Grazing on phytoplankton by microzooplankton is a critical process in making energy available to higher trophic levels, shaping marine food webs, and biogeochemical cycling. Despite its key role, the drivers of grazing remain poorly constrained due to the concurrent influences of biotic and abiotic factors. To elucidate the impact of microzooplankton biomass and community composition on grazing rates, we measured ciliate and dinoflagellate biomass in boreal summer and winter from 2018-2023, at three stations spanning the Northeast US Shelf from coastal Rhode Island, USA to the shelf break. This record of microzooplankton biomass encompasses the seasonal and spatial variability from shore to shelf. Dinoflagellate biomass showed a clear seasonal shift from larger (>20 μm) cells in winter to smaller ones in summer, while ciliate biomass lacked seasonal trends. Anomalies in community composition coincided with disruptions in the typical seasonal phytoplankton size structure, suggesting that microzooplankton size structure was linked to the size of available prey. In winter, microzooplankton biomass was positively correlated with microzooplankton grazing, indicating that the mechanism moderating the planktonic food web structure changes seasonally. These results inform our understanding of planktonic food webs by identifying the linkage between grazing and seasonal changes in phytoplankton community structure that impact energy transfer to higher trophic levels.
Understanding environmental drivers of plankton community assembly is critical for predicting ecosystem responses to environmental change in reservoir systems. This study employed environmental DNA (eDNA) metabarcoding to examine how temperature, dissolved oxygen, and spatial gradients structure plankton communities in Singal Reservoir, South Korea, across seasonal and spatial scales from 2021-2022. Water samples were collected from inflow, middle, and outflow zones during spring and autumn, with multi-depth sampling at the central site. The V9 region of 18S rRNA was amplified and sequenced to characterize eukaryotic plankton communities. PERMANOVA analysis revealed that environmental factors explained 39.72% of phytoplankton and 38.62% of zooplankton community variation, with total nitrogen showing the strongest statistical relationship (p = 0.03 for phytoplankton), while temperature and dissolved oxygen patterns revealed important ecological gradients. Phytoplankton communities (130 genera, 5 phyla) showed pronounced seasonal patterns, with autumn exhibiting significantly higher species richness (103 genera) than spring (48 genera) (PERMANOVA: F = 9.52, p = 0.001). Zooplankton communities (43 genera, 2 phyla) displayed similar seasonal trends (F = 7.06, p = 0.001). Spatial analysis demonstrated that sampling location explained 16.7% of zooplankton variance compared to only 1.2% for depth effects, contrasting with expectations about depth effects in shallow reservoirs. Temperature-dissolved oxygen interactions created distinct environmental niches: diatoms preferred high temperature-high oxygen conditions, while dinoflagellates were most common in high temperature-low oxygen environments. Spearman correlations showed environmental preferences, with taxa like Eudiaptomus showing preference for low nutrient conditions (rs = -0.860, p < 0.001 for electrical conductivity). These findings show that environmental selection, especially temperature and dissolved oxygen gradients, are the primary drivers of plankton community structure in reservoir ecosystems, with help predict community responses to climate change and guiding management decisions.
Due to the high sensitivity of zooplankton to environmental fluctuations, monitoring their taxonomic composition, abundance and biomass is of high priority to identify changes in the ecosystem. Recent advances in imaging and molecular technologies promise to greatly accelerate the processing of samples to determine both the diversity and quantity of the zooplankton community. In our study, we analyzed the diversity and quantity of an epipelagic Arctic zooplankton community using multi-marker metabarcoding and imaging analysis (ZooScan). We identified a total of 11 phyla and 58 species in the northern Barents Sea and the Nansen Basin. Metabarcoding identified more taxa than image analysis, while imaging provided quantitative information on abundance and biomass. Multivariate analyses revealed overall the same significant environmental drivers (temperature and percentage of Polar Surface Water in the sampling depth layer) explaining the similarity and spatial distribution of the zooplankton community. For all approaches, similar spatial patterns of the zooplankton community were found. Abundance, biovolume and biomass decreased with increasing latitude within the analyzed regions. Based on this study, we recommend ZooScan image analysis in combination with COI metabarcoding for future monitoring of Arctic zooplankton diversity and quantification to ensure the detection of changes in both aspects of these communities.
