Microplastic ingestion by deep-pelagic crustaceans and fishes

A size-selective loss of smaller microplastics (< 1 mm) from surface pelagic waters has been reported, yet few surveys have studied biological ingestion by deep-pelagic organisms as a sink for the "missing" plastic. Here, 557 individuals representing 35 species of vertically migrating and nonmigrating mesopelagic crustaceans and fishes were collected in the Gulf of Mexico from discrete-depth intervals (0-200 m; 200-600 m; 600-1000 m; 1000-1200 m; 1200-1500 m) and analyzed for microplastic ingestion. We observed that 29% and 26% of crustacean and fish individuals, respectively, ingested microplastics, with an average plastic length of 0.59 +/- 0.2 mm. A subsample of ingested polymers was identified using Fourier Transform Infrared Spectroscopy, revealing that alkyd resin (density 1.6 g cm(-3)) and cellophane (density 1.42 g cm(-3)) were mainly consumed. Our data indicate that nonmigratory crustaceans had significantly higher levels of microplastic ingestion than migratory crustaceans at all depths available for comparison. While migratory fishes ingested microplastics at higher frequencies (0.28) than nonmigratory fishes (0.23), the frequency of microplastic ingestion by nonmigratory fishes increased with depth and was highest at depths of 1200-1500 m (0.40). Paired with the data for crustaceans, these observations suggest that plastic ingestion may be higher at deeper depths. Feeding strategy also appeared correlated to microplastic ingestion, as species that rely on gelatinous materials and marine snow for energy had the highest levels of ingestion. Altogether, our data highlight a largely undescribed temporary reservoir and implicate important biological transport pathways for the smaller plastic size fractions in the open ocean.