Inventory of mangrove species diversity in Ruar village, Biak Numor Regency, Papua Province

Efforts to preserve mangrove forests through species diversity inventory are important input data in mangrove forest management. The purpose of this research is to investigate the potential and diversity of mangrove forest species in Ruar village, Biak Numfor Regency, Papua Province. Inventory of mangrove species using the grid line method which is laid systematically. The distance between the lanes is determined to be 200 meters and plots are placed to the left and right of the lanes, making up as many as six lanes/transects. The results of this study, there are 5 species, namely Sonneratia alba, Rhyzophora stylosa, Rhyzophora apiculata Bl, Bruguiera gymnorhyza (L) Lamk, Ceriops tagal (Perr). C.B.Rob. On tree growth rates were dominated by Rhyzophora apiculate Bl (INP 152.73%), sapling and seedling rates dominated by Bruguiera gymnoriza (L) Lamk (INP 137.85% and INP 128.46%). Species diversity index according to tree growth rate (0.874), sapling rate (0.678) and seedling rate (0.667). According to Shannon-Wienner criterion (H’ <1), the species diversity index in the mangrove forest of Ruar Village, Biak Numfor Regency is low. Species enrichment planting activities are needed in maintaining and increasing the diversity of mangrove species to control environmental disturbances.


Introduction
Mangrove forests are natural resources that play an important role in maintaining the balance between terrestrial and aquatic ecosystems [1] [2].The mangrove ecosystem is an area that functions as a bridge between land and sea.[3].Mangrove forests have an ecological function but also have an economic function, as a producer of firewood, and as a raw material for making charcoal [4].Wood from mangrove trees can be used as raw material for paper and this is what makes mangrove wood have a high selling value [5].Mangrove forests can be used as natural tourism areas [6].
The distribution of mangrove vegetation in Indonesia is spread over coastal areas from west to east.The species of vegetation that dominate in mangrove forests in Indonesia are diverse.According to [7], the distribution is spread across Indonesia for as many as 202 tree species, which are spread across the islands of Java, Sumatra, Kalimantan and Papua.Mangrove communities in Indonesia are generally divided into two communities, namely mixed communities and pure communities.For a mixed community dominated IOP Publishing doi:10.1088/1755-1315/1315/1/012024 2 by Bruguiera spp.and Rhizophora spp., while pure communities or consociations are Avicenia, Rhizophora, Sonneratia, Bruguira spp.and Rhizophora spp.Information on the distribution of these species is generally located on the main island and is different from the distribution of mangrove species in small/local areas.
The mangrove community on a small island like Biak has a different distribution from the main island.The condition of the mangrove community in the eastern coastal area is dominated by the mangrove species Bruguiera gymnorizha and Sonneratia alba [8].The mangrove community is currently still dominated by the species Bruguiera gymnorhyza and Sonneratia alba in the sapling and tree categories because the substrate conditions are very suitable, namely sandy mud substrate, while the density category is dominated by Rhyzophora apiculata and Sonneratia alba [9].Based on the results of satellite imagery management, the mangroves in the east coast of Biak Island cover an area of 144.81 Ha, consisting of the East Biak District covering an area of 69.73 Ha and the Oridek District covering an area of 75.08 Ha [10].The area of Ruar's Village mangrove forest is 24.03 hectares.The mangrove forest of Ruar Village stretches along the coast and is traversed by the main road from downtown Biak which connects the East Biak District and the Oridek District, this mangrove forest stands as a protector of water sources which are the main (water pom) inherited from the Dutch which supply clean water to the Biak District City.Ruar Village, Biak Numfor Regency, has a mangrove forest that is still well preserved, but information about the existing potential is still relatively lacking, so research is needed to obtain useful data for better development of the mangrove forest.The purpose of this study was to determine the potential and diversity of species in mangrove forests in Ruar Village, Biak Numfor Regency.

Research location
This research was conducted in Ruar Village, Biak Numfor Regency.The population in this study were all types of mangroves in the mangrove area of Ruar Village and the samples were all mangrove species found in the observation plots (Figure 1).

