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Abstract Efforts to reduce the frequency, extent, and toxicity of harmful algal blooms (HABs) require knowledge about drivers of algal growth, toxin production, and shifts in phytoplankton community composition to cyanobacterial dominance. Although labile nitrogen (N) and phosphorus (P) fuel primary production, micronutrients also play roles as the enzymatic engines that facilitate rapid and efficient growth and toxin production. Macro‐ and micronutrient availability can shape community composition and function by selecting for particular taxa. To address how phytoplankton in two Great Lakes subbasins respond to macro‐ and micronutrients, we conducted bottle incubation enrichment experiments using water collected from two blooming and two nonblooming sites in Lakes Erie and Michigan during late summer (August). Three of the four sites exhibited multi‐nutrient limitation of growth. Both blooming sites responded strongest to enrichment. Both nonblooming sites responded the strongest to enrichment, and three of the four sites responded in some way to a mix of micronutrients (Fe, Mn, Mo, Ni, and Zn).Microcystis aeruginosarelative abundance increased most with N enrichment, while P enrichment increased the abundance of diatoms and chlorophytes. At the Fox River, N‐enriched communities grew 10%–20% more than non‐N enriched communities (measured as chlorophylla), and N‐enriched communities had, on average, over twice as much microcystin (non‐N communities average MC = 2.45 μg · L−1, +N communities MC = 5.35 μg · L−1). These overarching trends support the idea that control of HABs may not be effective with a P‐only approach.
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Production of Cyanotoxins by Microcystis aeruginosa Mediates Interactions with the Mixotrophic Flagellate Cryptomonas
Eutrophication of inland waters is expected to increase the frequency and severity of harmful algal blooms (HABs). Toxin-production associated with HABs has negative effects on human health and aquatic ecosystem functioning. Despite evidence that flagellates can ingest toxin-producing cyanobacteria, interactions between members of the microbial loop are underestimated in our understanding of the food web and algal bloom dynamics. Physical and allelopathic interactions between a mixotrophic flagellate (Cryptomonas sp.) and two strains of a cyanobacteria (Microcystis aeruginosa) were investigated in a full-factorial experiment in culture. The maximum population growth rate of the mixotroph (0.25 day−1) occurred during incubation with filtrate from toxic M. aeruginosa. Cryptomonas was able to ingest toxic and non-toxic M. aeruginosa at maximal rates of 0.5 and 0.3 cells day−1, respectively. The results establish that although Cryptomonas does not derive benefits from co-incubation with M. aeruginosa, it may obtain nutritional supplement from filtrate. We also provide evidence of a reduction in cyanotoxin concentration (microcystin-LR) when toxic M. aeruginosa is incubated with the mixotroph. Our work has implications for “trophic upgrading” within the microbial food web, where cyanobacterivory by nanoflagellates may improve food quality for higher trophic levels and detoxify secondary compounds.
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- Award ID(s):
- 1632888
- PAR ID:
- 10097404
- Date Published:
- Journal Name:
- Toxins
- Volume:
- 11
- Issue:
- 4
- ISSN:
- 2072-6651
- Page Range / eLocation ID:
- 223
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/toxins11040223
