Potential Carbon Stock of Seagrass Biomass in Malang Regency

Research on blue carbon content in seagrass beds also has important implications for coastal ecosystem management. The goals of this research are: (1) To determine the composition of seagrass species; (2) to analyze the health of the seagrass ecosystem; and (3) and to analyze the carbon content stored in seagrass biomass on the coast of Malang Regency. This research was conducted in 2018 at five stations, namely: Kondang Merak Beach (St 1), Balekambang Beach (St 2), Gatra Beach (St 3), Sendangbiru Beach (St 4), and Waru-Waru Beach (St 5) of Malang Regency. The method used to collect data refers to Seagrass Watch. The biomass value of seagrass species can be estimated by measuring the wet weight and dry weight of seagrass. Analysis of carbon content in seagrass biomass can be calculated using a method that refers to The First Nation-Wide Assessment Identifies Valuable Blue-carbon. There are five types of seagrasses found on five beaches in Malang Regency, namely: Halodule pinifolia, Halodule uninervis, Halophila ovalis, Syringodium isotifolium, and Thalassia hemprichii. This seagrass meadow ecosystem is in an unhealthy condition, with a small biomass value. Seagrass beds that are formed only in the form of small spots (1.19 Ha) are known to be able to store carbon of 0.0544 Mg C.


Introduction
Climate change is an unavoidable phenomena that occurs due to both natural and anthropogenic causes.Therefore, mitigating climate change is important especially to reduce the occurring negative impacts [1].Mitigating climate change at sea involves a series of actions to reduce greenhouse gas emissions associated with marine activities and harness the potential of blue carbon [2].
Blue carbon is a term that describes the ability of the marine ecosystem to store and bind carbon dioxide (CO2).Most commonly, it refers to the role that salt marshes, soil and vegetation of mangroves 1328 (2024) 012010 IOP Publishing doi:10.1088/1755-1315/1328/1/012010 2 and seagrasses can play in carbon sequestration [3], [4].The blue carbon working method refers to the ability of coastal ecosystems such as seagrass beds to capture carbon dioxide (CO2) from the atmosphere and store it in plant tissue and underwater sediments [5], [6].This carbon storage reduces atmospheric CO 2 concentrations, which is one of the main greenhouse gases responsible for climate change.
Seagrass meadows can capture carbon dioxide (CO2) from the atmosphere and store it in plant tissue and underwater sediments.Thus, research on blue carbon in seagrass beds helps us understand the contribution of this ecosystem in reducing CO2 concentrations in the atmosphere, which is a key factor in overcoming climate change [7], [8].Seagrass beds also have function as habitats and food sources for various species of marine biota [9], [10], [11].A decline in seagrass communities can threaten marine biodiversity and affect the marine food chain.Research on blue carbon content in seagrass beds also has important implications for coastal ecosystem management.The aims of this research are: (1) To determine the composition of seagrass species; (2) to analyze the health of the seagrass ecosystem; and (3) and to analyze the carbon content stored in seagrass biomass on the coast of Malang Regency.The method used to collect data on seagrass cover, types and samples was a Line Intercept Transect drawn perpendicularly from the beach for a distance of 50 m, with a quadrat transect of 50 cm x 50 cm referring to Seagrass Watch [12], [13].Analysis of the health of the seagrass community was conducted by paying attention to the total cover value of the seagrass community at the research location and then compared to the standard value for the health quality of seagrass meadows in Indonesia [14].The biomass value of seagrass species can be estimated using an equation as conducted in research [15], it can also be obtained by measuring wet weight and dry weight, then analyzed referring to previous research [14].Analysis of carbon content in seagrass biomass can be calculated using a method that refers to [16], [17].1).The water temperature at the research location were between 29.90 and 29.30 °C, while the salinity of the water at the research location ranged from 33.7ppt to 35ppt, and the pH value of the water at the research location were 7.4 -7.9.This value is considered normal for tropical waters and is still within reasonable limits for seagrass growth [18].

Methodology
Seagrass can tolerate temperature changes up to 35 o C, the critical threshold for seagrass growth is 40 o C [19].Seagrass requires water with an alkaline pH for growth and can adapt to changes in pH values of 0.2 points [20].Seagrass growth will take place well at a salinity of 30 ppt -40 ppt but becomes critical if the water salinity reaches 45 ppt [21].

Seagrass Species Composition
The concept of additive partitioning analysis has been widely explored in ecological studies to understand the patterns of diversity and the mechanisms of coexistence among competing species.Additive partitioning of species diversity has been identified as a promising approach for analyzing diversity patterns sampled from hierarchically scaled studies [22].Additive partitioning estimates alpha diversity as the mean number of species found in each sample, while gamma diversity is is defined as the difference between diversity at a larger scale [23].The alpha diversity at Stations 1, 2, 3, and 5 is one, while at Station 4 there are three, and the seagrass gamma diversity on the coast of Malang Regency is five types (Table 2).The seagrass type Halodule pinifolia was found only at Station 4, forming a heterospecies community with Halophila ovalis and Thallassia hemprichii.Halodule uninervis is a type of seagrass found only at Station three and forms a monospecies seagrass community.The seagrass type Syringodium isotifolium is known to form a monospecies community at Station 1. Halophila ovalis and Thallassia hemprichii are types of seagrasses that are found at more than one station, and form heterospecies communities.
Halodule pinifolia is known as a type of seagrass that is tough and has a high tolerance for turbidity and low levels of sunlight [24].Halodule pinifolia is commonly found forming heterospecific communities with Halodule uninervis and Halophila ovalis in the Southeastern Gulf of Carpentaria, Australia and the Valaichchenai Lagoon, Sri Lanka [24], [25].Halodule uninervis and Syringodium isotifolium have also been reported to be found in Tanzanian waters and are known to have the ability to absorb and store carbon [26].Halophila ovalis and Thalassia hemprichii were also found to form heterospecific communities in the Dongsha Atoll and Penghu Islands of the Taiwan Strait, western Pacific [27].

