Conditions of Megabenthos on Coral Reef Ecosystem in Seribu Islands National Park, Jakarta, Indonesia

. Seribu Islands National Park is located off the north coast of Jakarta and consists of 110 islands. This study aims to determine the distribution and density of megabenthos in coral reef ecosystems in the Seribu Islands National Park. This research was conducted in November 2021 in the Seribu Islands National Park waters. Megabenthos observations were carried out using the Benthos Belt Transect method, a development of the Belt Transect Method for monitoring megabenthos combined with the Reef Check Benthos method. Based on observations in the waters of the Seribu Islands National Park, five types of megabenthos were found, including clams ( Tridacna sp.), lola ( Trochus sp.), Crown-of-torns starfish ( Acanthaster planci ), drupella ( Drupella sp.), and sea urchins ( Diadema sp.). The highest density of megabenthos was found on Kayuangin Genteng Island, with a density of 8,786 ind/ha, while the lowest was on Peteloran Barat Island, with 429 ind/ha. Based on the type of megabenthos at all observation stations, the most abundant megabenthos found was Diadema sp., with a density of 43,397 ind/ha. In comparison, the least was Acanthaster planci of 214 ind/ha. Megabenthos in the Seribu Islands National Park waters are in various conditions.


Introduction
Seribu Islands National Park is located off the north coast of Jakarta and consists of 110 islands with an area of 108,000 hectares, with an extended position from north to the south marked by small white sandy islands and coral reefs.The geomorphology of small islands in the Seribu Islands includes lowland islands with uplifted coral types formed from massive coral rock deposits [1].
Based on the research results, islands in the Seribu Islands are mostly surrounded by coral reefs, so the dominant ecosystem is the coral reef ecosystem, followed by the mangrove ecosystem and seagrass ecosystem.Coral reef ecosystems have an area of 3,147.93Ha, mangrove ecosystems cover an area of 575.09Ha, and seagrass ecosystems cover an area of 277.01 Ha [1].
Coral reefs are the habitat of various groups of marine biota, both permanent and temporary.One of the constituents of coral reef ecosystems is a group of benthic fauna, namely groups of fauna that live in the bottom waters (benthos) [2].Echinoderms, Molluscs, and Crustaceans are a group of benthic fauna that are often found living on coral reefs.Benthic fauna group (megabenthos), which is relatively large and has a high population, has an important role in the condition and stability of the ecosystem [3][4].
Megabenthos is the largest marine biota group that has an important role in the ecosystem [5].Suggested that benthic animals play a role in the nutrient cycle in waters [6].The nutrient cycle is an essential process in aquatic ecology because it is a source of energy for producers.On the other hand, macrobenthos is also a biological component that is often used as an indicator of pollution because it has a different sensitivity to pollutants and has low mobility so that it can be directly affected and easily captured for analysis [7].Benthic fauna that is easily recognizable and sensitive to changes in the aquatic environment is the megabenthic group.Megabenthos has a wide distribution, relatively large size, and a rather long life cycle, causing this organism to have a relatively slow movement so that it can continuously respond to water quality conditions [8][9].
This makes the megabenthos group of potential value to be used as an object for monitoring coral reef health.This study aims to determine the distribution and density of megabenthos in coral reef ecosystems in the Seribu Islands National Park, Jakarta.

