Characteristics of mangrove ecosystems in Weda Bay: Environment, Vegetation, and Aboveground Carbon Stocks

Abstract

Weda Bay is one of the largest mangrove habitat in North Maluku and one of mega-biodiversity spots in Indonesia. However, data and information of mangrove vegetation and its ecosystem services particularly carbon stocks were limited. Mangroves were mapped using GIS-remote sensing and vegetation were sampled using transects in five sites of mangroves across Weda Bay. Tansects were extended from seaward to landward to cover all vegetation variation and hydrodynamic conditions. Environmental data (water and substrate): temperature, pH, Dissolved Oxygen (DO), particle size of sediment, and nutrient (phosphate and nitrate) were collected. The objective is to identify characteristics of mangrove landscape and vegetation, it is environment, and it ecosystem services in term of aboveground carbon stocks. The study showed that the characteristics of landscape and vegetation of mangrove varied among hydrodynamic conditions. The bay is important habitat for 8.5% (17 species) of mangrove species in Indonesia. Rhizophora apiculata and Bruguiera gymnorrhiza were the most dominant mangroves. The environmental conditions of Weda Bay particularly northern part of the bay were suitable for mangrove growth. Substrate of mangrove did not vary significantly with distance from the seaward which was mainly dominated by mud and clay (3.9 - 63 μm). Mean water temperature in the mangrove area was 29.3°C, salinity 34.1 psu, mean water suspension was 46 mg l−1, mean dissolved oxygen was 3.2 mg l−1, and water current was 10 m s−1. Aboveground carbon stock was considerable (752 ± 17.6 Mg C ha−1). Change in aboveground carbon stocks over the distance from the seaward edge to landward edge was not significantly different. In contrast, aboveground carbon stocks varied among hydrodynamic conditions: estuarine, delta, and riverine mangroves. Delta mangrove contained the highest carbon stock (993 ± 27.7 Mg C ha−1), followed by estuarine mangroves (645 ± 12.2 Mg C ha−1) and riverine mangroves (244 ± 8.6 Mg C ha−1). However, this ecosystem faced some threats such as mangrove extraction and plastic pollution. Better mangrove management e.g. reducing mangrove extraction and pollution are required to protect the functions and ecosystem services of mangroves. In addition, conserving mangrove forests will allow the government to achieve blue economy goals and to mitigate climate change through carbon sequestration.