Impact of Coastal Reclamation on Seagrass Habitat in Palu Bay, Central Sulawesi, Indonesia

Coastal development by conducting reclamation for various uses, for example port construction and operations, is a growing threat to coastal ecosystems including seagrass meadows. For several decades, reclamation for coastal development in Palu Bay has included port construction or extension of single-purpose privately owned port facilities as well as public shipping ports. In addition, reclamation was carried out to provide land for the construction of hotels, housing, recreational areas and coastal protection. The majority of private port terminals are owned by mining companies exporting rock and aggregate from around Palu Bay. There are many quarries in the mountains along the western coast of Palu Bay, and alluvial materials around several rivers along the eastern shore are also exploited. The purpose of this study was to analyse the impact of reclamation on seagrass habitat in Palu Bay, especially the private ports, which the dominant reclamation purposes conducted in this area. This study found about 66 ports around Palu Bay, the majority privately owned by mining companies operating in Palu City and Donggala Regency. The effects of reclamation include reduced seagrass habitat and decreased water quality.


Introduction
Seagrass beds in Indonesia are threatened by various anthropogenic activities, especially the development of coastal areas and sedimentation from deforestation, while sand mining and seaweed cultivation are also major threats in central part of Indonesia [1].Reclamation for coastal development is one of the threats to seagrass beds in many parts of the world [2], including port development [3].Port development can be a threat to coastal ecosystems because, in addition to other impacts, both during construction and port operations, it generally entails the in-filling of coastal waters and/or dredging and can degrade or destroy potentially valuable habitat such as seagrass meadows, coral reefs and mangrove forests [4][5][6].
The coastal lands around Palu Bay comprise areas within Palu City and within Donggala Regency in the province of Central Sulawesi, Indonesia, while the waters of the bay to the high tide line are under provincial jurisdiction.Coastal ecosystems around Palu Bay are exposed to a range of anthropogenic activities such as coastal reclamation to extend the land area available for development along the coast, IOP Publishing doi:10.1088/1755-1315/1253/1/012106 2 sand and aggregate mining, domestic and industrial waste disposal, and from a range of public utilities and other aspects of development [7].Coastal reclamation projects around Palu Bay have been undertaken for many reasons, including to provide land for housing development, hotels, recreational areas including the promenade areas called anjungan, and ports.These ports include public ports and harbours as well as special terminals for use by specific organisations such as private sector companies.Moreover, based on manual measurements on Google Maps 2022, reclamation for housing development on the coast of Tondo Village is approximately 700 meters along the coastline.
Palu Bay is a busy sea area, with several active ports and a relatively high density of shipping and other marine traffic [8].According to an online media outlet (Portalsulawesi.idon 23 rd February 2023), there were six special terminals with the Terminal Khusus (Tersus) classification and 54 classified as Terminal untuk Kepentingan Sendiri (TUKS) spread around the Palu Bay coast.Many of the special terminals around Palu Bay that are classified as TUKS are private terminals owned and operated by aggregate mining companies with quarries in Palu City and Donggala Regency.Some of these ports were built without permission and operate illegally [9].Mining activities have expanded greatly since around 2014.
The proliferation of reclamation on the coast of Palu Bay is a phenomenon that urgently requires analysis, in particular with regard to the impact of these reclamations on the environment.In particular, there is a lack of data on the impact of reclamation on seagrass habitat in Palu Bay.The high number of TUKS terminals owned by aggregate mining companies reflects the similarly high number of mining/quarrying companies operating in the Palu Bay coastal area and hinterland.On 13 th February 2023, another online media outlet (Metro Sulawesi) reported that in a Hearing Meeting (RDP) held in May 2022, the Palu City Environment Service (DLH) had stated that there were around 42 active aggregate mining companies in the Palu City area alone.Meanwhile, according to [10], there were 36 mining companies licensed to quarry sand, aggregate or rock in Donggala Regency, some in the mountains and hills and others in or along the rivers flowing into Palu Bay.On 13 th February 2023, an online media outlet [11] stated that the aggregate and other quarried products were mostly shipped to Kalimantan, Papua, and other parts of Central Sulawesi.
In view of the provisions of Regional Regulation Number 16 of 2011 concerning the Palu City Spatial Plan (RTRW) for 2010-2030 article 42 paragraph 1, the presence of mining in Palu City is truly ironic because some of the areas being mined or quarried are designated as areas prone to natural disasters including earthquakes and landslides as well as tidal waves and tsunamis.Furthermore, article 43 paragraph 2 states that certain areas in Ulujadi District are Geological Protected Areas because they are on or traversed by active fault zones and designated as Geological Natural Disaster Prone Areas.
This study was conducted to analyze the impact of reclamation on seagrass habitat, especially reclamation carried out by mining companies to build special ports because there has been a massive increase in their number and they are now the predominant type of port in the bay.These mining companies each build their own port(s) to enable them to load and ship their commodities, mostly to other regions of Indonesia.The information obtained from this study is expected to provide a scientific basis for integrated management of Palu Bay coastal ecosystems.