Materials and Methods
The research activity was carried out on November 2-12, 2021.This activity was carried out in the Seribu Islands National Park area, with 14 monitoring stations.In detail, the monitoring stations in the waters of the Seribu Islands National Park can be seen in Table 1 and Figure 1.Megabenthos observations were carried out using the Benthos Belt Transect (BBT) method, which is a development of the Belt Transect Method for monitoring megabenthos [10] combined with the Reef Check Benthos method at fourteen stations with the help of SCUBA diving equipment [11].Observations were made using SCUBA equipment.Transects were synchronized for coral and reef fish observations on permanent transects.This method is done by pulling a scale tape (roll meter) parallel to the shoreline at a depth of 4-7 meters with a transect length of 70 meters, and the shoreline is always on the diver's left when pulling the transect tape.After the tape transect was installed, observations and records were made of the type and number of target megabenthos from 0 meters to 70 meters with an observation width of 1 meter to the left and 1 meter to the right of the transect line so that the observation area became 140 m 2 (2 x 70 m) (Figure 2).There are eight species or groups of megabenthos fauna species monitored, namely Sea Cucumber (Holothurians), Clams (Tridacna sp. and Hippopus sp.), Lobster (Panulirus spp.), Lola (Trochus spp.), Crown-of-torns starfish (Acanthaster planci), drupella snail (Drupella spp.), sea urchin (Diadema sp.), and Blue Starfish (Linckia laevigata) (Table 2).
All types of megabenthos that were targeted by transects were recorded for the number of species and the number of individuals.Megabenthos targets are biota that has high economic value and play an important role in coral health, consisting of seven groups of megabenthos indicator biota.Identification refers to [12].

Fig 2. Megabenthos Transect Simulation with Modified Benthos Belt Transect (BBT)
Method [12] Table 2. Types of Megabenthos Targets Observed After the observation data is collected, the information is transferred into a spreadsheet, for example, by using Microsoft Excel, including the type, number of individuals of each species, and abundance.Megabenthos density can be calculated using the following formula [13].

Presence and Composition of Megabenthos
At the location for observing the condition of megabenthos at fourteen observation stations in the waters of the Seribu Islands National Park, five types of megabenthos were found that became the object of observation.The following is the presence of the megabenthos target group and the number of megabenthos species at each observation station in the waters of the Seribu Islands National Park, which are presented in Table 3.Based on observations in the waters of Seribu Islands National Park, five types of megabenthos were found that were the target of observation, including clams (Tridacna sp.), Lola (Trochus sp.), spiny starfish (Acanthaster planci), drupella.Snails (Drupella sp.), and sea urchins (Diadema sp.), while sea cucumbers (Holothurians), lobsters (Panulirus spp.), and blue starfish (Linckia laevigata) were not found at the observation station.The megabenthos species that dominate the waters of Seribu Islands National Park are sea urchins (Diadema sp.) as much as 100%, followed by drupella snails (Drupella sp.) 57.14%, clams (Tridacna sp.) and Lola (Trochus sp.) respectively 50% each, and the Crown-of-torns starfish (Acanthaster planci) at 14.29%.Based on the number of species at each observation station, the highest number of species was found on West Penjaliran Island (KSBC02), Melinjo Island (KSBC04), and Bira Besar Island (KSBC06), while the lowest was on Pamagaran Island.(East) station (KSBC09) and Pulau Karya (KSBC11).

Megabenthos Density
Based on the calculation of the density of each type of megabenthos found at each observation station, the density of the type of megabenthos is quite varied, ranging from 429 -8,786 ind/ha.For the total density of megabenthos from each observation station, the highest is at Pulau Kayuangin Genteng station (KSBC07), with a megabenthos density of 8,786 ind/ha, while the lowest is at Pulau Peteloran Barat station (KSBC01) of 429 ind/ha.The results of the calculation of the density of megabenthos found at each observation station in the waters of the Seribu Islands National Park are presented in Figure 3.
Based on the type of megabenthos at all observation stations, the most abundant megabenthos found was sea urchin (Diadema sp.) with a total density of 43,397 ind/ha, while the least was Acanthaster planci at 214 ind/ha.For sea cucumber megabenthos, lobster and blue starfish (Linckia laevigata) were not found at all observation sites.The results of the calculation of megabenthos density for each species in the waters of the Seribu Islands National Park are presented in Figure 4. ) was found at seven observation stations with densities ranging from 71 -214 ind/ha, with a total of 857 ind/ha.Based on the types of clams found, there was hole clams (Tridacna corcea) and giantsclams (Tridacna maxima).The size of the hole clams (Tridacna corcea) found ranged from 7-13 cm, while the giants clams (Tridacna maxima) was >20 cm.The types of clams found at the observation station can be seen in Figure 5. Based on data on the density of clams in the waters of the Seribu Islands National Park, the value of clams density is relatively low.This is because the clams is a type of megabenthos that is used by the community (economically significant).The meat and shells can be used for various purposes.Clams meat is prevalent in the non-fish fisheries trade because of its delicacy, while the shell is often used as a raw material for handicrafts for souvenirs.These shells continue to be the target of the fishing community.These conditions can cause the population and its existence in the coral reef ecosystem of the Seribu Islands National Park to be threatened.Overfishing of economic biota will disrupt the balance of the ecosystem, where the absence of this biota will disrupt the web and food chain [3].

