Impact of microplastic white tide on the light and dark metabolism of the macroalgae Fucus serratus: petroleum-based vs biosourced polymers

In a context of global change, the rising intensity of extreme climatic and pollution events, particularly plastic pollution and accumulation of plastic pellets, threaten intertidal organisms’ living conditions and physiology. In response to the need for reduced fossil fuel reliance and the use of potentially toxic chemical compounds, the plastics industry is developing bioplastics marketed as "biosourced" or "biodegradable." However, bioplastics often share the same environmental issues as conventional plastics. To address gaps in understanding how conventional and bioplastics affect brown algae, we studied the impact of four virgin plastic polymers —polypropylene (PP), a biosourced polypropylene with a scallop shell matrix (PPSS), a biodegradable polylactic acid (PLA), and a biodegradable biopolyester (BioP)— on CO2 fluxes in Fucus serratus under massive microbead exposure. Results showed limited effects of PP, PPSS, and BioP on the algae's photosynthesis and respiration, indicating resilience to short-term plastic exposure. In contrast, PLA exposure significantly increased dark respiration rates, suggesting a metabolic stress. However, prolonged high energy demand could be detrimental to algal health and resilience. Our future research will explore the effects of these polymers in a wider ecological context, both under natural seasonal variations and/or combined with an exceptional thermal stress.