Overemphasis on blue carbon leads to biodiversity loss: A case study on subsidence coastal wetlands in southwest Taiwan

J. Biodiv. & Environ. Sci. Ueng et al. RESEARCH PAPER OPEN ACCESS Overemphasis on blue carbon leads to biodiversity loss: A case study on subsidence coastal wetlands in southwest Taiwan Yih-Tsong Ueng*1, Feng-Jiau Lin2, Ya-Wen Hsiao3, Perng-Sheng Chen4, Hsiao-Yun Chang5 1 Department of Environmental Engineering, Kun-Shan University, Taiwan 2Tainan Hydraulics Laboratory, National Cheng Kung University, Taiwan 3National Land Management Agency, Ministry of the Interior, Taiwan 4 Marine National Park Headquarters, National Park Service, Ministry of the Interior, Taiwan 5Department of Medical Laboratory and Biotechnology Asia University, Taiwan Key words: Avicennia marina, Carbon sink, Biodiversity, Land subsidence, Reservoir desilting DOI: https://dx.doi.org/10.12692/jbes/27.2.46-57 [ Published: August 10, 2025 ] ABSTRACT This paper presents a methodology that accounts for biodiversity in calculating the carbon storage of biocarbon sinks. The feasibility of this approach is demonstrated in the coastal wetlands of Tainan City. The wetland profiles adopted for this calculation method include information on local mangroves, such as Avicennia marina, Lumnitzera racemose, Kandelia obovat, and Excoecaria formosan. In the study area, wetlands, mangroves, windbreak forests, and biodiversity habitats collectively cover an area of 7, 789, 202, 240, and 1447 ha and have a carbon storage of 581,820, 53,222, 92,794, and 67,159 tons, respectively. This approach demonstrates that while maintaining the biodiversity of the original intertidal zone, mudflat or salt marsh ecosystem, better biodiversity and carbon sequestration can be achieved through mangrove planting and mosaic habitat management during the implementation of carbon sequestration projects, highlighting the key role of biodiversity in carbon sequestration projects. In particular, the findings indicate that dredging and sand removal in Tainan’s Zengwen Reservoir has substantially prevented coastal erosion and restored the ecology of the Zengwen Estuary Delt. Finally, A. marina mangroves should not be planted on salt pans with land subsidence, such as closed hydrological systems. *Corresponding Author: Yih-Tsong Ueng  ytue[email protected]om Journal of Biodiversity and Environmental Sciences | JBES ISSN: 2220-6663 (Print); 2222-3045 (Online) Website: https://www.innspub.net E-mail contact: [email protected] Vol. 27, Issue: 2, p. 46-57, 2025 J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 47 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net INTRODUCTION In response to the Kunming-Montreal Global Biodiversity Framework (KM-GBF), which calls for reducing the loss of mangroves, seagrasses and salt marshes, more experts recommend planting more mangroves and seagrasses to mitigate the global biodiversity and climate crisis (Fu et al., 2024). Taiwan enacted the Climate Change Response Act in February 2024 to reduce long-term greenhouse gas emissions, aiming to achieve net-zero emissions by 2050 (Ministry of Environment, 2023). Emission reduction strategies can incorporate local blue carbon ecosystems, which typically include coastal vegetative ecosystems, such as mangroves, seagrass beds, and salt marshes. In addition to their carbon sequestration potential, these ecosystems provide essential environmental functions. Emission reduction efforts often also involve carbon sinks, weights, and allowances; for example, trees may be planted to offset carbon emissions and renew forests. Crucial wetlands surrounding highly urbanized areas often face a loss of ecological integrity and diversity (Jiang et al., 2015; Yang and Ueng, 2011), and their protection during large-scale human activity, such as construction, remains challenging. Carbon sequestration, biodiversity-weighting, and carbon quotas are key components of protection efforts, which typically involve tree planting to regenerate forests and offset carbon emissions. Several researchers have