Lola (Trochus sp.)
Lola (Trochus sp.) was found at seven observation stations in the waters of the Seribu Islands National Park, including stations KSBC04, KSBC05, KSBC06, KSBC10, KSBC12, KSBC13 and KSBC14, with densities ranging from 71 to 143 ind/ha, with as many as 571 ind/Ha.Lola is relatively difficult to find because it usually lives hidden behind corals during the day.This follows the nature of his life, which is more active at night or nocturnal.This species usually lives among coral fractures, dead coral and coral crevices on coral reefs in intertidal to shallow subtidal areas [14].Another factor that makes it difficult to find this biota is the fishing factor.Based on the information, local fishermen make this biota a bycatch target for fishermen because it has a relatively high price.The types of lola found at the observation station can be seen in Figure 6.

Crown-of-Torns Starfish (Acanthaster planci)
Crown-of-torns starfish (Acanthaster planci) is one of the biotas that eats coral polyps.This species is quite popular because the impact of coral death it causes is quite severe.The spiny starfish (Acanthaster planci) was found at two observation stations, namely Penjaliran Barat Island (KSBC02) with a density of 143 ind/ha and Melinjo Island (KSBC04) with a density of 71 ind/ha, with a total density of 214 ind/ha.The spiny starfish (Acanthaster planci) found at the observation station can be seen in Figure 7.In this monitoring activity, the Crown-of-torns starfish (Acanthaster planci) was only found in a small number of individuals, but its presence needs to be watched out for considering the reproductive strategy of this species.Under stress conditions, Acanthaster planci will accelerate the process of gonad maturation and immediately lay eggs by releasing large numbers of eggs [15].In addition, the relatively long lifespan of planktonic larvae allows for a reasonably wide dispersal following the pattern of water currents.It will eventually grow and reproduce after finding suitable habitat.The absence of natural predators of this species is also a factor to worry about.

Drupella Snails (Drupella sp.)
Drupella snails (Drupella sp.) are found between dead and live corals.Drupella snails (Drupella sp.) were found at eight observation stations in the waters of the Seribu Islands National Park.The density of drupella snails (Drupella sp.) ranged from 71 -429 ind/ha, with the highest density being on Bira Besar Island (KSBC06).The total density of drupella snail (Drupella sp.) was 1,929 ind/ha.The density of drupella snails (Drupella sp.) below 1,400 to 6,400 ind/ha is not endemic [16].Drupella sp. is a golden snail who habitually eats coral polyps, especially on branching and massive corals [14].In small quantities, this type of gold snail does not significantly impact the corals' condition.Still, if there is a population explosion (epidemic), this gold snail can be fatal to coral damage.Ecologically, this coral polyp-eating snail acts as a natural controller of the balance of the coral reef ecosystem.However, the effect will be pretty significant in killing corals if it is present in relatively large aggregations [17].The types of Drupella snails found at the observation station can be seen in Figure 8. Sea urchins megabenthos (Diadema sp.) is the most common megabenthos found in bottom waters where algae, coral debris, live coral, and rocks are found.Sea urchins (Diadema sp.) were found in all observation stations in the waters of the Seribu Islands National Park.The highest density was found at Pulau Kayu Angin Genteng station (KSBC07) with a density of 8,719 ind/ha, while the lowest was at Pulau Peteloran Barat (KSBC01) with a density of 357 ind/ha.The total density of sea urchins (Diadema sp.) was 43,357 ind/ha.In a study conducted by, in five locations, the difference in density of sea urchins (Diadema sp.), namely: in Uyombo, as many as 8,250 ind/ha, in Kanani, as many as 4,710 ind/ha, in Lambis as many as 2,125 ind/ha.In addition, 690 ind/ha in Coral Gardens and 785 ind/ha in Bennets, but no statistically significant difference but had little effect on the coral cover.It is estimated that 30% of macroalgae cover changes can be caused by sea urchins (Diadema sp.) [18].Several types of sea urchins (Diadema sp.) found at the observation station can be seen in Figure 9. ) is one of the bioindicators of coral health, where its presence in large numbers indicates unhealthy corals [19].Furthermore, Diadema setosum in coral reef ecosystems plays a role in cleaning algae that grow on dead coral that has been overgrown with algae, according to its nature in terms of foraging as algae eaters.Therefore, this black sea urchin has a beneficial role for coral reef ecosystems because it helps clean algae, thus allowing corals to grow properly after the substrate is cleaned by Diadema setosum from the presence of algae [17].

