Temperature effects on seaweed-sustaining top-down control vary with season

Area of Science:

• Marine Ecology
• Climate Change Biology
• Oceanography

Background:

• Rising seawater temperature and CO2 concentrations (ocean acidification) are key climate change stressors impacting marine ecosystems.
• Full-factorial, seasonal, multispecies experiments are crucial for understanding climate change effects on marine food webs.
• Fucus vesiculosus is a dominant habitat-forming species in the Baltic Sea, providing essential ecosystem services.

Purpose of the Study:

• To investigate the seasonal responses of Baltic Sea Fucus vesiculosus communities to elevated seawater temperature and CO2 concentrations.
• To assess the direct and indirect effects of these stressors on marine food webs.
• To determine the relative importance of warming and ocean acidification on ecosystem structure and function.

Main Methods:

• Benthic mesocosm experiments were conducted over one year, simulating four seasons.
• The experiments utilized multispecies, cross-trophic-level settings.
• Responses of Fucus vesiculosus communities, grazers, and epiphytes to elevated temperature and CO2 were monitored.

Main Results:

• Elevated CO2 had minor effects, while warming significantly impacted grazers and Fucus communities.
• Seasonal effects were pronounced: summer warming led to grazer collapse and epiphyte overgrowth; fall/winter warming intensified grazing, reducing Fucus biomass.
• Warming altered top-down control in the food web, with seasonal variations in impact.

Conclusions:

• Future warming will influence marine food webs by altering top-down control, with seasonal context being critical.
• The decline of Fucus vesiculosus due to climate change threatens vital ecosystem functions and services in the Baltic Sea.
• Seasonal variability must be considered when predicting the ecological consequences of climate change in marine environments.