Marine organisms are increasingly exposed to multiple human-driven pressures at the same time. But when we talk about “multiple stressors”, we should not assume that all of them contribute equally to biological change.
In our new study, we exposed the Mediterranean coral Astroides calycularis to marine heatwaves, microplastics, and their combination.
The result was striking: temperature clearly outweighed microplastic exposure in driving physiological and biochemical changes.
Heatwave conditions altered coral metabolism, increasing respiration and excretion rates and strongly modulating antioxidant defences and energy metabolism.
Microplastics, at the environmentally relevant concentration tested, produced comparatively minor effects and did not significantly exacerbate most responses to thermal stress.
This does not mean that microplastic pollution is harmless. Plastic pollution remains a serious and persistent pressure on marine ecosystems, and reducing it is essential.
But our results highlight a broader message:
we need to understand which stressors actually drive biological responses — and under which conditions — rather than assuming that every pressure has the same ecological weight.
For A. calycularis, our experiment points clearly towards extreme warming as the dominant physiological challenge.
And as marine heatwaves become more frequent, intense and persistent across the Mediterranean, reducing local pressures alone may not be enough. Tackling climate change remains fundamental if we want to protect Mediterranean benthic communities.
Multiple stressors require multiple solutions — but also the right priorities