Study site and material
This study was conducted in the coastal areas around Palu Bay (Figure 1), Central Sulawesi Province, Indonesia.This study used satellite data consisting a Landsat 7 satellite imagery acquisition from 2012 and a Landsat 8 satellite imagery acquisition from 2022.Secondary data has also been used in this research such as national and local government regulations, and on-line news reports.Data from previous studies have also been used such as water quality data in Palu Bay.

Changes in the area of Palu Bay waters due to reclamation on the coast of Palu Bay
The result of band composite of both landsat 7 and landsat 8 satellite image are shown in Figure 2. Furthermore, digitized results on both images are shown in Figure 3. Image data processing showed that the coverage area of Palu Bay waters in 2012 and 2022 was around 19,907.37 Ha and 19,900.89Ha, respectively.This indicates that there has been a decrease in the area of Palu Bay waters by 6.48 Ha.This change in sea area is assumed to be a result of coastal reclamation and is assumed to be seagrass habitat loss.This condition is also happened in Sungai Pulai estuary, Malaysia where coastal reclamation is suggested as the main cause of loss or seagrass meadows degradation in this area [5].In addition, coastal ecosystems in the coastal zone of Cina were also at high risk due to tidal flat reclamation and sea-filling, mainly cause by industrial construction and agricultural development for a decade [13].

Figure 1. Map of Palu Bay
One of the causes of the decline in the coverage area of Palu Bay waters is the massive reclamation activities carried out along Palu Bay for various purpose, such as tourism and economic area, housing development, hotels, especially reclamation for the construction of private ports by rock mining companies.Many sites around Palu Bay have been in-filled to build port structures, especially the private terminals used to load and export materials mined or quarried from the mountains or riverbeds (Figure 4).The majority of these terminals have been built along the west coast of Palu Bay (western zone).The terminals with the TUKS designation comprise facilities such as jetties or harbours for the barges and tug boats to tie up and for loading the barges, as well as (often extensive) areas for piling up and storing the quarried materials (rock, sand and aggregate) and sometimes also have facilities for crushing rock to produce certain classes of aggregate.The sites of the private terminals and other ports or jetties around Palu Bay are shown in Figure 5.Some seagrass meadows experienced large scale changes, and coastal reclamation have been suggested as main factor responsible for seagrass habitat degradation, reduction in coverage, and total loss due to physical damage as well as high sedimentation [5].The in-fill processes associated with coastal development in general and port construction in particular have resulted in changes to the shoreline, including the degradation and total loss of intertidal and shallow coastal water habitats such as seagrass meadows.An analysis comparing satellite data from 2012 and Google Maps data highlighted the loss of seagrass meadows due to reclamation, including the construction of private terminals with the TUKS classification all around the Palu Bay coast, such as in the examples shown in Figure 6.Our research [14] showed that there has been a decrease in seagrass area in the coast of Palu Bay for a decade (2012 to 2022) by 43.29 Ha, where costal reclamation in this area might also be contributed.

