Biodiversity, community structure and potential uses of seaweeds and seagrass in transition zone of Taka Bonerate Kepulauan Selayar biosphere reserve, Indonesia

Macroalgae and seagrass play an important role in marine ecosystems. These organisms have important ecological roles that include primary producers, food sources for other biota, shelters and carbon sinks. Economically, many macroalgae and seagrass species can be exploited as commodities due to their nutritional values and benefits. In Indonesia, macroalgae is traditionally used as food and medicines, especially by communities living in coastal areas. This study aims to unravel the diversity and potential uses of seagrass and macroalgae in Polassi and Tambolongan islands, which is part of the transition zone of the Taka Bonerate Kepulauan Selayar Biosphere Reserve. Identification was performed to analyse several parameters, such as: frequency, density, closure, IVI, dominance and diversity index. Based on the identification results, 7 species of seagrass and 17 species of macroalgae were obtained. Five seagrass species and five algae species are known to contain compounds that are beneficial to humans such as antibacterial, antifungal, and bioactive compounds. Four algae species are used for consumption. The diversity index values of seagrass and macroalgae obtained were categorized as low-medium, with H’ 1.05 - 1.55 for seagrass and H’ 1.22 - 1.56 for algae. This study provides information that are useful for future utilization of marine resources.


Introduction
Indonesia is an archipelagic country with over 17,500 islands, and hosts one of the world's most diverse and abundant marine natural resources.Some of the most abundant resources of Indonesian coastal are seagrass and macroalgae (seaweed).Seagrasses are the only flowering plants that have true rhizomes, leaves and roots found in coastal areas.Macroalgae are plants that do not have true roots, stems and leaves but instead have a stem-like organ called a thallus.These two plants are scattered throughout the coast of Indonesia and naturally can be found living side by side.
Seagrasses usually form carpets/beds consisting of one species (mono-species) or more than one species (multispecies).Taxonomically, seagrass is included in the Angiosperms group, of which its habitation is limited to coastal areas.Seagrasses can form an ecosystem called seagrass beds the shallow water.Seagrass ecosystems are complex ecosystems and have ecologically important services [1,2].An example for this is various secondary metabolites produced by marine angiosperm, which have been shown to have potentials as effective drugs for various diseases [3].
Live macroalgae attach to the substrate so they are not easily carried away by currents and can be found in tidal areas.Macroalgae have four types of lifeforms, namely Rhizopitic, which are macroalgae that grow to immerse themselves in mud or sand substrates; Ephilitic are macroalgae that attach to rocks, coral rubble and other hard substrates; Epiphytic are macroalgae that live attached to seagrasses and other macroalgae; and Ephizoic are macroalgae that live attached to the shells of molluscs or other animals [4].Macroalgae have many ecological and economic benefits for society.Ecologically, macroalgae play an important role as producers of food chains in the sea, especially as food for herbivorous organisms.In addition, macroalgae also function as carbonate providers and basic substrate reinforcement which is beneficial for the stability and continuation of coral reefs [5].Several algae 1255 (2023) 012028 IOP Publishing doi:10.1088/1755-1315/1255/1/012028 2 species have a fairly high nutritional content, including protein, carbohydrates, fat and fiber [6] so they can be consumed.In addition, living in extreme conditions, secondary metabolites resulting from the defense mechanisms and adaptations of algae contain bioactive compounds that can be beneficial to humans [7].
Kepulauan Selayar Regency has high marine resources such as coral reef ecosystems, seagrass, macroalgae (seaweed), and other marine biotas that live in the ecosystem.The use of high resources and the vulnerability of coastal marine ecosystems in this region is the reason why this area adheres to the concept of a biosphere reserve and was recognized by UNESCO in 2015.Taka Bonerate Kepulauan Selayar Biosphere Reserve promotes a balanced relationship between humans and the environment by implementing a biosphere reserve zoning management system and mutual relate to one another.The Biosphere Reserve consists of 3 zones namely, the core zone, the buffer zone and the transition zone.These three zones are important elements for biosphere reserves and are interconnected with one another.The zone designated for sustainable and sustainable management and utilization of natural resources is a transition zone, so that this zone can be developed for community needs such as livelihoods [8].
The high use and resources of seagrass ecosystems in the Kepulauan Selayar is the reason for the need for a study of the potential size of seagrass and macroalgae resources in the area.This study provides baseline data that can be used as an initial assessment towards a more thorough investigation of the factors required for strategic management and sustainable use in the area.

