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.

We fully sequenced the genomes of 16 Vibrio cultivars isolated from eel larvae, plastic marine debris (PMD), the pelagic brown macroalga Sargassum, and seawater samples collected from the Caribbean and Sargasso Seas of the North Atlantic Ocean. Annotation and mapping of these 16 bacterial genome sequences to a PMD-derived Vibrio metagenome-assembled genome created for this study showcased vertebrate pathogen genes closely-related to cholera and non-cholera pathovars. Phenotype testing of cultivars confirmed rapid biofilm formation, hemolytic, and lipophospholytic activities, consistent with pathogenic potential. Our study illustrates that open ocean vibrios represent a heretofore undescribed group of microbes, some representing potential new species, possessing an amalgam of pathogenic and low nutrient acquisition genes, reflecting their pelagic habitat and the substrates and hosts they colonize.

While plastic has become omnipresent in the marine environment, knowledge of how plastic biofilm communities develop from functional metabolic and phylogenetic perspectives is nascent, although these data are central to understanding microbial ecology surrounding plastic substrates in the ocean. By incubating virgin microplastics during oceanic transects and comparing with naturally occurring plastic litter at the same locations, we constructed functional gene catalogs to contrast the metabolic differences between early and mature biofilm communities. Early colonization incubations were consistently dominated by Alteromonadaceae and harbored significantly higher proportions of genes associated with adhesion, biofilm formation, chemotaxis, defense, iron acquisition and utilization, and motility. Comparative genomic analyses with Alteromonas, Marinobacter , and Marisediminitalea metagenome assembled genomes (MAGs) spotlighted the importance of the mannose-sensitive hemagglutinin operon, adhesive genes genetically transposed from intestinal pathogens, for early colonization of hydrophobic plastic surfaces. Synteny alignments of the former operon also demonstrated apparent positive selection for mshA alleles across all MAGs. Early colonizers varied little in terms of large-scale genomic characteristics, despite the presence of latitudinal, salinity, and temperature gradients. Mature plastic biofilms, composed of predominantly Rhodobacteraceae followed by Flavobacteriaceae, that are critically important for carbon turnover in oceanic ecosystems, displayed significantly higher proportions of genes involved in oxidative phosphorylation, phosphonate metabolism, photosynthesis, secondary metabolism, and Type IV secretion. Our metagenomic analyses provide insight into early biofilm formation on virgin surfaces in the marine environment, as well as how early colonizers self-assemble, compared to mature, taxonomically, and metabolically diverse biofilms. Significance Statement Little is known about plastic biofilm assemblage dynamics and successional changes over time. Our results demonstrate that highly reproducible and predictable types of bacteria, with similar genomic characteristics, can initially colonize plastic in the marine environment across varying environmental gradients. The key gene sets involved in foundational bacterial colonization may have broad impacts for biofilm formation on plastic surfaces used in agriculture, biomedicine, environmental science, and food science. Genomic characteristics of early colonizers may metabolically underpin the origin of the ordered succession observed in marine microbial communities and be useful for predicting microbial community membership and biogeochemical processes.

Hundreds of studies have surveyed plastic debris in surface ocean gyre and convergence zones, however, comprehensive microplastics (MPs, ≤5 mm) assessments beneath these surface accumulation areas are lacking. Using in situ high-volume filtration, Manta net and MultiNet sampling, combined with micro-Fourier-transform-infrared imaging, we discovered a high abundance (up to 244.3 pieces per cubic meter [n m-3 ]) of small microplastics (SMPs, characteristically <100 μm) from the surface to near-sea floor waters of the remote South Atlantic Subtropical Gyre. Large horizontal and vertical variations in the abundances of SMP were observed, displaying inverse vertical trends in some cases. SMP abundances in pump samples were more than two orders of magnitude higher than large microplastics (LMPs, >300 μm) concurrently collected in MultiNet samples. Higher-density polymers (e.g., alkyd resins and polyamide) comprised >65% of the total pump sample count, highlighting a discrepancy between polymer compositions from previous ocean surface-based surveys, typically dominated by buoyant polymers such as polyethylene and polypropylene. Contrary to previous reports stating LMP preferentially accumulated at density gradients, SMP with presumably slower sinking rates are much less influenced by density gradients, thus resulting in a more even vertical distribution in the water column, and potentially longer residence times. Overall, our findings suggest that SMP is a critical and largely underexplored constituent of the oceanic plastic inventory. Additionally, our data support that weak current systems contribute to the formation of SMP hotspots at depth, implying a higher encounter rate for subsurface particle feeders. Our study unveils the prevalence of plastics in the entire water column, highlighting the urgency for more quantification of the deep-ocean MP, particularly the smaller size fraction, to better understand ecosystem exposure and to predict MP fate and impacts.

Vertical migrations into shallower waters at night are beneficial for migrators as they reduce predation risk and allow migrators to encounter a higher density of prey. Nevertheless, ocean acoustics data and trawl data have shown that a portion of some vertically migrating populations remain at depth and do not migrate. One hypothesis for this phenomenon is the Hunger-Satiation hypothesis, which in part states that the non-migrating portion of the migrating species-assemblage refrains from migrating if they have full or partially full stomachs from daytime or nocturnal feeding. However, stomach fullness of the non-migrating subpopulation compared to the migrating portion has rarely been studied, due to the difficulty in obtaining sufficient samples. The stomach fullness levels of numerically abundant crustacean and fish species with well-known depth distributions were quantified in the present study. Animals were captured during night trawls from discrete-depth intervals between 0 and 1,500 m. Stomach fullness indices were assigned from 0 to 5 and compared between migratory taxa caught in shallow and deep waters. Data from the crustaceans Acanthephyra purpurea, Gardinerosergia splendens, Plesionika richardi , and Systellaspsis debilis , as well as the fishes Lampanyctus alatus, Lepidophanes guentheri , and Notolychnus valdiviae , provided support for the Hunger-Satiation hypothesis, while data from the crustaceans Gennadas capensis and Gennadas valens and the fish Benthosema suborbitale did not. These findings suggest that stomach vacancy may be just one of several factors regulating the dynamics of vertical migration in those species whose behavioral plasticity suggests daily “choices” in whether or not to vertically migrate.