Trait strengthening in mussels

Plastic pollution is ubiquitous with increasing recognition of its direct
effects on species’ fitness.  Little is known, however,
about its more subtle effects, including the influence of plastic
pollution on the morphological, functional and behavioural traits of
organisms that are central to their ability to withstand disturbances.
Among the least obvious but most pernicious forms of plastic-associated
pollution are the chemicals that leach from microplastics. Here,
we investigate how such leachates influence species’ traits by
assessing functional trait compensation across four species of
intertidal mussels, through investigations of byssal thread production,
movement and aggregation behaviour for mussels held in natural seawater or
seawater contaminated by microplastic leachates. We found no evidence for
compensation of functional traits, but for each species, microplastic
leachates reinforced one trait while others remained unaffected. Two
species (Perna perna and Mytilus galloprovincialis),
were characterized by a resistance strategy to disturbance; they produced
more byssal threads in microplastic leachate seawater than in control
seawater, while motility and aggregation remained essentially unaffected.
In contrast, the other two species (M.
edulis and Choromytilus meridionalis), showed a
resilience strategy to disturbance through reduced motility and
aggregation in leachate seawater, while byssal thread production remained
unaffected. These results suggest that the competitive abilities
of intertidal mussels may be related to their sensitivity to microplastic
leachates or other chemical disturbance. Importantly, the trait
strengthening observed will affect the ability of these mussels to form
spatially patterned beds, with implications for their quality as autogenic
ecological engineers or foundation species. Thus, our findings
have implications for the ability of mussel beds to
tolerate disturbance, and hence for central ecosystem services, such as
their ability to support biodiversity and enhance secondary and tertiary
production. The results suggest that an inconspicuous aspect of
plastic pollution has the potential to influence other communities and
ecosystems in powerful ways.