The Indication of Gastropods Extinctions at Intertidal Zone of the Teluk Nipah Waters, the Pesisir Selatan Regency the Province of the West Sumatera Indikasi Kepunahan Gastropoda di Zona Intertidal Perairan Teluk Nipah Kabupaten Pesisir Selatan Provinsi Sumatera Barat

Intensive observation of gastropods, every March from the year 2008 to the year 2012, was carried out to document some indicators of gastropod extinction. The purposive sampling technic was used in this work. The physicochemical parameters of its habitat were also monitored during every sampling done. It was found that the intertidal substrate consist of sand, while the habitat parameters were more than 5,6 mg/L dissolved oxygen, pH around 7,0-7,2, salinity 30,2-32,2 ppt, temperature 28,6-29,6 0 C, the visibility 100%. The number of species, the number of found gastropods, the abundance, and the maximum shell size of found gastropods showed decreasing from year to year, while routine collecting by the visitor and the marine organism shell collector, and the disturbance by the fisherman activities occurred. This indication showed a tendency for gastropods extinction.


INTRODUCTION
Gastropods are the most common or the largest class (75%) of living molluscs, which includes snails and slags (Lerman, 1986;Fish & Fish, 1989), the most successful among other classes of molluscs (Barnes in Malik, 2013), but gastropods at the intertidal zone of Teluk Nipah waters Pesisir Selatan Regency West Sumatera Province is being disturbance by the human activities, event any of them disappeared from their habitat.This information got from a villager who lives around the research location.
There are three main causes when a species disappeared from its habitat, that is anthropogenic impacts, ecological disturbance, and genetic disturbance.All of that is being occurred at the intertidal zone of the Teluk Nipah waters.Gastropods are usually actively exploited by the visitors and bay marine organisms shell collectors in the tour destination said area.Fisherman activities are the other reason which supposed as causes that disappearance.Fisherman activities will influence the growth rate of gastropods, and so it will impact the genetics of gastropods, agree with Tanjung (2012) that if the speeding up of organism exploitation is higher than Tanjung the speeding up of its population growth rate, it will cause that organism will destroy in not so long time; therefore, the observation about the existence of the gastropods and also the human activities around its habitat should be done to know the indications of its extinction.
The investigation of the extinction of fishes are documented for the past 100 years in North America (Miller et al., 2011), whereas the investigation of the extinction of marine gastropods is not documented yet; therefore, documentation about some indicators of gastropods extinction has to be started as an effort to keep sustainable marine resources.

MATERIALS AND METHOD
Five kinds of information were needed to explain the indication of gastropods extinction., that is its species number, Pesisir Selatan Regency, its population number and abundance, its maximum size of collected shell from year to year, water quality, and frequency of human disturbance.
To know its species number, its population number and abundance, and its maximum size of shell, sampling of gastropods was out from three stations at the intertidal of the Teluk Nipah Water, The West Sumatera Province in five years.Observation on fisherman, Marine organisms shell collector, and beach visitor activities were done too.Sampling and observation were done every March yearly from 2008-2012 (Figure 1).Observation stations were fixed based on the purposive sampling technic (Tanjung, 2013).Station 1 is characterized by main tour activities, station 2 is placed at the fisherman activities and canal, and station 3 is fixed at a more natural condition area.Each station was taken ten plots 50 x 50 centimetres.
To get information about the habitat quality, measurement of water qualities (DO 2 , pH, salinity, temperature, and visibility) was done in the field directly, while the substrate analysis (fraction) was done in the laboratory.Dissolved oxygen (DO 2 ) was measured with DO metres, salinity was measured with handrefractometers, a pH indicator was used to measure pH, a thermometer was used for temperature, and a secchi disk for visibility.The samples of gastropods and substrate were taken at the time when the lowest tide occurred, and measuring the water quality was done at the time when the highest tide occurred.The sediment in each plot was dug for 50 x 50 x 10 centimetres for gastropod sampling, and the collected sediment was put into a macrobenthos sieve.The wet sediment sieving was done in the field directly, and then the found gastropods were put into a plastic bag and preserved with formalin 10%.The sample was identified based on Carpenter & Niem (1998); Robert et al. (1982); Buchanan (1984).(Linneaus, 1758), N.picea (Recluz 1841), and Monodonta labio.These data showed decreasing in species numbers which were found from the observed location from the year the two species, Pathya sp and Strombus sp (Linneaus 1758) disappeared from their habitat in 2009.Terebra sp lose its habitat in 2010, and N. polita lost too in 2011 (Table 1).

