamics and hypoxia evolution are significantly influenced by both physical processes and local biochemistry, with sedimentary oxygen consumption and vertical diffusion identified as key contributors. Summer hydrodynamics play a critical role in nutrient distribution and limitation: a notable expansion of Si limitation was simulated when coastal currents shifted eastward or northward. This effect, especially pronounced on the western part of the Louisiana–Texas shelf, underscores the importance of nutrient limitation in shaping DO dynamics. The model identifies a bi-peak primary production pattern in spring and early summer, aligned with satellite chlorophyll a variations, attributed to the complexity of the plankton community and interactions among different plankton groups. Our findings emphasize the necessity of integrating sophisticated plankton community dynamics into biogeochemical models to understand primary production variability and its impact on bottom hypoxia.

Polyphosphate phosphorus in the Great Lakes

AbstractPolyphosphate (polyP) is important to phytoplankton ecology, but a unified view of its variability and roles in ecosystem‐scale phosphorus (P) cycling is lacking. We study polyP in the world's largest freshwater ecosystem, the Laurentian Great Lakes, covering pelagic to nearshore areas across a wide nutrient gradient. We show that polyP (average 10.99 ± 3.90 nmol L−1) constitutes 3.8–30.2% (average 18.1 ± 7.2%) of total particulate P (TPP). PolyP accumulation is higher in low‐P pelagic waters compared with more productive nearshore areas. PolyP is preferentially degraded in the water column of the Great Lakes, enhancing P recycling and relieving the nitrogen (N) : P imbalance. Our data enables a coherent large‐scale freshwater‐to‐oceanic comparison. We show that while different plankton groups accumulate different levels of polyP with smaller plankton accumulating more, P availability is the key driver of polyP variability within and across systems.

Benthic assemblages in relation to planktonic assemblages in a eutrophic, thermally stratified reservoir

Few studies have explored the relationship between benthic and planktonic assemblages in reservoirs, despite their role in food chains and maintaining ecological functions. Macroinvertebrates play a crucial role in food webs and contribute about 42% of whole-lake secondary productivity. Therefore, their status is vital for maintaining good ecological functions. In this study, we selected Nanwan Reservoir, a eutrophic thermally stratified reservoir in China, to evaluate the community of macroinvertebrates in different seasons and explore the relationships between macroinvertebrate assemblages and different planktonic groups, including phytoplankton, protozoans, rotifers, and planktonic crustaceans. Cyanophyta and Bacillariophyta dominated the phytoplankton assemblages, and their proportions varied with seasons. The bad community of macroinvertebrates in summer, autumn, and winter could be attributed to the excessive growth of Cyanophyta or other phytoplankton. Based on the results of partial least squares regression, an algorithm used for prediction, we determined that the excessive growth of algae, crustaceans, protozoans, and Cyanophyta was detrimental to the development of macroinvertebrates, and was indicative of high nutrient loads in the reservoir. However, the growth of Bacillariophyta, Chrysophyta, and Euglenophyta was advantageous to macroinvertebrate assemblages and indicated a better ecological condition of the reservoir. The results of partial least squares structural equation modeling demonstrated close associations between phytoplankton and both zooplankton and macroinvertebrates, indicating their interdependence in this reservoir system. Our study results imply that the status of macroinvertebrates can be predicted by the abundance of some planktonic assemblages, and cost savings from selecting one of the planktonic groups to monitor ecological conditions could be accomplished in future studies.

Coherent response of zoo‐ and phytoplankton assemblages to global warming since the Last Glacial Maximum

