PROJECT
Background
Among the multiple stressors that affect aquatic ecosystems, plastic pollution is deemed a widespread and pervasive environmental issue. Since the ubiquitous presence of plastic debris in aquatic systems has been established, the focus of research has shifted towards assessing their impact on aquatic organisms and ecosystem functions.
The interaction of plastics with aquatic biota starts from low trophic levels; indeed, plastics represent a new habitat for rafting organisms to the point that the term “plastisphere” was coined to define the diverse community growing on the surface of plastic debris. Even if heterotrophic bacteria tend to be the focus of plastisphere research, the presence of microalgae within the epiplastic biofilm has been repeatedly documented. However, further research is needed to explore the microalgae-plastic interactions and several questions remain to be addressed, especially for freshwaters.
Aims of the project
The project is aimed at studying the temporal establishment and development of phytobenthos on different plastic polymers over a wide geographical scale to better characterize the interaction of plastics with key organisms of aquatic ecosystems, i.e. microalgae. The overreaching goal is to understand whether plastic debris can represent a new niche for the microalgal community in freshwater systems and determine whether substrate-specific properties or environmental factors prevail in shaping microalgal assemblages on plastic debris. In particular, the project aimed at:
Quantify the microalgae biomass developed on microplastics with different polymeric composition and determine whether biomass vary significantly among substrates across a
variety of aquatic systems
Identify the microalgae species that are able to develop on different substrates and understand whether plastics exert a strong enough selection to drive species sorting
Evaluate the temporal and seasonal evolution of the epiplastic community of microalgae in relation to several environmental variables
Methods
Experiments will be conducted in lentic systems with different features. Sheets of polyethylene, polypropylene, and glass (which serve as control being an inert substrate) will be deployed in each system. To assess the temporal and seasonal evolution of the colonization, samples will be collected in succession after 3, 7, 15, and 30 days and the experiment will be replicated in each season. Several physical and chemical parameters will be analyzed alongside (e.g., temperature, dissolved oxygen, nutrient concentration) to understand the relationship with the environmental variables. For each substrate and replicate, we will assess the phytobenthic biomass estimating the chlorophyll a, and the ash-free dry mass. Moreover, microalgae composition will be determined on a subset of samples to understand the community composition colonizing the different substrates. This will represent, at the best of our knowledge, the first coordinated experiment conducted at a large spatial scale to explore the plastisphere and, thereby, a unique dataset will be generated that will allow us to identify the key drivers of the process, leaving aside the site-specific and possibly confounding variables.