Density and nutrient content of Terebralia pallustris mangrove snails in mangrove ecosystems in Pannikiang Island, Barru Regency, South Sulawesi

Key word: Density Terebralia palustris Pannikiang Mangrove snail, Terebralia palustris Linnnaeus 1967, was also found on Pannikiang Island, Barru Regency, South Sulawesi. This study aims to describe the fluctuation of T. palustris density in a year of observation. This research was conducted for ten months from August 2018 to July 2019. There were two research stations. Each station has a large plot measuring 10m x 10m and in it, five small plots are measuring 1m x 1m. Measurements of environmental parameters such as temperature, salinity, and pH were carried out in situ. This snail meat as much as 100gr also analyzed proximate. The proximate analysis of the snail shows that crude protein content is 18.73% so that the snail is very suitable to be used as a source of protein. The highest density is in July 2019 and the lowest density is in August 2018. Article history: Received: 06/08/2019 Revised: 17/12/2019 Accepted: 17/04/2020


Introduction
The mangrove ecosystem located on Pannikiang Island, Barru Regency, is in good condition and is very dense with dense canopy cover. The area of mangrove cover on Pannikiang Island reaches 89.01 hectares or reaches 87.45% of the island's land area (Irmayansari, 2016).
Terebralia palustris mangrove snails are snails that live in mangrove ecosystems, especially on Pannikiang Island, Barru Regency, South Sulawesi (Samsi, 2017). This species has the largest size among members of the Potamididae family. The maximum length of T. palustris shell is 19 cm and most are 12 cm (Carpenter & Niem, 1998). The size of T. palustris shells is three to four times the size of T. sulcata and about twice the size of T. semistrata (Houbrick, 1991). Amounts are abundant and conspicuous in muddy mangroves and generally live in brackish water. The shell is large, elongated, and thick. The color of the shell is dark brown to bluishblack. The aperture is shiny and blackishbrown with a light brown columella (Carpenter & Niem, 1998). The density of these snails in each place must be different and depends on environmental factors that influence it. This is the aim of this study.

Materials and Methods 1. Research design
This research was conducted in the mangrove ecosystem on Pannikiang Island, Barru Regency, South Sulawesi from August 2018 to July 2019. Sampling was not conducted in December 2018 and January 2019 due to weather constraints. The coordinate points at station A are 4˚20'23 "S and 119'36'11" E while at station B are 4˚21'37 "S and 119'35'42" E.
In this study, two research stations were used. Station A is located in the northern part of the island and Station B is located in the southern part of the island. At each station, a plot of 10 m x 10 m was used and in this plot, there were small plots of 1 m x 1 m in a total of 5 units (Samsi, 2017).

Population and samples
The sample of this research is the T. palustris mangrove snail associated with mangroves.

Sample collection techniques and instrumental development
Samples found for each plot are then put into the plastic. Observations and sample counts were carried out at the Laboratory of Fisheries Biology, Faculty of Fisheries and Maritime Affairs, Hasanuddin University. Proximate analysis was carried out at the Laboratory of Animal Food Chemistry, Faculty of Animal Science, Hasanuddin University.
Measurement of environmental parameters (temperature, salinity, and pH of seawater) is done in-situ before sampling. Salinity is measured directly in the field using a hand-refractometer that has been previously rinsed with distilled water.

Data analysis techniques
The density of T. palustris is calculated using the following formula (Brower, Zar, & Von Ende, 1990):

Figure 2. The average density of T. palustris every month at stations A and B
The density of T. palustris each month at stations A and B is different. The density of T. palustris at station A is higher than at station B (Figure 2).This is caused by several factors, namely the temperature of seawater, salinity of seawater, acidity of seawater, sediments and dominant plant species.  The results of measurements of temperature and salinity of seawater at stations A and B show results that are not much different (Figures 3 and 4). However, slightly different results are shown in seawater acidity measurements at stations A and B ( Figure 5). This striking difference can be seen from September 2018 to March 2019.

b. The content of snails
This snail is consumed by local residents as a source of protein. These snails are also consumed in Merauke (Pasaribu, Buyang, & Monika, 2019). Proximate analysis results show that in every 100 grams of mangrove snails it contains 67.84% water, crude protein 18.73%, crude fat 0.39%, crude fiber 0.16%, the ash content of 4.16 %, and Extraction Material without Nitrogen of 8.72%. Pasaribu et al. (2019) showed slightly different results, namely an average water content of 78.66%, an average protein of 28.68%, an average fat of 3.31%, and an average ash content of 28.13 %. The difference in the nutritional content of T. palustris snails is influenced by several factors, namely body weight, feed, length and shape of the shell (Ademolu, Idowu, Mafiana, & Osinowo, 2004), environmental factors, age of the snail, and even gender. Sources of protein and nitrogen (feed) will affect the nutritional content of snails (Ademolu et al., 2004;Emelue & Dododawa, 2017;Zhang et al., 2014).