Biodiversity assessment promotes information on the state of an ecosystem. Zooplankton, as a sentinel group at the basis of aquatic food webs, are, thus, an important component to monitor for ecosystem conservation and management. For the first time, we characterized biodiversity of coastal zooplankton along the shallow Northern shoreline of the lower St. Lawrence estuary (LSLE) using an integrated taxonomic and trait-based approach. For 3 years (2019-2021), in July and October, the zooplankton community and environmental parameters were sampled at < 35 m depth. Mesozooplankton were identified at the lowest possible taxonomic level and assigned functional traits. Community structure and diversities revealed high spatio-temporal variations among three different geographic sectors and between seasons, mainly driven by water temperature, Chlorophyll-a concentration and less by salinity. Hotspots of taxonomic and functional diversities occurred in different sectors in the same month, underlining the complementarity of the two approaches. Seasonal shifts in functional diversity hotspots highlight how environmental variability affects biodiversity beyond taxonomic metrics alone. The results of our study in the LSLE establish a first robust baseline to improve our understanding of zooplankton dynamics in the coastal LSLE, to allow future tracking of ongoing change due to the increase of anthropogenic activities and climate changes and to support future monitoring efforts.
The Gulf of Maine has experienced pronounced changes in recent decades, including rapid warming and changes in circulation. Notably, a shift in water masses entering the Gulf occurred around 2010. Concurrent declines in critically endangered North Atlantic right whales, lobster recruitment and abundance of the foundational, subarctic copepod, Calanus finmarchicus, have designated the 2010 event as a possible regime shift. We present results from two time series stations documenting change in the mesozooplankton biomass and community composition before and after 2010. We examine both seasonal and interannual variability to elucidate potential changes in phenological drivers of the mesozooplankton population in Wilkinson Basin. Abundances of smaller copepod species increased across all seasons between the two time periods, and significantly lower abundance of late-stage C. finmarchicus was observed in late summer through winter, resulting in a decrease in mesozooplankton biomass but increases in biodiversity indices post-2010. The results highlight the contribution of ecologically important increases in chlorophyll-a concentration and warmer temperatures as drivers of mesozooplankton growth and reproduction. An important ecological influence on food availability to smaller copepods may be reduced grazing competition by late-stage C. finmarchicus, a consequence of its declined abundance due to increased predation loss and reduced advective supply.
The Canary Current Large Marine Ecosystem (CCLME), extending from Cape Spartel in Morocco to Guinea-Bissau, supports high primary and fisheries productivity driven by permanent or seasonal upwelling activity. During the current study, mesozooplankton and hydrographic sampling were conducted across the CCLME in the spring/summer of 2017 and the autumn/winter of 2019. The total mesozooplankton abundance and dry weight were found to be higher in 2017, partly due to the summer reproduction cycle of diplostracans. A prominent latitudinal gradient was observed in both the mesozooplankton standing stock and assemblage structure closely linked to a significant shift in oceanographic regimes at Cape Blanc (21°N). The area south of Cape Blanc, sampled during the upwelling relaxation in both years, was occupied by warmer South Atlantic Central Waters showing elevated mesozooplankton stock with a tropical assemblage structure. In contrast, cooler and more saline waters north of Cape Blanc, a result of the upwelling regime in that area, explained part of the observed variation in mesozooplankton composition among subregions and sampling periods. Our findings indicate that aside from the upwelling activity, spatiotemporal variation of mesoscale processes and topographical features at a subregional level may also shape mesozooplankton stock and assemblage structure in the CCLME.
