Abstract
Mismanaged plastic waste has resulted in the global accumulation of plastic pollution in the marine environment and consequently, accumulation of microplastics (MP). Some of the most prominent MP types in the marine environment are polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC). Attempts to mitigate this anthropogenic pollutant have resulted in the increased production of biodegradable plastics (biopolymers). However, there is limited knowledge of the effects these can have once ingested. Multiple studies have looked at the effects of ingesting one or two MP types, yet variation in physical and chemical properties of these different plastic types can cause a variety of adverse effects. Therefore, the primary aim of this study was to identify how a range of MP types affect New Zealand triplefin fish health and condition, specifically looking at changes in gut-morphology and oxidative stress. To address this aim, a 28-day feeding experiment exposing triplefins (Forsterygion capito) to either a biodegradable edible film coating (EFC), PE, PS or PVC MP was undertaken. Changes in gut-morphology were examined by measuring villi characteristics such as height, width, and surface area. Further, goblet cell coverage was quantified to understand effects on mucus layer coverage in the gut. Triplefins from all MP diets showed signs of mechanical damage with decreased villus height and width, decreased surface area, and reduced goblet cell abundance however, the magnitude of damage varied dependent on MP type. Ingestion of PVC MP incurred the most mechanical damage as evidenced by a significant reduction in villi surface area. Changes in oxidative stress was addressed by measuring antioxidant enzyme activity and oxidative damage biomarkers in the white muscle. A clear physiological cost of MP ingestion was demonstrated by an increased antioxidant response and subsequent oxidative damage for EFC, PS and PVC treated fish. This was most apparent in PVC treated fish where oxidative damage biomarkers increased more than 7-fold compared to control fish. Triplefins retained relatively good liver condition suggesting resource allocation due to stress. Although the oxidative effects were not reflected in the gut-morphology for EFC, PE and PS MPs, the significant change in oxidative damage highlights the importance of investigating a range of responses. Due to the continual increase in marine plastic pollution, understanding how organisms are directly affected by these pollutants can providing insight into which plastics may be more problematic and influence future management.