advocated for thinning old trees and replacing them with young trees to increase the sequestration capacity of carbon sinks. From 2013 to 2014, part of the mangroves was removed from Fangyuan beach, Changhua County. The Changhua Wild Bird Society commissioned Dr. Ueng to assist in supervision and conducted 7 collections, collecting a total of 1,635 specimens belonging to 60 species (Ueng, 2014). The dominant species in the dense forest sample area (site A) and the site where the sea cucumber was removed in the previous year (site B) were: crebs Parasesarma bidens, P. pictum (Sesarmidae), and Macrophthalmus banzai (Macrophthalmidae), mollusca Onchidium verruculatum (Onchidiidae) and Littoraria undulata (Littorinidae), respectively. The dominant species in the adjacent open mudflats (sites C and D) were: crebs Mictyris brevidactylus (Mictyridae), M. banzai, Austruca perplexa and Gelasimus borealis (Ocypodidae), and Lingula anatine (Lingulidae), respectively. Further analysis by SIMPER 6 SIMPER showed that the average dissimilarity between the two habitat types A+B and C+D was 92.5% (Ueng, 2014). Because the two distinct ecosystems—the enclosed, shady mangrove forest and the open, sun-soaked intertidal zone—follow planting or removal, their succession patterns shift in different directions. This means that the species communities and similarities here are constantly changing (Bordin et al., 2023). Salt pans with tidal inflows grow Enteromorpha algaes, providing habitat for mollusks such as Elysia chilkensis and Ecomania boodleae (Ueng and Wang, 2001; Ueng et al., 2001). The value of salt pan wetlands cannot be ignored due to unfamiliarity with species classification. Variations in carbon sequestration rates across habitats at different successional stages within carbon sinks warrant further investigation (Bordin et al., 2023). In this study, we introduce a biodiversity-weighted model to assess how biodiversity can enhance the capacity of carbon sinks. Our findings indicate that mangrove planting does not harm the biodiversity of exposed beach land but can improve carbon sequestration and restore the habitat’s biodiversity. Historical records indicate that indigenous communities in Taiwan engaged in mangrove bark trade with outsiders during the 17th century, including immigrants from Fujian and Guangdong who settled in Taiwan before 1662. Spanish priest Jacinto Esquive (1632) described how residents collected bark from mangroves near the Senae community on the north bank of the Tamsui Estuary (Taipei), which was then dried and sold to customers in China (Hsu, 2023). J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 48 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net Since the Last Glacial Maximum (c. 20,000 years BP), the Zengwen River has discharged directly into the sea after traversing now the Danei District of Tainan City. It was not until around 4000 years ago that the geomorphological emergence of Tainan Island altered the river’s terminus, diverting its flow into the proto-Taijiang Lagoon (Chen et al., 2005). In its early phases, the Zengwen River lacked a stabilized channel, contributing to the dynamic sedimentary and hydrological evolution of the evolving coastal plain. Over subsequent millennia, the Taijiang Lagoon underwent substantial transformations driven by alluvial deposition, overbank flooding, and anthropogenic modifications such as channelization and land reclamation. These processed collectively contributed to the formation of the modern Zengwen Estuary Delta, a complex deltaic landscape consisting of multiple distributaries and coastal wetlands. The present drainage system includes watercourses such as the Jiangjyun River, Cigu Creek, Luermen Creek, Yanshuei River, and Erren River. Before the 18th century, the coast of Tainan in southern Taiwan was an inner bay lined with lagoons and sandbars. The oldest map of this area is included in the Kangxi Taiwan Map, which is preserved in the National Taiwan Museum. The primary fish species in this area included Mugilidae, Sciaenidae, and