Zooplankton have been monitored on autumn cruises in the Barents Sea since the late 1980s. The time series shows a pronounced peak in zooplankton biomass in the inflow region of Atlantic water in 1994. The mean biomass was ~ 20 g dry weight m-2, which is more than twice the long-term average, and showed an atypical composition with dominance of the small size fraction (<1 mm). Analysis of stored samples revealed that the high biomass event in 1994 was due to a mass occurrence of two species of Limacina pteropods (Limacina retroversa and Limacina helicina) dominated by small juveniles < 1 mm in diameter. High biomass in the Atlantic inflow region also in 1995 was due to a strong but delayed summer generation of the dominant copepod Calanus finmarchicus. Estimated biomass of copepods (from numbers and individual weight by species and stage) was strongly dominated by C. finmarchicus in both years (~90%). The average biomass of Limacina spp. in 1994 was ~ 7 g dw m-2, estimated to be mainly in the small fraction, and contributed to the 1994 peak on top of a "typical" biomass of C. finmarchicus. The results contribute to a better understanding of the Barents Sea ecosystem.
Marine plankton are ecologically crucial, as they contribute to biogeochemical cycles and food web structure. This study investigated the structure and dynamics of marine plankton communities in relation to local environmental conditions and seasonal changes over 2 years in the coastal regions of Busan, Jinhae, and Masan in South Korea. The results revealed significant variations in the plankton community composition between Jinhae/Masan and Busan, driven by freshwater inputs, temperature fluctuations, and salinity changes. Dinoflagellates predominated the plankton communities of Jinhae and Masan, whereas high abundances of diatoms, cyanobacteria, and cryptophytes were found in Busan. In addition, seasonal dynamics were observed in microbial abundances, with cyanobacteria and diatoms predominating during summer when water temperatures were elevated, and two distinct blooms occurring in winter. The plankton community correlated with environmental variables and organisms, resulting in either co-clustering or niche segregation. Additionally, bacterioplankton and phytoplankton formed complex networks with each other. Our findings emphasize the interplay between abiotic and biotic factors in shaping plankton community structures and underscore the need for comprehensive studies integrating environmental monitoring with analyses of interspecies interactions. This research enhances our understanding of the dynamic changes in marine plankton communities and provides a valuable basis for future marine ecosystem management.
Offshore wind power pile foundation construction has pros and cons for the marine environment, yet comprehensive assessment of underwater ecosystems remains limited. This study assesses the impact of Bodhi Island Offshore Wind Farm's power pile foundation on marine environment sustainability through studying nutrients, plankton communities, and fishery resources. Furthermore, the research investigates the spatiotemporal variations in attached organisms on offshore wind power pile foundations and contrasts fishery resources between wind farm and non-wind farm areas. Additionally, the Ecopath model was used to evaluate the food web structure and ecological carrying capacity of underwater ecosystems in offshore wind farms. Findings demonstrate that the lower NO3- concentration in the wind farm area, compared to the reference area, results in diminished plankton levels. However, over time, the foundations provide substrate for biological attachment, with attached organism richness positively correlating with water depth, leading to increased fishery resources within the wind farm area. It is noteworthy that offshore wind farms have a high ecological carrying capacity for economically important species such as the Rapana venosa and Crassostrea gigas, increasing the reproductive potential of these organisms. This research provides valuable insights for the sustainable development of offshore wind energy and serves as an important reference site for the planning and management of wind farms, ensuring ecological safety.
Coexistence of competing species may be influenced by environmental variation. Specifically, theory suggests that short-term environmental variability can contribute to long-term coexistence among competitors. Here, we address the role of environmental variation on competitive interactions between two zooplankton species (Daphnia magna and D. pulex) which are found sympatrically, but where mechanisms allowing for such coexistence remain unclear. Using competition experiments, we show that under constant temperature conditions, one of the species (D. magna) was greatly outnumbered by their competitor (D. pulex). Furthermore, population simulations showed a significant possibility for extinction of the inferior competitor, and distributions of estimated niche differences and relative fitness differences included parameter sets that precluded stable coexistence. Under fluctuating temperature conditions, however, the numerical dominance by D. pulex was considerably reduced. Moreover, under these conditions the occurrence of extinction of D. magna in the simulations became negligible, and all parameter sets drawn from the estimated distributions of niche differences and relative fitness differences met the requirements for stable coexistence. Our results provide empirical support for previous model results showing how short-term variation in temperature can promote species coexistence.
