Planktonic Species Research Articles

Ecological impact of surfactant Tween-80 on plankton: High-scale analyses reveal deeper hazards

The ecological risks of surfactants have been largely neglected because of their low toxicity. Multiscale studies have indicated that even if a pollutant causes no acute toxicity in a test species, it may alter interspecific interactions and community characteristics through sublethal impacts on test organisms. Therefore, we investigated the lethal and sublethal responses of the plankton species Scenedesmus quadricauda, Chlorella vulgaris, and Daphnia magna, to surfactant Tween-80. Then, high-scale responses in grazer life-history traits and stability of the D. magna-larval damselfly system were further explored. The results showed that discernible adverse effects on the growth or survival of the three plankton species were evident only at exceptionally high concentrations (≥100 mg L−1). However, 10 mg L−1 of Tween-80 notably affected the MDA concentration in grazer species, simultaneously displaying a tendency to diminish grazer's heartbeat and swimming frequency. Furthermore, Tween-80 reduced the grazer reproductive capacity and increased its predation risk by larval damselflies, which ultimately jeopardized the stability of the D. magna-larval damselfly system at much lower concentrations (10–100 fold lower) than the individual-scale responses. This study provides evidence that high-scale traits are far more sensitive to Tween-80, compared with individual-scale traits for plankton organisms, suggesting that the ecological risks of Tween-80 demand careful reassessment. SynopsisThe concentration of Tween-80 needed to induce changes in community characteristics is markedly lower than that needed to produce individual-scale consequences. Thus, high-scale analyses have broad implications for understanding the hazardous effects of surfactants compared with an individual-scale analysis.

DNA metabarcoding focusing on the plankton community: an effective approach to reconstruct the paleo-environment

DNA metabarcoding (DNA-MB) targeting the whole plankton community is a promising approach in studies of sediment samples from water bodies, but its effectiveness in ancient material is not well demonstrated. We applied DNA-MB of plankton in a sediment core to reconstruct the paleo-environment of Lake Shinji, Japan, through a marine lagoon/freshwater lake transition during the past 2300 years. We interpreted core-sample plankton taxonomy and habitat by reference to the modern plankton community in water samples. OTUs (operational taxonomic units) belonging to Dictyochophyceae were 81.05% of the total reads in sediments. However, Ciliophora, Copepoda and Labyrinthulea formed the majority of plankton taxa in the water samples, suggesting that they are under-represented in sediment. A drastic change in plankton composition correlated with a large decrease in sediment sulfur concentration, implying the change of aquatic environment from marine lagoon to freshwater lake. This event took place ca. 1200 CE in Lake Shinji. A 250 year-long transitional period followed, during which the total DNA sequence reads were very low. This suggests that salinity fluctuations created a hostile environment for both marine and freshwater plankton species. Our results show that DNA-MB of the whole plankton community is effective in reconstructing paleo-environments.

Taxonomic diversity and structure of phytoplankton of the Polui River (tributary of the Ob River)

The study of the Polui River algoflora are resulted. A total of 249 taxa of species and subspecies ranks from 86 genera, 52 families and 8 divisions were identified: Cyanoprokariota, Chrysophyta, Bacillariophyta, Xanthophyta, Cryptophyta, Dinophyta, Euglenophyta, Chlorophyta. For the first time, a systematic list of algae is given, indicating the habitat, saprobicity and geographical distribution of species. The most diverse in the number of families, genera and species are the divisions Chlorophyta (41 % of the total number of taxa) and Bacillariophyta (34 %), as well as Cyanoprokariota (10 %) and Euglenophyta (9 %). Other divisions are not numerous in composition (6 %). Ten genera are leading, and 4 of them are from the Chlorophyta and Bacillariophyta divisions, 2 genera are from the Euglenophyta. Planktonic species with the presence of benthic forms, beta-mesosaprobes and cosmopolitan species predominate. Discovered cryptomonads in the modern period indicate eutrophication.