Engraulinae, which historically served as essential food source for spoonbills (Platalea minor) (Ueng, 2007b) and dolphins (Sousa chinensis taiwanensis) (Wang et al., 2015), as well as sustaining the livelihood of local Siraya indigenous communities (Lin et al., 2022). Due to heavy rain in 1823, the Taijian Lagoon filled with silt and became a shoal, and approximately 300 km2 of the lagoon’s area disappeared. The land was then reclaimed into salt pans, agricultural lands and fishponds, and mangroves grew in the tidal gullies (Huang, 1735; Vingboons, 1636). Environmental changes driven by human activity have led to the endangerment of several species, including Geloina erosa and Fronsella taiwanicae, while others, such as Terebralia sulcata, Telescopium telescopium, and Parafossarulus manchouric, are gradually extinction (Fig. 1). Fig. 1. Three species of shellfish have become extinct from Taijiang Lagoon. A. Terebralia sulcata, B. Telescopium telescopium, C. Parafossarulus manchouric Accordingly, Weiskopf et al. emphasize the close relationship between biodiversity, habitat and environment, and the sequestration capacity of carbon sinks (Weiskopf et al., 2024). Fig. 2. Distribution of sandbars and lagoons along the coast of Tainan in the 18th century Several place names in southern Taiwan originate from coastal fauna and flora, including Hai-uengsand (whale), Kun-shen (whale), Han-xi (Thryssa J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 49 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net hamiltonii), Kang-lang (Phoenix hanceana), and Lu-cao (Broussonetia papyrifera). Over the past 6,000 to 300 years, land-use patterns and ecological environment within this 300 km2 region—featuring waters ranging from −70 to −20 m deep—have undergone significant transformation0s (Huang, 1735; Vingboons, 1636) (Fig. 2). Numerous migratory Sciaenidae otoliths have been excavated from cultural relics near the lagoon (Lin et al., 2022). We therefore hypothesize that from 6,000 to 300 years ago, the Taijiang Lagoon, which is protected by Tainan Island and a series of sandbars to the west, functioned as a breeding habitat for the Taiwan’s white dolphin (Fig. 3). Fig. 3. Taiwan’s white dolphin family (photo by Yu-Chun Chien) Since the construction of Zengwen Reservoir was completed in October 1973, the intertidal zone of Tainan’s coast has experienced erosion. This study evaluated the effects of recent reservoir sands discharge and dredging on the restoration of coastal intertidal zones. Current policies in Taiwan focus primarily on short-term ecological change through carbon sequestration incentives and engineering approaches but ignore ecological diversity. We propose that the biodiversity within these habitats can be strategically utilized to enhance the sequestration capacity of carbon sink; this means that enterprises that contribute to comprises biodiversity should have their carbon quotas or taxes offset accordingly. MATERIALS AND METHODS Study area within Tainan city The study area encompasses the southwest coast of Tainan City, extending from Jiangjun River in the north to Sihkunshen Ditch in the south (Fig. 4). This region includes the coastal sites, estuaries, and lagoons of Taijiang National Park. Fig. 4. Map of the study area within Tainan city, Taiwan Estimation of mangrove, windbreak, and sand areas For area estimation, we selected images collected at the Center for Space and Remote Sensing Research, National Central University, Taiwan, by satellites SPORT 7 on March 22, 2017; SPORT 6 on November 19, 2023; and SPORT 6 on February 22, 2025 (Center for Space and Remote Sensing Research, 2025). The primary purpose of this study was to estimate the land area covered by mangroves, windbreaks, and sand within the study site. Estimation was conducted using the normalized difference vegetation index and unsupervised classification in ArcGIS Pro and Google Earth Pro images or through onsite comparison with Google Earth Pro (Center for Space and Remote Sensing Research, 2025; Chen et al.,2020). We then