Importance of prey size on investigating prey availability of larval fishes.

Prey availability plays an important role in determining larval fish survival. Numerous studies have found close relationships between the density of mesozooplankton and larval fishes; however, emerging studies suggest that small-size zooplankton are more important prey for some larval fish species. One arising question is whether the size of zooplankton determines the relationship between zooplankton and larval fish community in natural environments. To address this question, we collected small-size (50-200 µm) zooplankton, mesozooplankton (> 330 µm), and larval fish using three different mesh-size (50, 330, 1000 µm, respectively) nets in the East China Sea, and examined their relationships in density. Both meso- and small-size zooplankton densities showed positive relationships with larval fish density, while the relationship is much stronger for the small-size zooplankton. Specifically, the smallest size classes (50-75 and 75-100 µm) of small-size zooplankton showed the highest positive relationships with larval fish density. Temperature, salinity, and chlorophyll-a concentration did not significantly explain larval fish density. Based on these findings, we demonstrate the importance of considering prey size when investigating prey availability for larval fishes.

eDNA metabarcoding of small plankton samples to detect fish larvae and their preys from Atlantic and Pacific waters.

Zooplankton community inventories are the basis of fisheries management for containing fish larvae and their preys; however, the visual identification of early-stage larvae (the "missing biomass") is difficult and laborious. Here, eDNA metabarcoding was employed to detect zooplankton species of interest for fisheries from open and coastal waters. High-Throughput sequencing (HTS) from environmental samples using small water volumes has been proposed to detect species of interest whose DNA is the most abundant. We analyzed 6-L water samples taken from subtropical and tropical waters using Cytochrome oxidase I (COI) gene as metabarcode. In the open ocean, several commercial fish larvae and invertebrate species important in fish diet were found from metabarcodes and confirmed from individual barcoding. Comparing Atlantic, Mediterranean, Red Sea, and Pacific samples we found a lower taxonomic depth of OTU assignments in samples from tropical waters than in those from temperate ones, suggesting large gaps in reference databases for those areas; thus a higher effort of zooplankton barcoding in tropical oceans is highly recommended. This and similar simplified sampling protocols could be applied in early detection of species important for fisheries.

18S rRNA gene sequences of leptocephalus gut contents, particulate organic matter, and biological oceanographic conditions in the western North Pacific.

Eel larvae apparently feed on marine snow, but many aspects of their feeding ecology remain unknown. The eukaryotic 18S rRNA gene sequence compositions in the gut contents of four taxa of anguilliform eel larvae were compared with the sequence compositions of vertically sampled seawater particulate organic matter (POM) in the oligotrophic western North Pacific Ocean. Both gut contents and POM were mainly composed of dinoflagellates as well as other phytoplankton (cryptophytes and diatoms) and zooplankton (ciliophoran and copepod) sequences. Gut contents also contained cryptophyte and ciliophoran genera and a few other taxa. Dinoflagellates (family Gymnodiniaceae) may be an important food source and these phytoplankton were predominant in gut contents and POM as evidenced by DNA analysis and phytoplankton cell counting. The compositions of the gut contents were not specific to the species of eel larvae or the different sampling areas, and they were most similar to POM at the chlorophyll maximum in the upper part of the thermocline (mean depth: 112 m). Our results are consistent with eel larvae feeding on marine snow at a low trophic level, and feeding may frequently occur in the chlorophyll maximum in the western North Pacific.

Responses of the zooplankton community to the formation of a small reservoir on the Caveiras River, southern Brazil

We investigated changes in the species richness, abundance, and composition of the zooplankton community in response to the formation of a small reservoir in the Caveiras River, southern Brazil. Zooplankton were collected using a motor-pump and aplankton net (68 μm mesh), with 600 L of water filtered per sample. Sampling occurred during the pre-(April, August, and December 2011) and post-impoundment (July and October 2013, and January 2014) phases of the Caveiras River. We identified 86 taxa in this study, and rotifers were the predominant group. The species richness and abundance of the zooplankton increased after the filling of the reservoir. Furthermore, the zooplankton community showed a clear change in the species composition between the phases before and after the formation of the reservoir, with the emergence of typical planktonic species. Changes in the structure of the zooplankton community were related to changes in limnological characteristics due to the impoundment of the river, mainlyin the availability of food and in the concentration of nutrients.

