Temperature increase and fluctuation induce phytoplankton biodiversity loss – Evidence from a multi‐seasonal mesocosm experiment

Abstract

Global climate change scenarios predict lake water temperatures to increase up to 4°C and extreme weather events, including heat waves and large temperature fluctuations, to occur more frequently. Such changes may result in a reorganization of the plankton community structure, causing shifts in diversity and structure toward a community dominated by fewer species that are more adapted to endure warmer and irregular temperature conditions. We designed a long‐term (8 months) mesocosm experiment to explore how ambient water temperature (C: control), induced increased temperature (T: +4°C), and temperature fluctuations (F: ±4°C relative to T) change phytoplankton phenology, taxonomical diversity, and community structure, and how such changes affected zooplankton abundance and composition. Synthesis. Our results show that T and F relative to C significantly decreased phytoplankton diversity. Moreover, there was a clear effect of the temperature treatments (T and F) on phytoplankton size structure that resulted in a significantly lower growth of large species (i.e., large Chlorophyta) compared to C. Decreased diversity and evenness in the T and F treatments pushed the community toward the dominance of only a few phytoplankton taxa (mainly Cyanobacteria and Chlorophyta) that are better adapted to endure warmer and more irregular temperature conditions. The observed shift toward Cyanobacteria dominance may affect trophic energy transfer along the aquatic food web.

Moderate weather extremes alter phytoplankton diversity—A microcosm study

“…In accordance with our findings, Rasconi et al. () reported that long‐term temperature increases as well as temperature fluctuations significantly decreased phytoplankton SDiv (inferred from the number of genera) in a mesocosm study. Similarly, in their microcosm experiment with benthic microalgae, Eggers, Eriksson, & Matthiessen, demonstrated that Shannon diversity significantly declined after a heat wave.…”

“…In recent years, a growing number of studies have focused on how phytoplankton primary productivity and species composition are influenced by increasing water temperatures, triggered by an interest in how global warming affects ecosystem processes and properties (Burgmer & Hillebrand, 2011;De Senerpont Domis, Mooij, & Huisman, 2007;Deng et al, 2014;Urrutia-Cordero et al, 2017). Resulting from experimental observations, the species-shift hypothesis was formulated (Daufresne, Lengfellner, & Sommer, 2009;Rasconi, Gall, Winter, & Kainz, 2015;Rasconi, Winter, & Kainz, 2017;Sommer, Peter, Genitsaris, & Moustaka-Gouni, 2017), which predicted that the proportion of small-sized phytoplankton species generally increases with temperature; however, its general applicability is still controversial (Winder & Sommer, 2012). Several microcosm and mesocosm studies also demonstrated that heterotrophic bacteria benefit more than eukaryotic algae from lake warming (Rasconi et al, 2015;Weisse, Gr€ oschl, & Bergkemper, 2016;Weisse, Anderson, et al, 2016;Wohlers-Z€ ollner et al, 2012).…”

Do environmental factors influence the morphotypes in Artemia franciscana Kellogg, 1906 (Crustacea: Anostraca)?

“…The present study also indicated that air and water temperatures contribute to the abundance of morphotypes in different sampling sites as evident from scatter plot analysis [58]. Similarly, these two factors had the strongest effect in driving morphotypes abundance in an aquatic system [59]. Cluster analysis indicated existence of three different clusters, and it indicated that each cluster shared different parameters with their specific lineage.…”

Do current European lake monitoring programmes reliably estimate phytoplankton community changes?

“…In particular, we postulated that sampling during extreme events, which are often missed in low-frequency routine monitoring programmes, reduces the calculated annual biovolume of taxa that are sensitive to disturbances and increases the biomass of other, more robust taxa that may take advantage of increased temperature and/or reduced competition in the course of disturbances. Several experimental microcosm and mesocosm studies have already demonstrated these mechanisms for dominant freshwater phytoplankton taxa (Rasconi et al, 2015(Rasconi et al, , 2017Weisse et al, 2016). Secondly, we hypothesised that the methodology of the current monitoring programmes underestimates various phytoplankton groups, namely small and fragile cells or colonies that are sensitive to fixation and/or difficult to detect with the common resolution of light microscopy (Gieskes & Kraay, 1983;Rodriguez et al, 2002).…”