AbstractAimWe are using the fossil record of different marine plankton groups to determine how their biodiversity has changed during past climate warming comparable to projected future warming.LocationNorth Atlantic Ocean and adjacent seas. Time series cover a latitudinal range from 75° N to 6° S.Time periodPast 24,000 years, from the Last Glacial Maximum (LGM) to the current warm period covering the last deglaciation.Major taxa studiedPlanktonic foraminifera, dinoflagellates and coccolithophores.MethodsWe analyse time series of fossil plankton communities using principal component analysis and generalized additive models to estimate the overall trend of temporal compositional change in each plankton group and to identify periods of significant change. We further analyse local biodiversity change by analysing species richness, species gains and losses, and the effective number of species in each sample, and compare alpha diversity to the LGM mean.ResultsAll plankton groups show remarkably similar trends in the rates and spatio‐temporal dynamics of local biodiversity change and a pronounced non‐linearity with climate change in the current warm period. Assemblages of planktonic foraminifera and dinoflagellates started to change significantly with the onset of global warming around 15,500 to 17,000 years ago and continued to change at the same rate during the current warm period until at least 5000 years ago, while coccolithophore assemblages changed at a constant rate throughout the past 24,000 years, seemingly irrespective of the prevailing temperature change.Main conclusionsClimate change during the transition from the LGM to the current warm period led to a long‐lasting reshuffling of zoo‐ and phytoplankton assemblages, likely associated with the emergence of new ecological interactions and possibly a shift in the dominant drivers of plankton assemblage change from more abiotic‐dominated causes during the last deglaciation to more biotic‐dominated causes with the onset of the Holocene.

The culture of Nile tilapia (Oreochromis niloticus) juvenile at different culture technologies: autotrophic, bioflocs and synbiotic

Nile tilapia is a widely produced species due to its rusticity and technological culture package. However, there is a knowledge gap in youth production using new technologies. Therefore, this work aimed to evaluate the production of juvenile Oreochromis niloticus in different culture technologies: autotrophic, synbiotic, and bioflocs, through of water quality parameters, plankton groups, bacterial counts and zootechnical performance. The experiment lasted 40 days, time needed to reach a commercial weight of juveniles, and used tilápia fry weighing 3.60 ± 0.32 g stocking density of 500 fish m−3 and fed with commercial feed (46% crude protein and 9% lipids). Before stocking the fish, the experimental units were prepared for 30 days with inorganic (potassium nitrate and superphosphate - autotrophic - AUT) and organic (sugar - bioflocs - BFT; rice bran fermented with probiotic - synbiotic - SYNB) addition and control group (CTL). Regarding water quality parameters, temperature, salinity, dissolved oxygen (DO) and pH were within those recommended for the culture of the species. The nitrogen compounds (TAN and N-NO2) and water footprint were lower in BFT and SYNB as compared than AUT and CTL. The phytoplankton community had significantly higher Bacillariophyta count in BFT and SYNB as compared than AUT and CLT, however Chlorophyta in AUT and Cyanophyta in BFT, SYNB and CTL, prevailed. Zooplankton showed dominance of Rotifera in all treatments, with higher values in SYNB and BFT (p < 0.05). BFT had the higher standard bacterial count, SYNB had the higher Bacillus sp. count, and AUT and CTL showed the lower microbial counts (p < 0.05). The zootechnical performance: final weight, yield, SGR, FCR, feed efficiency and Fulton condition factor were better (p < 0.05) in the BFT and SYNB treatments as compared than to the AUT and CTL. The FI (feed intake) did not show statistical differences between treatments (p > 0.05). Regarding survival, the lower (p < 0.05) was observed in the control treatment. Therefore, we can conclude that the BFT and SYNB systems are promising for improving the results of nitrogen compounds (TAN and N-NO2) control, water footprint, plankton community, bacterial and zootechnical production of juvenile Nile tilapia.

Do weathered microplastics impact the planktonic community? A mesocosm approach in the Baltic Sea

