Journal of Plankton Research最新文献

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.

Cordylophora caspia, is considered an invasive species in America. We isolated this hydrozoan from the brackish water section of the River Tuxpan (State of Veracruz, Mexico) and cultured it in the laboratory on mixed prey of copepods and rotifers at a salinity of 20 g L^-1. C. caspia is tolerant of a wide range of salinities. Most studies on C. caspia report its feeding and population growth on Artemia nauplii. Here we tested the effect of salinity on functional response and prey preference on Brachionus plicatilis (Rotifera), Apocyclops panamensis (Copepoda, Cyclopoida) and Nitokra lacustris (Copepoda, Harpacticoida). Experiments were conducted at 25°C. The hydrozoan killed several prey during functional response studies, which we assumed that it would eventually consume. On all prey test species, C. caspia showed a Type II functional response. Prey consumption, in terms of biomass, and preferences was higher on copepods than on rotifers. Prey consumption was higher at salinities of 10 and 20 g L^-1 than of 30 g L^-1.

While the invasion of Eurasian cladoceran Bosmina (Eubosmina) coregoni to the Laurentian Great Lakes is well-documented, its spread to the west coast of North America is less understood. We provide evidence that Bosmina (Eubosmina) coregoni was present on the Pacific Coast of North America as early as 1965, ~45 years prior to its first observation in this region in 2008. While investigating dated sediment cores in the Kootenay Lake system, British Columbia, Canada, we found B. (E.) coregoni remains in multiple intervals pre-2008, where it was present in high concentrations (up to 1500 exoskeletons/g dry sediment) and a dominant part of the cladoceran assemblage (25-31.5% relative abundance), though it displayed irregular pulses in abundance. While the method of introduction remains unclear, this research reframes the timeline of B. (E.) coregoni introduction and improves our understanding of zooplankton invasion dynamics.

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.

Freshwater ecosystems are increasingly at risk of experiencing toxin-producing cyanobacterial blooms during the winter due to anthropogenic nutrient loading and climate change. However, understanding how increased light, temperature and nutrient levels impact cyanotoxin production during the winter is limited, as most research has historically focused on blooms during the summer and fall. We conducted 2 × 2 × 2 incubation experiments in February and March to test the individual and interactive effects of light intensity (50 and 150 μmol m^-2 s^-1 PAR), elevated temperature (+3°C), and nitrogen and phosphorus enrichment on microcystin concentrations in a Planktothrix agardhii-dominated community sampled from Grand Lake Saint Mary's, a hypereutrophic Ohio reservoir. Microcystin concentration significantly increased with elevated temperature in both months. In February, low light also promoted higher microcystin concentrations, particularly when combined with elevated temperature and nutrient enrichment. In March, nutrient enrichment had individual and interactive effects with temperature that caused higher microcystin concentrations. These results demonstrate that toxin-producing cyanobacteria are active in winter and that climate-driven changes in environmental conditions can interactively increase total toxin concentrations in the water column, even in the non-growing season.

The rise in shipping due to the reduction of sea ice in the Arctic is expected to increase oil spill incidents. Calanus hyperboreus is a key organism in the Arctic food web and has a complex life cycle including pronounced seasonality and wide vertical distribution. Reproduction and spawning take place at depth in late winter, and the eggs float toward the surface, where they may encounter brine release and oil at the interface between water and sea ice. In the laboratory, we exposed C. hyperboreus eggs and nauplii to crude oil (1 μL L^-1) and high salinity (35.5 ppt), reflecting such conditions. Hatching success and nauplii size were not affected by exposure to oil alone, but decreased when exposed to high salinity or a combination of the two. The stressors did not impact the mortality of eggs and nauplii, which varied between 13.7% and 33.7% for the entire 6-day study period.

Marine ciliates and dinoflagellates are key microzooplankton groups in oceanic food webs. A prevailing ecological framework suggests that ciliates dominate under cool, mixed conditions typical of late winter and early spring, whereas dinoflagellates prevail in warmer, stratified waters during late spring and summer. This review highlights how temperature, stratification, nutrient dynamics, prey composition, turbulence and top-down control shape seasonal and regional patterns. While the ciliate-dinoflagellate succession is often observed in temperate seas, it is not universal. Polar regions exhibit compressed seasonality, while tropical systems show weak seasonality, often dominated by mixotrophic dinoflagellates. The widespread occurrence of mixotrophy in both groups complicates this duality, allowing species to persist across contrasting environmental conditions. Ultimately, the relative dominance of ciliates or dinoflagellates reflects a context-dependent interplay of multiple drivers rather than a fixed seasonal rule. As climate change intensifies ocean stratification and alters nutrient regimes, understanding these dynamics becomes critical to predict shifts in plankton communities and their consequences for marine biogeochemical processes and ecosystem functioning.

Ecological networks offer a comprehensive view of communities by capturing potential species interactions. While valuable for studying ecological change in the Anthropocene, many studies lack data across expansive temporal and spatial gradients. We addressed this gap by applying network approaches to paleolimnological records capturing strong land-use changes. We analyzed cladoceran assemblages, key aquatic organisms with identifiable subfossils, using two paleolimnological methods: (i) top-bottom comparisons of sediment records from 101 Canadian lakes with varying land-use intensity, and (ii) high-resolution core records from two impacted lakes in eastern Canada. We used correlation matrices of taxon relative abundances to calculate network metrics across land-use types and time periods. We found that lake communities currently experiencing high human impact changed through time, showing a decrease in connectance (proportion of realized to potential links) and an increase in modularity (measure of network subcommunities); these patterns were also observed in our full core analyses as well as in our randomized simulation exercise. Overall, this first pan-Canadian study of zooplankton paleo-networks provides new insights into how lake food webs have changed over a period of accelerated anthropogenic change.

Cyanobacteria harmful algal blooms (cyanoHABs) are a complex threat to water quality. Most research to date on the drivers of cyanoHABs focuses on environmental factors in the typical "growing season" despite evidence that cyanobacteria overwintering dynamics may have substantial effects on cyanobacteria seasonal succession and bloom formation. Additionally, the growing season is now beginning earlier and ending later in many parts of the world. Here, we examine the impacts of light, temperature and nutrients on the magnitude and timing of cyanobacteria recruitment from sediments in two hypereutrophic reservoirs in the Midwestern USA in the early spring season via microcosm recruitment experiments. We observed that recruitment was greatest at the first sampling point (Day 3), then declined throughout the rest of the 18-day experiment for both reservoirs. Further, increasing light and temperature significantly promoted recruitment in both systems, while nutrient additions were only a significant driver of recruitment in one lake. The recruited cyanobacteria community identity was similar in both lakes, with Planktothrix, Raphidiopsis and Pseudanabaena being most abundant. This study highlights the complex, interactive effects of environmental variables on cyanobacteria recruitment.

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.