When dolphins splash about to corral baitfish in the shallows of Sarasota Bay, the result isn't just a few pinfish or toadfish in their stomachs — they also ingest some of the roughly 10,000 microplastics daily, researchers have concluded.
"Microplastics and plasticizers in these animals and their ecosystems has begun to raise concerns about threats to them," Randy Wells, then-director of the Sarasota Dolphin Research Program wrote with other researchers in a paper published this summer in the journal Marine Mammal Science. "Our results clearly indicate (the) predominant microplastic contamination present in Sarasota Bay."
Microplastics can make dolphins feel full when they are still in need of nourishment, scratch or damage the inside of their digestive tract, and cause inflammation and cell damage. Studies have also shown that a number of super-small shards of plastics leach hazardous chemicals.
Researchers said wastewater from washing machines are likely sources of those particles in Sarasota Bay. Other research has found many microplastics are too small to be screened out by most wastewater plants before the treated water makes its way back into the system.
The microfibers in the dolphins were largely the same shape, size and mix of colors as in the pinfish and toadfish, Nine other baitfish in Sarasota Bay known to be common food for the bottlenose were found to have similar size, shape and color as microplastics in earlier studies.
Much of that earlier research also found tiny pieces of plastic foam, like that used in Styrofoam food containers, in Sarasota Bay dolphins, while the newer study found mostly clothing-type fibers.
They also say the change from the prevalence of tiny pieces of plastic foam to those from clothing and textiles might be connected to Sarasota's 2020 restrictions on using Styrofoam food containers at city-owned properties.
Limitations involved in the study, such as it being unethical to feed dolphins pinfish they knew were loaded with microplastics so they could have controlled tests and results, left enough statistical open ends that researches could not say, without doubt, that microplastics they discovered in dolphins came from their diet.
It is possible the mammals breathed them in through the air or ingested them from the water taken in while feeding.
A dozen researchers working with Wells, who ran the dolphin research program from the Brookfield Zoo Chicago but housed at Mote Marine Laboratory and Aquarium, agreed their findings were rather strong all the same.
"The extensive overlap observed in particle shapes, colors, sizes, and polymers across species provides researchers with reason to suspect that (food chain) transfer may be occurring in the Sarasota Bay ecosystem," the researchers wrote.
"This study highlights the need for further research on how microplastics travel through marine food webs and the health implications of microplastic ingestion."
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