Decline in water quality
Based on data from a recent study in Palu Bay [15], some seawater quality parameters are considered still within or close to the range acceptable for supporting marine life according to Decree of the Minister of Environment Number 51 of 2004 (Table 1).However, several parameters can be considered high, especially turbidity, total suspended solids (TSS), nutrients (nitrate and phosphate), while salinity was lower than the national seawater standard for seagrass meadows.
Table 1.Water quality data for Palu Bay (Walalangi et al., 2022) Port construction and associated processes such as the dumping of sand and other in-fill materials, as well as dredging and the disposal of dredged materials, inevitably affect water quality parameters, in particular turbidity, especially in the absence of mitigating measures [16,17].The quarrying and mining of sand, aggregate and stone as well as other anthropogenic activities continue to put pressure on the coastal waters of Palu Bay, resulting in a decrease in water quality, increased sedimentation, and damage to coastal ecosystems [18].There have been increases in turbidity in Palu Bay not only during port construction but also afterwards due to the release of materials originating from the processing and stockpiling of mining products in the terminals and surrounding area.In addition, runoff from open quarries and cleared land in the mining areas also carries sediment that cause high turbidity and is strongly suspected to lead to high sedimentation in coastal waters of Palu Bay.Topography plays a role in determining the rate of sediment flow.According to [19], the rate at which sediment and pollutants enter Palu Bay is influenced by the slope and landcover around the bay.Mountainous or hilly landscapes surround both sides of Palu Bay, supplying sediment to the Palu River valley and to the waters of the bay.In the northern part of Palu Bay, the slope of the surrounding mountains is generally quite steep, mostly exceeding 15%.
According to Decree of the Minister for the Environment Number 51 of 2004 on Seawater Quality Standards, turbidity in seagrass ecosystems should be less than 5 NTU.High water turbidity will reduce the penetration of light needed by seagrasses to photosynthesize, and can therefore reduce the productivity of seagrass beds [20].While in Palu Bay, the average turbidity values greater than 5 NTU [15,21], meaning that turbidity has exceeded the national seawater quality standard.According to [3], high turbidity will be followed by the sedimentation process, while seagrasses include are sensitive to sedimentation and lack of light availability.
The problems caused by port development are not limited to construction of the port and associated facilities, and adverse impacts on the coastal environment continue to this day.The water quality issues mentioned above will of course have ongoing impacts on the composition and abundance of biotic communities, while the movements of the barges and tugboats transporting mining products (Figure 7) also have the potential to disrupt various aspects of the life-cycles of coastal and marine organisms.This continuous anthropogenic activity does not provide opportunities for ecosystems to recover naturally.Further research is needed on the impact of reclamation on the composition and abundance of coastal organisms.in coastal areas indicates that the development of Palu Bay is not proceeding in an environmentally friendly direction.Ecosystem damage caused by anthropogenic activities will be difficult to recover and the previously productive ecosystems can even disappear permanently if these activities continue without comprehensive environmental management efforts.
It is suggested to the coastal zone manager of Palu Bay to accelerate the implementation of Minister of Marine Affairs and Fisheries Decree No. 20 of 2019 conserning coastal Conservation Areas and Small Islands of Donggala, Boul, Toli-toli and Surrounding Water in Central Sulawesi Province, including seagrass meadows especially as rehabilitation zones.In addition, Palu City government should accelerate and evaluate the implementation of The Provisios of Regional Regulation Number 16 of 2011 concerning the Palu City Spatial Plan (RTRW) for 2010-2030.Furthermore, the government is expected to immediately issue an environmental policy in the form of trade-offs between coastal reclamation with conservation and restoration of the ecosystem that being taken.
1253 (2023) 012106 IOP Publishing doi:10.1088/1755-1315/1253/1/0121063 2.2.Data analysis The estimation of Palu Bay water area was carried out in several stages, namely the composite of satellite image bands, delineation of land and sea boundaries and overlay using the symmetrical difference technique.The combination of band composite on Landsat 7 satellite imagery in 2012 used band 432, meanwhile, the Landsat 8 satellite imagery in 2022 used a combination of band 543 to simplify interpretation.The composite combination of band 432 (Landsat 7 satellite image) and band 543 (Landsat 8 satellite image) was applied because band 4 (Landsat 7 satellite image) or band 5 (Landsat 8 satellite image) with a wavelength of 0.76 -0.90 (near infrared) is easy to delimit water bodies from land.While band 3 (Landsat 7 satellite imagery) or band 4 (Landsat 8 satellite imagery) with a wavelength of 0.63 -0.69 (red) is easy to see areas that absorb chlorophyll, especially mangrove plants on the coast.Band 2 (Landsat 7 satellite imagery) or band 3 (Landsat 8 satellite imagery) is used for the green reflectance value of plant shoots and the interpretation of aquaculture activities around the coastal area [12].Identification of shoreline changes at the study site has used on-screen digitization techniques on both images.