Most alpine-type lakes in the Tatra Mountains were stocked with salmonid fish during the 19th and 20th centuries, triggering profound ecological shifts. In the Five Lakes Valley, trout introductions into Przedni Staw Polski, Czarny Staw Polski and Wielki Staw Polski had contrasting effects on pelagic ecosystems. In the smaller and shallower Przedni Staw Polski and Czarny Staw Polski, fish introduction was associated with the loss of large-bodied zooplankton, increased trophic status and a rapid decline in water transparency-from 13-18 m to 5-7 m. Between 2021 and 2023, partial fish removal in Przedni Staw Polski resulted in a marked increase in water transparency (from 7 to 17 m), coinciding with reduced surface phytoplankton biomass. This improvement likely reflected decreased phosphorus input from fish excretion rather than enhanced zooplankton grazing. Large-bodied cladocerans did not recolonize the lake, although small-bodied taxa increased in abundance. In contrast, Czarny Staw Polski-where fish remain abundant-showed no signs of recovery: water transparency declined further and zooplankton community structure remained unchanged. Unlike the other stocked lakes, Wielki Staw Polski-the largest and deepest-retains high transparency and large-bodied zooplankton, likely due to low fish density or availability of predator-free refugia. While partial fish control in Przedni Staw Polski yielded rapid benefits, restoring natural ecosystem functioning in these fragile alpine ecosystems will require complete fish eradication.
Thermal fluctuations affect the physiology and ecology of organisms. To date, most studies quantifying the effects of temperature on phytoplankton have used mean constant conditions, thus overlooking the role of short-term thermal fluctuations. Here, we use a multi-trait analysis to quantify how thermal regime (constant vs. fluctuation by ±3°C around mean temperature) alters the effect of temperature (18 vs. 22°C) on the growth, elemental composition, photosynthetic performance and metabolism of five phytoplankton species (Emiliania huxleyi, Micromonas commoda, Skeletonema costatum, Synechococcus sp. and Thalassiossira rotula) during exponential growth and stationary phases. Our results showed a high degree of inter-trait and inter-specific variability in the response to the temperature treatments. The carbon-based growth rates tended to be reduced by thermal fluctuations (by 20-29%), particularly under warming conditions. By contrast, thermal fluctuations increased the photosynthesis rates up to 25%, regardless of the growth phase. The carbon-to-nitrogen and carbon-to-chlorophyll a ratios, maximum photochemical yield of photosystem II and relative maximum electron transport rates did not show a clear response to interactions between thermal fluctuations and temperature. These results suggest that, when assessing phytoplankton responses to temperature, it is essential to consider both thermal fluctuations and multi-trait analysis.
Algal biovolume is a standard measurement for limnological and oceanographic studies, which is used to proxy biomass and productivity. Manual and automatic methods can be applied to estimate biovolume from phytoplankton images. We examined the effects of algal shape and taxon (largely genus) on the accuracy of automatic image-based biovolume estimates for samples from a large oligotrophic embayment (Georgian Bay, Lake Huron). Specifically, we compared biovolume estimates based on equivalent spherical diameter, Feret-based diameter and two shape-based estimates (cylinder and prolate spheroid) against the manual biovolume measurements using correlation, linear regression and analysis of variance. The automatic biovolume estimates were all moderately to strongly correlated with the manual measurements, but the automatic cylinder method was the most accurate, overall. The automatic cylinder method overpredicted the manual total biovolume measurement of the community by 59%, but it had the strongest linear relationship with manual total biovolume, and the strongest correlation based on the biovolumes of individual genera. When algal taxa were assigned to 11 general shape categories, we observed significant differences in the accuracy with which they were measured. Results suggest that the cylinder biovolume method provides a reasonable estimate of total biovolume in algal communities that have a diversity of elongated shapes.
