Cyanobacterial Harmful algal blooms (cHABs) continue to be reported with increasing frequency in freshwater systems globally. cHABs are a perennial issue in many eutrophic areas but occur across nutrient and temperature gradients and in many relatively unimpacted lakes. These recent changes in the distribution and severity of cHAB events challenges widely-used models that rely upon nutrient loads and autecological preferences of individual species to explain blooms. Relationships between cyanobacterial species and environmental drivers are complicated by the inherent genomic and metabolic flexibility of cyanobacteria, as well as marked taxonomic ambiguity within the division, and further confounded by environmental stochasticity, anthropogenic disturbance, and interactions with non-cyanobacterial algae and other microbes. Many of the systems that are experiencing increasing cyanobacterial dominance and associated cHAB events are not warm, eutrophic, or otherwise impacted in an absolute sense. However, many are undergoing rapid change as a result of climate change, watershed modifications, and non-indigenous species. This session will gather research and encourage discussion around blooms in unexpected places, cyanobacterial bloom formers as opportunistic species, increasing cyanobacterial relative abundance in low biomass systems, and the microbial and algal community ecology of cHABs.
Lead Organizer: Mary Anne Evans, U S Geological Survey (maevans@usgs.gov)
Co-organizers:
Elena Lichtman, Carnegie Institution for Science (elitchman@carnegiescience.edu)
Rebecca Gorney, USGS – New York Water Science Center (rgorney@usgs.gov)
Presentations
02:00 PM
Phytoplankton responses to nutrients and increased temperature in three Great Lakes regions susceptible to cyanobacterial blooms (7747)
Primary Presenter: Robert Sterner, University of Minnesota Duluth (stern007@d.umn.edu)
There is increased recognition that cyanobacterial blooms occur under diverse environmental circumstances. In project CYBORG (CYano BlOoms dRivers and Genes) labs from three universities looked at factors driving blooms in Lake Superior, Green Bay, and Lake Erie. We performed short (2-4 d) nutrient addition assays in comparable ways in the three environments, with a total of 26 such experiments performed across the three lakes over two years. Treatments included adding P, several forms of N (nitrate, ammonium, urea), and incubating under both ambient and at plus 3-degree temperatures. Using a Fluoroprobe for coarse community resolution, we found that nutrient additions sometimes disfavored greens compared to cyanobacteria, diatoms, and cryptophytes and that warmer temperatures sometimes favored cyanobacteria at the expense of greens. Extracted chlorophyll measurements indicated that elevated temperatures increased growth in all three lakes, but with interactions with nutrients, especially in Green Bay. Lake Superior was consistently responsive to P and possibly slightly to N whereas both lower lakes responded more variably to P and to different forms of N. Our work helps to define the diverse limiting factors operating in steering algal communities in bloom-susceptible areas in the Great Lakes. It also shows how networked experimental work can provide insights into environmental variability at a large spatial scale.
02:15 PM
RESPONSES OF GREAT LAKES HAB FORMING ALGAE TO SHIFTS IN NUTRIENTS AND TEMPERATURE (7760)
Primary Presenter: Reane Loiselle, University of Minnesota (loise031@d.umn.edu)
The impact of increased temperature and nutrients on harmful algal blooms (HABs) has been extensively studied in recent decades. However, less is known about how changes in temperature, nitrogen and phosphorus impact the relative abundance of specific bloom forming taxa in the Laurentian Great Lakes. To better understand these shifts we conducted 4 identical 28 day nutrient addition bioassays in Mawikwe Bay Lake Superior and Sandusky Bay Lake Erie during 2022 and 2023. This timeframe was selected to allow for competition to take place. A Fluoroprobe was used to track broad changes in communities every 3 days and microscopy was used to obtain detailed community information on days 14 and 28. Microscopy analyses allowed us to track changes in relative abundance of dominant bloom forming species, shifts in major phytoplankton groups, and changes in dominant functional traits in each treatment. In Lake Superior the dominant bloom forming genera Dolichospermum was significantly more abundant in treatments with lower N:P ratios. In Lake Erie Microcystis was significantly more abundant in treatments with higher N:P ratios and Dolichospermum more abundant in treatments with lower N:P ratios.
02:30 PM
NUTRIENT DISTURBANCES AND HARMFUL ALGAL BLOOMS IN GREEN BAY: IMPLICATIONS FOR THE NORTH AMERICAN GREAT LAKES (8346)
Primary Presenter: Anjana Adhikari, University of Wisconsin-Milwaukee (adhikar8@uwm.edu)
This research investigates the role of nutrients (nitrate, ammonia, and phosphorus) in promoting harmful algal blooms (HABs) and the production of cyanotoxins in Green Bay, an estuary of Lake Michigan. We conducted bioassays in which water samples from Green Bay were spiked with nitrogen and phosphorus. The samples were analyzed for toxins using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS). Microcystins (MCRR), cyanopeptolins (C1007 and C1041), and anabaenopeptins (AptB and AptF) were the dominant toxins detected. The samples spiked with N-rich nutrients and at elevated temperatures showed higher concentrations of cyanotoxins than samples spiked with P-nutrients or at ambient temperature. The quantified range of cyanotoxins was between 0.3 - 1.5 µg/L for MC, 0.5 - 27 µg/L for Apt, and toxin concentration showed seasonal variations. The study showed that nutrients, primarily nitrogen, and increasing temperature impacted algal growth and cyanotoxin production. The results provide some insights into the impacts of nutrient management strategies and climate change on algal blooms and toxin production.
