Phytoplankton community dynamics in a changing world : Ecological drivers of Microcystis and Naiadinium polonicum dominance
(2026)- Abstract
- Lakes provide critical ecosystem services and are therefore particularly sensitive to disruptions such as harmful algal blooms (HABs). Cyanobacteria are the most common HAB-forming species in lakes, and their prevalence is expected to increase with climate change. However, during a 2018 heatwave in southern Sweden, Lake Vombsjön experienced an unexpected shift from its usual cyanobacterial dominance to a bloom of the dinoflagellate Naiadinium polonicum. This event provided a rare opportunity to examine how ecological drivers shape the population dynamics of cyanobacteria and dinoflagellates, two groups predicted to do well under future climate change scenarios due to shared functional traits, though freshwater dinoflagellates remain... (More)
- Lakes provide critical ecosystem services and are therefore particularly sensitive to disruptions such as harmful algal blooms (HABs). Cyanobacteria are the most common HAB-forming species in lakes, and their prevalence is expected to increase with climate change. However, during a 2018 heatwave in southern Sweden, Lake Vombsjön experienced an unexpected shift from its usual cyanobacterial dominance to a bloom of the dinoflagellate Naiadinium polonicum. This event provided a rare opportunity to examine how ecological drivers shape the population dynamics of cyanobacteria and dinoflagellates, two groups predicted to do well under future climate change scenarios due to shared functional traits, though freshwater dinoflagellates remain comparatively understudied. In particular, this thesis focuses on Microcystis, a toxin-producing cyanobacterium of global importance, and N. polonicum, a bloom-forming dinoflagellate whose autoecology is largely unresolved. Across the first three papers, I examined field biomass dynamics, recruitment and growth responses to temperature, and allelopathic interactions between Microcystis and N. polonicum. In Lake Vombsjön, N. polonicum biomass was associated with higher temperatures, elevated soluble reactive phosphorus concentrations, water column stratification, and anoxic conditions near the sediment surface. While higher temperatures in 2018 did not directly enhance N. polonicum growth, temperature-dependent recruitment from sediments likely allowed it to establish earlier than Microcystis, whose recruitment was temperature independent. These findings point to seasonal timing as a key determinant of species dominance. Co-culture experiments revealed no evidence that N. polonicum inhibited Microcystis, whereas Microcystis was able to suppress N. polonicum growth at ecologically relevant densities. In my fourth paper, I focused on Microcystis and identified abiotic and biotic factors favoring toxigenic strains in natural populations. Toxigenic strains were associated with elevated nitrogen concentrations, consistent with the high nitrogen demands of microcystins, while microcystin concentrations were most strongly linked to phosphorus availability and overall Microcystis biomass, supporting dual nutrient reduction strategies to mitigate toxic blooms. Together, these results highlight two broader implications. First, freshwater dinoflagellates remain underrepresented in phytoplankton ecology despite evidence that they may become more prominent under future climate conditions, potentially impacting cyanobacteria bloom dynamics. Second, benthic life stages, particularly recruitment from sediments, must be incorporated into future research on cyanobacterial HABs. As climate change drives phenological shifts and alters pelagic conditions, understanding benthic-pelagic links will be essential for predicting and managing HAB events. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/01168dc3-1586-467c-a1e9-dbbb7ea70400
- author
- Rabow, Sandra LU
- supervisor
-
- Karin Rengefors LU
- Per Carlsson LU
- opponent
-
- Professor Litchman, Elena, Michigan State University
- organization
- publishing date
- 2026-02-20
- type
- Thesis
- publication status
- published
- subject
- keywords
- harmful algal blooms, cyanobacteria, Microcystis, dinoflagellates, Naiadinium polonicum, functional traits, lakes, microcystins
- pages
- 64 pages
- publisher
- Lunds universitet
- defense location
- Blå Hallen, Ekologihuset
- defense date
- 2026-02-20 09:00:00
- ISBN
- 978-91-8104-756-1
- 978-91-8104-755-4
- language
- English
- LU publication?
- yes
- id
- 01168dc3-1586-467c-a1e9-dbbb7ea70400
- date added to LUP
- 2026-01-19 13:17:07
- date last changed
- 2026-01-21 15:25:28
@phdthesis{01168dc3-1586-467c-a1e9-dbbb7ea70400,
abstract = {{Lakes provide critical ecosystem services and are therefore particularly sensitive to disruptions such as harmful algal blooms (HABs). Cyanobacteria are the most common HAB-forming species in lakes, and their prevalence is expected to increase with climate change. However, during a 2018 heatwave in southern Sweden, Lake Vombsjön experienced an unexpected shift from its usual cyanobacterial dominance to a bloom of the dinoflagellate Naiadinium polonicum. This event provided a rare opportunity to examine how ecological drivers shape the population dynamics of cyanobacteria and dinoflagellates, two groups predicted to do well under future climate change scenarios due to shared functional traits, though freshwater dinoflagellates remain comparatively understudied. In particular, this thesis focuses on Microcystis, a toxin-producing cyanobacterium of global importance, and N. polonicum, a bloom-forming dinoflagellate whose autoecology is largely unresolved. Across the first three papers, I examined field biomass dynamics, recruitment and growth responses to temperature, and allelopathic interactions between Microcystis and N. polonicum. In Lake Vombsjön, N. polonicum biomass was associated with higher temperatures, elevated soluble reactive phosphorus concentrations, water column stratification, and anoxic conditions near the sediment surface. While higher temperatures in 2018 did not directly enhance N. polonicum growth, temperature-dependent recruitment from sediments likely allowed it to establish earlier than Microcystis, whose recruitment was temperature independent. These findings point to seasonal timing as a key determinant of species dominance. Co-culture experiments revealed no evidence that N. polonicum inhibited Microcystis, whereas Microcystis was able to suppress N. polonicum growth at ecologically relevant densities. In my fourth paper, I focused on Microcystis and identified abiotic and biotic factors favoring toxigenic strains in natural populations. Toxigenic strains were associated with elevated nitrogen concentrations, consistent with the high nitrogen demands of microcystins, while microcystin concentrations were most strongly linked to phosphorus availability and overall Microcystis biomass, supporting dual nutrient reduction strategies to mitigate toxic blooms. Together, these results highlight two broader implications. First, freshwater dinoflagellates remain underrepresented in phytoplankton ecology despite evidence that they may become more prominent under future climate conditions, potentially impacting cyanobacteria bloom dynamics. Second, benthic life stages, particularly recruitment from sediments, must be incorporated into future research on cyanobacterial HABs. As climate change drives phenological shifts and alters pelagic conditions, understanding benthic-pelagic links will be essential for predicting and managing HAB events.}},
author = {{Rabow, Sandra}},
isbn = {{978-91-8104-756-1}},
keywords = {{harmful algal blooms; cyanobacteria; Microcystis; dinoflagellates; Naiadinium polonicum; functional traits; lakes; microcystins}},
language = {{eng}},
month = {{02}},
publisher = {{Lunds universitet}},
school = {{Lund University}},
title = {{Phytoplankton community dynamics in a changing world : Ecological drivers of Microcystis and Naiadinium polonicum dominance}},
url = {{https://lup.lub.lu.se/search/files/239995355/Avhandling_Sandra_Rabow_LUCRIS.pdf}},
year = {{2026}},
}