Microalgae colonization of different microplastic polymers in experimental mesocosms across an environmental gradient

Area of Science:

• Environmental Science
• Ecology
• Microbiology

Background:

• Microplastic surfaces are colonized by organisms, forming biofilms (plastisphere).
• While bacteria are often studied, microalgae also form significant epiplastic biofilms.
• Understanding freshwater microplastic biofouling is crucial but data remains scarce.

Purpose of the Study:

• To assess microalgal biomass development and species composition on different plastic polymers.
• To investigate if plastic substrates drive species sorting in freshwater biofilms.
• To determine factors influencing microalgal community diversity on microplastics.

Main Methods:

• Microplastic pellets (HDPE, PET, mixed) were deployed in 15 lentic mesocosms across five Iberian Peninsula locations.
• Biofilm microalgal species composition and biomass were analyzed after one month.
• Environmental parameters (nutrients, conductivity, macrophyte coverage) were recorded.

Main Results:

• Microplastic colonization occurred across diverse lentic ecosystems and environmental conditions.
• Higher microalgal biomass developed on polyethylene terephthalate (PET) compared to high-density polyethylene (HDPE).
• A rich community of 242 microalgal species was supported, but colonization was not polymer-specific.
• Local species pool and nutrient concentration were key drivers of community diversity, not plastic type.

Conclusions:

• Microplastics exhibit significant carrying capacity for diverse microalgal communities in freshwater.
• Local environmental factors and species availability, rather than polymer composition, dictate microalgal biofilm diversity.
• The findings have implications for understanding the ecological role of microplastics in aquatic systems.