Seagrass rehabilitation in Thousand Islands, Jakarta: step to restore

Seagrass plays an essential role in coastal areas with ecological functions as a marine habitat, sediment trap, sediment stabilizer, nutrients filter, and dampen current. Fisheries and tourism are the seagrass ecosystem services that are the primary community livelihood in Thousand Island. However, seagrass condition has decreased in the last decade, influenced by coastal development, mass tourism, and climate change. This study aims to assessed the seagrass status and identify the threat in the last decade. Seagrass coverage was assessed in 2007 and 2018 using plot transect, and then seagrass threats were documented and collected from research articles, manuscripts, proceedings, and unpublished reports. Seagrass coverage has significantly decreased on Thousand Islands. Seagrass threats include pollution, reclamation, vessel activities, mass tourism, coastal development, climate change, and biotic factors (macroalgae and epiphyte coverage). The threats impact seagrass conditions, such as species diversity, area, and ecosystem services. Rehabilitation is needed to recover seagrass conditions using a direct or indirect approach. These findings recommend that managers should arrange the seagrass rehabilitation action plan to minimize seagrass degradation.


Introduction
Seagrasses are marine plants with a wide distribution from topical to subtropic region [1-3]. Indonesia had a seagrass area of about 293,464 hectares in 2018 and reported 16 species [4]. Seagrass plays an essential role in a coastal area such as marine habitat [5], sediment trap, sediment stabilizer, nutrients filter, and dampen current [6,7]. Furthermore, seagrasses provide ecosystem services such as provisioning (nursery and feeding grounds for fish, food), regulating (coastal protection), cultural (recreation, aesthetic, and spiritual), and supporting services (biodiversity, primary production) [8][9][10].
Thousand Islands are one of the seagrass distribution areas in Indonesia. Fisheries and tourism are the primary community livelihood influenced by population growth [17,18]. Land-use becomes driven based on the coastal community livelihood [19]. Accordingly, tourism is the alternative income. These activities can threaten the seagrass's existence, including the condition and area. The impact of disturbances is the loss of seagrass ecosystem services [10]. This study will assess seagrass condition, identify and evaluate the seagrass condition decline, and describe the mitigation.

Material and methods
This study was conducted in 2018 in Thousand Islands, including Pari Island, Tidung Island, Payung Island, Pramuka Island, Panggang Island, Harapan Island, Kelapa Island, and Panjang Island (figure 1). Seagrass coverage assessment used the plot transect method (50x50 cm) from the beach to slope with an interval of 10% each plot by snorkelling. Seagrass coverage of 2007 was used to compare the seagrass condition between 2018 collected from E Estradivari, E Setyawan and Yusri [20]. Seagrass threats that affected seagrass conditions were documented directly in the field and identified from scientific articles and unpublish reports. Threat mitigation will be evaluated using the DAPSIR framework, a tool to   [21]. Seagrass threats are divided into drivers and activities [22]. The driver is a trigger; the disturbance and activities are the threat that arises by the driver. Pressure is affected by the activities (threats), the state represents environmental change by the stressor, whereas impacts are consequences of environmental changes. Responses mitigate socio-economic problems and manage, detect, prevent, and restore the seagrass meadow.
In 2018, the highest coverage was Panggang Island, while the lowest was Kelapa Island. In 2007, the highest coverage was Panggang Island, and the lowest was Tidung and Payung Island. Seagrass coverage has decreased from 2007 to 2018 for Pari Island, Pramuka Island, Panggang Island, Harapan   Island, Kelapa Island, Panjang Island. However, it increased for Tidung Island and Payung Island (figure 3). Seagrass coverage variation was caused by island geomorphology, water quality, coastal activities, and seagrass species composition [23].
Community residence influenced the nutrient enrichment in sediment [15,24]. Furthermore, the type of substrate and sediment characteristics trigger the seagrass species composition and coverage. Sediment size can decrease the biomass, while sediment characteristics only influence leaf morphology [25]. Lamit and Tanaka [26] reported that seagrass with silt and clay sediment had the highest biomass and leaf length. In some cases, seagrass grew longer on the sandy than rocky substrate [27]. Kaewsrikhaw and Prathep [28] showed that leaf length, width and petiole length were more significant on the sand substrate.

DAPSIR analysis for seagrass rehabilitation
Three main drivers had been identified with local activities, namely population growth, coastal development, and climate change. The Pressure, state, and impact are represented in figure 6. The activities and pressures harm the seagrass meadow. Coastal development that is disposed of human activities is related to population growth. For the last decade, population growth increased in Thousand Island, changing the land use and income needed (figure 4). Mass tourism occurred in Thousand Island   5). Increasing population will enhance human activities in the coastal area. The anthropology activities increase side-by-side with population enhancement: seaweed culture, mariculture, fishing, boat fishing, and boat anchoring. Activities of coastal development are reclamation, sand dredging, mass tourism ( Figure 5), conversion into the residence, and domestic sewage. Climate change impacts sea-level rise, so it constructs breakwater to mitigate this problem in the small island. These disturbances involve multiple stressors for seagrass meadows. For example, mass tourism, residence, and domestic sewage led to nutrient enrichment, and reclamation caused land-use changes. Nutrient enrichment cause increasing algal growth, decreasing seagrass productivity, and change ecosystem functioning. Furthermore, the activities and pressure will impact water quality change, habitat loss, and loss of ecosystem services.
Based on the DAPSIR framework, rehabilitation is a possible response to reduce and minimize the seagrass meadow disturbance. Direct and indirect approaches separate to conduct rehabilitation action. Direct rehabilitation would be done by replanting or preserving seagrass such as transplantation, environmental clean-ups, water quality monitoring, and increasing research monitoring. Managers could lead indirect rehabilitation to minimize the disturbance by arranging the protected area, education and awareness, regulatory and policy, and community capacity development. The DAPSIR framework recommends monitoring water quality after the pandemic. Education, awareness, and capacity development for the community is necessary action to manage the disturbance. A regulatory and policy is needed to manage the mass tourism in Thousand Island.

Conclusion
In conclusion, seagrass meadow decreased in Thousand Island and will continue now and in the future if there is no action to mitigate the disturbance. Population growth, coastal development, and climate changes are identified as a driver of seagrass decline. Coastal development cannot ignore because it relates to human livelihood and income. This result recommends that managers should arrange the seagrass rehabilitation action plan to minimize seagrass degradation. A transdisciplinary approach is needed to make a policy for seagrass conservation.