Study location
Sample data collection was carried out in two islands which are included in the transition zone of the Taka Bonerate Kepulauan Selayar Biosphere Reserve, namely Tambolongan Island and Polassi island, South Sulawesi Province (Figure 1) on 2 -12 October 2018.

Sampling technique
Data collection was carried out at 4 stations, 2 on Tambolongan Island (west side S1 and east side S2) and other 2 stations on Polassi Island (west side S3 and east side S4) with criteria based on beaches that have seagrass beds with 2 transects for each station and data taken left and right so that a total of 40 observation points.The method used is the quadratic transect method.The position of the transect begins with the installation of the transect from when seagrasses and macroalgae are found for the first time.With a distance between transect 1 and transect 2 of 50 m, two transect lines are drawn perpendicular to the coast for 100 m.This is done in order to see whether there are community differences between each transect and to represent the community at each station.The first squared plot was placed where seagrass and macroalgae started to grow, then moved 10 m apart along the transect line, plots were placed left and right up to 100 m or 20 plots.After that, seagrass and macroalgae species found were identified.Observations were made by means of snorkeling on the surface of the water following the path of the line transect and this transect activity was carried out when the sea water was receding.Sulawesi, Indonesia.

Analysis
Several parameters are used to measure and evaluate biodiversity and its ecology, namely the Shannon-Wiener Diversity Index (H') and Index of Evenness (E) [9,10].Analysis of community structure, namely density, frequency, abundance [11] and Important Value Index (INP).

Results and Discussion
There are 7 species of seagrasses found in the waters of Tambolongan and Polassi islands, namely Cymodocea rotundata, Halodule pinifolia, Thallasia hemprichii, Enhalus acoroides, Sryngodium isoetifilium, Halophila minor, Halophila ovalis.Seaweed is also commonly found side by side with seagrasses in seagrass ecosystems and 17 species have been identified belonging to 13 genera and 3 divisions (Table 1).The results of the analysis of the Shannon-wiener (H') and evenness (J') diversity index values, seagrass diversity in the Polassi coast is low, while Tambolongan Island is categorized as medium with an H' value of 1.55 and J' close to 1 (Table 2).Seagrass density is quite high, especially on Tambolongan Island.The average seagrass density of the two islands was 707.43 shoots/m 2 and 39.77 %/m 2 cover.The most common seagrass species found at the four stations was C. rotundata and the least common seagrass species was H. ovalis.Meanwhile, seaweed was found to be much smaller than seagrass, with an average density of 28.95 colony/m 2 .
C. rotundata is a species of seagrass that can grow on all types of substrates [12].C. rotundata is a pioneer species in seagrass ecosystems, due to its excellent adaptability to its root system.This root system can absorb nutrients in various types of substrates.At stations S3 and S4, the C. rotundata species had the highest density values compared to other species with values of 394.3 ind/m 2 and 140.4 ind/m 2 .This is because this species can grow in almost all types of substrates [12].Both of these stations have various types of substrates so that this species has a high density compared to the other seagrass species at stations S3 and S4.At station S2 the species that has a high density is T. hemprichii with a value of 312.3 ind/m 2 .According [13], the density of seagrass shoots for expansion of the area depends on the species, if the seagrass species has a large morphology such as E. acoroides then it will have a low density compared to seagrass species that have a small morphology such as T. hemprichii.At station S2 S. isoetifolium has the highest density value with a value of 295.1 ind/m 2 .Based on the results of this observation, the Chlorophyta division is the division that is most commonly found compared to the other 2 divisions.This is because most of Chlorophyta species grow in shallow waters and can adapt easily.In addition, Chlorophyta is the largest of the three algae divisions and easily attaches to various substrates such as sand, muddy sand, crushed coral and coral [14].Chlorophyta is also a macroalgae division that is able to grow in various water conditions because it has tolerance to adapt to high environmental factors [15].The Phaeophyta division is the least number of divisions found on Polassi Island and Tambolongan Island, besides that the Phaeopyta division is a division that has a low number of species at all stations.This is caused by various factors, one of which is the type of substrate that is not suitable for the growth of macroalgae from the Phaeophyta division.According to Kadi and Atmajaya (1998) [18], locations with sand substrates tend to be a habitat for Chlorophyta.Areas with substrates of broken coral and live coral or reef-flat sections are suitable for Phaeophyta habitat because they have disc-shaped holdfasts that can grip hard substrate, while the type of substrate at four stations is dominated by sand.The most common species found were H. cylindracea and H. micronesica from the Chlorophyta division.According to Hillis-Colinvaux (1980) [16], Halimeda sp. can grow because it has a holdfast that can stick to sandy substrates and can grip hard substrates such as rocks, coral rubble and coral cover.Its holdfast is in the form of a collection of fibrous roots, capable of hooking coarse substrates and sand particles [17].The fewest species found were P. australis and D. bartayresiana from the Phaeophyta division because these divisions can live on dead coral or rock substrates, while the substrate at the four stations is dominated by sand so that the species in this division cannot grow well [18].
The Importance Value Index (IVI) provides an overview of the influence of the role of a seagrass species in a seagrass community (Figure 2).The IVI value depends on the value of relative frequency, relative density and also relative closure.C. rotundata and T. hemprichii were the species that had the highest IVI among all species at the four stations, with each species having an average IVI of 26% and 29% (Table 3).This indicates that the two species have an important role for the seagrass community at the four stations.The higher the IVI of a species against other species in a community, the higher the role of this species in the community [9].In terms of frequency, density, closure and IVI, the species with the lowest values were H. ovalis and H. minor.This small number is due to the fact that the Halophila genus tends to have a substrate of broken coral and rocks, so that at four stations it is rare to find H. ovalis and H. minor    At the four stations, the highest Importance Value Index was in the Chlorophyta division.This can be caused by various factors of the type of substrate and environmental factors that support the growth of macroalgae in the chlorophyta division.The type of substrate at these four stations is sand and coral rubble at the west station of Polassi and Tambolongan islands while at the east station of Polassi and Tambolongan islands the sand is muddy.Based on the above data Halimeda sp. has a high importance value index at 3 of the 4 stations that were observed.This is because the holdfast possessed by this species is in the form of a mass of fibrous roots so that it is able to grip hard substrates to sand.

