Microplastics, Oysters, and the Indian River Lagoon – Final Report to IRL NEP, March 2021

UCF and partners initiated microplastics (MP) sampling in the Indian River Lagoon in March 2019, with monthly sampling of water samples at 35 locations, and quarterly sampling of oysters through February 2020. Additionally, the ability of the eastern oyster Crassostrea virginica to excrete microplastics was examined. Forty-four percent of water samples contained MP and there was an overall mean (± S.E.) of 1.47 (± 0.05) MP per liter of lagoon water (range: 0 – 25 MP). Fibers were the dominant MP type of MP (95.6%) and no nurdles or microbeads were collected. The dominant color of MP in water was clear followed by light blue, black and dark/royal blue. The mean length of MP was 1.94 (± 0.13) mm with a range in length from 0.1 to 30 mm. Water from the southern regions of the lagoon contained significantly higher abundances of MP and these MP were smaller in length. A significant difference in MP abundance across sampling months was also detected. Samples collected during April, May, June, October, December and February samples had significantly more MP than all other months. Oyster sampling took place in May, August, and November 2019, and February 2020. Overall, 70% of 1440 oysters contained MP. A total of 3181 MP was found in oysters. Lagoon-wide, the mean abundance of MP in oysters was 2.26 (± 0.08), and mean density per gram tissue weight was 2.43 (± 0.26) MP. The mean length of MP was 2.79 (± 0.06) mm. Fibers dominated collections (95.0%) and black, clear and dark blue were the dominant colors. Smaller oysters (\u3c 35 mm) contained higher densities of MP per gram tissue weight than adults and contained larger MP. Oysters from the southern IRL had more MP than other regions, but there was no difference in MP length between locations. Experimental trials to examine MP in oyster biodeposits (feces + pseudofeces) were conducted from 15 July through 18 July 2019. MP were present in both feces and pseudofeces from both small and adult oysters. Overall, 67% of oysters produced biodeposits that contained MP. MP ranged in length from 0.05 - 20 mm in pseudofeces and 0.05 - 6 mm in feces. Mean length of MP in pseudofeces was 1.73 (± 0.16), and 1.46 (± 0.08) mm in feces. Fibers accounted for 88.3% of MPs found in biodeposits, and black MPs were the most abundant color. MPs in biodeposits from small oysters were significantly larger than those in adult biodeposits by an average of 1.07 mm. Oysters had a mean MP egestion efficiency of 62.1%, and 32% of oysters were able to egest all MP from their tissues during the 2-h trials. There was no egestion efficiency difference among IRL regions. MP egestion efficiency decreased significantly with increasing oyster shell height and tissue mass; AIC model selection revealed tissue mass was best at predicting MP egestion efficiency in C. virginica. Egestion efficiency decreased by 0.8% for every 1-gram increase in tissue weight. Overall, results indicated that oysters excreted at a rate of approximately 1 MP per 1 hour through feces, and 1 MP per 2 hours through pseudofeces