analyzed the ecological impacts of dredging, beach maintenance, and Water Resources Agency management activities in the study area within the past sevent years (2017–2024) on spatiotemporal satellite J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 50 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net images (Chen, 2014; Chen et al., 2020). Our analysis focused on the effects of heavy rains associated with Typhoon Gaemi (July 2024) and of sand removal and dredging during the flood discharge of the Zengwen Reservoir, containing approximately 2.58 million cubic meters of sand discharge (Southern Region Water Resources Branch, WRA, 2024). Benthic organisms, crustaceans, and waterbirds inhabit the intertidal zone across five habitat types: forests, grasslands, dry sand dunes, wet sand beaches, and shallow water areas (0–20 cm or up to 30 cm). The wet beach is a crucial foraging area for the Kentish Plover (Charadrius alexandrinus) (Chen et al., 2015), serving as the eastern boundary of our study area, which is marked by roads and embankments. These habitats can be divided into eight types: aqueous habitats (with water depths of >90, 90–60, 60–30, or 30–0 cm); wetlands; forests; dry sand dunes; and highly reflective surfaces (Chen et al., 2020; Chen, 2014). The wet beach area has been preserved to ensure foraging opportunities for the Kentish Plover population, and roads and embankment serve as the eastern boundary of the study site (Chen et al., 2015). The SIMPER program in Primer 7 was used to analyze differences in characteristics between both satellite images, including habitat composition (Krebs, 1999). Carbon sink According to Lin (2024), blue carbon ecosystems in Taiwan include mangroves (938.8 ha), seagrass beds (7,818 ha), and salt marshes (188.3 ha) (Lin, 2024). Although the land area of salt marshes is small, this habitat is crucial for aquatic insect larvae and snails, including Dolichopodidae, Ephydridae, Stenothyridae, and Stratiomyidae, respectively (Ueng et al., 2009; Ueng, 2013; Ueng and Wang, 2003; Wang et al., 2007). These larvae play a key role in the food chain of waterbirds. The carbon stock for mangroves, seagrass beds, and salt marshes within the study area is approximately 263.5, 26.4, and 85.0 t C/ha, respectively (Lin, 2024; Ueng et al., 2021). Organic matter of coastal sand dunes and intertidal zone Qrganic matter (OM) in coastal sand dunes, beaches, and intertidal zones serves as a major carbon sink. A study by Ueng et al. (2021) analyzing soil samples from the southwest coast of Taiwan reported the following average OM concentrations: 24.3, 21.9, and 7.7 g/kg in the Sinfulun sand dune, Zengwun Estuary sand dune (Fig. 5), and Cigu intertidal zone sites, respectively (Ueng et al., 2021). Fig. 5. On April 8, 2025, the Sinfulun Sand dune at the Zengwen Estuary was reformed into a small lagoon where oysters can be cultured Carbon sink biodiversity-weighting The Shannon-Wiener diversity index H’ (log base e) was used as our biodiversity index (H’) (Parker and Pianka, 1975; Krebs, 1999). The Jhuoshuei Estuary in western Taiwan has an H’ of 1.20, 2.79, and 1.80 in benthic, fish, and crustacean species, respectively (Chen et al., 2016). The H’ for fish species in Cigu Lagoon is 1.90 (Chen et al., 2005), and the H’ for bird species in Cigu Salt Pan is 2.67 (Chen et al., 2020). Additionally, the H’ for mangrove spider species is 1.21 and 1.69 in the Jishuixi and Puzixi estuaries, respectively (Chen, 2012). The H’ for fry fish families is 2.02 in the Cigu Wetland (Chen, 2012). The rough average estimate of these H’ values is approximately 2.01 ± 0.56. We recommend increasing the carbon allowance of these wetlands by 10% - 15% of their carbon sequestration for their contribution to biodiversity. J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 51 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net Given these values and the scope of administrative discretion of government agencies, we recommend increasing the carbon quota of each wetland or subhabitat by 1–15% of their