Diversity of Macroinvertebrates in the Mangrove Forest of Brgy. Nabago, Surigao City, Philippines

Macroinvertebrate assemblages in the mangrove forest were assessed to determine the baseline information on the marine ecosystem in Barangay Nabago. Physicochemical parameters of soil and water were also determined to correlate with these bio-indicators. Three sampling stations were established. Live specimens were collected from natural substrates such as rocks, leaves, wood, and other debris through hand picking. To obtain macrobenthos, soil samples were collected using a core method with six-core samples from each plot. A 500 micrometer (0.5 mm) mesh size sieve was used to separate the macroinvertebrates from the sediments and any debris. A multiparameter checker determined the physicochemical parameters of water such as dissolved oxygen, pH, temperature, total dissolved solids, and conductivity. Biodiversity indices such as species richness, abundance, density, Shannon-Weiner diversity index, and evenness were calculated using the Paleontological Statistical Software Package (PAST) version 3.20 with correlation analysis using Canonical Correspondence Analysis (CCA). Station 3 obtained the highest frequency count of macroinvertebrates compared to the first (1) and second (2) stations, which correlate to the highest numerical value of the physicochemical parameters such as dissolved oxygen (DO), conductivity, and pH. These physicochemical parameters were favourable for macroinvertebrate species to thrive. Soil characterized with the highest percentage of the sandy substrate also contributed to macroinvertebrates’ diversity, particularly in station 3, which obtained the highest diversity index (H’=2.436).


INTRODUCTION
Marine macroinvertebrates play vital roles in maintaining the ecological balance of the aquatic ecosystem through circulation and recirculation of nutrients, breakdown of decaying organic matter, and serve as prey for aquatic chordates such as fishes.Since these organisms are sensitive to the different physical and chemical conditions, their survival is related to the water quality, making them good bioindicators in evaluating and monitoring water quality (Flores, 2012;Tomanova et al., 2008;Jackson et al., 2006).Aside from using ecological data on aquatic macroinvertebrates, the use of physical and chemical limnology would also determine the quality of marine water.However, the coastal ecosystem in which these macroinvertebrates inhabit host anthropogenic stressors affecting the assemblage of these ecologically important organisms and altering the physical and chemical quality of the water.The mangrove forest is one of the most altered coastal ecosystems on the planet in which conversion for aquaculture practices are top among global concerns.Aside from habitat destruction, the populations of marine macroinvertebrates were also threatened for they are harvested for food consumption and ornamentation.These practices are very evident in the coastal regions of the Philippines, including the coastal areas of Surigao City in the island of Mindanao.
Barangay Nabago is one of the coastal barangays of Surigao City with a vast mangrove belt.However, houses and buildings in the vicinity started to grow along with the utilization of mangrove forests.There was no report yet on biological monitoring in the area; besides, basic information regarding the occurrence and conservation status of marine macroinvertebrates is lacking in Asia, Africa, and South America (Bautista et al., 2017).It is, therefore, useful to determine the marine macroinvertebrates assemblages found in the area to assess the health of the marine ecosystem.These biological indicators will be used together to determine physicochemical parameters of soil and water to provide baseline data useful for policymaking tools in the protection and conservation of the area.

Study site
Based on the 2016 Surigao City Ecological Profile, Barangay Nabago is classified as a mainland coastal barangay with a population of 1,143 individuals.It is located at 9° 44' 05.14'' North and 125° 33' 50.60"East.Barangay Capalayan bounds it on the East and Barangay Cabonbongan on the North.Barangay Nabago has a total land area of 3.7538 km 2 with an average elevation of seven ( 7) meters above sea level.
The mangrove forests of Nabago belong to the Cagniog-Balibayon-Day-asan-Orok-San Isidro-Capalayan-Nabago mangrove belt which serves as the spawning ground for various marine organisms.In 2008, a 500-hectare Mariculture Park was established in Barangays Nabago, Day-asan, Capalayan, Cabongbongan, and San Isidro (Roa et al., 2017) to support the fishing community in the area.The Mariculture Park, later on, became a recipient of the city's Mobile Mariculture Platforms (MPPs) program (Crismundo, 2016).However, the mangrove forests in the area are threatened by destructive activities by the local community as they use the mangroves for construction and firewood (Arbis et al., n.d.).