Modeling the trophic impacts of invasive zooplankton in a highly invaded river.

The lower Columbia River (Washington and Oregon, USA) has been heavily invaded by a large number of planktonic organisms including the invasive copepod Pseudodiaptomus forbesi and the planktonic juveniles of the invasive clam, Corbicula fluminea. In order to assess the ecological impacts of these highly abundant invaders, we developed a multivariate auto-regressive (MAR) model of food web dynamics based upon a 12-year time-series of plankton community and environmental data from the Columbia River. Our model results indicate that plankton communities in the lower Columbia River are strongly impacted by the copepod P. forbesi at multiple trophic levels. We observed different ecological effects across different life stages of P. forbesi, with nauplii negatively impacting ciliates and autotrophs, and copepodite stages negatively impacting Daphnia and cyclopoid copepods. Although juvenile C. fluminea were highly abundant in the summer and autumn of each year, our best fit MAR model did not show significant C. fluminea impacts. Our results illustrate the strong ecological impact that some zooplankton invaders may cause within rivers and estuarine systems, and highlight the need for further research on the feeding ecology of the planktonic life-stage of C. fluminea. Overall, our study demonstrates the manner in which long-term, high resolution data sets can be used to better understand the ecological impacts of invasive species among complex and highly dynamic communities.

In situ observations show vertical community structure of pelagic fauna in the eastern tropical North Atlantic off Cape Verde.

Distribution patterns of fragile gelatinous fauna in the open ocean remain scarcely documented. Using epi-and mesopelagic video transects in the eastern tropical North Atlantic, which features a mild but intensifying midwater oxygen minimum zone (OMZ), we established one of the first regional observations of diversity and abundance of large gelatinous zooplankton. We quantified the day and night vertical distribution of 46 taxa in relation to environmental conditions. While distribution may be driven by multiple factors, abundance peaks of individual taxa were observed in the OMZ core, both above and below the OMZ, only above, or only below the OMZ whereas some taxa did not have an obvious distribution pattern. In the eastern eropical North Atlantic, OMZ expansion in the course of global climate change may detrimentally impact taxa that avoid low oxygen concentrations (Beroe, doliolids), but favour taxa that occur in the OMZ (Lilyopsis, phaeodarians, Cydippida, Colobonema, Haliscera conica and Halitrephes) as their habitat volume might increase. While future efforts need to focus on physiology and taxonomy of pelagic fauna in the study region, our study presents biodiversity and distribution data for the regional epi- and mesopelagic zones of Cape Verde providing a regional baseline to monitor how climate change may impact the largest habitat on the planet, the deep pelagic realm.

Grazing pressure-induced shift in planktonic bacterial communities with the dominance of acIII-A1 actinobacterial lineage in soda pans.

Astatic soda pans of the Pannonian Steppe are unique environments with respect to their multiple extreme physical and chemical characteristics (high daily water temperature fluctuation, high turbidity, alkaline pH, salinity, polyhumic organic carbon concentration, hypertrophic state and special ionic composition). However, little is known about the seasonal dynamics of the bacterial communities inhabiting these lakes and the role of environmental factors that have the main impact on their structure. Therefore, two soda pans were sampled monthly between April 2013 and July 2014 to reveal changes in the planktonic community. By late spring in both years, a sudden shift in the community structure was observed, the previous algae-associated bacterial communities had collapsed, resulting the highest ratio of Actinobacteria within the bacterioplankton (89%, with the dominance of acIII-A1 lineage) ever reported in the literature. Before these peaks, an extremely high abundance (> 10,000 individuum l-1) of microcrustaceans (Moina brachiata and Arctodiaptomus spinosus) was observed. OTU-based statistical approaches showed that in addition to algal blooms and water-level fluctuations, zooplankton densities had the strongest effect on the composition of bacterial communities. In these extreme environments, this implies a surprisingly strong, community-shaping top-down role of microcrustacean grazers.

