Kontaminasi Mikroplastik pada Air, Sedimen, dan Polycarpa aurata (Asidian) di Ekosistem Terumbu Karang Pantai Malalayang Kota Manado

Abstract

Mikroplastik merupakan salah satu kontaminan yang mengancam ekosistem terumbu karang. Perairan Kota Manado, Sulawesi Utara, termasuk dalam kawasan Segitiga Terumbu Karang yang merupakan pusat keanekaragaman hayati laut dunia, sehingga penilaian kontaminasi mikroplastik pada ekosistem terumbu karang di wilayah ini memiliki urgensi tersendiri. Kajian potensi organisme penyaring di ekosistem terumbu karang sebagai agen biomonitor kontaminasi mikroplastik juga masih terbatas. Penelitian ini bertujuan untuk mendeskripsikan kondisi tutupan bentik, mengidentifikasi karakteristik dan kelimpahan mikroplastik di ekosistem terumbu karang. Penelitian dilaksanakan pada November 2025 hingga April 2026 di dua stasiun yang mewakili area dekat dan jauh dari sungai. Tutupan bentik diamati dengan metode Underwater Photo Transect. Sampel mikroplastik diambil dari air permukaan, sedimen, dan jaringan asidian P. aurata dengan lima ulangan abiotik dan tiga spesimen asidian per stasiun. Mikroplastik diekstraksi melalui proses digesti (H2O2 30% atau KOH 10%) dan pemisahan densitas (ZnCl2 1,7 g mL?¹). Mikroplastik diidentifikasi berdasarkan bentuk, warna, ukuran dan polimer. Tutupan karang keras 9% di stasiun Dekat Sungai dan 27% di stasiun Jauh Sungai. Stasiun Dekat Sungai memiliki tutupan karang mati beralga (30%) dan makroalga (25%) serta tanpa Acropora, sedangkan Jauh Sungai memiliki makroalga lebih rendah (14%) dan Acropora hadir (7%). Karang masif merupakan bentuk pertumbuhan dengan tutupan terbesar di kedua stasiun. Kelimpahan mikroplastik pada sedimen lebih tinggi di Dekat Sungai (390 ± 74 n kg?¹ bk) dibandingkan Jauh Sungai (118 ± 32 n kg?¹ bk), sedangkan pada air permukaan relatif setara (838 ± 191 dan 790 ± 317 n m?³). Asidian P. aurata mengakumulasi mikroplastik pada kedua stasiun, dengan nilai lebih tinggi di Dekat Sungai (11,17 ± 3,21 n ind?¹) daripada Jauh Sungai (7,50 ± 2,31 n ind?¹). Partikel pada seluruh matriks didominasi bentuk fiber dan warna biru. Polimer yang teridentifikasi didominasi karet sintetik dan poliester, yang mengarah pada sumber domestik, perikanan, dan transportasi darat. Kemiripan komposisi partikel tertinggi terdapat pada pasangan air permukaan dan sedimen, diikuti sedimen dan asidian, sesuai dengan jalur perpindahan dari air permukaan ke sedimen lalu ke jaringan asidian. Hasil ini menempatkan mikroplastik sebagai kontaminasi asal daratan yang masuk melalui limpasan sungai sekaligus mendokumentasikan potensi P. aurata sebagai biomonitor paparan mikroplastik di ekosistem terumbu karang.

Microplastics are among the contaminants threatening coral reef ecosystems. The waters of Manado City, North Sulawesi, lie within the Coral Triangle, the global centre of marine biodiversity, making the assessment of microplastic contamination in coral reef ecosystems in this region particularly pressing. Studies on the potential of filter-feeding organisms in coral reef ecosystems as biomonitoring agents for microplastic contamination also remain limited. This study aimed to describe benthic cover conditions and to identify the characteristics and abundance of microplastics in the coral reef ecosystem. The research was conducted from November 2025 to April 2026 at two stations representing areas near to and far from a river. Benthic cover was assessed using the Underwater Photo Transect method. Microplastic samples were collected from surface water, sediment, and the tissue of the ascidian P. aurata, with five abiotic replicates and three ascidian specimens per station. Microplastics were extracted through digestion (30% H2O2 or 10% KOH) and density separation (ZnCl2, 1.7 g mL?¹), and were identified based on shape, colour, size, and polymer type. Hard coral cover was 9% at the Near- River station and 27% at the Far-River station. The Near-River station showed higher cover of dead coral with algae (30%) and macroalgae (25%) and an absence of Acropora, whereas the Far-River station showed lower macroalgal cover (14%) and the presence of Acropora (7%). Massive corals were the growth form with the greatest cover at both stations. Microplastic abundance in sediment was higher at the Near-River station (390 ± 74 n kg?¹ dw) than at the Far-River station (118 ± 32 n kg?¹ dw), whereas abundances in surface water were comparable between stations (838 ± 191 and 790 ± 317 n m?³). The ascidian P. aurata accumulated microplastics at both stations, with higher values at the Near-River station (11.17 ± 3.21 n ind?¹) than at the Far-River station (7.50 ± 2.31 n ind?¹). Particles across all matrices were dominated by fibres and by blue-coloured items. The identified polymers were dominated by synthetic rubber and polyester, pointing to domestic, fisheries, and land-transport sources. The highest similarity in particle composition was found between the surface water-sediment pair, followed by the sediment-ascidian pair, consistent with a transfer pathway from surface water to sediment and subsequently into ascidian tissue. These results indicate microplastics as land-derived contamination entering through river runoff, and document the potential of P. aurata as a biomonitor of microplastic exposure in coral reef ecosystems.