RESULT AND DISCUSSION
The number of individuals of each species was also decreasing from year to year, except Neverita sp a little bit increase in 2011 (10 ind) and then decrease again in 2012 (7 ind), while Polinices sp increased in 2009 (14 ind) and 2011 (15 ind) and decrease again (11 ind) in 2012 (Table 1).It has occurred a decrease in the species number which lives in the intertidal zone of the Teluk Nipah water from 2008-2012.This case is supposed due to the anthropogenic impacts: Every day fishermen do their activity in Station 2, the visitor comes to this area for a picnic, especially in Station 1, and the overhunting of marine organism shell collector.The activities like hanging down and starting sailing from land to the sea and back to the land again will cause instability on the substrate of the beach floor.This case will influence coastal organisms which live there, and so that place was not fit for an organism.Agree with Chiba & Roy (2013) said that the anthropogenic impact has led to widespread extinctions of species on oceanic islands.It can be seen from Table 1.It is shown by two species Pithya sp and Strombus sp disappeared from their habitat in 2009, and so Terebra sp and Nerita polita did after that.The activities of the collector and visitor will cause an ecological and genetic disturbance.2).This fact showed that the decreasing abundance from station to station and decreasing too from year to year have occurred in this area.The average abundance of Station 3 is the highest abundance (20,8 ind per m 2 ) followed by Station 1 (18,4 ind per m 2 ), and Station 2 has the lowest abundance (17,2 ind per m 2 ), see Table 2.
Based on the analysis of 50 g of the substrate which took from each plot, it could be told that the intertidal of the Teluk Nipah consists of sand.The activities of fishermen hanging down in the afternoon and to start sailing their fishing boats in the morning were routine every day, almost 8-12 fishing boat per day did their activities every day (Table 3).Almost every visitor will collect everything marine organism which is found in Tanjung the intertidal zone.If they did not get enough in number and satisfaction collection they will walk along the coast of the intertidal zone from Station 1 to Station 2, and the last to Station 3. Different from the collector of marine organism shells for the accessories material, they hunt weekly until they got enough in number.It is reasonable to say that human activities influenced the existence of gastropods in the intertidal zone.It can be seen from the value of gastropod abundance in each station, where station 2 had the lowest average abundance 17,20 ind per m 2 of gastropods among the others due to the highest level of disturbance that occurred there (Table 2).
At the station, the activities of fishermen were higher than the other two stations, with about 8-12 boat activities every day, while at station 1 and station 3 were almost nothing activities (Table 3).Station 1 is the station which is characterized as the place for a picnic or marine tour, whereas station 3 was characterized by the place's more natural aspect because nothing activity there.The highest average abundance of gastropods at station 3 was 20,8 ind per m 2 (Table 2).It showed that the station which has not have so many disturbances will have the highest abundance when compared with the station's many disturbances.
Not only will the fishermen's activities responsible for coastal organism disappearance from their habitat but also the habits of each visitor and the collector of marine organism shells cause that case.The effects of human activities did not affect directly in a short time, but the effects will destroy the habitat in a long time.The disturbance of habitat will reduce and isolate the space for gastropods' life.This statement agreed with Hogan (2010), who said that the most important causal anthropogenic impact are habitat destruction, overexploitation, pollution, and the introduction of alien species to an environment.More detail He said that habitat destruction is the greatest contributor to the extinction of many species; moreover, impacts on biota from habitat fragmentation is a critical mechanism of driving species to extinction.According to Nybakken (1988) that the decreasing average size of fish is an indication of overfishing.
The species lost from its habitat is the species which unable to adapt to the situation and condition changes.The species is able to adapt to the changes in their environment and will survive, but the habitat is not fit for them.It can be proved from the number and the maximum size.The number of species decreases from year to year and also the maximum size of found species decreases too (Table 1 and Table 5).It is agree with Chiba and Roy (2013) explained that body size itself is a well-recognized correlation of extinction.

Table 1 .
Number of individuals for each species and number of species

Table 2 .
The abundance of gastropods at the sampling station

Table 4 .
Waters quality at research location 2008-2012