Abstract
Of the suite of anthropogenic impacts facing marine ecosystems, plastic pollution poses one of the largest threats at present. The excessive production and subsequent mismanagement of single-use plastics has resulted in an estimated 14 million tons of marine plastic debris entering our oceans annually, a trend that does not appear to be decelerating. Much of this plastic debris is in the form of microplastics (<5mm), which are easily ingested, both intentionally and unintentionally, and have the potential to move through trophic levels. Microplastics in the marine environment are rapidly colonised by a microbial community, forming a biofilm. This biofilm has been shown to be unique from the surrounding seawater and often contains infochemical-producing species associated with regular food sources. This study investigates whether juvenile Seriola lalandi (yellowtail kingfish) are more attracted to biofouled plastics and whether there is an additional fitness cost associated with consumption of biofouled plastics compared with clean plastic. Polystyrene sheets and polyethylene microbeads were exposed to unfiltered seawater for a month to cultivate a microbial community on the surface. Olfactory behavioural response and ingestion experiments were used to determine if juvenile kingfish had a preference to biofouled plastic over clean plastic. Acute feeding (1-2 days) experiments followed by intermittent-flow respirometry and oxidative stress analysis were used to determine if a fitness cost was incurred due to the ingestion of biofouled microplastics compared to clean. Results demonstrated that S. lalandi ingested fewer biofouled microplastic particles compared to clean plastics, but this likely attributed to bioavailability of the biofouled microplastics. Interestingly, S. lalandi displayed an increased olfactory response to the biofilm odour than clean plastic or control odour. Moreover, fish exposed to biofouled microplastic were found to have a wider aerobic scope than those exposed to clean plastics, but narrower than the control (no plastics) treatment. Similarly, antioxidant enzyme activity (superoxide dismutase, catalase, and glutathione peroxidase) and lipid peroxidation levels in fish exposed to biofouled plastics were higher than the control, but still lower than those exposed to clean plastics. The findings of this study highlight that while the biofilm on microplastics may be rendering them less accessible in the water column, there is still some attraction and subsequent cost to fitness incurred from ingestion in yellowtail kingfish. Due to the transferable and accumulative nature of microplastics, these findings have implications for taxa throughout the trophic levels, such disease transfer and bioaccumulation, and may also pose a risk on human health via seafood consumption.