Turbulence effects on phytoplankton morphofunctional traits selection

Turbulence can regulate phytoplankton community structure in aquatic ecosystems by affecting sedimentation and nutrient acquisition. In rivers, nutrient concentrations are often high enough to sustain phytoplankton growth without limitation. Hence, turbulence mainly acts on phytoplankton by controlling its vertical position in such ecosystems. We conducted a laboratory experiment to see if the response of phytoplankton to turbulence could be predicted from morphofunctional traits related to sinking velocity and maximum growth rate. Turbulence was generated by horizontally oscillating grid systems in three 5 L chambers, which also constituted three chemostats. Two turbulence levels typical of lowland rivers (ε = 7.9 × 10−5 m² s−3 and ε = 7.8 × 10−3 m² s−3) were tested on an experimental community composed of six species from different taxonomic lineages. The species selected displayed different values for five morphofunctional traits related to sinking velocity and maximum growth rate (S : V ratio, algal unit size, density, shape, and motility). We showed that community structure could be partly predicted from morphofunctional traits. Under low turbulence (LT) (ε = 7.9 × 10−5 m² s−3), species displaying traits leading to high sinking velocity (i.e., large size and high density) were unable to sustain stable populations, whereas species which displayed the opposite traits (i.e., small size, flattened shape, or low density) dominated the community. Furthermore, one of the six species exhibited phenotypic plasticity in size and could adapt to both high and LT conditions.© 2014 Association for the Sciences of Limnology and Oceanography