Graduate Thesis Or Dissertation
 

Spatial and Temporal Assessment of Vertically Migrating Myctophids as Biotransporters of Microplastics to Mesopelagic Food Webs

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/f4752r18g

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  • It is well documented that microplastics and semi-synthetic particles (<5 mm) pervade the marine environment, with their ingestion by marine fauna eliciting global concern. While fishes exposed to microparticles in a laboratory setting have exhibited both sub-lethal and lethal effects, the diversity in material, morphology, and size of these contaminants in the ocean make it challenging to pinpoint the risks to wild organisms. Highly abundant, vertically-migrating myctophids play a crucial role in nutrient cycling between the epi- and mesopelagic zones, but may also serve as significant conduits for dispersing surface microparticles throughout the food web. Here, I examined the digestive tracts of newly-caught and museum-archived myctophids from the Northern California Current to determine (a) if myctophids caught closer to a presumed point source (i.e., Columbia River mouth) ingest more microplastics, and (b) if microplastic ingestion has increased over time. There was no relationship between microplastic consumption and distance from the river mouth or differences between the stations. However, body depth (a proxy for size) and water temperature exhibited a significant, positive association in the best-fit model. Overall, the number of suspected microplastics extracted from the museum specimens did not indicate an increasing trend over the compiled time series but a detailed analysis by geographic region identified a positive temporal microplastics presence trend in those myctophids captured near the continental United States. Approximately 30% of all specimens analyzed contained microparticles (~21% synthetic and ~79% anthropogenically modified), suggesting that myctophids are likely multidirectional transporters of these particles in Northern California Current food webs, with potential impacts on fisheries and human food systems. Exploring the spatial drivers and temporal trends of microplastic ingestion by mesopelagic fishes can help predict future vulnerability and direct efforts to reduce further contamination.
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