02:45 PM
RECONSTRUCTING HISTORICAL PHYTOPLANKTON COMMUNITIES WITHIN LAKE HURON THROUGH PIGMENT AND GENOMIC BIOMARKERS (8089)
Primary Presenter: Emma MacNeill, Large Lakes Observatory - University of Minnesota (macne029@d.umn.edu)
In recent decades, the Laurentian Great Lakes have seen an increase in harmful and nuisance algal blooms. Despite increased off-shore water quality, Lake Huron has seen a sustained prevalence of cyanobacterial blooms in the Georgian and Saginaw Bays. This raises questions about the potential factors leading to these blooms and whether the bloom-forming species have changed with time. Using dated sediment cores, identification of phytoplankton communities using 16S rDNA sequencing, photosynthetic pigments (from cyanobacteria, green algae, and diatoms), and bulk elemental analysis, we seek to reconstruct historic communities to answer these questions. Three sediment cores were collected from Huron in the North Channel, Severn Sound, and Saginaw Bay. Preliminary results show that all cores contain a mix of freshwater algae and terrestrial organic matter inputs. In more recent sediments, there is a shift towards relatively more cyanobacteria-produced pigments and a minor shift away from diatom-specific pigments, indicating that at all core locations, cyanobacteria have become more dominant members of the phytoplankton community. These results show that in recent years the phytoplankton community within areas of concern in Lake Huron has veered toward potentially harmful cyanobacteria populations.
03:00 PM
PIGMENT BIOMARKERS OF HISTORIC CYANOBACTERIAL PRESENCE IN THE SOUTHWESTERN LAKE SUPERIOR REGION (8004)
Primary Presenter: Lily Karg, University of Minnesota Duluth (karg0038@d.umn.edu)
Since the first documentation in 2012, cyanobacteria blooms in Lake Superior have raised concerns regarding the health of the lake. To address whether these blooms are a new phenomenon, a series of sediment cores were collected from Siskiwit Bay on Lake Superior’s Wisconsin shoreline. Elemental (%OC and %N), isotopic (δ13C), and molecular (algal pigments) signatures were used to reconstruct historical profiles of productivity and bloom periods. Carotenoid pigments were extracted from water samples collected during a nearby bloom to develop a pigment profile for cyanobacterial blooms in Lake Superior and tracked downcore in the Siskiwit Bay core samples. Overall algal productivity, measured via the sum of chlorophyll and carotenoid pigments, has significantly increased towards the present day. Diatom-associated pigments have been in higher concentrations than cyanobacteria pigments since 170 cal year BP, aligning with previous studies indicating that diatoms are currently the dominating phytoplankton species in Lake Superior. Despite diatom community dominance, peaks in cyanobacteria-associated pigments correlate with the 2012 bloom and likely an earlier bloom around 470 cal year BP. As the first study of sedimentary pigments within the southwestern region of Lake Superior, this work provides historical context that informs our understanding of modern-day cyanobacteria presence.
03:15 PM
Spatio-temporal dynamics of cyanobacterium Dolichospermum lemmermannii populations in a bloom-prone region of Lake Superior (7931)
Primary Presenter: Andrew Wood, University of Minnesota Duluth (wood0795@d.umn.edu)
Cyanobacterial Harmful Algal Blooms (cHABs) are increasingly common in marine and freshwater environments, including the Laurentian Great Lakes (LGL). Lake Superior has seen two large-scale cyanobacterial blooms (2012 and 2018) along the Wisconsin shoreline west of the Apostle Islands, caused by the cyanobacterium Dolichospermum lemmermannii. The drivers of bloom formation in Lake Superior are unclear, with many factors known to trigger blooms elsewhere in the LGL absent in Lake Superior. Furthermore, little is known about D. lemmermannii’s spatial structure or phenology. Thus, we tracked the seasonal population dynamics of D. lemmermannii to shed light on its growth, physiology, and abundance. In 2021, we used 16S rRNA amplicon and shotgun metagenomic sequencing to characterize spatio-temporal patterns of D. lemmermannii abundance and diversity along the bloom-prone Wisconsin shore of Lake Superior. In 2022, we performed net tows and direct colony counts in another localized area. No large-scale bloom event was observed during either year, though several smaller blooms were observed. D. lemmermannii abundances were low at nearly all sites and sampling times. Spikes in abundance occurred in July and September, particularly near Siskiwit Bay, a hotspot of bloom formation. Most striking was the seasonal turnover of D. lemmermannii strains, suggesting strain adaptation to specific environmental conditions. These results offer valuable and actionable insights for managers and provide a foundation for additional work to clarify drivers of bloom formation in Lake Superior.
SS39B - cHABs as a Response to Ecosystem Disturbance
Description
Time: 2:00 PM
Date: 7/6/2024
Room: Lecture Hall