Stoichiometric mismatch causes a warming-induced regime shift in experimental plankton communities

Area of Science:

• Ecology
• Aquatic Ecosystems
• Climate Change Impacts

Background:

• Ecosystems face temporal mismatches between consumer needs and resource availability due to warming.
• Food quality mismatch, driven by shifts in producer communities, is a significant but under-recognized threat.
• Warming often leads to producers with higher carbon content and lower essential nutrient levels, creating stoichiometric imbalances.

Purpose of the Study:

• To investigate the impact of warming and grazer presence on plankton community dynamics and stoichiometric mismatch.
• To empirically demonstrate the 'paradox of energy enrichment' in a multispecies phytoplankton community.
• To assess how warming affects the temporal coherence of producer-consumer interactions.

Main Methods:

• A mesocosm experiment manipulated temperature (ambient vs. +3.6°C) and grazer types (ciliates and Daphnia).
• Monitored plankton community succession, phytoplankton bloom dynamics, and grazer population responses.
• Analyzed stoichiometric properties of phytoplankton, focusing on nutrient ratios (e.g., phosphorus content).

Main Results:

• Warming accelerated algal growth rates more than grazer growth, triggering a massive, low-quality phytoplankton bloom.
• Extreme stoichiometric mismatch, characterized by low phosphorus in algae, led to Daphnia extinction.
• Grazer presence (ciliates) temporarily slowed the bloom but did not prevent the eventual regime shift and grazer population crash.
• The experiment provided the first empirical evidence of the 'paradox of energy enrichment' in a multispecies phytoplankton context.

Conclusions:

• Warming exacerbates stoichiometric mismatch at the producer-herbivore interface, limiting energy transfer to higher trophic levels.
• Altered food quality under warming can lead to alternative stable states and ecosystem regime shifts.
• Understanding stoichiometric dynamics is crucial for predicting climate change impacts on aquatic food webs.