Comparison of seasonal distribution patterns of Discostella stelligera and Lindavia bodanica in a boreal lake during two years with differing ice-off timing

Abstract

Widespread changes in the relative abundances of Cyclotella sensu lato taxa have occurred in lakes of the Northern Hemisphere over the last ∼150 years, with these changes often attributed to climate-driven physical changes in lakes. While the links between Cyclotella ecology and lake thermal structure have been investigated extensively now, the role of the timing of ice-off in driving these diatom patterns remains unclear. We compared the seasonal distribution patterns of Cyclotella taxa in a boreal lake with high water transparency during two years with differing timing of ice-off. Vertical distributions of taxa in Jordan Pond (Maine, USA) were assessed every 5–24 days from early May to late October during an early ice-off year (19 March 2012) and a late ice-off year (29 April 2015). Seasonal succession patterns differed over the two years. During the early ice-off year, Lindavia bodanica cell densities were higher and peaked in the hypolimnion from July to October. The abundance of this taxon during the late ice-off year may have been negatively affected by fungal infection, which was visible with microscopic investigation. In contrast, Discostella stelligera cell densities were higher during the late ice-off year and peaked from May to August. This taxon was distributed uniformly in the water column throughout July, during phosphorus-limited conditions, and was then more abundant in the epilimnion during August, during nitrogen-limited conditions. Multiple linear regression models suggested that variation in D. stelligera cell densities was explained by year, number of days since ice-off and mixing depth (R2 = 0.55), while variation in L. bodanica cell densities was explained by year, number of days since ice-off, total phosphorus, dissolved oxygen, and Secchi disk depth (R2 = 0.16). Our results reveal variable seasonal distribution patterns of these two taxa over the two years and suggest that these patterns are the result of many drivers, some of which may be affected by ice-off timing.