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Master's Monday Blog - Microplastic ingestion in deep-sea fauna
Hello! My name is Ryan Bos and I am a Masters Candidate in Marine Science at Nova Southeastern University. Currently, I am doing an appraisal of microplastic ingestion in deep-pelagic fishes and crustaceans in the Gulf of Mexico (GoM) with Dr. Tamara Frank and Dr. Tracey Sutton.
Each day, nearly every person on Earth uses plastic items. It is all around us. It is in our clothes, cosmetics, vehicles, and if you carry a smartphone around with you, odds are that it has a plastic component. As humans, we manufacture and use plastic at alarming rates, and take it for granted. Plastic production is projected to increase with increases in the human population, yet plastic pollution is already infesting our oceans and will continue to persist for hundreds to thousands of years because of plastic’s inherent resiliency. I want to put the plastic crisis we are facing into perspective. There are ~34,000 extant species of fishes, with the most abundant genus of fish, Cyclothone, consisting of 13 species. These 13 species comprise an estimated 1,000,000,000,000,000 individuals. By the year 2050, the number of fishes in our oceans will be equal to the number of plastics. What is alarming about this statistic other than the number of fishes and plastic particles being equal? There are 33,987 more species that contribute to the total number of individual fishes in our oceans, and most of these plastic particles cannot be seen with the naked eye!
Deep-sea micronekton are integral parts of pelagic ecosystems, as they serve as key intermediates in oceanic food webs, contribute significantly to overall abundance and biomass, make substantial contributions to carbon flux, and serve as links between shallow and deep-pelagic waters. Thus, they are exemplary targets for microplastic studies.
Microplastics, as the name implies are small pieces of plastic that range in size from 1 µm - 5 mm that are categorized as being a fragment, film, spherule, foam, or fiber. Once ingested, an animal may experience pseudosatiation (the feeling that they are full but have not received any nutrition), obstruction of feeding appendages, decreased reproductive fitness, and death. Pictures of these categories are portrayed below, excluding foams, of which none were found. To determine if a particle is a piece of plastic, we used the ‘hot-needle,’ or ‘burn-test.’ It is a rapid and cost-effective technique for plastic determination. When plastic is probed with a hot-needle it either leaves a burn mark, melts, or in the case of fibers, curls up and is repelled by the needle.
Regrettably, there are no previous estimates of microplastic ingestion by deep-sea fishes and crustaceans in the GoM, despite the commercial importance of this ecosystem. A total of 723 individuals (316 fishes and 407 crustaceans) from a combined 48 species and 11 families were dissected and visually inspected for microplastics. Plastic items were found in both fishes and crustaceans. A total of 263 microplastics were identified, with crustaceans and fishes consuming 146 and 117 microplastics, respectively. Total micronektonic crustacean and fish plastic ingestion was approximately 31 % (n = 190/618) while 16 % of euphausiids (n = 96) and 11 % of crabs (n = 9) contained at least one piece of plastic.
Interestingly, there were apparent differences in type and number of microplastics ingested by fishes and crustaceans, with crustaceans ingesting predominantly fibers, as opposed to fishes, which consumed a substantial number of fragments. Further, vertically migrating taxa of fishes contained more microplastics than non-migratory taxa, but the opposite trend was observed in crustaceans. In fact, non-migratory crustaceans consumed significantly more plastic than all other taxa. Curiously, the non-migratory crustacean taxon with the highest frequency of plastic ingestion, the Benthesicymidae, are all habitual consumers of marine snow. That, coupled with the smaller size classes of microplastics found in this study, may be indicative of marine snow’s importance in biogeochemical cycling of microplastics.
As commercial fishing efforts scale up to harvest the deeper layers of the ocean, these results will be important for assessing risk associated with consumption or indirect consumption by the deep-sea biota. Importantly, larger deep-pelagic crustaceans appeared to have more plastic in them than small conspecifics, but size was not indicative of plastic ingestion by fishes, and no significance was observed for either group of animals.
Empirical cumulative distribution functions of carapace length of crustaceans (A) and standard length of fishes (B) that did and did not ingest microplastics. Two separate (one for crustaceans, one for fishes) Kolmogorov-Smirnov tests generated p-values of 0.09 and 0.924, respectively.
Deep-sea food webs are largely understudied relative to coastal studies, but results to date suggest a great deal of complexity. Our data reveal that more scrutiny should be given to deep-sea ecosystems with regards to plastic ingestion. These food webs are understudied because of the enormous expense and difficulty of obtaining deep-sea samples, highlighting the importance of projects such as DEEPEND.
A brilliant new way to aid in the fight against plastic by doing laundry: https://coraball.com/
A resource for learning more about plastic: https://marinedebris.noaa.gov/info/plastic.html
An article about how plastic is killing our oceans, by Wendy Lipscomb from the website 'It's a fish thing': https://www.itsafishthing.com/plastic-in-the-ocean/