The combined effects of ocean warming and microplastic pollution on marine phytoplankton community dynamics

Microplastics (MPs) and ocean warming present a dual threat to marine phytoplankton, with significant but not fully understood effects. This study assessed how projected MP pollution and rising water temperatures influence phytoplankton biomass, abundance, and diversity. While MPs at future concentrations did not impact biomass or abundance at current temperatures, under projected warming conditions, biomass decreased by 41 % and diversity by 38.8 % in MP-exposed samples. This suggests that MP toxicity, aggregation, and reduced light penetration, intensified by warming, can inhibit phytoplankton growth. Diatoms, crucial for global primary productivity, were especially affected, with declines in their abundance and diversity potentially reducing carbon sequestration by up to 10.45 billion tons annually. Community composition shifted towards fewer genera, implying lower biodiversity and resilience, which could disrupt marine food webs and affect human populations. Seagrass wetlands, a Nature-based Solution, might mitigate some impacts by trapping MPs and limiting their effects on phytoplankton. These results highlight the urgent need for further research to address and mitigate the combined impacts of MPs and warming on marine ecosystems, due to potential broad ecological and socioeconomic repercussions.