Does habitat influence bivalve microplastic concentration?

Microplastics (<5mm) are ubiquitous in the marine environment. Industrial and residential wastewaters are major sources of microplastics along with the degradation of macroplastics from recreational and commercial activities. There is increasing concern regarding the influence of fisheries and aquaculture industries on microplastic pollution and seafood. In southern British Columbia, shellfish aquaculture is an important industry, and shellfish aquaculture often uses plastic infrastructure (anti-predator netting, fencing, rope, cages, trays, floats). We conducted a study assess microplastic concentrations in bivalves found in deep water and intertidal habitats, including both farmed and un-farmed beaches. We focused on two commonly cultured species - Manila clams (Venerupis philippinarum) and Pacific oysters (Crassostrea gigas). To assess bivalves in farmed and un-farmed beaches, clams and oysters were transplanted from an initial population to 6 regions with varying degrees of farming intensity and left for 2-3 months. To compare deep water versus intertidal habitats, oysters were collected from three paired sites in 2 of the 6 regions. After collection, bivalves were chemically digested and analysed visually for microplastics. No differences were observed in microplastic concentration between farmed and un-farmed beaches for clams or oysters, or between deep water and intertidal habitats. Further, there appears to be no relationship between bivalve microplastic concentration and proximity to shellfish aquaculture. Our results suggest that habitat does not influence microplastic concentrations in the bivalves studied.