Strong temperature gradients in the ice age North Atlantic Ocean revealed by plankton biogeography

The cold Last Glacial Maximum, around 20,000 years ago, provides a useful test case for evaluating whether climate models can simulate climate states distinct from the present. However, because of the indirect and uncertain nature of reconstructions of past environmental variables such as sea surface temperature, such evaluation remains ambiguous. Instead, here we evaluate simulations of Last Glacial Maximum climate by relying on the fundamental macroecological principle of decreasing community similarity with increasing thermal distance. Our analysis of planktonic foraminifera species assemblages from 647 sites reveals that the similarity-decay pattern that we obtain when the simulated ice age seawater temperatures are confronted with species assemblages from that time differs from the modern. This inconsistency between the modern temperature dependence of plankton species turnover and the simulations arises because the simulations show globally rather uniform cooling for the Last Glacial Maximum, whereas the species assemblages indicate stronger cooling in the subpolar North Atlantic. The implied steeper thermal gradient in the North Atlantic is more consistent with climate model simulations with a reduced Atlantic meridional overturning circulation. Our approach demonstrates that macroecology can be used to robustly diagnose simulations of past climate and highlights the challenge of correctly resolving the spatial imprint of global change in climate models.

PHYTOPLANKTON IN THE LAKES OF THE REPUBLIC OF BASHKORTOSTAN

The phytoplankton in a number of lakes in the Bashkir Trans-Urals (Atavdy, Sultankul (2017), Bursunsy, Kuldybay (2019), Bolshiye Uchaly, Uzunkul (2021)) and Bashkir Pre-Urals (Bolshoy Tolpak, 2022)) was studied. As a result of the study, the taxonomic structure, quantitative characteristics, dominant species, distribution features of main algal groups were reveald, and their ecological and geographical characteristics werre identified. 257 species and intraspecific taxa of algae from 9 divisions were registered in the algal flora. Green algae (33%), cyanoprokaryotes and diatoms (21% each of total species number) show the highest species diversity in the lakes. The algal flora is specific for each lake and has low degree of floristic similarity (0.13–0.57 according to Sørensen coefficients). In the ecological and geographical terms, the algal floras of lake plankton is represented by typical planktonic species, widespread in waterbodies of the globe, indifferent to water salinity, living only in fresh waterbodies and preferring neutral waters. Quantitative indicators of phytoplankton varied in a wide range of values: number of cells from 4.4 to 344 mln cells/L, biomass from 0.23 to 22.97 mg/L. Dominant species in terms of abundance are represented predominantly by cyanoprokaryotes (Snowella lacustris, Aphanocapsa delicatissima, A. incerta, Aphanizomenon flos-aquae, Gloeotrichia echinulata, Merismopedia tenuissima, Pseudanabaena galeata, Planktolyngbya limnetica, Woronichinia compacta, Anathece clathrata, Rhabdoderma lineare), in terms of biomass by green (Oocystis lacustris, O. borgei, O. marssonii, Scenedesmus apiculatus), dinophyte (Peridinium cinctum, Gymnodinium sp., Ceratium furcoides), desmidium algae (Staurodesmus cuspidatus, Cosmarium contractum, C. cucumis) and cyanoprokaryotes (Pseudanabaena galeata, Aphanizomenon flos-aquae, Gloeotrichia echinulata). According to the value of the saprobity index (Pantle – Bucc by number 1.57–2.80), the lake waters correspond to β- and α-mesosaprobic types of waterbodies with III and IV water quality classes (moderately polluted or dirty water).

Temporal distribution of plankton and fish species at Mithamoin Haor: Abundance, composition, biomass and ecosystem based management approach

Wetlands are the major climatically vulnerable habitat globally. In Bangladesh, Haors are the representative of wetland habitat that plays a significant role in ecology, economy, and social structure. In the present study, physicochemical and biological properties and their interaction at Mithamoin haor of Kishoreganj district of Bangladesh were depicted based on the samples collected from July 2020 to June 202. In total, 46 genera representing 4 different groups of phytoplankton were identified comprising the highest percentages of Chlorophyceae (44.52 %). Zooplankton was represented with 13 genera which was dominated by rotifer. During the study, 56 fish species of 7 orders were documented and the dominance was showed by Cypriniformes (46.84 %). Fish biomass was highest during January and the lowest during May. Planktivores were represented the predominant (55.32 %) group in the haor. Water temperature, transparency, pH and water depth were considered as the major environmental factors influencing the phytoplankton, zooplankton and fish biomass of the haor. Although some fish and plankton species have declined over time, the overall diversity of fish and plankton in the Mithamoin haor was relatively stable. Multiple strategies, including an ecologically oriented framework, might be useful for conserving the prevailing fishery resources of this wetland in future.

