Mangroves Assessment and Diversity in Coastal Area of Barangay Cagdianao, Claver, Surigao Del Norte, Philippines

According to the National Mapping and Resources Information Authority (NMRIA), Philippines has about 7,641 islands with 3 major islands, Luzon, Visayas, and Mindanao and about 300,000 square kilometers area with vast areas of mangrove ecosystem along shoreline. Government policies, which dictated development in both the uplands and coastal areas, have been based mainly on abundant available resources without due consideration for sustainability. The study was conducted for the purpose to identify mangroves diversity and assessment in barangay Cagdianao particularly near the mining area for the purpose of rehabilitation and conservation. Random sampling was used and with a total number of six stations having three (3) 10 x 10 meters’ quadrat. Results revealed a total of 9 species of mangroves within the areas of Barangay Cagdianao. Family Combretaceae and Rhizoporaceae dominated the area. Lumnitzera littorea and Lumnitzera racemosa dominated in all sampling stations. Eight species were recorded to be Least Concern and one species was considered Vulnerable ( Avicennia rumphiana ). Among the species, Lumnitzera littorea was the most dominant speciesfollowed by mangrove fern Acrostichum speciosum. Based on the results, mangrove areas of the Brgy. Cagdianao, Claver, Surgao del Norte falls under the category of very low biodiversity. Even if the area has low biodiversity, results revealed that the mangroves in Cagdianao experienced minimal disturbances from any anthropogenic activity.


Mangroves
In the tropical coastline, mangroves and seagrass beds are prominent features [1] with great ecological and economic value [2]. Mangroves are one of the most exceptional floras group in the world and grow in the coastlines of tropical and sub-tropical countries and are well adapted to extreme conditions such as high salinity and temperature [3]. The remaining mangrove areas of the world in 2000 was 53,190 square miles (137,760 km²) spanning 118 countries and territories all throughout [4]. Mangroves provide many and useful human products, resources and ecological services such as wood-fire, ethnomedicinal, clean air and typhoon/flood protection. Moreover, it helps maintain ecological balance in an ecosystem. According to mangroves maintain coastal water quality and form a barrier for coastal protection from wave storm and flood damage [5]. Mangroves very important area in an ecosystem. Provides food to many fishes, invertebrates and birds and provide protection to any coastal catastrophic events [6,7]. The Philippines has very rich biodiversity in terms of number and percentage and regarded as one of 17 mega biodiversity countries due to its geographical isolation [8]. The country holds 50% of the world's mangrove species [9] from 65 known species of mangroves in the world [3]. One for the top 15 countries in the world [10].
The rehabilitation, conservation, and protection of mangrove forests along coastal areas of the Philippines should be the collaborative effort between the Local Government Units, Department of Environment and Natural Resources (DENR) as main agency for environment in the Philippines and all stakeholders to make sustainable long term plans. The study of Goloran et al. [11] in selected part in Caraga Region particularly in Agusan del Norte showed that the mangrove community present in mentioned area were under ecological threat due to many identified anthropogenic factors.
To address some issues on mangrove degradation and habitat loss, this study purposely conducted to mangrove assessment,   The study area was within the mangrove and rehabilitation areas near Platinum Group Metals Corporation (PGMC) located at Brgy. Cagdianao, Claver, Surigao Del Norte ( Figure 1). It is one of large scale mining areas in the province of Surigao del Norte specifically located at 9°29'42.13"N and 125°52'18.10"E. There were 6 sampling stations established with three 10 x 10m quadrats per site ( Figure 2).

Transect line and sampling station establishment
Six permanent sampling stations were established within the mangrove areas. Each station had a transect line ranges from 100 to 200 meters perpendicular to the shoreline. Every station and transect line (3) three 10 x 10 plots were established randomly with a distance ranges 15-30 meters and depend on the structure of mangrove community [11,12]. Random sampling allows the researcher to easily determine the composition of mangroves and its type of species. Because individuals are rarely evenly distributed within an area, it is important to sample randomly to ensure that we get a true representation of the population. Mangrove species inside the plot were identified and counted including diameter breast height (dbh), canopy cover (cc), density and height were measured as described by English et al. [13]. Three (3) 1x1m subplots were established in counting of individuals for seedlings and saplings (planted seedlings not included in the counting). Each mangrove within the plots was characterized as seedling, sapling and mature tree based on the definition of Deguit et al. [14].

Mangrove identification
The mangroves within sub-plots and plots were identified and classified taxonomically using the field guide manual to Philippines Mangroves by Primavera et al. [10].

Diversity indices and scale
Using Paleontological Statistical Software Package (PAST) developed by Hammer et al. [15], Shannon-Weiner diversity index, species richness, relative abundance, and evenness were calculated. PAST software is the free-ware widely used by many researchers for flora and fauna inventory including mangroves.

Mangrove species ecological status, occurrences and population trends
Mangrove species status, occurrences, and trends are classified and identified using the recorded online tool, the International Union for Conservation of Nature (IUCN) red list and the DENR Administrative Order No. 11 series 2017 known as the Updated List of Threatened Philippine Plants and their Categories [16].  (Table 1 & 2) Based on IUCN, all species of mangroves identified in all sampling sites were considered widespread throughout the countries and other continents outside Philippines. This is also related to studies conducted by Demetillo et al. [17], that some species in Caraga Region were threatened and endangered. Though all species are considered widespread and only was vulnerable, eight (8) species out of 9 are decreasing in population trends as recognized by the IUCN Red List.   In China, it is an endangered species confined to restricted regions of Hainan Province [18]. Tomlinson et al. [19] stated that L. littorea is pollinated predominantly by honey-eaters such as the graceful honeyeater (Meliphaga gracilis (Gould), various sunbirds, bees and wasps. This could be a good indicator that there are still many faunal species found and relied on L. littorea within the mangrove area of Brgy Cagdianao.