Conclusion
Megabenthos in the Seribu Islands National Park waters are in various conditions.Groups of clams megabenthos (Tridacna sp.) and lola (Trochus sp.), which have significant economic value, can still be found in several observation stations with relatively few individuals.The existence of megabenthos Crown-of-torns starfish (Acanthaster planci), sea urchins (Diadema sp.), and drupella snails (Drupella sp.) have not endangered coral life in the waters of the Seribu Islands National Park.

Fig 3 .Fig 4 .
Fig 3.The density of megabenthos species (ind/ha) at each station in the waters of the Seribu Islands National Park

Fig 5 .
Fig 5. Types of Clams Found at the Water Observation Station of the Seribu Islands National Park

Fig 6 .
Fig 6.Types of Lola Found at the Water Observation Station of the Seribu Islands National Park

Fig 7 .
Fig 7. Types of Crown-of-torns starfish (Acanthaster planci) Found at the Water Observation Station of the Seribu Islands National Park

Fig 8 .
Fig 8. Types of Drupella snails Found at the Water Observation Station of the Seribu Islands National Park Sea urchins (Diadema sp.)Sea urchins megabenthos (Diadema sp.) is the most common megabenthos found in bottom waters where algae, coral debris, live coral, and rocks are found.Sea urchins (Diadema sp.) were found in all observation stations in the waters of the Seribu Islands National Park.The highest density was found at Pulau Kayu Angin Genteng station (KSBC07) with a density of 8,719 ind/ha, while the lowest was at Pulau Peteloran Barat (KSBC01) with a density of 357 ind/ha.The total density of sea urchins (Diadema sp.) was 43,357 ind/ha.In a study conducted by, in five locations, the difference in density of sea urchins (Diadema sp.), namely: in Uyombo, as many as 8,250 ind/ha, in Kanani, as many as 4,710 ind/ha, in Lambis as many as 2,125 ind/ha.In addition, 690 ind/ha in Coral Gardens and 785 ind/ha in Bennets, but no statistically significant difference but had little effect on the coral cover.It is estimated that 30% of macroalgae cover changes can be caused by sea urchins (Diadema sp.)[18].Several types of sea urchins (Diadema sp.) found at the observation station can be seen in Figure9.

Fig 9 .
Fig 9. Types of Sea urchins (Diadema sp.) Found in the Water Observation Station of the Seribu Islands National Park Sea urchin (Diadema sp.) is one of the bioindicators of coral health, where its presence in large numbers indicates unhealthy corals[19].Furthermore, Diadema setosum in coral reef ecosystems plays a role in cleaning algae that grow on dead coral that has been overgrown with algae, according to its nature in terms of foraging as algae eaters.Therefore, this black sea urchin has a beneficial role for coral reef ecosystems because it helps clean algae, thus allowing corals to grow properly after the substrate is cleaned by Diadema setosum from the presence of algae[17].

Table 1 .
Location and Geographical Position of Megabenthos Condition Monitoring Station in the Waters of the Seribu Islands National Park