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Concerted efforts have been made to reduce the occurrence and frequency of algal blooms in the Great Lakes via phosphorus abatement. Despite this, blooms remain common in shallow, nutrient enriched nearshore habitats. From a food web perspective, algal blooms are complex ecological entities that include autotrophs (phytoplankton, picoplankton) and heterotrophs (bacteria, nanoflagellates, ciliates, rotifers, zooplankton). Our research and monitoring programs have captured a variety of blooms (Cyanobacteria, diatoms etc) from the Bay of Quinte and Hamilton Harbour in Lake Ontario as well as from western Lake Erie. The contribution of heterotrophs during bloom events can be similar to or even larger than that of phytoplankton. In the Bay of Quinte (2018), for example, heterotrophs accounted for 38 - 63% of the total planktonic biomass during bloom events with varying contributions from bacteria (17 - 22%), heterotrophic nanoflagellates (4 - 38%) and zooplankton (2 - 20%). Preliminary results suggest that all types of algal blooms, not just ones exhibiting toxicity, can have a significant ecological impact. The current paper will explore the taxonomic structure of the phytoplankton community during bloom events and consider the heterotrophic contributions in order to promote a better understanding of the ecological implications of algal blooms. [ABSTRACT FROM AUTHOR]

Toronto Harbour is a highly urbanized embayment with a history of eutrophication due to municipal wastewater and stormwater runoff. Although nutrient levels have decreased since the 1970s and the harbour is considered mesotrophic, wet weather conditions flush high concentrations of nutrients from the watershed into the harbour. Starting in 2016 seasonal patterns in phytoplankton community structure and primary productivity were measured. In 2019 phytoplankton biomass averaged 0.7 g m-3 at the centre station and 1.3 g m-3 at the Don River station. Diatoms were often the highest contributors to biomass but Chrysophyceae and Cryptophyceae were also important. Seasonal productivity rates averaged 14 mg C m-3 hr-1 in the central harbour compared to 22 mg C m-3 hr-1 near the Don River. Bacterial productivity near the Don River averaged 3.3 mg C m-3 hr-1, more than twice the central harbour value. This indicates that a considerable amount of organic matter is being deposited into the harbour from the river. The presentation will discuss how the Don River impacts phytoplankton and bacterial dynamics in Toronto harbour. [ABSTRACT FROM AUTHOR]

Long term seasonally intensive plankton data sets are important for understanding food web dynamics and assessing resilience. To complement lake wide cruises, nutrients and lower food web parameters from one nearshore (8m) and one offshore (60m) station in western Lake Ontario were sampled from May to October beginning in 2013. The results showed that the stations were both oligotrophic. Total Phosphorus was similar at both stations at around 15 µg/l and Chlorophyll a was 2-3 µg/l. Total phytoplankton biomass was 455 µg/l at the offshore site and slightly higher at 538 µg/l at the nearshore site. Diatomeae contributed the most (35%) to total phytoplankton biomass at the offshore site followed by phytoflagellates (Chrysophyceae + Cryptophyceae + Dinophyceae). Composition at the shallow site was more variable. Mean primary productivity was similar at both sites (5-6 mg C/m3/hr) and was dominated by nanoplankton (>40%) and picoplankton (30%). The above data plus species composition changes will be presented to discuss the continued the oligotrophication of the western Lake Ontario. The necessity and utility of long term trophic data sets to supplement the routine lake wide seasonal surveys will be emphasized. [ABSTRACT FROM AUTHOR]

During monthly surveys of Toronto Harbour in 2016, Fisheries and Oceans Canada (DFO) Food-webs and Ecosystem Research determined that the inner harbour was impaired for phytoplankton and zooplankton populations based on finding very few large zooplankton and high rates of bacterial growth. However, the source of this impairment could not be identified, and this sampling was within the main inner harbour only. From 2018-2022 DFO returned to include important fish habitat restoration locations within the Toronto Islands and in Tommy Thompson Park (embayments and habitat cells). We find high annual and seasonal variability in community composition, but consistently find that zooplankton in the surrounding embayment's, Toronto Islands, and the habitats within Tommy Thompson Park have higher densities and more seasonal variability compared to the inner harbour. Physical water characteristics in the inner harbor such as temperature, turbidity and nutrient do change seasonally compared to the surrounding habitats, yet low zooplankton counts of particular species groups still persists. We will summarize the report assessing plankton populations and discuss implications for fish populations. [ABSTRACT FROM AUTHOR]