Equatorial Pacific Sea‐Air CO2 Exchange Modulated by Upper Ocean Circulation During the Last Deglaciation

AbstractThe eastern equatorial Pacific (EEP) is a source of atmospheric CO2 during the last deglaciation, but the associated oceanic dynamics in the broader low‐latitude Pacific is not fully understood. Here, we report 30,000‐year‐long surface and subsurface pCO2 records for the western equatorial Pacific (WEP), based on boron isotopes in two planktonic foraminiferal species from core MD10‐3340. Our results show that the WEP surface became a significant atmospheric CO2 sink despite that its subsurface waters were enriched by CO2 during the last deglaciation to early Holocene. Combined with EEP proxy data and model results, we suggest that a deglacial‐early Holocene zonal seesaw of sea‐air CO2 exchange across the equatorial Pacific led to a net CO2 outgassing much greater than the modern situation. This can be ascribed to strengthened Subtropical‐Tropical Circulation, resulting in stronger upper ocean stratification in the WEP concurrent with enhanced upwelling of CO2‐rich subsurface waters in the EEP.

Plankton assemblages from microplastics of tropical coastal environments reveal high diversity and evidence of toxic species

Microplastics are a major constituent of plastic waste and are of an increasing global concern. Although microplastics are prevalent in marine ecosystems, the characterisation of plankton communities has been largely neglected in this aspect, especially in tropical ecosystems. To better understand the role of microplastics as a carrier of harmful plankton in marine ecosystems, epiplastic plankton communities in tropical marine ecosystems were studied from beach sediments along the Johor and Singapore Straits. Complementary analysis of microscopy and high throughput sequencing of the 16S rRNA (V3–V4) and 18S (V4) rRNA regions provided evidence that the plastisphere provided an appropriate environment to host a wide range of planktonic organisms. An average of 781 OTUs were identified across the three sampling sites. The structures of plankton communities were distinct across the sampling sites and were generally dominated by dinoflagellates, fungi and chlorophytes. We demonstrate that marine microplastics serve as microhabitats that are a host to harmful phytoplankton species, including viable resting cysts of dinoflagellates. Furthermore, plastics isolated from the location with the greatest anthropogenic influence demonstrated the greatest plankton diversity. This study presents evidence of diverse toxic plankton species present on the plastisphere and highlights its importance as a vector of the transport of harmful opportunistic species in relation to anthropogenic influence, in the marine environment.

COI metabarcoding better reveals the seasonal variations in the zooplankton community in the western Pacific Warm Pool

The environment of the western Pacific Warm Pool is considered to be pronouncedly uniform and stable compared with other tropical ocean environments. Knowledge of the seasonal variations in the zooplankton community structure in this region with a high plankton species diversity remains limited. In this study, three methods, including identification using microscopy, ZooScan digital imaging, and DNA metabarcoding, were used to analyze zooplankton samples collected in three seasons, and to detect the seasonal variations in the community. The results show that the metabarcoding method based on the mitochondrial cytochrome c oxidase I (COI) marker detected up to 2.3 times more zooplankton taxa than identification using microscopy. In contrast, the small subunit ribosomal RNA (18S) marker revealed fewer taxa than microscopy. Significantly positive correlations were observed between the sequence counts and three types of quantitative data, including the biovolume, dry weight biomass, and carbon biomass in all three seasons. The COI sequence counts exhibited a stronger correlation with the dry weight biomass than the biovolume and carbon biomass. Although both the microscopic and molecular methods detected seasonal variability of the zooplankton community, the COI metabarcoding method was more sensitive in detecting seasonal variations in the community, which was positively correlated with the taxonomic resolution of the different methods. In summary, the results of this study suggest that COI metabarcoding is an ideal tool for monitoring the seasonal variations in the diversity and community structure of zooplankton in the tropical open ocean regions with a stable environment all year round.

Physicochemical parameters and plankton diversity in water from selected ponds within Makurdi Metropolis

Physicochemical parameters and plankton diversity in water from five (5) selected ponds was investigated. In the investigation, some physicochemical parameters of water, the composition and abundance of plankton were determined. Some of the parameters include temperature, electrical conductivity, pH, dissolved oxygen, nitrates and phosphate. The samples were collected and transported to the laboratory of the Department of Fisheries and Aquaculture, Joseph Sarwuan Tarka University Makurdi for analysis. The preserved plankton samples were observed using a digital Celestron compound microscope and digital Celestron cosmos dissecting microscope. A combination of keys and guides provided were used for identification of the plankton species. A total of 13 different plankton species, with a total abundance of 308 were observed. The most abundant species was Chlorella vulgaris with an abundance of 85 and was observed in all three pond types. This was followed by Scenedesmus acutus (45) which was observed only in the concrete and liner ponds. Paramecium was next and was observed only in the earthen and concrete ponds. The rest of the plankton species were observed in only one pond type. The physicochemical parameters for the selected earthen, concrete and liner ponds were also selected. The pH and dissolved oxygen were observed to be higher in the concrete pond and lowering the liner pond. The electrical conductivity and total dissolved solid were however lower in the concrete pond and higher in the earthen pond, both the temperature and turbidity were higher in the liner pond and lower in the earthen pond. The phosphate concentration was also higher in the linear pond and lower in the earthen pond, while the concentration of Nitrite was equal in both earthen and concrete pond with no amount observed in the liner pond.