Community Health Seagrass
The lowest total seagrass density was found at Station 2, namely 586 stands/m2 of the Thalassia hemprichii type, while the highest was found at Station 3 (1,950 stands/m2) of the Halodule uninervis type (Table 3).The number of seagrasses stand in an area is influenced by its growth pattern, especially the addition of shoots and the connectivity of the rhizome tips to one another.Even the nutrient content in the water column has little influence on the growth of seagrass stands [28].The highest total seagrass cover was found at Station 2, while the lowest was at Station 5 (Table 4).The total seagrass cover at Station 2 was 24.54% and all of it was of the Thalassia hemprichii type, while at Station 5 it was 3.57% consisting of the Halophila ovalis type.This can happen because Thalassia hemprichii has the morphology of seagrass leaves in the form of elongated rope-like sheets, while Halophila ovalis has round and very narrow oval leaves [29].The total cover of seagrass at each station shows a value of less than 30%, this shows that the health of the seagrass ecosystem on the coast of Malang Regency is in the poor category [14].

Biomass
The biomass value is obtained from the dry weight of seagrass tissue, which is analyzed in the laboratory, then processed using a biomass calculation formula which refers to seagrass biomass calculations [30], [31].The highest total seagrass biomass was found at Station 4 (198.5 grams dry weight/m2), while the lowest was at Station 3, namely 53.4 grams dry weight/m2 (Figure 2).The highest value at Station 4 was caused by the emergence of seagrass species Thalassia hemprchii, Halophila ovalis, and Halodule uninervis.Meanwhile, the lowest value at Station 3 occurred because it only had one type of seagrass, Halodule uninervis.Halodule uninervis has a small morphology, with elongated flat leaves like ribbons, the leaf width is less than 1 cm, so it is very natural that it has a low biomass value [32].

Seagrass Carbon Stock
The value of the carbon content of seagrass networks were obtained from the value of the organic material content resulting from the ashing processes (loss on ignition) divided by the constant value of the organic material expressed in the form of carbon percent.The estimated value of total carbon stock at the research location ranges from 24.96 Carbon/m2 to 88.36 Carbon/m2.The carbon stock value at the research location varies, the carbon stock at Station 4 is the highest, while the lowest is found at Station 1 (Figure 3).The variation in carbon values found in the research location is a variation in values caused by differences for biomass between types and between seagrass networks [17].In general, carbon stocks at the research location show the same pattern in which carbon stocks under the substrate are higher than above the substrate (Figure 3).This happens because the lower part of the seagrass body (roots and rhizomes) is larger than the upper part (leaves).The pattern of carbon stocks under the substrate being greater than above the substrate was also reported to occur in seagrass beds in Bakau Bay -Bintan, Minahasa -North Sulawesi, Pari Island -Seribu Islands, and Benan Island, Lingga Regency [7], [8], [31], [33]

Potential Seagrass Carbon Stock on the Coast of Malang Regency
The potential carbon stock stored in seagrass biomass on the coast of Malang Regency can be calculated using the sum of seagrass cover values at each station and the biomass of seagrass at each station.This estimation was conducted to obtain values that can be used to make policies, making seagrass beds Blue Carbon Storage that has also been done in a study in Australia [34].
The area of seagrass beds at each station varied, between 0.093 and 0.450 hectares, with a total area of seagrass beds on the coast of Malang Regency of 1,182 hectares.The potential carbon stock stored in seagrass biomass at each research station is 0.002 MgC -0.019 MgC, with the total potential carbon stock stored in seagrass biomass on the coast of Malang Regency being 0.054 MgC (Table 5).This value is quite low when compared with the results of carbon stock research on seagrass biomass conducted in different locations in Bakau Bay -Bintan, Minahasa -North Sulawesi, Pari Island -Seribu Islands, and Benan Island, Lingga Regency [7], [8], [33], [35].This is because the seagrass habitat on the coast of Malang Regency is particularly challenging for seagrass recruitment and growth, so the area of seagrass beds is limited.This seagrass meadow ecosystem is in an unhealthy condition, with a small biomass value.Seagrass beds that are formed only in the form of small spots (1.19 Ha), are known to be capable of storing carbon of 0.0544 Mg C. The potential seagrass carbon stock obtained in this study is sufficient to conclude that although the seagrass on the coast of Malang Regency is patchy, it is patchy.In the long term, it has the potential to reduce carbon emissions in the atmosphere so that it can help reduce the rate of climate change that continues to occur.This research suggest that efforts need to be made to protect the seagrass ecosystem on five beaches in Malang Regency, as a form of climate change mitigation and protecting important habitats for the organisms that live there.
This research was conducted in 2018, consisting of several stages, namely: (1) Data collection; (2) Processing seagrass samples; and (3) Data analysis.Data collection and seagrass samples were carried out at five stations, namely: Kondang Merak Beach (St 1), Balekambang Beach (St 2), Gatra Beach (St 3), Sendangbiru Beach (St 4), and Waru-Waru Beach (St 5) Malang Regency (Figure 1).Processing of seagrass samples was conducted at the Central Laboratory of Life Sciences -LSIH Brawijaya University.Meanwhile, data analysis and writing of scientific articles are conducted within the Faculty of Fisheries and Marine Sciences -FPIK Brawijaya University.

Figure 1 .
Figure 1.The research areas across the Malang Regency.

Table 2 .
Composition of Seagrass Types on the Coast of Malang Regency

Table 4 .
Seagrass cover on the coast of Malang Regency