Interaction strength between different grazers and macroalgae mediated by ocean acidification over warming gradients

Area of Science:

• Marine Ecology
• Climate Change Biology
• Oceanography

Background:

• Rising atmospheric CO2 drives ocean warming and acidification, impacting marine ecosystems.
• Macroalgae-herbivore interactions are key to marine community structure via top-down control.
• Warming effects on metabolism can alter trophic interactions, but acidification and grazer composition impacts are less understood.

Purpose of the Study:

• To investigate the combined effects of warming and acidification on macroalgae-herbivore interactions.
• To assess how these climate stressors influence grazer survival and consumption rates.
• To understand the role of grazer assemblage composition in modulating these interactions.

Main Methods:

• Two mesocosm experiments were conducted using the green macroalga Ulva rigida and two grazers, Melita palmata (amphipod) and Gibbula umbilicalis (gastropod).
• Experiments utilized two CO2 treatments (ambient and elevated, ~450 μatm) across a temperature gradient (13.5–22.1 °C).
• Grazer consumption rates and macroalgae-herbivore interaction strengths were measured.

Main Results:

• Both warming and acidification negatively affected grazer survival, with species-specific consumption rate differences.
• Melita palmata exhibited higher grazing per biomass and was more sensitive to climate stressors.
• Interaction strength varied with temperature, and acidification lowered the thermal optimum for grazing.

Conclusions:

• Warming and acidification can intensify top-down control in marine communities.
• Future increases in disturbances may shift communities towards bottom-up regulation.
• Grazer assemblage composition can significantly modulate future macroalgae-herbivore interactions under climate change.