Deep living Planktothrix rubescens modulated by environmental constraints and climate forcing

Abstract

The cyanoprokaryote Planktothrix rubescens has been studied for over four decades in an alpine lake, Mondsee, Austria. We hypothesise that impacts of climate change can be distinguished from other environmental constraints controlling its population dynamics. During thermal stratification, P. rubescens formed a deep chlorophyll maximum in the metalimnion. Seasonal and diurnal depth distributions indicated that Planktothrix lived well below the euphotic zone, at low light levels and moderate temperatures. Photosynthetic parameters indicated a shade adapted population. The eutrophication and rehabilitation periods of Mondsee were characterised by fluctuations controlled by phosphorus, with periods below the P-threshold associated with low biovolumes and relatively stable populations. Positive net changes of Planktothrix biovolume occurred during the springsummer transition and in autumn. During summer, the population usually declined to an annual minimum. The standardised residuals of annual biovolumes responded positively to the climate signal of the Winter North Atlantic Oscillation and the timing of the onset of stratification. An inverse relationship existed between off-set and persistence of stratification. P. rubescens only benefits from climate warming early in the year, during late spring overturn and early summer. Longer periods of summer stratification did not favour biovolume development.

Modelling the plankton groups of the deep, peri-alpine Lake Bourget

“…Occurrence of P. rubescens is usually attributed to the nutrient availability, when long-term dynamics (Dokulil and Teubner, 2012;Posch et al, 2012) and lakes at di erent trophic states are considered (Salmaso et al, 2012;Anneville et al, 2015). Within our study period, winter DIP fell from 0.9 to 0.46 mmolP/m 3 (corresponding to 27.9 to 14.3 mgP/m 3 ) between 2004 and 2010 ( Fig.…”

“…In Lake Bourget (Vinçon-Leite et al, 2002;Jacquet et al, 2014b;Anneville et al, 2015), as well as in other deep lakes like Lake Zurich (Walsby et al, 1998;Posch et al, 2012), Lake Garda (Salmaso, 2010) and Mondsee (Dokulil and Teubner, 2012), the abundance of P. rubescens by the end of winter is largely determined by meteorological conditions during winter. In such deep, warm monomictic lakes, cooling in mild winters may end up being insu cient to cause a full overturn, leading to a reduced dilution of the P. rubescens concentrations, as well more P. rubescens cells survive the winter (Walsby et al, 1998).…”

“…Starting from 1996, the toxic cyanobacterium, Planktothrix rubescens became a dominant species in the lake (Vinçon-Leite et al, 2002;Jacquet et al, 2005, see also Fig.1). P. rubescens is a wide-spread cyanobacterial species especially prevalent in peri-alpine lakes (e.g., Ernst et al, 2009;Salmaso et al, 2012;Dokulil and Teubner, 2012;Posch et al, 2012), but also observed elsewhere (e.g., Konopka, 1982;Halstvedt et al, 2007;Naselli-Flores et al, 2007;Padisák et al, 2010). Being a potentially microcystin producing species , its occurrence in lakes and reservoirs has been of major concern for livestock and human health (Naselli-Flores et al, 2007;Ernst et al, 2009).…”

“…Analysis of the longterm changes in individual lakes and inter-comparison between lakes suggest that phosphorus (and nitrogen, see Posch et al, 2012) availability is the primary determinant (Dokulil and Teubner, 2012;Jacquet et al, 2014b;Anneville et al, 2015). P. rubescens is characterized by their slow growth rates (Bright and Walsby, 2000) and tolerance to low light conditions (Walsby and Schanz, 2002).…”

Strict coupling between the development ofPlanktothrix rubescensand microcystin content in two nearby lakes south of the Alps (lakes Garda and Ledro)

“…rubescens is a very well-known cyanobacterium which develops in many deep lakes north and south of the Alps. Besides Lake Garda and the deep lakes south of the Alps (Buzzi, 2002;Morabito et al, 2002;Salmaso, 2002Salmaso, , 2011Salmaso et al, 2012a), the environmental factors controlling the development of this cyanobacterium were extensively studied in other large subalpine lakes Jacquet et al, 2005;Gallina et al, 2011Gallina et al, , 2013Dokulil and Teubner, 2012), as well as in smaller, deep lakes (Nu¨rnberg et al, 2003;Carraro et al, 2012) and reservoirs (Naselli-Flores and Barone, 2000; Almodo´var et al, 2004;Paulino et al, 2009). The increase of P. rubescens during the summer months is partly due to its ability to form strong thickening in the metalimnetic layers provided that the light intensity is not below the Lim.…”