Zooplankton biogeographic boundaries in the California Current System as determined from metabarcoding.

Within the southern California Current ecosystem there are two well-documented breaks in marine community structure at Point Conception and Punta Eugenia. We explored the presence of similar breaks in a diverse zooplankton community through metabarcoding of mixed net tow tissue samples collected during an expedition from Monterey to Baja California in February of 2012. We recovered a high diversity of species as well as patterns of species presence that align with their previously documented ranges in this region. We found a clear break at Punta Eugenia in overall zooplankton community structure, while Point Conception was weakly linked to changes in community structure. We analyzed this dataset through two parallel bioinformatic pipelines to examine the robustness of these results. Our overall conclusions were consistent across both pipelines, however there were differences in species detection. This study illustrates the utility of metabarcoding analysis on mixed tissue samples for recovering known patterns of diversity, as well as allowing elucidation of broad patterns of community differentiation across many groups of organisms.

Effects of suspended micro- and nanoscale particles on zooplankton functional diversity of drainage system reservoirs at an open-pit mine.

Water from mining drainage is turbid because of suspensions. We tested the hypothesis that the chemical composition as well as shape and size of particles in suspensions of natural origin affect the density and functional diversity of zooplankton. The suspensions were analyzed with atomic force microscopy (AFM), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), and optical microscopy. Elements found in the beidellite clays were also identified in the mineral structure of the particles. As the size of the microparticles decreased, the weight proportions of phosphorus, sulfur, and chlorine increased in the suspensions. These conditions facilitated the biomass growth of large and small microphages and raptorials. As the size of the nanoparticles decreased, the shares of silicon, aluminum, iron, and magnesium increased. These conditions inhibited raptorials the most. Ecosystem functionality was the highest with intermediate suspension parameters, which were at the lower range of the microphase and the upper range of the nanophase. The functional traits of zooplankton demonstrate their potential for use as sensitive indicators of disruptions in aquatic ecosystems that are linked with the presence of suspensions, and they facilitate gaining an understanding of the causes and scales of the impact of suspensions.

Biological consequences of environmental pollution in running water ecosystems: A case study in zooplankton.

Biodiversity in running water ecosystems such as streams and rivers is threatened by chemical pollution derived from anthropogenic activities. Zooplankton are ecologically indicative in aquatic ecosystems, owing to their position of linking the top-down and bottom-up regulators in aquatic food webs, and thus of great potential to assess ecological effects of human-induced pollution. Here we investigated the influence of water pollution on zooplankton communities characterized by metabarcoding in Songhua River Basin in northeast China. Our results clearly showed that varied levels of anthropogenic disturbance significantly influenced water quality, leading to distinct environmental pollution gradients (p < 0.001), particularly derived from total nitrogen, nitrate nitrogen and pH. Redundancy analysis showed that such environmental gradients significantly influenced the geographical distribution of zooplankton biodiversity (R = 0.283, p = 0.001). In addition, along with the trend of increasing environmental pollution, habitat-related indicator taxa were shifted in constituents, altering from large-sized species (e.g. arthropods) in lightly disturbed areas to small-sized organisms (e.g. rotifers and ciliates) in highly disturbed areas. All these findings clearly showed that anthropogenic activity-derived water pollution significantly influenced biological communities. Thus, biotic consequences of human-induced environmental pollution in running water ecosystems should be deeply investigated. More importantly, the findings of biotic consequences should be well integrated into existing monitoring programs to further assess impacts of anthropogenic disturbance, as well as to advance the management of running water ecosystems for conservation and ecological restoration.

Spatio-temporal patterns of zooplankton in a main-stem dam affected tributary: a case study in the Xiangxi River of the Three Gorges Reservoir, China.