Species richness
In 6 sampling stations, station one (S1) obtained the highest value in terms of individuals and species richness with a total of 162 individuals and 9 species respectively. Station 6 (S6) got high diversity results with 1.542 and Station 4 (S4) got the Dominance value of 0.7022 ( Figure 5).

Canopy Cover
Canopy cover plays an important role in the amount of sunlight that penetrates the forest floor. Scientists classify forest canopies as open (10-39% of the sky is obstructed by tree canopies), moderately closed (40-69% of the sky is obstructed by tree canopies) or closed (70-100% of the sky is obstructed by tree canopies). Densiometer is used to measure this light however because of resources, many researchers used the alternative way in measuring canopy cover and this is to position at the center of every quadrat. In all 6 stations, station 1 (S1) (73.33%) was estimated denser compared to the rest of the stations (Figure 6). The estimation affirmed that station 1 (S1) has a high number of individuals of mangrove trees. It was also recorded that station 1 obtained the high number of species density. The total average canopy cover within the mangrove area of PGMC has a total value of 43.88 or 43% which is interpreted as Moderately Closed (MC) canopy per square meter (m 2 ). With these results, this can be interpreted that the area still has an intact mangrove population density but need close monitoring and be provided with a systematic rehabilitation plan for more improvements.

Regeneration and estimated average height
The regeneration count for sapling and seedlings was calculated using the formula described in the methodology.
Planted seedlings by the personnel were not included and only natural seedlings/saplings are recorded below the mangrove tree species. Figure 7 shows the regeneration per square meter (m 2 ) and estimated average height of mangrove trees.

International Journal of Environmental Sciences & Natural Resources
Based on the classification given by Deguit et al. [14], the regeneration (3 individuals per m² was considered excellent and moderate category for average height (3.64 meters) of mangroves. Excellent means undisturbed to any negligible disturbances and fair means moderate disturbances. Though mangrove habitat assessment provides good results within mangrove areas of Cagdianao there were still minimal disturbances observed during the actual sampling and this was illegal cutting of mangrove trees (Figure 8) used as firewoods by locals and illegal hunting of faunal species. Illegal hunting of different faunal species is a clear violation of RA 9147 otherwise known as "Wildlife Conservation Act". If this will continue, it will affect the whole mangrove community because faunal species found within the mangrove areas are the main pollinators and the natural planters of this type of ecosystem. Conservation, protection, and education should strictly observe.

Vegetation analysis
The mangroves community structure was evaluated by using the values of population density, relative density, frequency, relative frequency, dominance and relative dominance. The summations of these values were added to attain species importance value (SIV) in the entire sampling area. The species Lumnitzera littorea was noted of having the highest population density indicating that this species has the highest count per unit area, followed by Acrostichum speciosum and Lumnitzera racemosa (Figure 9). For relative frequency, Lumnitzera littorea and Bruguiera sexangula had the highest value followed by Lumnitzera racemosa ( Figure  10). Dominance still dominated by Lumnitzera littorea (Figure 11) including the species importance value as shown in Figure 12.

List of mangrove species
Nine (9) species were found and recorded within the sampling station in Cagnianao, Claver Surigao Del Norte mangrove areas excluding the planted (through rehabilitation program) seedlings ( Figure 13). Other mangrove species are planted by the Mine Environment Division through its rehabilitation program. These species are Nypa fruticans (Nipa) and Rhizophora mucronata (Bakhaw Bae).

Conclusion
Based on the results and findings of the study, it was concluded that the mangrove areas of Brgy. Cagdianao, Claver, Surigao del Norte falls under very low biodiversity. The area has a total number of nine mangrove species in seven families. Among the 9 mangrove species, Lumnitzera littorea and Acrostichum speciosum dominated the area in terms of abundance, frequency and individuals recorded. Habitat assessment showed that regeneration (3 individuals) per m² was considered excellent and moderate category for average height of mangroves. This means that the area experienced very low disturbances from anthropogenic activity. The total average canopy cover (cc) within the mangrove area of Cagdianao had a total value of 43.88 almost 43% in which it is interpreted as Moderately Closed Canopy (MC) per square meter still intact mangrove density. Mangrove vegetation analysis showed that Lumnitzera littorea had the highest value in terms of relative frequency, relative density, relative dominance, and species importance value followed by Acrostichum speciosum and Lumnitzera racemosa repectively. Some important other species of plants such as X. verdugonianus, P. utilis and Q. indica were identified and thrived together with true mangrove species.

Recommendation
With the presented result, mangroves play very important role in maintaining ecological balance both living organism and nonliving. Conservation effort must be considered knowing that the area has a number of threatened species and experience anthropogenic damages. With that, the area obtained a very low biodiversity of mangroves. For Future studies, it is highly recommended to have a comprehensive assessment on soil and water analysis along mangroves area of Cagdianao, Claver, Surigao del Norte.

International Journal of Environmental Sciences & Natural Resources
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