Rapidly evolving zooplankton in a salinizing world: To what extent does microevolutionary adaptation to one salt increase tolerance to another one?

AbstractSalinization is a worldwide emerging threat to freshwater systems. It can be caused by various salts with different toxicity to freshwater organisms. Populations of freshwater organisms have been shown to rapidly evolve adaptations to salinity, yet it remains unclear whether adaptation to one salt increases tolerance or, conversely, susceptibility to other salts. Using an experimental evolution approach, we subjected replicate populations of a planktonic monogonont rotifer species (Brachionus calyciflorus Pallas) to non‐saline and NaCl‐enriched environments. A subsequent multigenerational common garden (CG) transplant experiment demonstrated rapid microevolutionary adaptation to salinity. A second CG experiment provided evidence that adaptation to NaCl increases tolerance mainly to CaCl2 but to a much lesser extent to Na2SO4. Increased tolerance to CaCl2 was associated with increased tolerance to Ca2+ ion toxicity. In contrast, acquired tolerance to Na2SO4 could not be shown to involve an improved ability to cope with ion toxicity. Our results highlight that the evolution of cross‐tolerance may expand the temporal and spatial dimensions under which the ecological consequences of salt adaptation apply.

Global gradients in species richness of marine plankton functional groups

Abstract The patterns of species diversity of plankton functional groups (PFGs) remain poorly understood although they matter greatly for marine ecosystem functioning. Here, we use an ensemble of empirical species distribution models for 845 plankton species to estimate the global species richness of three phytoplankton and 11 zooplankton functional groups as a function of objectively selected environmental predictors. The annual mean species richness of all PFGs decreases from the low to the high latitudes, but the steepness and the shape of this decrease vary significantly across PFGs. Pteropods, small copepods (Oithonids and Poecilostomatoids) and Salps have the steepest latitudinal gradients, whereas Amphipods and the three phytoplankton groups have the weakest ones. Temperature, irradiance and nutrient concentration are the first-order control on the latitudinal richness patterns, whilst the environmental conditions associated to upwelling systems, boundary currents and oxygen minimum zones modulate the position of the peaks and troughs in richness. The species richness of all PFGs increases with net primary production but decreases with particles size and the efficiency of the biological carbon pump. Our study puts forward emergent biodiversity–ecosystem functioning relationships and hypotheses about their underlying drivers for future field-based and modelling research.

Impact of critical eddy diffusivity on seasonal bloom dynamics of Phytoplankton in a global set of aquatic environments

The intensity of eddy diffusivity and the spatial average of water velocity at the depths of the water column in oceans and lakes play a fundamental role in phytoplankton production and phytoplankton and zooplankton biomass, and community composition. The critical depth and intensity of turbulent mixing within the water column profoundly affect phytoplankton biomass, which depends on the sinking characteristic of planktonic algal species. We propose an Nutrient-Phytoplankton-Zooplankton (NPZ) model in 3D space with light and nutrient-limited growth in a micro-scale ecological study. To incorporate micro-scale observation of phytoplankton intermittency in bloom mechanism in stationary as well as oceanic turbulent flows, a moment closure method has been applied in this study. Experimental observations imply that an increase in turbulence is sometimes ecologically advantageous for non-motile planktonic algae. How do we ensure whether there will be a bloom cycle or whether there can be any bloom at all when the existing phytoplankton group is buoyant, heavier, motile, or non-motile? To address these questions, we have explored the effects of critical depth, the intensity of eddy diffusivity, spatial average of water velocity, on the concentration as well as horizontal and vertical distribution of phytoplankton and zooplankton biomass using a mathematical model and moment closure technique. We quantify a critical threshold value of eddy diffusivity and the spatial average of water velocity and observe the corresponding changes in the phytoplankton bloom dynamics. Our results highlight the importance of eddy diffusivity and the spatial average of water velocity on seasonal bloom dynamics and also mimic different real-life bloom scenarios in Mikawa Bay (Japan), Tokyo Bay (Japan), Arakawa River (Japan), the Baltic Sea, the North Atlantic Ocean, Gulf Alaska, the North Arabian Sea, the Cantabrian Sea, Lake Nieuwe Meer (Netherlands) and several shallower lakes.

