Phytoplankton is an essential resource in aquatic ecosystems, situated at the base
of aquatic food webs. Plastic pollution can impact these organisms, potentially affecting
the functioning of aquatic ecosystems. The interaction between plastics and phytoplankton
is multifaceted: while microplastics can exert toxic effects on phytoplankton, plastics
can also act as a substrate for colonisation. By reviewing the existing literature,
this study aims to address pivotal questions concerning the intricate interplay among
plastics and phytoplankton/phytobenthos and analyse impacts on fundamental ecosystem
processes (e.g. primary production, nutrient cycling). This investigation spans both
marine and freshwater ecosystems, examining diverse organisational levels from subcellular
processes to entire ecosystems. The diverse chemical composition of plastics, along
with their variable properties and role in forming the "plastisphere", underscores
the complexity of their influences on aquatic environments. Morphological changes,
alterations in metabolic processes, defence and stress responses, including homoaggregation
and extracellular polysaccharide biosynthesis, represent adaptive strategies employed
by phytoplankton to cope with plastic-induced stress. Plastics also serve as potential
habitats for harmful algae and invasive species, thereby influencing biodiversity
and environmental conditions. Processes affected by phytoplankton-plastic interaction
can have cascading effects throughout the aquatic food web via altered bottom-up and
top-down processes. This review emphasises that our understanding of how these multiple
interactions compare in impact on natural processes is far from complete, and uncertainty
persists regarding whether they drive significant alterations in ecological variables.
A lack of comprehensive investigation poses a risk of overlooking fundamental aspects
in addressing the environmental challenges associated with widespread plastic pollution.