Microplastics (MPs) are ubiquitous pollutants of increasing concern in aquatic systems. However, little is still known about the impacts of weathered MPs on plankton at the community level after long-term exposure. In this study, we investigated the effects of weathered MPs on the structure and dynamics of a Baltic Sea planktonic community during ca. 5 weeks of exposure using a mesocosm approach (2 m3) mimicking natural conditions. MPs were obtained from micronized commercial materials of polyvinyl chloride, polypropylene, polystyrene, and polyamide (nylon) previously weathered by thermal ageing and sunlight exposure. The planktonic community was exposed to 2 μg L-1 and 2 mg L-1 of MPs corresponding to measured particle concentrations (10–120 μm) of 680 MPs L-1 and 680 MPs mL-1, respectively. The abundance and composition of all size classes and groups of plankton and chlorophyll concentrations were periodically analyzed throughout the experiment. The population dynamics of the studied groups showed some variations between treatments, with negative and positive effects of MPs exhibited depending on the group and exposure time. The abundance of heterotrophic bacteria, pico- and nanophytoplankton, cryptophytes, and ciliates was lower in the treatment with the higher MP concentration than in the control at the last weeks of the exposure. The chlorophyll concentration and the abundances of heterotrophic nanoflagellates, Astromoeba, dinoflagellate, diatom, and metazooplankton were not negatively affected by the exposure to MPs and, in some cases, some groups showed even higher abundances in the MP treatments. Despite these tendencies, statistical analyses indicate that in most cases there were no statistically significant differences between treatments over the exposure period, even at very high exposure concentrations. Our results show that weathered MPs of the studied conventional plastic materials have minimal or negligible impact on planktonic communities after long-term exposure to environmentally relevant concentrations.

Distribution of selenium: A case study of the Drava, Danube and associated aquatic biotopes

This paper presents the results of the research on the overall distribution of selenium (Se) in various aquatic compartments (water, sediment, plankton and macrophytes) at six selected sites of the Croatian part of the Drava and Danube rivers, the connected floodplain lake and the melioration channel system carried out in two sampling periods (flooding in June and the drought period in September). In addition, the physicochemical water properties, plankton composition and biomass were analysed. Our study revealed low mean Se contents in sediments and water, indicating Se deficiency in the studied freshwater systems. The physicochemical environment, including Se distribution, was primarily influenced by hydrology rather than site-specific biogeochemical and morphological characteristics. The flooding period was characterised by higher Se content in water and higher transparency, nitrate and total nitrogen concentrations than drought conditions. At the river sites, sediment Se content was the highest during the flood period, while at all other sites, higher concentrations were found during the drought, reaching the maximum in the lake. Although Se concentrations were below the threshold for aquatic ecotoxicity, they increased in the following order: water (0.021–0.187 μg Se L−1) < sediments (0.005–0.352 mg Se kg−1) < macrophytes (0.010–0.413 mg Se kg−1) < plankton (0.044–0.518 mg Se kg−1) indicating its possible biomagnification at the bottom of the food chain. Species known for high Se accumulation potential dominated the biomass of the main plankton groups and the composition of the macrophyte community, which may provide a more sensitive and accurate steady-state compartment monitor for Se assessment in freshwater biotopes.

Effects of physical forcing on short-term plankton dynamics in a narrow coral reef lagoon (Ouano, New Caledonia): a two-week high-frequency study

Abstract The response of plankton communities to short-term climatic events was studied in a narrow coral reef lagoon representative of the channel-type lagoons of the high islands of the tropical Pacific. Phyto- and zooplankton data (abundance and taxonomic composition) were sampled at high frequencies for 2 weeks in April–May 2017 under various tidal conditions and combined with environmental and physical measurements and modeling hydrodynamic products. The short-term external events (wind, waves and rain) that occurred caused changes in the circulation patterns and increased nutrient concentrations in the lagoon. The plankton reacted quickly to this enrichment, with an increase in chlorophyll a and the rapid development of a microphytoplankton community dominated by diatoms, and of opportunistic herbivorous zooplankton (tintinnids, appendicularians). Zooplankton composition and distribution were strongly modulated by the circulation patterns through advection and mixing. Our results show that the tidal and diel components of the temporal variability of planktonic groups were blurred by sporadic event components (i.e. wind, wave and rainfall events). Environmental and biological responses to these external physical forcings occurred at lagoon scale in this channel-like lagoon, unlike what is observed in larger lagoons (such as the southern lagoons of New Caledonia) where spatial variability is much higher.

Towards high-throughput parallel imaging and single-cell transcriptomics of microbial eukaryotic plankton.

