Microplastic pollution in a Philippine protected area: evidence from Siargao Island’s surface waters and Siganus spp.

The Philippines is recognized as a major contributor to global marine plastic pollution; however, information on microplastic contamination within protected coastal ecosystems remains limited. This study assessed the occurrence of microplastics in surface waters and in two rabbitfish species, Siganus fuscescens and Siganus guttatus, from selected coastal sites within the Siargao Island Protected Landscape and Seascape. Surface water samples (20 L per station) and fish specimens (S. fuscescens, n = 80; S. guttatus, n = 22) were collected and examined. Microplastics in both water samples and fish gastrointestinal tracts were extracted using alkaline digestion followed by density separation. Water samples collected from six stations revealed an average concentration of 1000 particles/m3. Most were fibers (95%) and black in color (32%), ranging from 0.01 to 0.10 mm size (26%). The Kruskal–Wallis’s test indicated significant difference in microplastic abundance across sampling stations (p = 0.01185). Additionally, 80 (78.43%) out of 102 examined fish samples contained microplastics. S. fuscescens contained an average of 3.32 particles individual⁻1, while S. guttatus contained 2.76 particles individual⁻1, with a higher frequency of occurrence observed in S. guttatus (95.45%). Microplastics found on the studied fish species were mostly fibers (98.4%), black in color (38%), and in the 0.11–0.20 mm size range (34.65%). It was also noted that with increasing microplastic size, the numbers found in the gastrointestinal tract of the examined fish species decreases significantly. While there was no significant difference in microplastic abundance between species (p = 0.48585), notable differences were observed across sampling sites for S. fuscescens (p = 0.02848). These findings highlight the need for expanded microplastic research in other areas of Siargao, particularly in assessing the potential environmental and health impacts. There is also a need to conduct several measures such as promoting proper waste disposal, reduce plastic consumption, increase public awareness, and encourage innovative solutions to mitigate plastic contamination on the island.