As the ecologically important recipient channels for riverine ecosystems, tributaries provide unique microhabitats for microorganisms, among which zooplankton constitutes the most important heterotrophic organisms. In particular, the reduced water velocity caused by dams is more favorable for zooplankton development; therefore, dammed rivers are expected to support extremely diverse and abundant zooplankton communities and notably different spatiotemporal distribution patterns. So far, however, only very few molecular studies support these assumptions. Using high-throughput sequencing, a high number of 350 operational taxonomic units (OTUs; 97% cutoff) were retrieved from 30 samples collected in the Xiangxi River, the nearest large tributary upstream of the Three Gorges Dam. Zooplankton did not show significant spatial distribution in the channel. Instead, the community structures varied significantly over sampling dates, corroborating the seasonal patterns found in lakes and ponds in the subtropical zone. As expected, the community compositions were deterministically governed by environmental filtering processes (phylogenetic clustering), in which water velocity appeared to be much less important than other investigated environmental factors. Moreover, most of the detected phylotypes (OTUs) had a relatively high (>90%) sequence similarity to previously deposited sequences, suggesting a mediocre degree of genetic novelty within the zooplankton communities in the Xiangxi River.

Temporal and spatial variations in zooplankton communities in relation to environmental factors in four floodplain lakes located in the middle reach of the Yangtze River, China.

A comparative limnological study of the zooplankton communities and their relationship with environmental factors was conducted to test the temporal and spatial changes among lake groups. In our study of four lakes, the lowest gamma (γ) diversity was recorded in January 2017, with a total of 25 zooplankton taxa. The highest γ diversity was recorded in May 2016, with a total of 55 zooplankton taxa. Species turnover in space (ß) were from 14.98 to 25.81. Markedly temporal and spatial variations were observed in the zooplankton community. The higher mean cladocera density (57.70 ind. L-1 and 39.85 ind. L-1) was observed in May and August, then decreased gradually with the lowest in January. The mean copepoda density ranged from 8.71 ind. L-1 in January 2017 to 32.04 ind. L-1 in August 2016. The mean rotifera density was significantly higher than that of the other two crustacean zooplankton (p < 0.01), within the range of 89.36-1139.2 ind. L-1. We also observed that zooplankton density exhibited significant seasonal changes from NMDS (Nonmetric multidimensional scaling analysis). Redundancy analysis revealed that environmental factors, such as water temperature and transparency, have significantly influenced the zooplankton community structure.

Global change drives modern plankton communities away from the pre-industrial state.

The ocean-the Earth's largest ecosystem-is increasingly affected by anthropogenic climate change1,2. Large and globally consistent shifts have been detected in species phenology, range extension and community composition in marine ecosystems3-5. However, despite evidence for ongoing change, it remains unknown whether marine ecosystems have entered an Anthropocene6 state beyond the natural decadal to centennial variability. This is because most observational time series lack a long-term baseline, and the few time series that extend back into the pre-industrial era have limited spatial coverage7,8. Here we use the unique potential of the sedimentary record of planktonic foraminifera-ubiquitous marine zooplankton-to provide a global pre-industrial baseline for the composition of modern species communities. We use a global compilation of 3,774 seafloor-derived planktonic foraminifera communities of pre-industrial age9 and compare these with communities from sediment-trap time series that have sampled plankton flux since AD 1978 (33 sites, 87 observation years). We find that the Anthropocene assemblages differ from their pre-industrial counterparts in proportion to the historical change in temperature. We observe community changes towards warmer or cooler compositions that are consistent with historical changes in temperature in 85% of the cases. These observations not only confirm the existing evidence for changes in marine zooplankton communities in historical times, but also demonstrate that Anthropocene communities of a globally distributed zooplankton group systematically differ from their unperturbed pre-industrial state.

The effects of environmental factors and geographic distance on species turnover in an agriculturally dominated river network.

