Evaluating microplastic pollution across various size classes in tropical remote islands using the ascidian community

Recent developments in rapidly developing archipelagic nations like Indonesia have led to encroachment on remote islands and an increase in pollution, particularly from microplastics. Due to their remoteness and limited resources, there is a need for versatile bioindicators for microplastics. It has been hypothesized that ascidians can serve as effective bioindicators because of their filter-feeding mechanism. Although research on microplastics in ascidians has been conducted in temperate waters, information regarding this issue in tropical environments remains limited. This study evaluated the ascidian community represented by the species Botrylloides crystallinus, Clavelina moluccensis, Didemnoides patella, and Leptoclinides reticulatus, sampled from four tropical islands with distances of 17.48-117.62 km from the main islands. Microplastic contents varied significantly according to differences in species (p = 0.001) and islands (p = 0.001). These ascidian species can serve as proxies for fiber and transparent microplastics. For microplastics less than 300 µm, the order of the ascidian species in terms of microplastic accumulation was as follows: D. patella > L. reticulatus > C. moluccensis > B. crystallinus. The polymer analysis revealed that polyethylene terephthalate (PET) is especially prevalent in C. moluccensis, D. patella, and L. reticulatus. In contrast, the polymer composition in B. crystallinus was predominantly polypropylene (PP) (67%), followed by PET (33%). As efficient filter-feeders and being widely distributed, ascidians present fundamental opportunities for the versatile, reliable, and low-cost environmental monitoring of microplastics, in particular, tropical remote islands.