Microplastics from the gut of a marine apex predator, the bottlenose dolphin (<i>Tursiops truncatus</i>): Challenges of measurement and first results from South Carolina, USA
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Battaglia, Francesca
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A growing number of studies report exposure of diverse biota to microplastics (<5 mm, MP), however research on MP ingestion at higher trophic levels is limited and presents some unique challenges. The bottlenose dolphin (<i>Tursiops truncatus</i>) is a long-lived apex predator and can be a sensitive gauge for environmental quality within its range. MP ingestion was measured in <i>T. truncatus</i> by analyzing the gut contents of stranded dolphins recovered in South Carolina, USA. A method was developed with features that harmonize with recently published protocols for monitoring MP in cetaceans. The gastrointestinal tract of stranded dolphins was removed, sectioned (forestomach, fundic+pyloric chambers, intestine) and the contents sieved. Potassium hydroxide (1M) was added to samples to eliminate organic material and a density separation using calcium chloride (1.4 g/mL) was applied as needed to samples containing sediment and recalcitrant organic matter. Samples were then filtered, dried, and MP were visually detected under a stereomicroscope with the aid of a hot needle test. MP were found in all animals (N = 7). Total MP load ranged between 123-422 pieces in individuals. Fibers were observed in the highest abundance, and white/clear, black/grey, and blue were the most common color categories observed. No correlation was found between the MP load and total length or stomach contents, however a correlation was found between MP load and intestine contents. MP research in cetaceans is challenging due to their large size, heterogeneous gut contents, and difficulty of acquiring quality samples. Findings from this investigation will aid future studies examining MP in marine apex predators like <i>T. truncatus</i>.