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Marine heatwaves outweigh microplastic exposure in driving physiological changes in the coral Astroides calycularis
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Scientists tested how a Mediterranean coral handles two modern ocean stressors—warmer water (mimicking a heatwave) and microplastic pollution—and found that heat was by far the bigger threat, throwing off the coral's metabolism and stress-defense systems, while microplastics alone barely affected it. This matters because it shows that as oceans warm, marine life may be more vulnerable to heat stress than to plastic pollution, which helps researchers prioritize where conservation efforts and further research are needed most to protect ocean ecosystems we depend on for food and coastline protection.
Global climate change and anthropogenic pollution are major threats to marine ecosystems, with heatwaves and microplastics posing a particular risk to corals. The combined effects of these stressors are still poorly understood, especially for non-symbiotic species like the Mediterranean coral Astroides calycularis. In this study, the combined effects of a simulated heatwave (HW) and microplastics (MPs) on physiological (respiration and excretion rates) and biochemical responses (oxidative stress and energy metabolism biomarkers) of this coral were studied for the first time. Colonies were exposed for four weeks to four conditions: control (26 °C), HW (29 °C), MPs, and a combination of both. Results show that the HW was the primary driver of change, significantly increasing respiration and excretion rates and modulating the antioxidant system. Superoxide dismutase (SOD) activity increased, while catalase (CAT) and glutathione-S-transferases (GSTs) decreased. This indicates a strong metabolic and antioxidant response to thermal stress. In contrast, MPs had only a minor physiological effect on respiration and did not induce a significant biochemical stress response. No significant interaction was detected between the two stressors, suggesting they act independently. Our findings highlight the vulnerability of A. calycularis to thermal stress and underscore the need to study multiple stressors to better understand coral resilience in a changing ocean.
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Researchers tested the combined effects of microplastic pollution and heat stress on five reef-building coral species in controlled laboratory experiments. They found that while heat stress caused significant bleaching, tissue death, and reduced photosynthetic efficiency, microplastics alone had only minor effects at ambient temperatures, suggesting that climate change remains a far greater threat to coral reefs than microplastic pollution.
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Researchers exposed two coral species to ambient and elevated temperatures and then fed them microplastics, Artemia nauplii, or both, finding that thermal stress significantly reduced feeding on prey but did not decrease microplastic ingestion. Notably, one species only ingested microplastics when live food was simultaneously present, suggesting incidental rather than selective uptake and highlighting species-level variability in microplastic risk under climate change.
Heterotrophic feeding modulates the effects of microplastic on corals, but not when combined with heat stress
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Researchers tested whether providing extra food to corals could help them cope with microplastic pollution and heat stress. While supplemental feeding did offset some negative effects of microplastics alone, it could not protect corals when microplastics were combined with elevated temperatures. The study suggests that during marine heatwaves, corals face compounding stressors that feeding alone cannot overcome.
Physical and cellular impact of environmentally relevant microplastic exposure on thermally challenged Pocillopora damicornis (Cnidaria, Scleractinia)
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Corals exposed to microplastics at levels currently found in the ocean showed more cellular damage when also stressed by warm water temperatures. The microplastics triggered inflammation-like responses and slowed down tissue repair in the corals. This matters because coral reefs are already under severe pressure from climate change, and microplastic pollution appears to make their situation worse.
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