The relationship between mangroves and bivalves abundance in Cengkrong Beach, Trenggalek Regency

Cengkrong Beach in Trenggalek Regency has extensive mangrove forest. Mangrove forests play an important role in maintaining aquatic productivity and supporting people’s lives. Bivalve is one of the biota that lives in mangroves and is used by the people around the mangrove forest. The research aims to identify mangroves and bivalves, analyze the abundance of mangroves and bivalves, and determine the relationship between mangroves and bivalves. Mangrove sampling was carried out on 6 transects. Each transect was made 7 with plots measuring 10 m x 10 m with a distance of 5 m and bivalve samples were taken using a 1 m x 1 m plot with 5 plots in that plot. Research data were analyzed using PAST 4.13. The results of the study found 15 species of mangroves and 4 genera of bivalves. The highest mangrove abundance value was Rhizophora apiculata with a value of 0.0092 indiv./m2 and bivalves were of the genus Isognomon with a value of 4.138 indiv./m2. The results of the analysis showed that there was a relationship between the mangrove Sonneratia caseolaris and the bivalve of genus Pilsbryoconcha, the mangrove Aegiceras floridum and the bivalve of genus Geloina, the mangrove Avicennia alba and the bivalve of genus Saccostrea and the mangrove R. apiculata and the bivalve of genus Isognomon.


Introduction
Mangroves are a very productive ecosystem.The invertebrate and vertebrate fauna in mangrove forests is rich in the number of species and the number of individuals of each species.The waters where mangroves grow provide suitable living and breeding places for large numbers of fish, shrimp, crayfish, shellfish and other aquatic organisms [1].Mangrove forests have many functions: preventing erosion, stabilizing beaches, and providing suitable conditions for spawning.Mangrove forests also act as nurseries for many species of economic importance and function as pollution traps.For centuries, Indonesian people have used mangroves for wood, firewood, charcoal, tanning dye, and boat building.Genera often used for this purpose include Rhizophora, Avicennia, Bruguiera, Ceriops, Nypa, and Oncosperma [2].
Bivalves have an important role in mangrove forests, both ecologically and economically.Ecologically, bivalves have an important role in the food chain, namely as detritivores [3].Several types of bivalves have important economic value as food, craft, and industrial ingredients [4].Bivalves are one of the biota that live in mangrove forests and are used by communities around the mangrove forests.
The mangrove forests on Cengkrong Beach, Trenggalek Regency, are a conservation and recreation area.The research that has been carried out here shows that in each zone, the same types of species are still found due to natural factors and sea tides, so fallen fruit will be carried and grow in several mangrove zones [5].According to [6], successful mangrove rehabilitation can increase the diversity and population of aquatic biota.Considering the importance of the function of mangrove ecosystem areas for ecological balance and water productivity, information about biodiversity and the reciprocal relationship between mangroves and bivalves will be important to research.The research aims to identify mangroves and bivalves, analyze the abundance of mangroves and bivalves, and determine the relationship between mangroves and bivalves

Data Collection
Mangrove sampling was carried out on 6 transects.Each transect was made into 7 plots measuring 10 m x 10 m with a distance of 5 m.Bivalve samples were taken by making 5 plots measuring 1 m x 1 m on the mangrove sampling plot.The number of mangroves and bivalves found in the plot was recorded, and samples of mangroves and bivalves were taken for identification in the laboratory.

Data Analysis
Data on the number of mangroves and bivalves were analyzed to determine their abundance.Clustering and Pearson's correlation analysis was carried out to determine the relationship between Mangroves and Bivalves using PAST 4.13.

Identification of Mangroves and Bivalves
The research results on Mangroves in Cengkrong Beach, Trenggalek Regency, found 2 classes, 6 orders, 8 families, 11 genera, and 15 species.The Mangrove classes are Polypodiopsida and Magnoliopsida.The Magnoliopsida class was found to be more numerous than Polypodiopsida.Mangroves from the Malpighiales order, Rhizophoraceae family, are found in greater numbers than other groups.There are 15 mangrove species have been identified, as shown in table 1.The bivalves research in Cengkrong Beach, Trenggalek Regency, found 1 class, 3 orders, 4 families, and 4 genera: Geloina, Saccostrea, Isognomon, and Pilsbryoconcha.

Abundance of Mangroves and Bivalves
Mangroves found abundantly in Cengkrong Beach, Trenggalek Regency, are Rhizophora apiculata (0.0092 idiv./m 2 ) and R. Mucronata (0.0088 idiv./m 2 ) as shown in table 2. According to [7], the Rhizophora genus has characteristics that spread quickly and can grow and develop in habitats with high salinity to almost fresh water.[8] stated that Rhizophora has a level of dominance that can reach 90% of the vegetation growing in a location.From the analysis results, as shown in table 2, the bivalve found abundantly in Cengkrong Beach, Trenggalek Regency, is the Isognomon genus, namely 4.138 indiv./m 2 .[9] stated that the Isognomon genus is abundant because it has the characteristic of living attached to mangrove roots.Isognomons are arboreal bivalves that are often found in the mangrove areas of the Indo-Pacific.

The relationship between Mangroves and Bivalves
Clustering results using Morisita's similarity index (figure 2) show that at a similarity level of 80%, there is a relationship between the mangrove Sonneratia caseolaris and the bivalve of genus Pilsbryoconcha.Meanwhile, at a similarity level of 92.5%, there is a relationship between mangrove species and bivalve genera, namely Aegiceras floridum with Geloina, Avicennia alba with Saccostrea, and R. Apiculata with Isognomon.Based on the results of Pearson correlation analysis (table 3), it can be seen that mangrove species are positively correlated with the bivalve genus, namely S. Caseolaris with Pilsbryochonca, A. Floridum with Geloina, A. Alba with Saccostrea and R. Apiculata with Isognomon with correlation coefficient values of 0.74, 0.72, 0.89 and 0.93 respectively.Saccostrea live attached to the pneumatophores of Avicennia and Sonneratia [10].Saccostrea live attached to mangrove roots, because this organism cannot move or move places [11].Geloina can live in various types of habitats in mangrove forest waters, such as various types of substrates and varying levels of salinity, including the habitat conditions of the A. floridum species, which tends to have muddy substrates and is constantly flooded by water with high salinity levels [12].
The mangrove R. Apiculata species has the highest positive correlation value with the bivalve of the Isognomon genus.In research, the Isognomon genus was found clustered on the roots of R. apiculata.[13] stated that the genus Isognomon can form aggregations consisting of 20 individuals at one point of tree root branching.Mangrove of the S. caseolaris species has a positive correlation with bivalve of the Pilsbryochonca genus.S. caseolaris and Pilsbryoconcha have similar habitats.Namely, they are not tolerant of high salinity levels and high temperatures [8,14].

Table 1 .
Identification of mangroves and bivalves in Cengkrong Beach Trenggalek Regency.

Table 2 .
The abundance of mangroves and bivalves in Cengkrong Beach Trenggalek Regency.

Table 3 .
Correlation between mangroves and bivalves.This study found 15 species of mangroves and 4 genera of bivalves.The highest mangrove abundance value was R. apiculata with a value of 0.0092 indiv./m 2 , and the bivalve was of the genus Isognomon with a value of 4.138 indiv./m 2 .The analysis results show that there is a relationship between mangrove species and bivalve genera, namely S. caseolaris with Pilsbryoconcha, A. floridum with Geloina, A. alba with Saccostrea, and R. apiculata with Isognomon.