Feeding and grazing impact by the bloom-forming euglenophyte Eutreptiella eupharyngea on marine eubacteria and cyanobacteria

Phytoplankton ecology in the early years of a boreal oil sands end pit lake

BACKGROUND

Base Mine Lake (BML) is the first full-scale end pit lake for the oil sands mining industry in Canada. BML sequesters oil sands tailings under a freshwater cap and is intended to develop into a functional ecosystem that can be integrated into the local watershed. The first stage of successful reclamation requires the development of a phytoplankton community supporting a typical boreal lake food web. To assess the diversity and dynamics of the phytoplankton community in BML at this reclamation stage and to set a baseline for future monitoring, we examined the phytoplankton community in BML from 2016 through 2021 using molecular methods (targeting the 23S, 18S, and 16S rRNA genes) and microscopic methods. Nearby water bodies were used as controls for a freshwater environment and an active tailings pond.

RESULTS

The phytoplankton community was made up of diverse bacteria and eukaryotes typical of a boreal lake. Microscopy and molecular data both identified a phytoplankton community comparable at the phylum level to that of natural boreal lakes, dominated by Chlorophyta, Cryptophyta, and Cyanophyta, with some Bacillariophyta, Ochrophyta, and Euglenophyta. Although many of the same genera were prominent in both BML and the control freshwater reservoir, there were differences at the species or ASV level. Total diversity in BML was also consistently lower than the control freshwater site, but consistently higher than the control tailings pond. The phytoplankton community composition in BML changed over the 5-year study period. Some taxa present in 2016-2019 (e.g., Choricystis) were no longer detected in 2021, while some dinophytes and haptophytes became detectable in small quantities starting in 2019-2021. Different quantification methods (qPCR analysis of 23S rRNA genes, and microscopic estimates of populations and total biomass) did not show a consistent directional trend in total phytoplankton over the 5-year study, nor was there any consistent increase in phytoplankton species diversity. The 5-year period was likely an insufficient time frame for detecting community trends, as phytoplankton communities are highly variable at the genus and species level.

CONCLUSIONS

BML supports a phytoplankton community composition somewhat unique from control sites (active tailings and freshwater lake) and is still changing over time. However, the most abundant genera are typical of natural boreal lakes and have the potential to support a complex aquatic food web, with many of its identified major phytoplankton constituents known to be primary producers in boreal lake environments.

Highly-resolved interannual phytoplankton community dynamics of the coastal Northwest Atlantic

Microbial observatories can track phytoplankton at frequencies that resolve monthly, seasonal, and multiyear trends in environmental change from short-lived events. Using 4-years of weekly flow cytometry along with chloroplast and cyanobacterial 16S rRNA gene sequence data from a time-series station in the coastal Northwest Atlantic (Bedford Basin, Nova Scotia, Canada), we analyzed temporal observations for globally-relevant genera (e.g., Bolidomonas, Teleaulax, Minidiscus, Chaetoceros, Synechococcus, and Phaeocystis) in an oceanic region that has been recognized as a likely hotspot for phytoplankton diversity. Contemporaneous Scotian Shelf data also collected during our study established that the major phytoplankton within the Bedford Basin were important in the Scotian Shelf during spring and fall, therefore pointing to their broader significance within the coastal Northwest Atlantic (NWA). Temporal trends revealed a subset of indicator taxa along with their DNA signatures (e.g., Eutreptiella and Synechococcus), whose distribution patterns make them essential for timely detection of environmentally-driven shifts in the NWA. High-resolution sampling was key to identifying important community shifts towards smaller phytoplankton under anomalous environmental conditions, while further providing a detailed molecular view of community compositions underpinning general phytoplankton succession within the coastal NWA. Our study demonstrates the importance of accessible coastal time-series sites where high-frequency DNA sampling allows for the detection of shifting baselines in phytoplankton communities.

Stable C and N Isotope Composition of Suspended Particulate Organic Matter in the Neva Estuary: The Role of Abiotic Factors, Productivity, and Phytoplankton Taxonomic Composition

Knowledge of carbon and nitrogen isotopic ratios in organic matter and their changes is important when studying nutrient cycles in aquatic ecosystems. Relationships between δ13C and δ15N values of suspended particulate organic matter (POM), water temperature, salinity, pH, redox potential, chlorophyll a concentration, primary production, and biomasses of different taxonomic groups of phytoplankton in the Neva Estuary were statistically analyzed. We tested the hypothesis that the studied physicochemical and biogeochemical characteristics, as well as the species composition of phytoplankton and its productivity, can be significant predictors of changes in the isotopic ratios of suspended particulate organic matter in estuaries. In the Neva Estuary, δ13CPOM (−16.8–−27.6‰) and δ15NPOM (2.3–7.3‰) changed synchronously. Statistical analysis showed that for both isotopes, the photosynthetic activity and taxonomic composition of phytoplankton are important. For 13CPOM, the second most important factor was water salinity, which was apparently associated with the transition of algae from CO2 to HCO3 consumption during photosynthesis in estuarine waters. For 15NPOM changes, the most important abiotic factor was pH. The study showed that the dependences of POM isotopic ratios on environmental variables obtained for continental and oceanic waters are also valid in transitional zones such as the Neva Estuary.

Environmental factors associated with toxic cyanobacterial blooms across 20 drinking water reservoirs in a semi-arid region of Brazil

Cyanobacteria are known to produce a wide variety of bioactive, toxic secondary metabolites generally described as hepatotoxins, neurotoxins, cytotoxins, or dermatoxins. In Brazil, the regular monitoring of cyanobacterial toxins has intensified after the death of 65 patients in a hemodialysis clinic in Caruaru in the state of Pernambuco due to microcystin exposure. The primary objective of this study was to use multivariate statistics that incorporated environmental parameters (both biotic and abiotic) to forecast blooms of cyanobacteria and their toxic secondary metabolites in 20 drinking water reservoirs managed by the Water Treatment Company of Ceará (CAGECE) in the semi-arid region of Ceará, Brazil. Across four years (January 2013 to January 2017), 114 different phytoplankton taxa were identified, including 24 cyanobacterial taxa. In general, Ceará reservoirs were dominated by cyanobacteria due to eutrophication but also because of the dry and warm climate found throughout the region. Interestingly, specific cyanobacterial taxa were influenced by different biotic and abiotic factors. For example, nitrogen-to-phosphorus (N:P) and evaporation were positively related to saxitoxin-producing taxa, especially Raphidiopsis raciborskii, while temperature, electrical conductivity, total phosphorus, and transparency (measured as Secchi depth) were positively associated with microcystin-producing taxa, such as Microcystis aeruginosa. Climate forecasts predict higher evaporation and temperatures in the semi-arid Ceará region, which will likely magnify droughts and water scarcity as well as promote toxic cyanobacterial blooms in reservoirs in the future. Therefore, understanding the factors associated with algal blooms dominated by specific taxa is paramount for water resource management.