Climate warming restructures an aquatic food web over 28 years.

Area of Science:

• Ecology
• Climate Change Biology
• Aquatic Ecosystems

Background:

• Lake food webs are sensitive to climate warming, but empirical evidence of restructuring and its mechanisms is limited.
• Differential thermal responses among trophic levels can alter predator-prey dynamics and food web structure.

Purpose of the Study:

• To investigate the impact of climate warming on the pelagic food web structure of Lake Maggiore, Italy.
• To identify the primary drivers of food web restructuring, distinguishing between temperature, trophic state, and fishing pressure.

Main Methods:

• Analysis of weekly to yearly abundance and biomass data for five trophic levels spanning 1981–2008.
• Statistical assessment of temperature effects versus changes in fish predation and trophic state on food web dynamics.

Main Results:

• Lake warming (up to 2°C) was the primary driver of food web restructuring, overriding changes in trophic state or fishing.
• Numerical abundance shifted towards middle-trophic-level predators, notably the spiny water flea (Bythotrephes longimanus).
• Bythotrephes prospered, limiting the keystone grazer Daphnia and strengthening top-down control, with advanced population peaks and extended growth periods.

Conclusions:

• Long-term climate warming significantly restructures lake food webs by favoring higher trophic levels.
• Warming enhances top-down control in aquatic ecosystems, with potential cascading effects on ecosystem function.
• The study provides rare natural evidence of warming-induced food web shifts and their ecological consequences.