Research procedure
The type of research data is quantitative data and its source is obtained from observations and measurements.Secondary data obtained from related agencies.The data collection technique is direct observation in the field.Determination of the sample used the check line method which is placed systematically perpendicular to the vegetation.The length of the transect line varies according to the thickness of the mangrove vegetation.Pick a starting point at random and make a path or transect from the mainland zone towards the coastline, the distance between the lines is 200 meters, determine (plots) on the left and right of the route.Data collection included identifying each type of mangrove, counting the number, measuring the diameter of the tree at breast height or 20 cm above the buttresses and filling in the observation table.
Determination of the sampling intensity is 5%, the area of the study site is 24 ha (total sample area of 1.2 ha), the width of the observation strip is 10 meters, the distance between lanes is 200 meters, the length of the lane is 1200 meters, the number of lanes is 6 lanes and 120 sample plots.The size of the plot/plot is based on the plant class, so the plot size is determined as follows;  The research method used is a survey method, where the data collected is primary data obtained directly from the field using vegetation analysis techniques.The research procedure consists of 3 stages, namely; 1. Preparation includes obtaining permits, secondary data collection, field observations, preparation of tools and materials.2. Determining the sampling design includes determining the vegetation samples using the quadratic transect method (checked line), namely by making a transect line perpendicular to the shoreline cutting through the vegetation.3. Data collection includes vegetation data.Vegetation analysis techniques are aimed at determining the structure and species composition of a forest stand.Ecology: Estuaries, pond borders, grow well in the zone inner mangroves, dry areas, and regions of high salinity [12].There are 4 types of mangrove communities at the tree level, namely Sonneratia alba, Rhizophora apiculata, Rhizophora Stylosa and Bruguira gymborisa.Rhyzophora apiculate Bl was the dominant species at the growth rate of trees with a density of 202 trees/ha and an IVI of 152.73%, while the lowest species was Rhyzophora stylosa with a density of 7 trees.ha-1and an IVI of 3.52%.This is related to research by Setyadi et al (2021) who found the dominant species of R. apiculata in Mimika Regency, Papua.The IVI can be used to determine the importance value index of each species in the community structure [13] [14].

Mangrove vegetation composition
In Table 3, Bruguiera gymnoriza (L) Lamk was the dominant species at the growth rate of saplings with a species density of 192 ind.ha -1 and an IVI of 137.85%, while the lowest species was Sonneratia alba with a species density of 2 ind.ha-1 and IVI of 2.15%.4, Bruguiera gymnoriza (L) Lamk was the dominant species at seedling growth rate with a density of 452 seedlings/ha and an IVI of 128.46%, while the lowest species was Ceriops tagal (Perr).C.B.Rob with a density of 7 seedlings ha -1 and IVI of 3.82%.Density is the number of individual types per unit area or per unit volume.The results of the vegetation analysis showed that the types of Rhyzophora apiculata Bl and Bruguiera gymnoriza (L) Lamk were evenly distributed in each observation plot with a higher number of individuals than the types Soneratia alba, Rhyzophora stylosa and Ceriops tagal (Perr).C.B. Rob.
According to [15] if the frequency value ranges from 1-20% it is categorized in class A (very low), then if the frequency value ranges from 21-40% it is categorized into class B (low), 41-60% in class C category (moderate), 61-80% class D (high), and category 82-100% (very high).The high value of the relative frequency of the species Rhyzophora apiculate Bl and Bruguiera gymnoriza (L) Lamk is because they are always found in each observation plot and the growth rate of trees, saplings and seedlings.
Rhyzophora sp is the dominant type of mangrove plant in a mangrove forest area because it is able to adapt well to its environment when compared to other species [16] [17] [18] [19].The stability and existence of mangrove ecosystems is largely determined by the types of mangrove ecosystem constituents where the role of one type of mangrove against another can be observed from the importance value index.If a species shows a high important value then the role of that type is very large against other types in the mangrove ecosystem.

