Climate change affects timing and size of populations of an invasive cyanobacterium in temperate regions

Abstract

Cylindrospermopsis raciborskii, an invasive freshwater cyanobacterium, originated from the tropics but has spread to temperate zones over the last few decades. Its northernmost populations in Europe occur in North German lakes. How such dramatic changes in its biogeography are possible and how its population dynamics in the newly invaded habitats are regulated are still unexplained. We therefore conducted a long-term (1993-2005) study of two German lakes to elucidate the mechanisms behind C. raciborskii population dynamics and to identify the abiotic constraints on its development. Our data revealed that pelagic populations of C. raciborskii thrived for three months during the summer, contributing up to 23% of the total cyanobacteria biovolume. Population sizes varied greatly between years without exhibiting any distinct long-term trends. In the annual lifecycle, C. raciborskii filaments emerged in the pelagic habitat when the temperature rose above 15-17 degrees C. At that time, mean photosynthetically active radiation in the mixed water column (I (mix)) overstepped its maximum. Rates of population net increase were highest at the beginning of the season (0.15-0.28 day(-1)), declined continuously over time, and were significantly positively correlated with I (mix). This indicates that the onset of the pelagic population is temperature-mediated and that I (mix) controls its growth. Since I (mix) peaks before the population onset, the time of germination is of crucial importance for successful development. To test this hypothesis, we designed a model to simulate pelagic population size, starting at different dates in the annual cycle. Moving the population onset forward by 30 days resulted in a doubling of the population size. We therefore conclude that an earlier rise in water temperature associated with climate change has promoted the spread of C. raciborskii to the temperate zone. Earlier warming permits earlier germination, thereby shifting the pelagic populations to a phase with higher I (mix), which advances growth and the population establishment.

Effects of light intensity and temperature on Cylindrospermopsis raciborskii (Cyanobacteria) with straight and coiled trichomes: growth rate and morphology

“…Nitrogen fixation is a process known to require considerable energy expenditure and species from the order Nostocales require high degrees of luminosity in order to maintain it (MacCausland et al, 2005;Wiedner et al, 2007). According to Padisák (1997), the production of heterocysts occurs when there is a deficiency of nitrogen in the environment.…”

“…In a study on populations of C. raciborskii in two lakes in Germany, Wiedner et al (2007) found that growth initiated under light intensity ranging from 90 to 130 µmol.photons.m -2 .s -1 and at a temperature between 15 and 17 °C. The authors concluded that light intensity is the most important factor in the regulation of population dynamics.…”

The response of temperate aquatic ecosystems to global warming: novel insights from a multidisciplinary project

“…A well-studied aquatic example is the northward range expansion of the invasive cyanobacterium Cylindrospermopsis raciborskii (Wiedner et al 2007). Biogeographic studies within the AQUASHIFT consortium were focussed on dragonflies, snails, and ciliates.…”

The ecology of the invasive cyanobacteriumCylindrospermopsis raciborskii(Nostocales, Cyanophyta) in two hypereutrophic lakes dominated byPlanktothrix agardhii(Oscillatoriales, Cyanophyta)

“…Temperature has been considered the major limiting factor for growth of C. raciborskii (Pa´disak, 1997;Wiedner et al, 2007), with its optimal growth rate in laboratory experiments being at 25-35 C (Saker & Griffiths, 2000;Briand et al, 2004;Castro et al, 2004;Chonudomkul et al, 2004). Furthermore, its akinete germination is temperature dependent, and germination occurs primarily from 22-23.5 C (Pa´disak, 1997).…”