Element ∕ Ca ratios in Nodosariida (Foraminifera) and their potential application for paleoenvironmental reconstructions

Abstract. The chemical composition of foraminiferal shells is a well-known tool in paleoceanography to reconstruct past environments and climate. Their application is based on the relation between environmental variables and the concentration of elements incorporated or stable isotope fractionation during calcification. The vast majority of these so-called proxy relationships are based on the foraminiferal order of the Rotaliida, which, for example, encompasses all living planktonic species. However, there are more orders of foraminifera with calcifying members, some of which have fundamentally different biomineralization pathways, such as the Nodosariida, the Polymorphinida and the Vaginulinida. All these belong to the class of the Nodosariata and produce calcite shells, which may serve as carriers of paleoenvironmental and climate signals. The microstructures of these shells and overall morphology of these foraminifera strongly deviate from the Rotaliida, suggesting that their elemental and stable isotopic composition do not necessarily respond similarly to environmental parameters. A potential advantage of the Nodosariata is that they appear considerably earlier in the fossil record (Carboniferous) than the Rotaliida (Jurassic), thereby possibly extending the range of foraminifer-based paleoceanographic reconstructions considerably. To test the potential application of Nodosariata foraminifera as paleoproxies, we investigated incorporation of 5 elements in 11 species as a function of environmental parameters from a transect sampled in the Gulf of Mexico. Their element composition (B / Ca, Na / Ca, Mg / Ca, Sr / Ca and Ba / Ca) shows a distinct geochemical signature for these foraminifera, different to that of members of other foraminiferal orders. Results also show an increase in Mg / Ca values with increasing temperature, similar to that known for the Rotaliida, which suggest that Nodosariata shells might be useful for paleotemperature reconstructions. The difference in Mg / Ca–temperature calibration in Nodosariata compared to Rotaliida, with the large differences in their morphology, shell microstructures and overall geochemical composition, suggests that the Mg / Ca-to-temperature relationship is partly independent of the exact calcification mechanism. We compare Mg / Ca–temperature sensitivities across foraminiferal orders and describe a relationship between the average Mg / Ca and the sensitivity of the Mg / Ca–temperature calibration. For other elements, the variability across orders is smaller compared to that in Mg / Ca, which results in more similar El / Ca–environmental calibrations.

How does speciation in marine plankton work?

Marine plankton species are ecologically important, yet, it remains unclear how they originate in the ocean, where few barriers are apparent to cause the most common type of speciation - divergence in isolation. Here I discuss the use of modern evolutionary genetic approaches to shed light on longstanding questions regarding their evolution.

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 < 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 < 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.

Morphological variation in extinct Aulacoseira (Bacillariophyta) species from Lake Towuti, with a description of novel species

Recent studies examining the fossil records of ancient Lake Towuti found this tropical lake once had abundant Aulacoseira spp. that no longer exist in the lake. Varying considerably in cell shape and size, these frustules were found deep within the sediments from the early stages of lake formation (>1 My) and formed two population maxima approximately 300 and 400 kya. We examined the morphological variation and taxonomy of the genus Aulacoseira in the fossil record of Lake Towuti and used principal component analysis (PCA) to confirm six different morphological forms of Aulacoseira. A taxonomic investigation identified one novel species (A. towutiensis sp. nov.), one regionally endemic species (A. malayensis stat. nov. com. nov.), and four new varieties of A. sumatrana sp. nov. not previously reported in the literature. The four varieties of A. sumatrana (var. elongata var. nov., var. miniscula var. nov., var. crustula var. nov., var. rectangularis var. nov.) formed a complex morphological continuum. Aulacoseira sumatrana was originally identified as Aulacoseira granulata var. valida from sediments in Lake Toba, but would now appear to be a unique regionally distributed taxon. PCA further revealed two distinct endmembers (A. towutiensis and A. malayensis), based on areola and cell size. The complex morphological variation observed in Aulacoseira in the sediments of Lake Towuti is suggestive of being the result of differing environmental conditions favouring one species over the other. It is concluded that, historically, Lake Towuti supported selected endemic planktonic diatom species that are now extinct.

