Symbiont-induced intraspecific phenotypic variation enhances plastic trapping and ingestion in biogenic habitats

Nicastro, Katy; Seuront, Laurent; McQuaid, Christopher D.; Zardi, Gerardo I.

http://hdl.handle.net/10400.1/18347

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Authors

Nicastro, Katy

Seuront, Laurent

McQuaid, Christopher D.

Zardi, Gerardo I.

Abstract(s)

Plastic contamination has major effects on biodiversity, enhancing the consequences of other forms of global anthro-pogenic disturbance such as climate change and habitat fragmentation. Despite this and the recognised importance of intraspecific diversity, we still know relatively little about how plastic pollution affects diversity below the species level. Here, we assessed the effects of intraspecific variation in a habitat forming species (the Mediterranean mussel Mytilus galloprovincialis) on the trapping and ingestion of microplastics. We focused on symbiont-induced phenotypic variation in mussel beds. Using fractal analysis, we measured an increase in the complexity of mussel bed surfaces by ca. 15% caused by phototropic shell-degrading endoliths. By simulating high tide flow conditions and incoming waves, we found that symbionts significantly increased microplastic accumulation in mussel beds. This likely reflects deceleration of near-bed flow velocities, creation of turbulence in the bottom boundary layer and consequently in-creased particle retention. This effect was not constant at high tide, with no effect of infestation on retention at the base of the mussel bed under mid and high flow conditions and reduced microplastic trapping on the surface of mussel shells. Nevertheless, under natural conditions, the ingestion and trapping of microplastic were higher by the mussels comprising beds with symbionts than those in beds without symbionts. Given the dependency of many species on mus -sel biogenic habitats, there is an increased risk of plastics moving up the food chain in mussel beds infested by symbi-otic endoliths. Our results highlight how the effects of within-species phenotypic diversity may influence the consequences of rising levels of plastic pollution.