carbon sequestration as an incentive to ensure that carbon sequestration is promoted without sacrificing biodiversity (Ueng et al., 2025). For the prediction of mangrove carbon sink in the land subsidence area, It is recommended to adjust the k value by the formula Y(t) = −k(t − a)2 + b, where k is the decline rate of annual radius growth and should be reduce, t and a is years, and (a, b) is the maximum sequestration capacity of the carbon sink within that habitat. RESULTS Carbon sink Based on satellite images of the coastal areas surrounding Tainan City, taken by SPORT7 on March 22, 2017, and SPORT 6 on November 19, 2023, the total area of the four nationally important wetlands from Jianqjyun Estuary to Sikunshen Ditch was 7,788.8 ha in 2023, with a yellow carbon storage capacity of 581,826 tons. We calculated the total mangrove area as 202.0 ha and the total area within the national wetland as 150.2 ha, which is 35.6 ha more than the national wetland area in 2017. The area outside the national wetlands was 51.8 ha in 2023, which is 20.4 ha more than in 2017. The windbreak habitats in 2023 were approximately 240.4 ha, which is 16.3 ha less than in 2017, with a carbon stock of 92,794 tons (Table 1, Fig. 6). The Water Resources Agency (2024) reported that the cumulative dredging volume of the Zengwen Reservoir reached 138.7 million m3 between 2017 and 2024, with an annual average of 6.3 ± 3.2 million m3/yr. This exceeds the annual average sand volume (5.6 million m3/yr) recorded from 2002 to 2023. Consequently, the Zengwen Estuary Delta is on the cusp of full restoration, and the yellow carbon along the Tainan coast can be included in carbon sink calculations (Fig. 6). Table 1. Characteristics of carbon sinks within the study area Sample sites Area of 2017 (ha) Area of 2023 (ha) +/−(ha) Stock (t C/ha) Total carbon stock (t C) Wetland (n= 4) 7,395.0 7,788.8 393.8 74.7 581,826 Mangroves in wetlands (n= 4) 114.6 150.2 35.6 263.5 39,578 Mangrove outside the wetland (n= 6) 31.4 51.8 20.4 263.5 13,644 Windbreak forest (n= 3) 256.7 240.4 −16.3 386.0 92,794 Biodiversity weighting (n= 8) 1,447.4 46.4 67,159 Total 8,231.2 433.5 795,002 Fig. 6. Distribution of mangrove and windbreak forests from the Jiangjun Estuary to the Sikunshen Ditch, Tainan City, in 2017 and 2023. BFS: Blackfaced Spoonbill Reserve, A1-A3: zoning of Sihcao Wetland, the green ones are the mangroves and windbreaks in 2017, and the red ones are the new additions in 2023 Based on satellite images of the coastal areas surrounding Tainan City, captured by SPORT 7 on March 22, 2017, and by SPORT 6 on February 22, 2025, the total mangrove area within the Zengwun Estuary Wetland (including BFS and EFP), and Cigu West Campus of National University of Tainan (WCT) was 57.3 ha in 2023, and 62.6 ha in 2025, reflecting an overall increase of 5.3 ha. This change was primarily attributed to a 21.2 ha J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 52 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net expansion of BFS (from 4.1 ha to 25.2 ha), a 19.4 ha reduction in EFP (from 32.7 ha to 13.3 ha), and 3.5 ha increase in WCT (from 20.8 ha to 24.1 ha). The spatial similarity between the two periods was only 22.6% (Figs. 7 and 8). Fig. 7. The mangrove area in Zengwun Estuary Wetland on March 22, 2017. BFS: Black-faced Spoonbill Reserve, EFP: East Fish-pond site, WCT: Cigu West Campus site of Tainan University Fig. 8. The mangrove area in Zengwun Estuary Wetland on February 22, 2025. BFS: Black-faced Spoonbill Reserve, EFP: East Fish-pond site, WCT: Cigu West Campus site of Tainan University Reservoir sand removal and dredging Analysis of satellite images from March 22, 2017, and February 22, 2025, revealed that water areas with a depth of >90 cm and 90–60 cm decreased by 4,015.4 ha, whereas water areas with a depth of 60–30 or 30–0 cm and wetlands increased by 3,902.2 ha, totaling 7,917.6 ha (Table 2), indicating large storage capacity for yellow carbon. The SIMPER program in Primer 7 was used to analyze satellite images and divided the total intertidal