Winter severity determines functional trait composition of phytoplankton in seasonally ice‐covered lakes

Abstract

How climate change will affect the community dynamics and functionality of lake ecosystems during winter is still little understood. This is also true for phytoplankton in seasonally ice-covered temperate lakes which are particularly vulnerable to the presence or absence of ice. We examined changes in pelagic phytoplankton winter community structure in a north temperate lake (Müggelsee, Germany), covering 18 winters between 1995 and 2013. We tested how phytoplankton taxa composition varied along a winter-severity gradient and to what extent winter severity shaped the functional trait composition of overwintering phytoplankton communities using multivariate statistical analyses and a functional trait-based approach. We hypothesized that overwintering phytoplankton communities are dominated by taxa with trait combinations corresponding to the prevailing winter water column conditions, using ice thickness measurements as a winter-severity indicator. Winter severity had little effect on univariate diversity indicators (taxon richness and evenness), but a strong relationship was found between the phytoplankton community structure and winter severity when taxon trait identity was taken into account. Species responses to winter severity were mediated by the key functional traits: motility, nutritional mode, and the ability to form resting stages. Accordingly, one or the other of two functional groups dominated the phytoplankton biomass during mild winters (i.e., thin or no ice cover; phototrophic taxa) or severe winters (i.e., thick ice cover; exclusively motile taxa). Based on predicted milder winters for temperate regions and a reduction in ice-cover durations, phytoplankton communities during winter can be expected to comprise taxa that have a relative advantage when the water column is well mixed (i.e., need not be motile) and light is less limiting (i.e., need not be mixotrophic). A potential implication of this result is that winter severity promotes different communities at the vernal equinox, which may have different nutritional quality for the next trophic level and ecosystem-scale effects.

Ecology under lake ice

“…; Özkundakci et al . ), division level (Carey et al . ), or by functional traits (Özkundakci et al .…”

“…), or by functional traits (Özkundakci et al . ) with winter assemblages characterised by taxa that are more tolerant to cold and low‐light conditions. Despite constraints by cold temperature, light limitation or altered mixing under the ice, winter species diversity has been found to be rather high (Salonen et al .…”

“…Even more scarce is information about nutrient and dissolved organic carbon concentrations under the ice that may help to drive many of these plankton dynamics (but see Özkundakci et al . ).…”

“…; Özkundakci et al . ), and that these differences would be modified by geophysical characteristics of lakes. Furthermore, we hypothesise that lake conditions can carry‐over across seasons, as suggested in the revised PEG model (Sommer et al .…”

Interrelationship between nutrients and chlorophyll-a in an urban stormwater lake during the ice-covered period

“…Both lakes favored the development of nanoplankton when they were ice covered in one winter, but produced microplankton when they were completely ice-free in the second winter. Phytoplankton community structure was found to be strongly correlated with ice thickness (Ozkundakci et al, 2016). High species diversity has been found under ice despite unfavorable conditions, including limited light availability, low water temperatures, restricted air-water gas exchange and prevention of wind-induced mixing (Salonen et al, 2009, Schröder, 2013.…”