Establishment of sampling stations
Three sampling stations were established in the mangrove forest of Barangay Nabago (Figure 1).Sampling station 1 lies geographically at 125° 34' 19.632" N and 9° 44' 5.388" E; while sampling station 2 is at 125° 33' 42.6" N and 9° 44' 39.0984" E; and sampling station 3 at 125° 33' 33.228" N and 9° 44' 54.132" E. Biophysical description of the three sampling stations were made during the field visit.Entry protocol such as meetings with the barangay local government officials to obtain necessary permits was done.Gratuitous Permit from the Regional Office of DENR was secured before the conduct of the study.
A 100-meter transect line was established in each station parallel to the shoreline, which served as the baseline.From the baseline, three (3) 150-meter transects were established (perpendicular to the shoreline) with a 50 meters distance between transects.Five (5) 100 square meter quadrats were established in every line transect with 20 meters distance between plots.

Collection of macroinvertebrates samples
Field sampling was done from September 2020to April 2021.Visible live macroinvertebrates situated within the established plots were recorded and tallied.Live specimens were collected from natural substrates such as rocks, leaves, wood, and other debris through hand picking.To obtain macrobenthos, soil samples were collected through core method.Six core samples were collected from each plot using an improvised corer with a 10cm diameter and 25-cm in height.The corer was inserted 20-cm deep into the sediment layer for each plot.The collected samples were then sieved using a 500 micrometer (0.5 mm) mesh size to separate the macroinvertebrates from the sediments and any debris.All collected specimens were separately placed in a container with proper labels.

Sorting, Photo Documentation, and Species Identification
The collected macroinvertebrates were sorted in the biology laboratory of Surigao State College of Technology, Surigao City.Photo documentation using the digital camera was done for larger organisms, and the dissecting microscope was utilized to capture photographs for smaller organisms.The macroinvertebrates were identified up to the species level using journals and the internet databases such as the World Register of Marine Species (WoRMS) and marinespecies.org.

Physico-chemical Parameters of Water and Soil
The physicochemical parameters of water such as dissolved oxygen, pH, temperature, total dissolved solids, and conductivity were determined using a multiparameter checker.This was done in triplicate for each plot before the collection of soils and macroinvertebrates.Three (3) 500-g of soil samples were collected per plot using soil corer.Soil samples were sent to the Regional Soil Laboratory, Department of Agriculture, Butuan City, for soil analyses.

Data Analysis
Biodiversity indices such as species richness, abundance, density, Shannon-Weiner diversity index, and evenness were calculated using the Paleontological Statistical Software Package (PAST) version 3.20 developed by Hammer et al. (2001).
The correlation analysis was used to elaborate on which water quality parameters and soil characteristics were correlated to species abundance.Canonical Correspondence Analysis (CCA) using Paleontological Statistics (PAST) software version 3.20 was employed to produce a biplot showing the species-environment association.
CCA is a multivariate method to elucidate the relationships between biological assemblages of species and their environment, including Eigenvalues (Ter Braak & Verdonschot, 1995).
Under Bivalvia, there are two families such as Lucinadae and Ostreidae.There are two (2) species under Family Ostreidae, Crassostrea angulata and Saccostrea cuccullata, which are found in Stations 1 and 2, which the latter can also be found in station 3. Anodontia edentula is the only species under the Lucinidae family observed in Stations 1 and 2. Diadema antillarum is the only species found in stations 2 and 3 under the family Diadematidae of class Echinoidea.Under class gastropoda are the family Discodorididae, Ellobiidae, Littorinidae, Muricidae, Neritidae, Potamididae, Strombidae and Trochida.
Meanwhile, the Malacostraca class consisted of four families: Ocypodidae, Portunidae, Penaeidae, and Varunidae.There are single species found in the Discodorididae and Ellobiidae, the Jorunna funebris, and Cassidula aurisfelis, respectively, found in station 3.There are three species under family Littorinidae, namely Littoraria melanostoma, Littoraria scabra, and Littoraria angulifera, observed in all three stations.There are two species found in each family of Muricidae, Neritidae, and Holothuriidae.These are Chicoreus capunicus and Tenguella musiva for Muricidae, Nerita exuvia and Nerita lineata for Neritidae, and Holothuria atra and Holothuria scabra for Holothuriidae, respectively.There are single species found in families Ocypodidae , Portunidae, Penaeidae, Varunidae, Nereididae, Sipunculidae such as Uca tetragonon, Thalamita crenata, Penaeus monodon, Varuna litterata, Perinereis sp., and Sipunculus nudus, respectively.Station 3 has the highest frequency count compared to Stations 1 and 2 stations with a sandy substrate.Station 1 has a muddy substrate, while Station 2 has a mixed muddy and sandy substrate.According to Duan et al. (2008), substrates such as grain size, shape, porosity and or cobbles, stones, pebbles, and coarse and fine sand affect the taxa richness and density macroinvertebrates.It can be gleaned from Table 2 that the H-values go along with the species richness of the sampling sites.This result conforms to the study of Duan et al. (2008) on the macroinvertebrates' assemblages, where species richness is also considered the measure for diversity.A high diversity in mollusks as one of the macroinvertebrates indicates that the niche space, habitat, food sources, more minor disturbance, and tolerable environmental conditions are adequate for their survival (Superales & Zafaralla, 2008).

