Microplastics and Paramecium bursaria: impacts on symbiosis and oceanic oxygen

Pollution by microplastics reduces energy production in aquatic life. In marine and brackish waters, Paramecium bursaria thrives as a ciliate that forms a mutual partnership with the green alga zoochlorella. The algae live inside the ciliates, supplying nutrients through photosynthesis, while the ciliates offer mobility and protection that benefit the algae. Recent laboratory trials exposed Paramecium bursaria to water contaminated with microplastics, at levels higher than typically found in all of the world’s oceans but comparable to extreme regional conditions. Researchers measured growth rate, symbiont density (the number of algae inside each ciliate), metabolic rate, feeding rate, and photosynthetic efficiency to assess the impact of microplastics versus clean controls. The key finding is clear: photosynthesis suffers when microplastics are present, while other cellular functions show less immediate disruption. This decline in photosynthetic activity translates into reduced energy supply for the host organism and affects the nutrient exchange that sustains the symbiotic relationship. Overall oxygen production from this photosynthetic process dropped by roughly half in the tested scenarios. Given the significant share that symbiotic algae contribute to oceanic photosynthesis, experts emphasize that this factor must be incorporated into broader assessments of global oxygen generation and carbon cycling. In this context, the study underscores how microplastic pollution can cascade through microbial partnerships to influence ecosystem energy budgets and regional oxygen levels. The findings also suggest that protecting marine symbioses could be important for sustaining biogeochemical processes that support life in coastal and offshore habitats. An older note from biologists about animal behavior mentioned that extreme social structures in certain species can influence survival dynamics, illustrating how even distant observations can prompt questions about energy use and life history strategies in marine environments (Exeter researchers).