Sometimes — but not everyone benefits.
Seagrass meadows and macroalgal forests do much more than provide habitat. During the day, intense photosynthesis can strongly increase oxygen concentrations in the surrounding water, potentially helping marine animals meet the increasing metabolic demands imposed by high temperatures.
But can this extra oxygen actually make animals more resistant to marine heatwaves?
In our new study, we tested marine invertebrates from different sites across the Venice Lagoon, exposing them to increasing temperatures under normal and oxygen-supersaturated conditions.
The answer was clear — but not simple.
More oxygen increased upper thermal limits in some species, in some cases allowing animals to tolerate temperatures more than 1 °C higher.
Others, particularly echinoderms, gained little or no benefit from oxygen supersaturation.
Even populations of the same species responded differently depending on where they came from, suggesting that local environmental history can shape not only thermal tolerance, but also the capacity to exploit oxygen-rich conditions.
So, can primary producers create thermal refugia for marine life?
Yes — but not for everyone, and not everywhere.
Their capacity to buffer extreme warming depends on species physiology, respiratory mechanisms and the environmental history of local populations.
And there is another important limitation: oxygen supersaturation generated by photosynthesis occurs mainly during daylight. At night, respiration can reverse the picture and potentially drive oxygen below saturation.
Nature can provide powerful mechanisms of resilience, but they are context-dependent — not universal safety nets against climate change.
Protecting seagrass meadows and macroalgal forests is essential. But their buffering capacity cannot replace the need to tackle the underlying driver: ocean warming itself.