Both environmental and geographic factors interact to structure the metacommunities in river networks, but the importance of these factors is difficult to distinguish. We used six aquatic taxonomic groups to test the relationship between environmental and geographic factors and their effect on species turnover patterns in an agriculturally dominated river (Chaohu Lake Basin, China). The relationships between three dissimilarity indices and geographic distance were assessed using the Mantel test while considering the differences in environmental factors between sites. Then, we employed a variation partitioning method to distinguish the isolated and combined effects of environmental and geographic distance on species turnover. There were significant relationships between environmental distance and species turnover in all groups. All organisms except periphytic diatoms were significantly correlated with two geographic (Euclidean and network) distances when the Chao dissimilarity index was considered. The results suggest that the strength of the correlations changed with environmental and geographic distances and with the aquatic community. The communities displayed more complex relationships with the distance measures when different dissimilarity (Jaccard, Chao, and Bray-Curtis dissimilarity) indices were considered. Nevertheless, aquatic communities are strongly influenced by both environmental and geographic distance, and the former has a stronger effect than the latter.

Marine environmental DNA biomonitoring reveals seasonal patterns in biodiversity and identifies ecosystem responses to anomalous climatic events.

Marine ecosystems are changing rapidly as the oceans warm and become more acidic. The physical factors and the changes to ocean chemistry that they drive can all be measured with great precision. Changes in the biological composition of communities in different ocean regions are far more challenging to measure because most biological monitoring methods focus on a limited taxonomic or size range. Environmental DNA (eDNA) analysis has the potential to solve this problem in biological oceanography, as it is capable of identifying a huge phylogenetic range of organisms to species level. Here we develop and apply a novel multi-gene molecular toolkit to eDNA isolated from bulk plankton samples collected over a five-year period from a single site. This temporal scale and level of detail is unprecedented in eDNA studies. We identified consistent seasonal assemblages of zooplankton species, which demonstrates the ability of our toolkit to audit community composition. We were also able to detect clear departures from the regular seasonal patterns that occurred during an extreme marine heatwave. The integration of eDNA analyses with existing biotic and abiotic surveys delivers a powerful new long-term approach to monitoring the health of our world's oceans in the context of a rapidly changing climate.

Temporal variation in zooplankton and phytoplankton community species composition and the affecting factors in Lake Taihu-a large freshwater lake in China.

Monitoring diverse components of aquatic ecosystems is vital for elucidation of diversity dynamics and processes, which alter freshwater ecosystems, but such studies are seldom conducted. Phytoplankton and zooplankton are integral components which play indispensable parts in the structure and ecological service function of water bodies. However, few studies were made on how zooplankton and phytoplankton community may respond simultaneously to change of circumstance and their mutual relationship. Therefore, we researched synchronously the phytoplankton communities as well as zooplankton communities based on monthly monitoring data from September 2011 to August 2012 in heavily polluted areas and researched their responses to variation in environmental parameters and their mutual relationship. As indicated by Time-lag analysis (TLA), the long-term dynamics of phytoplankton and zooplankton were undergoing directional variations, what's more, there exists significant seasonal variations of phytoplankton and zooplankton communities as indicated by Non-Metric Multidimensional scaling (NMDS) methods. Also, Redundancy Analysis (RDA) demonstrated that environmental indicators together accounted for 25.6% and 50.1% variance of phytoplankton and zooplankton, respectively, indicating that environmental variations affected significantly on the temporal dynamics of phytoplankton as well as zooplankton communities. What's more, variance partioning suggested that the major environmental factors influencing variation structures of zooplankton communities were water temperature, concentration of nitrogen, revealing the dominating driving mechanism which shaped the communities of zooplankton. It was also found that there was significant synchronization between zooplankton biomass and phytoplankton biomass (expressed as Chl-a concentration), which suggested that zooplankton respond to changes in dynamic structure of phytoplankton community and can initiate a decrease in phytoplankton biomass through grazing in a few months.

Zooplankton in Adriatic port environments: Indigenous communities and non-indigenous species.

The zooplankton community was analyzed in ten Adriatic ports as part of the port biological baseline surveys carried out within the framework of the BALMAS project. We provide the first inventory of resident zooplankton taxa and five detected non-indigenous zooplankton species (NIS), and their spatial and seasonal distribution patterns. Copepoda and meroplankton larvae, particularly of Mollusca, dominated the zooplankton in all sampled ports. We recorded a total of 76 indigenous copepod species and five NIS, among which Parvocalanus crassirostris detected in Sibenik and Rijeka ports and Oithona davisae in Venice port, are new for the Adriatic. All detected NIS were widely distributed within the recipient ports. Co-occurrences of NIS were observed in the ports of Venice, Bari, Ancona and Trieste. The results are expected to contribute to the quality of practical monitoring of zooplankton NIS and facilitate the synchronization of efforts in creating NIS-related policies for the Adriatic sub-region.

