Invasive Mougeotia from Lake Kinneret: a versatile filamentous alga

Mougeotia sp.(Zygnematales,Charophyta) appeared in the plankton of Lake Kinneret for the first time in June 1998. While initially quite rare, from 2004 onwards it was present in the water column most of the time, forming occasional massive blooms in Spring (2005, 2006, 2012) and in late-autumn/early-winter (2010/11). Here we report on the temporal biomass pattern of this invasive filamentous alga and the environmental conditions supporting its growth. A suite of statistical methods was applied to the long-term record of Mougeotia biomass to understand Mougeotia – environment relationships. Using only year and month as explanatory predictors, generalized additive modeling (GAM) explained 36% of the variation in Mougeotia biomass. However, the temporal dynamics of Mougeotia biomass could not be explained by any of the environmental parameters considered. Rather, Mougeotia was capable of growing or at least maintaining its population under a wide range of water temperatures, nutrient concentrations, solar radiation, pH levels and stratification patterns, indicating it as a highly versatile alga. Modelling the temporal dynamics of Mougeotia biomass as autoregressive integrated moving average (ARIMA(1,0,0)), a strong density dependence was found. Thus, it seems that various intra-specific factors, such as competition for nutrients and self-shading, play an important role in determining the seasonal and long-term dynamics of Mougeotia biomass. We speculate that Lake Kinneret may host two or more cryptic species of Mougeotia, that look alike under the microscope but are genetically distinct; this may hinder any inference on Mougeotia – environment relationships. This hypothesis remains to be confirmed.