Single-cell transcriptomics has the potential to provide novel insights into poorly studied microbial eukaryotes. Although several such technologies are available and benchmarked on mammalian cells, few have been tested on protists. Here, we applied a microarray single-cell sequencing (MASC-seq) technology, that generates microscope images of cells in parallel with capturing their transcriptomes, on three species representing important plankton groups with different cell structures; the ciliate Tetrahymena thermophila, the diatom Phaeodactylum tricornutum, and the dinoflagellate Heterocapsa sp. Both the cell fixation and permeabilization steps were adjusted. For the ciliate and dinoflagellate, the number of transcripts of microarray spots with single cells were significantly higher than for background spots, and the overall expression patterns were correlated with that of bulk RNA, while for the much smaller diatom cells, it was not possible to separate single-cell transcripts from background. The MASC-seq method holds promise for investigating "microbial dark matter", although further optimizations are necessary to increase the signal-to-noise ratio.

ASSESSMENT OF WATER QUALITY AND SEASONAL FLUCTUATION OF ZOOPLANKTON POPULATION IN THE DORA BEEL ECOSYSTEM OF KAMRUP DISTRICT, ASSAM

The present investigation deals with the seasonal variations in physico-chemical characteristics and abundance of zooplankton population in Dora Beel, Kamrup District of Assam. The survey was undertaken from March, 2022 - February, 2023 and done in four different seasons viz. Monsoon, Pre-monsoon, winter and Post-monsoon. The physico-chemical studies include the seasonal study of water temperatures, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), pH and Free Carbon dioxide (CO2 ). The result of water analysis reveals that in winter season water temperature and free CO2 were minimum but dissolved oxygen was maximum. In the monsoon season water temperature and BOD were maximum but DO was in minimum level. Free carbon dioxide was maximum but BOD was minimum in post-monsoon. The pH level was minimum in pre-monsoon season and maximum in post-monsoon. A total 24 numbers of zooplankton species were recorded belonging to five different planktonic groups such as Protozoa, Rotifera, Cladocera, Ostracoda and Copepoda. The post-monsoon season observe as peak abundance season for all the zooplanktons and pre-monsoon as low abundance season. Protozoa is the dominant group (based on abundance) followed by Rotifera, Cladocera and Copepoda. But the number of species was highest in Rotifera group. The Copepoda and Ostracoda were the lowest abundant group.

Environmental DNA captures diurnal fluctuations of surface eukaryotes on a tropical coral reef

AbstractEnvironmental DNA (eDNA) metabarcoding has been widely employed to describe biological communities in the marine environment and to compare the richness and diversity of sites across large spatial scales. However, fine‐scale temporal eDNA dynamics are poorly understood and the time of eDNA sample collection is rarely reported in publications. Here, we collected surface eDNA samples every 6 h, for 3 days, at two coral reef sites to assess fine‐scale changes in the eukaryotic communities detected. Distinct eukaryotic communities were detected at two sites within the same lagoon. Sampling time was found to have a significant effect on ESV and class richness, both peaking during the 1 p.m. sampling time at both sites. Sampling time also had a significant effect on the detection of eukaryotic taxa, with relative read frequency showing clear diurnal patterns in line with the migratory behavior of planktonic groups. Other groups of organisms showed considerable variation in read frequency, highlighting the dynamic nature of marine eukaryotic communities and potential stochasticity of eDNA detections. For eukaryotic communities, eDNA samples can provide a “snapshot” of contemporary biodiversity and provide information on short‐term community dynamics on hyperdiverse coral reefs. However, our findings add to growing evidence that sampling time should be clearly considered and reported in marine eDNA studies and that multiple samples from the same site are needed to facilitate more robust comparisons across sites.

