Cell size explains shift in phytoplankton community structure following storm-induced changes in light and nutrients

Area of Science:

• Ecology
• Limnology
• Climate Change Biology

Background:

• Community structure and dynamics are vital for understanding ecosystem responses to climate change and extreme weather.
• Phytoplankton cell size is a key trait influencing competition and grazing resistance, offering predictive power for community dynamics.
• Storm events can alter lake conditions through nutrient and colored dissolved organic matter (cDOM) inputs, impacting aquatic communities.

Purpose of the Study:

• To investigate if phytoplankton cell size can explain community structure shifts in response to storm-induced changes in nutrient and light availability.
• To assess the impact of colored dissolved organic matter (cDOM) and nutrient inputs on phytoplankton community composition and cell-size distribution.
• To determine the role of cell size in predicting phytoplankton community dynamics under altered environmental conditions.

Main Methods:

• A 6-week large-scale enclosure experiment was conducted using a crossed gradient design to simulate realistic lake conditions.
• Environmental variables, including nutrient levels, light availability (affected by cDOM), and mesozooplankton presence, were manipulated.
• Phytoplankton community structure, biovolume, and cell-size distribution were analyzed over the experimental period.

Main Results:

• Phytoplankton community structure was significantly explained by cell size when light availability decreased due to cDOM addition.
• A shift in cell-size distribution was observed, moving from small-celled species dominating initially to large-celled species as light declined.
• Nutrient levels and mesozooplankton abundance did not influence the observed shift in cell-size distribution.

Conclusions:

• Larger phytoplankton species exhibit a competitive advantage under reduced light conditions resulting from storm-induced cDOM inputs.
• The distinct clustering of species into size classes highlights the importance of interspecific size differences in community dynamics.
• Analyzing cell-size distributions is crucial for forecasting community and ecosystem responses, including food-web structure and biogeochemical cycles, to environmental change.