Soil characteristics and water quality parameters in the mangrove forest of Barangay Nabago
The soil characteristics and water quality parameters of the sampling site are shown in Table 3. Station 1 recorded the most acidic with 6.02 compared to Station 2 (pH=7.82)and Station 3 (pH= 8.11).
Among the three stations, Station 3 is far from the household community compared to the other two stations.Correspondingly, the highest recorded physico-chemical parameters in Station 3 include DO, and pH, meanwhile, with the highest percentage of sand and zero percent of clay.Station 2 obtained the highest TDS, salinity, turbidity, temperature and conductivity.This result shows that these water parameters exhibit direct relationship with one another.As temperature increases the conductivity increases as well (Washington State Department of Ecology, 1991).According to Whipple (2002), conductivity is affected by temperature through increasing ionic mobility and the solubility of many salts and minerals.Discharges flowing through water bodies may also influence conductivity depending on their composition (EPA, 2012).A failing sewage system would raise conductivity due to chloride, phosphate, and nitrate.This may explain the water condition of Station 2 as it is located near the milkfish mariculture farms of locals where synthetic feeds are being supplied.
Moreover, Station 2 also recorded the highest percentage of silt and clay, which may contribute to its conductivity.EPA (2012) stated that clay contributes to conductivity, with waters observed as the most turbid.The highest salinity may be accounted for by highly mineralized water inflow depending on the geology (EPA, 2012).In this case, the high percentage of clay soil contributes to conductivity and minerals in clay that would ionize as they dissolved (EPA, 2012) which impacted the high account for salinity which will affect the conductivity and TDS (Tally, 2000).
Results revealed that Station 2 has the lowest species richness among the three stations, (Table 2) lowest % DO but the highest salinity and conductivity values (Table 3).Langland and Cronin (2003) posited that conductivity and salinity are strongly correlated.Conductivity is a measure used in algorithms estimating salinity and TDS, which affect water quality and aquatic life.Salinity affects dissolved oxygen solubility.The higher the salinity level, the lower the dissolved oxygen concentration.