The Impact of Anthropogenic Disturbance on Bacterioplankton Communities During the Construction of Donghu Tunnel (Wuhan, China).

Bacterioplankton are both primary producers and primary consumers in aquatic ecosystems, which were commonly investigated to reflect environmental changes, evaluate primary productivity, and assess biogeochemical cycles. However, there is relatively less understanding of their responses to anthropogenic disturbances such as constructions of dams/tunnels/roads that may significantly affect the aquatic ecosystem. To fill such gap, this study focused on the bacterioplankton communities' diversity and turnover during a tunnel construction across an urban lake (Lake Donghu, Wuhan, China), and five batches of samples were collected within 2 months according to the tunnel construction progress. Results indicated that both resources and predator factors contributed significant to the variations of bacterioplankton communities, but the closed area and open areas showed different diversity patterns due to the impacts of tunnel construction. Briefly, the phytoplankton, TN, and TP in water were still significantly correlated with the bacterioplankton composition and diversity like that in normal conditions. Additionally, the organic matter, TN, and NH4-N in sediments also showed clear effects on the bacterioplankton. However, the predator effects on the bacterioplankton in the closed-off construction area mainly derived from large zooplankton (i.e., cladocerans), while small zooplankton such as protozoa and rotifers are only responsible for weak predator effects on the bacterioplankton in the open areas. Further analysis about the ecological driving forces indicated that the bacterioplankton communities' turnover during the tunnel construction was mainly governed by the homogeneous selection due to similar environments within the closed area or the open areas at two different stages. This finding suggests that bacterioplankton communities can quickly adapt to the environmental modifications resulting from tunnel construction activities. This study can also give references to enhance our understanding on bacterioplankton communities' response to ecological and environmental changes due to intensification of construction and urbanization in and around lake ecosystems.

Potential transfer of aquatic organisms via ballast water with a particular focus on harmful and non-indigenous species: A survey from Adriatic ports.

Ballast water discharges may cause negative impacts to aquatic ecosystems, human health and economic activities by the introduction of potentially harmful species. Fifty untreated ballast water tanks, ten in each port, were sampled in four Adriatic Italian ports and one Slovenian port. Salinity, temperature and fluorescence were measured on board. Faecal indicator bacteria (FIB), phyto- and zooplankton were qualitatively and quantitatively determined to identify the species assemblage arriving in ballast water. FIB exceeded the convention standard limits in 12% of the sampled tanks. Vibrio cholerae was not detected. The number of viable organisms in the size groups (minimum dimension) <50 and ≥10 µm and ≥50 µm resulted above the abundances required from the Ballast Water Management Convention in 55 and 86% of the samples, respectively. This is not surprising as unmanaged ballast waters were sampled. Some potentially toxic and non-indigenous species were observed in both phyto- and zooplankton assemblages.

Diversity of marine planktonic ostracods in South China Sea: a DNA taxonomy approach.

Ostracods (Crustacea, Ostracoda) are small bivalved crustaceans, contributing over 200 described species to the marine zooplankton community. They are widely distributed and are relatively abundant components of the mesozooplankton, playing an important role in the transport of organic matter to deep layers. However, identification of ostracods based on micro-morphological characters is extremely difficult and time-consuming. Previous fragmentary taxonomic studies of ostracods in the South China Sea (SCA), were based solely on morphology. Here, by analysing the mitochondrial COI gene, we explore the taxa across the SCA using molecular tools for the first time. Our results show that sequence divergence among species varies within a large range, from 12.93% to 35.82%. Sixteen of the taxonomic units recovered by DNA taxonomy agree well with morphology, but Paraconchoecia oblonga, Conchoecia magna and Halocypris brevirostris split into two clades each, each of which contains cryptic species.