Samuel Pruhs, “Methods to Assess Ingestion of Microplastics by the Invasive Crustacean, Hemimysis anomala”
Mentor: John Berges, Biological Sciences, Letters & Science (College of)
Oral Presentation: 9:00am Union E260
The opossum shrimp, Hemimysis amomala invaded Lake Michigan in the mid 2000’s and is now found widely in harbors where they form large swarms. Previous work has shown they feed on zooplankton and algae, and can also ingest microplastic particles in the laboratory. Hemimysis collected from the field have plastics particles in their guts. In the present study, we wanted to refine methods to accurately quantify what they are ingesting by: a) evaluating methods to digest away organic matter and remove interference, and b) refining digital image analysis methods to visualize and quantify plastic particles. Hemimysis were collected from Lake Michigan using lighted funnel traps. Animals were measured and frozen for analysis of gut contents with Nile Red, a stain which cause most plastic to fluoresce. Analysis of samples included filtration onto different types of filters, digestion of organic matter with peroxide or alkali solutions, analysis of epifluorescence microscope images with ImageJ software. Peroxide proved superior to alkali digestion and Nile Red was a reliable and easy to apply method. With some simple adjustment to the code, the ImageJ macro MP-VAT could be used to analyze images. For Hemimysis, an average of 235 (± 546) plastic particles, 19 fragments and 2 fibers per animal was found, (average equivalent diameters of 10.8 µm, 21.3 µm and 36.4 µm, respectively). Assuming a density of 1.05 g/cm³ (polystyrene), this is a total of 0.163 µg per animal, or about 0.1% of the average mass of an animal. This study demonstrated that Hemimysis ingests microplastics in the field. Because these animals are food sources for a variety of fish species in Lake Michigan, these findings are cause for concern when considering how microplastics may move up the Lake Michigan trophic levels, especially when recent research suggests that microplastics can bind and release harmful chemicals.