Canonical Correspondence Analysis of Macroinvertebrates from the Sampling Stations
The triplot scatters diagram, Canonical Correspondence Analysis (CCA), showing the relationship between macroinvertebrates and the environmental variables of the mangrove forest, is presented in Figure 2. 11 environmental ecological variables and 26 macroinvertebrate species were considered in this study.The Eigenvalue on axis 1 (0.2581) indicates a relatively low gradient, while axis 2 (0.1780) is much weaker.The first ordination axis presented a 59.19 % variation while a 40.81 % variation was in the second ordination axis.
Among the three stations, Station 2 has five (5) environmental variables affecting macroinvertebrates namely, S. cuccullata, N. lineata, D. antillarum, L. scabra and V. litterata.These are the % silt, salinity, TDS, conductivity, and temperature.In Station 1, turbidity, % DO, % clay, and % sand influence several observed macroinvertebrates species such as L. melanostoma, L. angulifera, C. decollata, N. exuvia, C. capunicus, U. tetragonon, P. monodon, It can be gleaned in Figure 2 that soil and water pH greatly influence the macroinvertebrates found in Station 3. As the soil and water pH increase, the number of individual species of S. nudus, T. palustris, P. sp. and J. funebris decrease.This result conforms to the study of Sharma et al. (2016) and Wagey et al. (2018) that pH showed a negative relationship to the abundance and diversity of mangrove-associated mollusks.
Variation in water pH is significantly related to edaphic conditions of wetlands (Custodio et al., 2018), agricultural activity (Rim et al., 2017), wastewater discharges (Christia et al., 2014), and the photosynthetic activity of flora during the day (Craft et al., 2017).Moreover, % sand obtained the highest in station 3, which comprised the highest diversity species and diversity index (Table 3).
As turbidity and percent (% ) clay increase, an immediate increase in the species of C. angulata, T. sulcata, and A. edentula (Station 1), whereas conductivity, TDS, temperature and salinity, and % silt are directly proportional to the increase number of species such as N. lineata, S cuccullata, and L scabra (Station 2).This finding indicates that the population of these C. angulata, T. sulcata, A. edentula, N. lineata,S.cuccullata, and L. scabra species increases when water quality parameters, including turbidity, conductivity, TDS, temperature, and salinity, as well as the percentages of silt and clay for soil characteristics also increase.These requirements for the quality of the soil and water may create a favorable environment for the macroinvertebrate species to develop and thrive.Meanwhile, N. exuvia, C. capunicus, C. decollata, L. melanostoma, P. monodon are directly influenced by DO and % sand.Figure 3 illustrates how a drop in DO and sand percentage affects the population of gastropods, particularly in Station 1 of the stay area.A decrease in DO and% sand in Station 1 may be attributed to the area's proximity to homes where organic waste and garbage are frequently disposed of, as well as to anthropogenic activities that could affect the quality of the water and soil.According to Rangan (1996), the substrate's condition has an impact on how biotic communities develop, and gastropods prefer a muddy, clay-rich substrate.The triplot diagram clearly showed the influence of edaphic characteristics on the macroinvertebrates' spatial distribution in the study area.The % sandy influences the various species more than the other environmental parameters as the sandy substrate is characterized by greater oxygen-carrying capacity (Irma and Sofyatuddin, 2012).

Bray -Curtis similarity index among sampling stations
The bray-Curtis similarity index was used to compare the three sampling stations, as shown in the dendrogram (Figure 4).Stations 1 and 2 are more related with 0.600 similarities than Station 3 with only a similarity distance of 0.460 compared to Stations 1 and 2. This result could be attributed to the substrate, the environmental variables, and the species richness.Moreover, the species that could not be found similarly in both Stations 1 and 2 but existed in Station 3 are remarkably observed such as Lambis lambis, Tyctus pyramis, Holothuria atra, Holothuria scabra, Tenguella musa, Jorunna tubelaris and Cassidula auresfelis.

CONCLUSIONS AND RECOMMENDATION
The diversity of macroinvertebrates and its correlation to physicochemical parameters of soil and water in the mangrove forest of Barangay Nabago were considered in the study.Thehighest percentage of sandy substrates, particularly in station 3, contributes to the highest frequency count and highest diversity index (H'=2.436) of macroinvertebrates compared to the first (1) and second (2) stations.It correlates to the physicochemical parameters, which also obtained the highest numerical value for dissolved oxygen (DO), conductivity, and pH.These physicochemical parameters had indicated a more favorable environmental condition for the macroinvertebrates to thrive.Meanwhile, both stations 1 and 2 exhibited less DO but had more acidic waters, more turbid, increased temperature, greater conductivity and TDS, and a soil substrate of both silt and clay owed to fewer species richness and diversity index.

Figure 1 .
Figure 1.Study area and sampling sites

Figure 2 .
Figure 2. Canonical Correspondence Analysis of the Relationship between Macroinvertebrates and the Environmental Variables in the Mangrove Forest of Barangay Nabago

Figure 3 .
Figure 3. Bray -Curtis Similarity Index of Macroinvertebrates among Sampling Stations

Table 1 .
List of Macroinvertebrates present in the study area and their Conservation Status.
Legend: + present; -absent; Conservation Status: LC -Least Concern;NE -Not Evaluated; EN -Endangered; DD -Data  Deficient Table 2 presents the diversity indices of macroinvertebrates observed in the sampling areas.Station 3 has the highest species richness (19) followed by Station 1 (15) and Station 2(13).As to Shannon H values, Station 3 earned the highest with H' = 2.436 followed by Station 1 (H'=2.284)and Station 2 with H' = 2.236.Station 2 obtained the lowest diversity index and species richness but received the highest dominance.

Table 2 .
Diversity Indices of Macroinvertebrates in the Mangrove Forest of Brgy.Nabago, Surigao City

Table 3 .
Water Quality Parameters and Soil Characteristics of the Mangrove Forest