Diversity index (H')
Species diversity was measured on the growth rate of trees, saplings and seedlings.The level of diversity of vegetation types can be seen from the number of individuals in each species.According to [20], the components of species diversity consist of distribution and species richness.The diversity index of mangrove species at tree, sapling and seedling levels can be showed in Tables 5, 6 and 7.  7 shows that at the seedling level, 3 species were found, namely Rhyzophora apiculata Bl, Bruguiera gymnorisa (L) Lamk and Ceriops tagal (Perr).C.B. Rob with 659 seedlings.Soneratia alba and Rhyzophora stylosa were not found at the seedling level.The diversity index value is 0.667 or classified as low according to the Shannon-Wienner diversity index value criterion (H') = H' < 1.
Based on the results of the analysis of mangrove vegetation, it can be concluded as follows; The types of mangrove plants that make up the forest in Ruar Village consist of 5 speciess, namely Sonneratia alba, Rhizophora stylosa, Rhizophora apiculata Bl, Bruguiera gymnorhiza (L) Lamk, Ceriops tagal (Perr).C.B.Rob.Vegetation analysis results according to tree growth rate were dominated by Rhizophora apiculata Bl (INP 152.73%), saplings and seedlings were dominated by Bruguiera gymnorhiza (L) Lamk (IVI 137.85% and IVI 128.46%).Species diversity index according to tree growth rate (0.874), sapling level (0.678), and seedling level (0.667).The species diversity index in the mangrove forest of Ruar Village is low according to the Shannon-Wienner criteria (H') = H'< 1.

Figure 1 .
Figure 1.The research location is in the mangrove forest of Ruar Village, Biak Numfor Regency a. Class of trees, size 10 m x 10 m b.Stake class (sapling), size 5 m x 5 m c.Tiller class (seedling), size 1 m x 1 m Measurement of the growth class level uses the following criteria: a. Trees: a class of plants having a diameter at breast height ≥10 cm.b.Saplings: a class of plants that have a height of ≥1.5 m and a diameter of < 10 cm.c.Seedlings: plant class ranging from 2 leaves to <1.5 cm high.

Figure 3 .
Figure 3. Sonneratia alba Classification of Sonneratia alba plants: Kingdom: Plantae; Division: Magnoliophyta; Class: Magnoliopsida; Order: Mytales; Family: Lythraceae; Genus: Sonneratia; Species: Sonneratia alba Local name: Sawawir, Swaikur (Biak Numfor) Tree; Diameter: up to 40 cm; Height: up to 20 m Rooting: respiratory root, wedge-like, firm, sharp; The diameter of the root base reaches 5 cm; Outer skin: gray to brown, cracked elongated and peeled off; Inner skin: brown to pink Leaf arrangement: opposite; Composition: single Shape: obovate to oval; Size: length 6-9 cm, width 3.5-7 cm; Tip: obtuse; Base: acute or obsute Leaf surface Top: light green -green; Bottom: light green; Stem: 1 cm long; Headboard: solid and compact Flower Type: cyme, or solitary; Calyx: green outside, red inside, lobe 6-8; Petals: cream to white Fruit: old hard fruit, green with a 2-3 cm long filament, the calyx does not shed like a star Habitat: generally in the confluence of the river ramps or bays Ecology: Seaside, along the estuaries of tidal rivers, on muddy or rocky ground, in mud sand from estuarine rivers, often forming shores bordering the sea, land with salinity high relatively [12].2.General description of Rhizophora apiculata Bl

Table 2 .
Tree level mangrove vegetation structure

Table 3 .
Sapling level mangrove vegetation structure

Table 4 .
Seedling level mangrove vegetation structure

Table 5 .
Mangrove species diversity index at tree level

Table 5 shows
that at the tree level, 4 species were found, namely Soneratia alba, Rhyzophora apiculate Bl, Rhyzophora stylosa and Bruguiera gymnorisa (L) Lamk with a total of 407 trees.Type Ceriops tagal (Perr).C.B.Rob at tree level not found.The diversity index value is 0.874 or classified as low according to the Shannon-Wienner diversity index value criteria (H') = H'< 1.

Table 6 .
Sapling level mangrove species diversity index

Table 6
shows that at the sapling level, 4 species were found, namely Soneratia alba, Rhyzophora apiculata Bl, Bruguiera gymnoriza (L) Lamk and Ceriops tagal (Perr).C.B.Rob with a total of 262 saplings.Rhyzophora stylosa species at the sapling level were not found.The diversity index value is 0.678 or classified as low according to the Shannon-Wienner diversity index value criteria (H') = H'< 1.

Table 7 .
Seedling level mangrove species diversity index