Seagrass
The seagrass bed ecosystem in the Taka Bonerate Kepulauan Selayar Biosphere Reserve has the potential for bioactive compounds from either seagrass or algae.Many laboratory tests have been carried out on seagrass and algae for the content of bioactive compounds that can work as anticancer, antiinflammatory, antidengue fever, antidiabetic, reduce cholesterol or obesity, antioxidant, antibacterial and antiviral (Table 3).Bioactive compounds as antioxidants and antibacterials have the potential to be abundant at the study site (Table 4).Antioxidants are chemical compounds that can reduce free radicals in the human body [20].The abundant of T. hemprichii at the study site is known to have a strong antioxidant content with an inhibitory concentration value of IC50 ˂50 ppm [21].Similar to seagrass, H. micronesica algae in the antioxidant effect test using the DPPH (1,1-diphenyl-2-picryhydrazyl) radical was indicated to inhibit free radicals with an IC value of 5052.81 ppm [22].In testing the bioactive compounds of the T. hemprichii against bacteria, they showed antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa bacteria [23].Meanwhile, C. rotundata inhibited the growth of E. coli and P. aeruginosa [24].Based on laboratory tests by Dini et al (2019) [25], H. cylindraceae has antibacterial bioactive compound activity against S. aureus, E. coli, and S. typhi.In addition to antioxidants and bacteria, hexadecanoic acid isolated from methanolic aqueous extract of T. hemprichii and C. rotundata showed inhibition of HIV-1 protease [25].

Conclusion
The seagrass ecosystem in Tambolongan and Polassi islands has a high density of around 324.60 -838.70 ind/m 2 with low and medium diversity of seagrass and algae species.Seagrass species T. hemprichii and C. rotundata play a high role with an important value index of around 15 -37% in the community structure on the coast of Tambolongan and Polassi islands.While H. cylindraceae and H. micronesica are species that play a high role in this ecosystem with an important value index of around 7 -52% at each observation station.The high content of antioxidants and antibacterials in these four species indicates that the seagrass ecosystem on Tambolongan and Polassi islands has great potential as a natural source of pharmacological purposes for health and the treatment of human diseases such as antioxidants, antibacterial and antivirals.Future research can be directed towards the explorations into pharmacological applications for sustainable use of these organisms.

Figure 2 .
Figure 2. Importance value index of seagrass species found on the islands of Tambolongan and Polassi

Table 2 .
Index of seagrass and algae structure community in Tambolongan and Polassi

Table 3 .
Important Value Index for seaweed species found on the islands of Tambolongan and Polassi