“Storm-blitz”: Impact of storms on phytoplankton composition

Storm-blitz is part of a series of The Theory Working Group (TTG) projects, related to the effects of physical disturbances and water column stability on plankton communities. These projects have been designed to provide explanations for the paradox of plankton formulated by Hutchinson, and providing new frameworks to answer questions on rules of community assembly and succession.

Ongoing GLEON TTG projects have revealed phytoplankton traits associated with stable and mixed water column conditions, strengthening our understanding on the main role of thermal stratification in steering phytoplankton composition and succession at the annual scale. However, the extent to which phytoplankton species become organized is not only dependent upon thermal stability but also upon its longevity. At the annual scale, phytoplankton successions can easily be analogized to the Odum’s ecological succession driven by intrinsic species interactions. Margalef pointed out the unidirectional nature of the succession; nevertheless succession can be set back by alterations of the ambient environment due to the intervention of external disturbances such as floods, storms or episodes of increased wind mixing. Depending upon the severity and duration of the disturbance in relation to the structural stability already acquired, the succession may be abruptly halted and return to a prior stage. Consequently, changes in phytoplankton composition, in term of diversity and morpho-functional traits, are expected to follow the occurrence of extreme meteorological events.

Two existing TTG projects are addressing the effects of water column disturbance on phytoplankton assembly, but not specifically focusing on storms. The objectives of storm-blitz are 1) to test whether water column disturbance driven by storms may affect phytoplankton assembly, in term of diversity, species and morpho-functional traits, 2) to characterize the changes in the phytoplankton community to address mechanisms that led to the new community. The results should offer excellent examples to question the sensitivity of aquatic ecosystems to extreme weather events. They would also provide us with the possibility to be reanalyzed within the framework of the Catastrophe Theory.

In a first step, our questions will be addressed using long-term dataset of phytoplankton communities and environmental conditions monitored in several lakes around the world. Time-series analyses and inter-lake comparisons will be used i) to identify the impact of storms on phytoplankton composition, ii) to provide information on how to define storms and sampling frequency to capture phytoplankton changes and iii) to discuss some experiments that will be run in a second step in order to address mechanisms.

Other people involved: G. Morabito, T. Zohary, N. Salmaso, D. Straile, S. Ban, G. Dur...