Taming the data deluge: A novel end‐to‐end deep learning system for classifying marine biological and environmental images

AbstractUnderwater imaging enables nondestructive plankton sampling at frequencies, durations, and resolutions unattainable by traditional methods. These systems necessitate automated processes to identify organisms efficiently. Early underwater image processing used a standard approach: binarizing images to segment targets, then integrating deep learning models for classification. While intuitive, this infrastructure has limitations in handling high concentrations of biotic and abiotic particles, rapid changes in dominant taxa, and highly variable target sizes. To address these challenges, we introduce a new framework that starts with a scene classifier to capture large within‐image variation, such as disparities in the layout of particles and dominant taxa. After scene classification, scene‐specific Mask regional convolutional neural network (Mask R‐CNN) models are trained to separate target objects into different groups. The procedure allows information to be extracted from different image types, while minimizing potential bias for commonly occurring features. Using in situ coastal plankton images, we compared the scene‐specific models to the Mask R‐CNN model encompassing all scene categories as a single full model. Results showed that the scene‐specific approach outperformed the full model by achieving a 20% accuracy improvement in complex noisy images. The full model yielded counts that were up to 78% lower than those enumerated by the scene‐specific model for some small‐sized plankton groups. We further tested the framework on images from a benthic video camera and an imaging sonar system with good results. The integration of scene classification, which groups similar images together, can improve the accuracy of detection and classification for complex marine biological images.

The hydrodynamics and kinematics of the appendicularian tail underpin peristaltic pumping.

Planktonic organisms feed while suspended in water using various hydrodynamic pumping strategies. Appendicularians are a unique group of plankton that use their tail to pump water over mucous mesh filters to concentrate food particles. As ubiquitous and often abundant members of planktonic ecosystems, they play a major role in oceanic food webs. Yet, we lack a complete understanding of the fluid flow that underpins their filtration. Using high-speed, high-resolution video and micro particle image velocimetry, we describe the kinematics and hydrodynamics of the tail in Oikopleura dioica in filtering and free-swimming postures. We show that sinusoidal waves of the tail generate peristaltic pumping within the tail chamber with fluid moving parallel to the tail when filtering. We find that the tail contacts attachment points along the tail chamber during each beat cycle, serving to seal the tail chamber and drive pumping. When we tested how the pump performs across environmentally relevant temperatures, we found that the amplitude of the tail was invariant but tail beat frequency increased threefold across three temperature treatments (5°C, 15°C and 25°C). Investigation into this unique pumping mechanism gives insight into the ecological success of appendicularians and provides inspiration for novel pump designs.

Structure and functional characteristics of zooplankton and food supply for nekton in the western Bering Sea

Structure and functional characteristics of zooplankton and feeding of the most abundant nekton species (pollock, herring and salmons) are analyzed using the data of ecosystem survey in the western Bering Sea in 2020 and compared with the structural indices for 2015−2019. The main patterns of composition and distribution of zooplankton and production of organic matter by zooplankton are determined. High values and turnover rate of production are noted for the non-predatory zooplankton (mainly copepods and euphausiids) in the eastern Anadyr Bay, the area at Cape Navarin, the shelf of Koryak coast, and the continental slope of Olyutorsky Bay. High production of predatory zooplankton (mainly hyperiids) is found on the slope of Karaginsky Bay, presumably because of these species transport from the southern areas with later stage of the seasonal succession. In autumn 2020, walleye pollock and pacific herring consumed from 15 to 55 % of the copepod, euphausiid and hyperiid production. This level of consumption did not affect their food supply because of very high turnover rate of these taxonomic groups of plankton. In the deep-water areas, salmons did not use more than 3 % of their food resource. Thus, the survey data indicate a good food supply for the most abundant nekton species in the western Bering Sea in the fall season.

The biphasic life cycle of the non-spinose planktonic foraminifera is characterised by an aberrant coiling signature