zone of the Zengwen Estuary Delta (6,477 ha) into two sample areas: Cigu Salt Pan Wetland (Cigu S.P.) and Zengwen Estuary Wetland (Zengwen E.), , all bounded by the west seawal. Each sample area was further divided into eight ecological habitats. Following sand removal from the reservoir and tidal transport between 2017 and 2024, the average dissimilarity of habitat classifications between both satellite images was 61.4% (Table 2). Discrepancies were primarily observed between areas with a water depth of 60–30 cm (34.3%), >90 cm (30.7%), and 90–60 cm (19.1%). Separate calculation for the northern and southern areas within the study site revealed that the average similarity of the west side of the seawall in the Cigu Salt Pan Wetland over both years was 56.5%, primarily comprising areas with a water depth of 0–60 cm (41.7% of the similarity), >90 cm (29.7%), and 30–0 cm (15.6%) and wetland areas (7.5%), accounting for 94.53% of the observed similarity. The average similarity of the west side of the Zengwen Estuary seawall over both years was 85.5%, primarily comprising areas with a water depth of 30–0 cm (44.6% of the similarity) and 60–30 cm (43.0%) and wetland areas (5.2%), totaling 92.8% of the observed similarity. These findings indicate that the replenishment of sand sources from upstream decreased the area with a water depth of >60 cm and increased the area with a water depth of 60–30 and 30–0 cm and wetland areas, forming an intertidal ecosystem suitable for Scopimera longidactyla and Mictyris brevidactylus crabs and shore birds (Figs. 9 and 10). J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 53 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net Table 2. Impact of sand discharge and dredging of Zengwen reservoir on different types of habitats at the Zengwen Estuary Delta. (ha) Water deep and land 2017 2025 Variation from 2017 to 2025 Cigu S.P. Zengwen E. Cigu S.P. Zengwen E. > 90 cm 544.1 2293 26.7 294.6 −2515.8 90–60 cm 928.0 762.1 121.2 69.4 −1499.5 60–30 cm 57.4 97.2 1191.3 1694.6 2731.2 30–0 cme 1117.1 286.1 1236.7 1296.3 1129.8 Wetland 136.9 138.7 142.8 174.1 41.2 Green plant 9.4 27.5 8.3 21.6 −6.9 No grass land 25.4 33.4 85.0 84.2 110.5 High reflection 13.0 7.8 19.4 11.0 9.6 Total 2831.3 3645.7 2831.3 3645.7 Zengwen E. was Zengwen Estuary Wetland, and Cigu S.P. was Cigu Salt Pan. Wetland Fig. 9. Landscape classification of the Zengwen Estuary was performed using SPORT 7 satellite images (March 22, 2017) and processed with ENVI 4.8 software. BFSR: Black-faced Spoonbill Reserve Fig. 10. Landscape classification of the Zengwen Estuary was performed using SPORT 6 satellite images (February 22, 2025) and processed with ENVI 4.8 software. BFSR: black-faced Spoonbill Reserve Biodiversity weighting We recommend increasing the carbon allowance of the wetlands in the study area by 10% to 15% of their carbon stock based on their contribution to biodiversity. This process would increase the carbon stock by biodiversity weighting 67,168.89 tons (approximately 9.2% of the original carbon sink). The carbon stock allowances identified within the study area were 795,002 tons. DISCUSSION Entities that maintain biodiversity by planting or cutting down trees should be compensated accordingly in the form of carbon sink rights, as indicated by the proposed diversity-weighted carbon sink model. This model allows for a nuanced understanding of the necessity of biodiversity beyond species counts. A promising method for biodiversity weighting is the creation of gaps in mangrove forests for greater biodiversity, as indicated by the index H’. Applications for carbon sink rights must first be accompanied by at least four ecological field surveys. Between 2017 and 2024, mangrove coverage within the study site expanded naturally by Estuarine J. Biodiv. & Environ. Sci. Vol. 27, Issue: 2, p. 46-57, 2025 54 Ueng et al. Journal of Biodiversity and Environmental Sciences | JBES Website: https://www.innspub.net interactions play a crucial role in carbon storage (Water Resources Agency, MOEA, 2024). At the