In the face of changing climate and global water cycle, the plastic response of phytoplankton species to salinity fluctuations is increasingly important. This study used a multivariate approach to determine interspecific trait variability and plasticity of 10 Baltic Sea phytoplankton species along the salinity gradient. Phytoplankton species representing a broad range of sizes and taxonomic groups were grown at six salinity conditions (0, 5, 15, 20, 30 and 35 psu), and 15 different traits were measured at the end of the experiment. Results showed species-specific salinity preferences. Nutrient uptake and resource use efficiency (RUE) explained interspecific trait variability among the species. Variability in nutrient uptake reflected species-specific differences in cell size. RUE and cellular elemental content were the most plastic traits across the salinity gradient and did not scale with cell size. Interestingly, low trait plasticity did not always translate into low biomass production, as a diatom Phaeodactylum tricornutum exemplified. As expected, the salinity range between 5 and 20 psu was optimal for most phytoplankton species, corresponding to the brackish Baltic Sea where they were isolated. Many species survive in salinities above this range, but not in freshwater, which can have consequences for the plankton community functioning with predicted Baltic Sea freshening.
The survival of Faroe Plateau cod larva to the juvenile stage varies significantly between years, impacting recruitment. Zooplankton abundance is likely a key driver in this variability, but to what extent specific prey species are key to survival of the larvae has been unclear. This study explores a seasonally resolved zooplankton dataset from a high-recruitment year (2017) and two following low-recruitment years (2018 and 2019) collected along a hydrographic/biological transect extending from the central shelf to the open ocean west of the Faroes; a key region, with strong influxes of oceanic waters to the shelf. The aim was to identify zooplankton species crucial for cod larval growth and survival. Analyses suggest a positive relationship between pelagic juvenile indices and primary production on the central shelf as well as the oceanic abundance of the copepod Calanus finmarchicus. Using partial least square regression on previously unpublished longer term data on copepod abundances in the upper layer in the Faroe Bank Channel and a primary production index for the Faroe shelf, we found that the shelf primary production combined with the abundance of late-stage C. finmarchicus in oceanic waters in May account for half of the interannual variability in juvenile cod abundance.
The Canary Current Large Marine Ecosystem (CCLME) is among the most productive upwelling systems globally, supporting high fish biomass and biodiversity. We examined horizontal patterns of early fish stages along a 241-nautical-mile transect and vertical distributions down to 800 m at four of 11 stations, within the strong permanent upwelling area of the CCLME in December 2019. An inshore-offshore transition of the larval assemblages was observed, shifting from dominance of European pilchard (Sardina pilchardus) within the upwelling domain to an offshore assemblage dominated by mesopelagic families such as Myctophidae, Phosichthyidae, and Gonostomatidae. Mesoscale activity near the 3000 m isobath significantly influenced larval distribution patterns. A distinct vertical structuring was evident, with transforming stages of mesopelagic taxa contributing increasingly toward deeper layers. The gonostomatid Cyclothone prevailed between 400 and 800 m, showing no evidence of diel vertical migration, unlike other mesopelagic fish species. Size distributions of Cyclothone revealed a clear ontogenetic vertical pattern, with larger individuals occurring at greater depths, while transforming stages comprised a substantial proportion of total sampled net biomass within the deeper strata (up to 34.9%). These findings are discussed in the context of the ecology of this genus and its importance to the carbon flow in the mesopelagic zone.
