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Keberlangsungan ekosistem mangrove merupakan aspek penting karena berkaitan dengan pengurangan atau penambahan akumulasi sedimen seperti proses abrasi dan akresi. Mangrove di pesisir Tanjung Batu telah mengalami penurunan sejak 2001-2010 yang disebabkan oleh aktivitas masyarakat seperti penebangan pohon, pembukaan lahan untuk tambak dan perkebunan kelapa sawit. Penelitian ini bertujuan mengestimasi laju akumulasi sedimen mangrove di Tanjung Batu. Penelitian dilakukan pada bulan Februari-Juli 2018. Pengambilan sampel dilakukan pada 3 stasiun meliputi identifikasi jenis mangrove, pengukuran Diameter at Breast Height (DBH) mangrove dan pengambilan sedimen corring menggunakan pipa stainless. Sampel sedimen dipotong berdasarkan interval 5 cm (kedalaman 0-15 cm), dan interval 2 cm (kedalaman 48-50 cm) yang digunakan sebagai Pb-210 supported (Stasiun 1 dan 3). Stasiun 5 dipotong dengan interval 4, 6 dan 8 cm (kedalaman 1-50 cm). Analisis sampel menggunakan alpha spektrometer dengan radioisotop Pb-210. Penentuan umur sedimen dan laju akumulasi sedimen menggunakan model Constant Rates of Supply (CRS). Hasil menunjukkan bahwa laju akumulasi sedimen selama 20 tahun terakhir (1998-2018) berkisar 0,09-0,20 g cm-2 tahun-1. Laju akumulasi tertinggi adalah Stasiun 1 yang merupakan lokasi dengan umur sedimen paling tua dan didominasi mangrove dengan DBH > 5 cm, sedangkan laju akumulasi terendah adalah Stasiun 5 yang memiliki umur sedimen paling muda dan didominasi mangrove dengan DBH < 5 cm.

Heavy metal pollution is one of serious problem for tropical mangrove ecosystem. Heavy metals can decrease the quality of a waters. The decreasing in water quality can caused by pollutants such as heavy metals with high concentrations greatly affects the aquatic environment, especially living organisms. The aimed of study is to determine the accumulation level of heavy metals such as Al, Cu, Pb, As, Ni, Cr, Ti, Mn, dan Fe, in root, leaves and stem of E. acoroides. The sampling was carried out in the northern and southern parts of Tunda Island, in March 2015. The method used for seagrass destruction is 6 mL 65% HNO3 and mL H2O2 30%, sediment destruction using Milestone Start D microwave labstation. and using ICP-OES (Inductive Coupled Plasma-Optical Emission Spectrometry) Thermo Scientific iCAP 700 Series. The result show that, the Al, was the dominant heavy metals observed both in sea water and sediment surrounding the observed sea grass areas. Similar result was also observed for seagrass. The dominant sediment grain size absorbing heavy metals is silt-clay because it has more organic matter to control the binding of heavy metals. Heavy metal bioaccumulation is predominant in seagrass leaves and stems due to heavy metal entry into seagrass, substance storage tissue, and seagrass characteristics that are completely submerged in water. Seagrass meadow ecosystem in Tunda Island has been contaminated by several heavy metals.

Coral is one of marine organisms that can accumulate heavy metals such as Pb in its skeleton. The purpose of this study was to determine the concentration of heavy metals Pb in growth bands of coral P. lutea at windward and leeward regions of Tunda Island. The results showed that P. lutea accumulated heavy metals Pb in their growth bands. The results of Pb concentrations in windward region were in range of 6.17-14.76 mg kg-1/year, with the average concentration rate of 9.69 mg kg-1/year. Meanwhile, in leeward region, the Pb concentrations were in range of 8.37-17.66 mg kg-1/year whith the average concentration rate of 13.33 mg kg-1/year. The Pb concentration in leeward regions was higher than in the windward region. Keywords: heavy metal Pb, coral P. lutea, Tunda Island