The complete lifecycle of the planktonic foraminifera has continued to remain obscure. Benthic foraminifera exhibit an obligate alternation of generations between haploid gamonts and diploid agamonts, yet despite years of observation, the fusion of gametes to form a zygote, gamont or agamont has never been observed in the planktonic groups. Recent evidence from Neogloboquadrina pachyderma culture confirms that they do have a biphasic reproductive cycle and the agamonts may exhibit dimorphism in coiling direction. In this study we examine the morphology of normal and aberrant coiling tests of both N. pachyderma and N. incompta from three Arctic and North Atlantic water masses, to explore whether aberrant coiling is an indicator of a biphasic life cycle in the non-spinose planktonic foraminifera group as a whole. Using a Nano-Computed Tomography scanning approach, we morphologically compared the proloculus and growth trajectories of aberrant and normal coiling tests. Aberrant coiling tests were found to have a slightly larger proloculus and test size, consistent with a left coiling N. pachyderma agamont in the literature. This degree of dimorphism is insufficient to discriminate agamonts in the wild population and coiling direction remains their only distinguishable feature without further morphological investigation. The constant low-level aberrant coiling signature in a range of non-spinose planktonic foraminiferal genera implies that a biphasic life cycle is the principal mode of reproduction in the non-spinose planktonic group.

Preferential dreissenid mussel grazing on small plankton can favor cyanobacteria: Experimental evidence from western Lake Erie

Abstract Herein we provide experimental evidence for the effects invasive mussels (Dreissena) grazing can exert on a natural assemblage of plankton that included both hetero- and photo-trophic components in western Lake Erie. Five mussel feeding experiments were performed seasonally in 2018 (May, June, July August, October). Pre- and post-grazing samples were collected from seven 20-L mesocosms (3 control, 4 mussel), and analyzed using microscope cell counts. Results from our experiments showed that Dreissena were active grazers of plankton on all dates, with significant correspondence between mussel clearance rates measured using microscopy versus size-specific chlorophyll and FluoroProbe based estimates (Spearman rank correlation, r = 0.45, and r = 0.48, respectively, p &amp;lt; 0.05). Clearance rates (ml mg-1 h-1) were variable among taxonomic groups and seemed to track the abundance of ambient plankton assemblage (range 1.70 to 25.00, mean ± SE 11.70 ± 1.33). Dreissena grazed consistently on nano-sized hetero- and phototrophic plankton that constituted key trophic linkages in the Lake Erie foodweb. The most actively grazed plankton were phototrophic cryptophytes (Rhodomonas minuta, Cryptomonas spp.), centric diatoms (Cyclotella sp. and Discotella spp.), and non-pigmented chrysomonads (Chromulina sp., Ochromonas sp.). Conversely, clearance rates were low for cyanobacteria (e.g. Microcystis), dinoflagellates (Gymnodinium varians), and some colonial chlorophytes (Desmodesmus, Pediastrum); these plankton groups occurred during specific temporal windows (one-way ANOVA, p &amp;lt; 0.05). Our results indicate the potential mussel grazing can suppress typical, non-harmful plankton species in the nanoplankton size range, thereby favoring the occurrence of less-edible, larger cyanobacteria and chlorophyte species in western Lake Erie.

Ocean-wide comparisons of mesopelagic planktonic community structures

For decades, marine plankton have been investigated for their capacity to modulate biogeochemical cycles and provide fishery resources. Between the sunlit (epipelagic) layer and the deep dark waters, lies a vast and heterogeneous part of the ocean: the mesopelagic zone. How plankton composition is shaped by environment has been well-explored in the epipelagic but much less in the mesopelagic ocean. Here, we conducted comparative analyses of trans-kingdom community assemblages thriving in the mesopelagic oxygen minimum zone (OMZ), mesopelagic oxic, and their epipelagic counterparts. We identified nine distinct types of intermediate water masses that correlate with variation in mesopelagic community composition. Furthermore, oxygen, NO3− and particle flux together appeared as the main drivers governing these communities. Novel taxonomic signatures emerged from OMZ while a global co-occurrence network analysis showed that about 70% of the abundance of mesopelagic plankton groups is organized into three community modules. One module gathers prokaryotes, pico-eukaryotes and Nucleo-Cytoplasmic Large DNA Viruses (NCLDV) from oxic regions, and the two other modules are enriched in OMZ prokaryotes and OMZ pico-eukaryotes, respectively. We hypothesize that OMZ conditions led to a diversification of ecological niches, and thus communities, due to selective pressure from limited resources. Our study further clarifies the interplay between environmental factors in the mesopelagic oxic and OMZ, and the compositional features of communities.