by Brendan Donovan and Sarah Berger

Summary: A novel methodology for studying microplastic contents in C. andromeda jellyfish using light microscopy, electron microscopy, and Raman spectroscopy reveals microplastic presence in specimens is dependent on density and polarity of material.

Microplastics are a growing threat to marine ecosystems, but they remain understudied in no small part due to insufficient means of measuring them. Benthic jellyfish, such as Cassiopeia andromeda, are a good starting point for studying marine ecosystems because they are low on the food chain and live close to the shoreline. This both increases their exposure to microplastics and makes them a potential source of microplastic transportation from the ocean to land via sea birds.

This paper focuses on establishing a protocol for looking at microplastics in fixed Cassiopeia jellyfish. Authors studied interactions with both C1RG dye-stained polyethylene terephthalate (PET) and polypropylene (PP) microplastics. They exposed live jellyfish to microplastic-contaminated water, then removed the jellyfish and stained them. For each exposed jellyfish, they utilized a control.

In order to analyze the interactions that occurred, cLSM and TEM microscopes were used. The dye in the microplastic samples, toluidine blue stain in the jellyfish flesh and chlorophyll within C. andromeda endosymbionts, were used in brightfield microscopy and cLSM to confirm the presence of large PET, but not large PP microplastics in the tissue. Due to the possibility of fragments smaller than what can be observed with a light microscope, a transmission electron microscope was used. This revealed the presence of small PET but not PP pieces.

Because jellyfish caught in the field lack the dyes used in brightfield and cLSM imaging, having a reliable way to detect dyeless plastics is extremely important for the viability of the author’s methodology in future studies. Raman spectroscopy was utilized in order to match the unique chemical signature of various types of microplastics to their identities based on how they absorb and re-emit light. The authors of this paper found that they dyed and undyed PET spectra matched a PET control sample whereas PP exposed individuals matched an unexposed control. These findings allow the authors to conclude that Raman spectroscopy is a viable method to determine the presence of microplastics in C. andromeda.

The authors explain the PET vs PP presence in the jellyfish via density. Because PP is more buoyant (and hydrophobic), it sits at the top of the water, while C. andromeda intakes particles that sink to the substrate, like PET.

Reference

Caldwell, J., Loussert-Fonta, C., Toullec, G., Lyndby, N.H., Haenni, B., Taladriz-Blanco, P., Espiña, B., Rothen-Rutishauser, B., & Petri-Fink, A. (2023). “Correlative Light, Electron Microscopy and Raman Spectroscopy Workflow To Detect and Observe Microplastic Interactions with Whole Jellyfish.” Environmental Science & Technology, 57(16), 6664-72. Doi: 10.1021/acs.est.2c09233