The success of Gonyostomum semen (Raphidophyceae) in a boreal lake is due to environmental changes rather than a recent invasion

Browning of boreal lakes: Do public perceptions and governance align with the biological foundations?

“…An increasing humic content (and simultaneously increasing nutrient concentrations) often leads to a higher abundance of the nuisance algae Gonyostomum semen that is problematic both to humans and food webs by forming slimy surfaces and by being too large for many zooplankton species to forage on (Hagman et al, 2019(Hagman et al, , 2020Strandberg et al, 2020). Such consequences could be reflected in users' perceptions, but most of the implications of water browning are nonetheless measures that cannot be directly, visibly observed and may not be reflected in studies concerning public perceptions.…”

“…The most evident effect of browning is the reduction in light penetration, which, combined with higher levels of allochthonous organic matter, changes the net metabolism of lake ecosystems toward heterotrophy (Ask et al, 2009) and may therefore increase the efflux of greenhouse gases from the affected lakes (Kankaala et al, 2019;Nydahl et al, 2019). Increasing DOC alters bacterial abundance and phytoplankton community structure and the nutritional strategies of bacterio-and phytoplankton by favoring mixotrophs and motile algae (e.g., Hagman et al, 2020;Lenard & Ejankowski, 2017;Senar et al, 2021). Browning, when treated as the sole loading of DOC, usually reduces aquatic primary production (Karlsson et al, 2009(Karlsson et al, , 2015Taipale et al, 2018), while examples with no significant impact also exist (Eie et al, 2021;Erratt et al, 2021).…”

“…Browning, when treated as the sole loading of DOC, usually reduces aquatic primary production (Karlsson et al, 2009(Karlsson et al, , 2015Taipale et al, 2018), while examples with no significant impact also exist (Eie et al, 2021;Erratt et al, 2021). Browning often results in a higher abundance of the nuisance algae Gonyostomum semen (Hagman et al, 2019(Hagman et al, , 2020Strandberg et al, 2020). The interactive effects of warming and browning and consequent alterations in energy transfer to higher trophic levels are complex, since different responses occur at each trophic level (Hansson et al, 2013).…”

Lake browning counteracts cyanobacteria responses to nutrients: Evidence from phytoplankton dynamics in large enclosure experiments and comprehensive observational data

“…Climate‐proofing of lake management requires considering also other aspects than P thresholds, such as hypolimnetic oxygen depletion promoted by high temperatures and prolonged stratification periods, with negative impacts on zooplankton, benthic fauna and fish (Brothers et al., 2014); phosphorus and methane release from sediments as a result of anoxia (Bartosiewicz et al., 2021; Knoll et al., 2018); or the role of N availability in controlling cyanobacteria biomass and cyanotoxin production (Gobler et al., 2016; Hellweger et al., 2022; Litchman, 2023). Furthermore, for brownwater lakes attention is needed to reduce the risk of other harmful algal blooms, such as the rapidly spreading, skin irritating Gonyostomum semen , which tends to be favoured by nutrients and browning (Hagman et al., 2020), especially if high concentrations of iron (and Mn) contribute to the brown color (Lebret, Östman, et al., 2018). Thus, the combination of nutrient and climate change‐related stressors (global warming and more frequent summer storms) will require tailored nutrient management schemes to reduce the risk of cyanobacterial bloom formation in lakes (Huisman et al., 2018; Reinl et al., 2023; Sterner, Reinl, et al., 2020).…”

“…or the role of N availability in controlling cyanobacteria biomass and cyanotoxin production (Gobler et al, 2016;Hellweger et al, 2022;Litchman, 2023). Furthermore, for brownwater lakes attention is needed to reduce the risk of other harmful algal blooms, such as the rapidly spreading, skin irritating Gonyostomum semen, which tends to be favoured by nutrients and browning (Hagman et al, 2020), especially if high concentrations of iron (and Mn) contribute to the brown color . Thus, the combination of nutrient and climate change-related stressors (global warming and more frequent summer storms) will require tailored nutrient management schemes to reduce the risk of cyanobacterial bloom formation in lakes (Huisman et al, 2018;Reinl et al, 2023;Sterner, Reinl, et al, 2020).…”