Riverine discharge plays a crucial role in shaping planktonic food web dynamics in coastal systems, though its effects can vary across estuaries. This study investigated the influence of riverine discharge on key biological variables-primary productivity, nitrogen uptake (nitrate and ammonium), biomass, community composition, and mesozooplankton feeding rates-across estuarine gradients in Gwangyang Bay, a low-turbidity temperate estuary in Korea. Principal component analysis identified riverine discharge as the main driver of environmental variation, influencing salinity, light availability, and nutrient concentrations. Microphytoplankton, particularly diatoms, dominated across the estuarine gradient, with diatom peaks in the polyhaline zone and nanophytoplankton in the oligohaline zone, reflecting size-based phytoplankton responses. Riverine nutrient inputs and low turbidity supported high nitrate uptake and primary productivity in the oligohaline zone. Chlorophyll peaks in the polyhaline zone indicated diatom transport and accumulation from upstream. Mesozooplankton feeding rates were highest in the polyhaline zone, suggesting selective grazing on diatoms, while lower feeding rates on smaller phytoplankton was likely due to trophic cascades via predation on microzooplankton. An interplay of selective grazing and trophic cascades across the estuarine-marine continuum drove spatial variations in mesozooplankton feeding. These findings demonstrate how riverine discharge drives planktonic food web dynamics shifts, affecting energy transfer and ecosystem productivity.
Until the 1950s, large-bodied calanoids and cladocerans dominated the zooplankton community of Lake Victoria, whereas cyclopoid copepods only comprised 10% of microcrustaceans. From the 1960's onwards, cyclopoid copepods increased to 70-90% of zooplankton and cladocerans, now dominated by small species, decreased to ca. 5%. Concomitantly phytoplankton biomass increased and shifted from dominance of diatoms to Cyanobacteria, which were hypothesized to be of less nutritional quality, causing the shift in zooplankton. We investigated whether the natural assemblage of Cyanobacteria in Mwanza Gulf negatively affected growth and fecundity of cladocerans. In 2010-2011, we performed life-history experiments with the cladoceran Daphnia lumholtzi, feeding it natural seston from Mwanza Gulf from three different locations. A laboratory-strain of the green alga Scenedesmus obliquus, proven to be high-quality food, was used as a control. Growth of D. lumholtzi in the rainy season and at one station in the dry season was just as high as in the control treatment. If there were negative effects of natural seston these were small. Although the evidence is circumstantial, this suggests that Cyanobacteria and/or their detritus could have been better food than expected and that food quality is not limiting the growth of D. lumholtzi in L. Victoria.
A database of nutritional strategies of nanoplankton genera present in North American lake surface waters is presented. This work represents an integrated and updated database of nutritional strategies for nanoplankton genera commonly found in surface waters of North American lakes. We tabulate the nutritional strategies (autotroph, phago-mixotroph and phago-heterotroph) for nanoplankton genera identified during several pan-continental lake surveys: the EPA-NLA surveys conducted in 2012 and 2017 across the continental USA and the NSERC Canadian Lake Pulse survey campaign conducted from 2017 to 2019. We expect that this work will serve others in the plankton community interested in assessing nanoplankton feeding strategies.
The ecology of eukaryotic picoplankton in oxygen minimum zones (OMZs) is crucial to understand global primary production, trophic dynamics and plankton diversity. This study analyses picoeukaryotic diversity and distribution patterns along the water column at two locations (slope and oceanic) in the tropical Mexican Pacific OMZ using metabarcoding and flow cytometry. Well-known groups of Chlorophytes (Mamiellophyceae) and Ochrophytes (Chrysophyceae, Dictyochophyceae, Pelagophyceae) occurred in high relative abundances, whereas less-known groups such as Chloropicophyceae and Prasinodermophyta were found in lower abundances. Picoeukaryotic diversity was higher at the lower end of the oxycline (10 μM O2) than at the surface and subsurface layers. Differential distributions of picoeukaryotes were also detected along the water column, with almost exclusive communities at each depth. Mamiellophyceae dominated the surface and subsurface layers, whereas Syndiniales (parasitic dinoflagellates), Radiolaria, Ochrophyta, and Sagenista (MArine STramenopiles -MAST groups-) were prevalent at the oxycline. Post-upwelling oceanographic conditions possibly contributed to shape the differences in community composition and distribution. These findings highlight that oxygen concentration is a key factor driving microbial distribution and that oxyclines provide specialized niches that promote high picoplankton diversity and multiple trophic strategies including autotrophy, mixotrophy, heterotrophy and parasitism.