Ecosystem and Commercializing of Fish in a Rich-Minerals, Low-Salinity Closed Lake

Wadi El Natrun is an elongated narrow depression in the Western Desert of Egypt. The depression characterized by many ancient alkaline salt lakes. These lakes are filled with water in winter and dried up in summer. Recently, some lakes become permanently dried, while others become submerged throughout the year as El Bieda Lake. El Bieda Lake has undergone ecological changes due to the prolonged extraction of minerals and the continual discharging of freshwater. This study investigates the recent biotic and abiotic changes of this lake and discusses its fisheries opportunities. The lake’s water is well-oxygenated, rich with different inorganic nutrients, and characterized by a low salinity. Sodium and chloride ion concentrations are lower than the equivalent surface seawater, while magnesium, calcium, potassium, sulfate, and bicarbonate ions are higher. The lake has low plankton species richness with high biomass and high nutritional values. More recently, two cichlid species, Oreochromis aureus and Coptodon zillii, have colonized the lake. Summer characterized by a very low mortality for Oreochromis aureus and a poor representation of Coptodon zillii. However, both species shared the catch the rest of the year. The high biomass and nutritional quality of plankton communities, as well as the dense phytobenthic film, indicate that the lake is currently below its carrying capacity. The well-oxygenated water, high biomass of plankton and phytobenthic diatoms, and the expected changes in salinity suggest that introducing the euryhaline, commercially valuable, and fast-growing Mugil cephalus or Chelon ramada in El Bieda Lake is highly advisable.

Seasonal and vertical distribution of living planktonic foraminifera in the western tropical Pacific Ocean

To investigate the seasonal and vertical distributions of planktonic foraminiferal species in the western tropical Pacific Ocean, we collected planktonic foraminifera seasonally and diurnally from eight water depths from 0 to 600 m using the Multiple Opening/Closing Net and Environmental Sensing System. We identified 23 living foraminiferal species (size fraction 212–1000 μm) and examined their abundances at the sites of oligotrophic areas. Seasonal changes were characterized by an increase in the diversity and abundance of planktonic foraminifera in summer. We estimated the habitat depth of planktonic foraminifera based on their vertical distribution. Planktonic foraminifera can be classified into species living in the surface mixed layer, uppermost thermocline, upper thermocline, and lower thermocline in the water column. The uppermost thermocline layer is characterized by the occurrence of subsurface chlorophyll maximum (water depth, 100–150 m). The boundary between the upper and lower thermocline layers (approximately 300 m) is at the depth at which the dissolved oxygen concentration begins to rapidly decrease. The species inhabiting the surface mixed layer were Globigerinoides sacculifer and Globigerinoides ruber white in spring. In summer, G. sacculifer dwelled in the surface mixed layer during night time, whereas they existed in the uppermost thermocline during daytime. Many species were found in the uppermost thermocline layer in summer, including G. ruber white, Globigerinoides conglobatus, Globigerinella siphonifera, Pulleniatina obliquiloculata, Globoquadrina conglomerata, Orbulina universa, Neogloboquadrina dutertrei, Globigerinella calida, and Hastigerina pelagica. The species Globorotalia hirsuta dwelled in the upper thermocline in spring, whereas it occurred in the lower thermocline in summer. Globorotaloides hexagonus inhabited the lower thermocline in all seasons. Our results will provide useful information for reconstructing changes in water column structure using planktonic foraminiferal shells in marine sediments.

Toward phytoplankton parasite detection using autoencoders

Phytoplankton parasites are largely understudied microbial components with a potentially significant ecological influence on phytoplankton bloom dynamics. To better understand the impact of phytoplankton parasites, improved detection methods are needed to integrate phytoplankton parasite interactions into monitoring of aquatic ecosystems. Automated imaging devices commonly produce vast amounts of phytoplankton image data, but the occurrence of anomalous phytoplankton data in such datasets is rare. Thus, we propose an unsupervised anomaly detection system based on the similarity between the original and autoencoder-reconstructed samples. With this approach, we were able to reach an overall F1 score of 0.75 in nine phytoplankton species, which could be further improved by species-specific fine-tuning. The proposed unsupervised approach was further compared with the supervised Faster R-CNN-based object detector. Using this supervised approach and the model trained on plankton species and anomalies, we were able to reach a highest F1 score of 0.86. However, the unsupervised approach is expected to be more universal as it can also detect unknown anomalies and it does not require any annotated anomalous data that may not always be available in sufficient quantities. Although other studies have dealt with plankton anomaly detection in terms of non-plankton particles or air bubble detection, our paper is, according to our best knowledge, the first that focuses on automated anomaly detection considering putative phytoplankton parasites or infections.