Calcium and pH interaction limits bloom formation and expansion of a nuisance microalga

Raphael Gollnisch,Magdalena Grabowska,Maria Stockenreiter,Dag Ahrén,Teodor Alling,Karin Rengefors

doi:10.1002/lno.11896

Abstract

AbstractMicroalgal range expansions are increasing in frequency and magnitude but generally remain unnoticed until mass development occurs. Gonyostomum semen is a freshwater raphidophyte that causes nuisance blooms in lakes and has recently expanded its distribution across Europe. G. semen was considered to mainly occur in humic lakes in the boreal region but is now found in high density also in other freshwater habitats on a larger geographic scale with growing incidence. In this study, we focused on which environmental factors limit its expansion. Our hypothesis was that G. semen occurs in many different lake types, except for high alkalinity lakes, in which high pH in combination with high calcium concentration would inhibit its growth. Results from our field study illustrate the environmental heterogeneity of G. semen bloom sites across Europe and the United States. Nevertheless, none of these sites combined high pH and high calcium concentration. In a mesocosm study, as well as a laboratory experiment, we further demonstrated that growth of G. semen is inhibited in conditions combining both high pH and high calcium concentration. We also discuss the function of Sphagnum peat mosses in rendering an alkaline habitat suitable to G. semen growth. Our study highlights that high alkalinity environments act as a major colonization barrier to G. semen. While this finding explains which environmental filters limit G. semen distribution it also helps in understanding its current expansion. With globally decreasing calcium concentrations in freshwater ecosystems, new habitats have and will become conducive to G. semen growth.

Highlights

We focused on environmental barriers to G. semen distribution, rather than factors that favor its expansion
We tested the hypothesis that high Ca and high pH provide a dispersal barrier for the expanding bloom-forming phytoplankton species G. semen
Evidence from our field observations, a mesocosm study, as well as a laboratory experiment demonstrated that growth of G. semen is inhibited in conditions with combined high pH and high Ca concentration

Summary

Introduction

Besides direct economic or health consequences like shellfish poisoning (Anderson 1989) or toxic drinking water (Codd et al 1999), mass development of microalgal species that are toxic or unpalatable to herbivore grazers can substantially alter microbial community composition and affect ecosystem functions by disrupting nutrient transfer to higher trophic levels (Sunda et al 2006; Karpowicz et al 2020) Such harmful algal blooms, including those formed by non-toxic species, can further indirectly cause fish kills and recreational losses following oxygen-depletion, or render freshwater unsuitable for drinking water supply (e.g., Hallegraeff 2003). Mass development of G. semen often implies complete community dominance (Cronberg et al 1988) and can cause shifts in lake food webs due to limited grazing pressure by zooplankton (Lebret et al 2012; Johansson et al 2016), resulting in a decrease of the recreational value of lakes (Sörensen 1954; Trigal et al 2013)

Objectives

Methods

Results

Conclusion