Zengwen, Zhuoshui, and Wu (Dadu) estuaries along Taiwan’s west coast, extensive mudflats have formed due to the accumulation of drifting sediment. Given that Avicennia marina seeds disperse via seawater, the species can rapidly establish expansive mangrove forests, extending into tidal gullies and drainage channels, thereby impeding water flow and compromising flood management. However, along Taiwan’s western coastline, intertidal mudflats biodiversity need not be sacrificed to enhance carbon storage; targeted A. marina mangrove planting can achieve carbon sink objectives while preserving ecological integrity. On May 12, 2025, Taiwan’s Ministry of Environment held a meeting to review the reduction of greenhouse gas through mangrove planting. Scholars and experts suggested limiting planting areas to idle salt pans, fishponds, and abandoned ponds instead of coastal areas, somewhat resolving existing disputes. However, the salt pans along the southwest coast of Taiwan are located in areas with severe land subsidence: by 2024, land subsidence was −233.6, −179.4, −153.3 and −50.2 cm in Dongshi, Budai, Beimen, and Cigu, respectively Water Resources Agency, MOEA, 2024). During the annual rainy season, the salt pan habitat, which is dominated by aquatic plants (Ruppia maritima) and aquatic insects (Berosus tayouanus, Tendipus tainanus, Ochthera sauteri), serves as a breeding ground for the Black-winged Stilt (Himantopus himantopus), an indicator species within salt pan ecosystems. Salt pan ecosystems provide 17 orders, 39 families, and 48 species of animal food for stilt chicks (Ueng et al., 2009). However, to prevent flooding, residents and gate managers have closed all water diversion and drainage gates around the salt pans in the study area. Consequently, nutrients in the habitat have gradually dried up, decreasing the biodiversity of benthic animals, fish, and shrimp (Water Resources Agency, MOEA, 2024; Ueng, 2007a). Forestry Bureau aerial photographs from 1984 show that these fishponds, which block tidal and sediment-laden currents, did not exist before this time (Ueng and Kuo, 1992; Forestry Bureau Aerial, 1984; Tainan County Government,1992). A lack of tidal exchange restricts both the growth of mangroves and the anticipated carbon sequestration effect (< 15 tC/ha per year). Fossil evidence of Stenotyra tainanica in the Tainan Formation (45008400 YBP), together with the contemporary presence of S. chilkaensis and S. orissaensis in southwest Taiwan’s brackish wetlands, and the other new species Odontomyia halophila (Stratiomyidae) was described from salt marshes of western Taiwan (Wang et al., 2007). These salt marsh wetlands are shaped by long-term successional dynamics and exhibit inherently slow species turnover due to hypersaline conditions and hydrological constraints. Afforestation or removed mangroves may increase carbon sinks or flood control (Huang, 2021; Wu, 2023), but this is accompanied by the emergence of new and different biological communities, which will also affect the assembly, diversity and species similarity percentage of its organisms (Ueng, 2014). Uninformed afforestation with A. marina— disregarding these ecological parameters—risks disrupting established assemblages and eroding native biodiversity. Such losses not only impair ecosystem integrity but also diminish carbon sequestration capacity, a pattern increasingly evident in global terrestrial carbon systems (Ueng, 2014; Weiskopf et al., 2024; Li, 2016; Liu et al., 2021). ACKNOWLEDGEMENTS We are grateful to Mr. Po-Ling Deng, Mr. Yu-Chun Chien, Mr. Ching-Lung Liu, and Mr. Chih-Hao Liao. This study was supported by Ocean Conservation Administration, OAC, and Tainan City Government. REFERENCES Bordin RM, Esquivel-Muelbert A, Klipel J, Picolotto RC, Bergamin DS, da Silva AC, Higuchi P, Capellesso ES, Marques NCM, Souza AF, Müller SC. 2023. No relationship between biodiversity and forest carbon sink across the subtropical Brazilian Atlantic Forest. Perspectives in Ecology and Conservation 21(2), 112–120. https://doi.org/10.1016/j.pecon.2023.02.003