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The pH values in station 1 and 2 shows that the water is slightly acidic due to the human activities at nearby water body. However, from station 3 until station 5 shows increasing in alkalinity due the station are located nearby the sea which caused them subjected to the influence of alkaline seawater. The temperature shows that the increasing from station 1 until station 5. This might due to the decreasing of riparian vegetation along the river. The values are normal for riverine water system. The dissolved oxygen values increasing from station 1 until station 5. This might because of the water current and the windy weather which are common nearby the sea. Besides that it might due of the excess respiration which caused by input of organic matter. The turbidity in station 1 is highest. This was due of the oil palm plantation at the upstream and the waste produce by the resident in Lundu town and the turbidity are reduce in values the station nearby the seawater. The salinity from station 1 until station 3 shows that the water body is freshwater while station 4 to station 5 show that the water bodies influence by the seawater. According to Bouchet (1977), the area with higher salinity will give impact to species diversity and richness. Beside that water with pH range 5.0-6.5 was considered water consist of pH weak acid and pH range 7.5-8.0 was considered as a strong alkalinity (Nyabakken, 1993). The differences of pH value also influenced the species diversity and richness.
Molluscs community in batang kayan
The species of molluscs are different in the distribution of each individual species at high to low tide zone due to the adaptation to environmental condition which is influenced by hydroperiod, availability of organic matter and sediment characteristic (Lee, 2008). The molluscs community in Batang Kayan Estuary were represented by 11 families, comprising at least 10 families from gastropoda with 20 genera and 1 family of bivalve with 1 genera (Table 13) that were recorded on October. The species are Nerita lineata, Neritina sp, Clithon faba, Clithon sp1, Littorina scabra, Littorina fasciata, Batillaria cumingi, Cerithidea rhizophararum clypeomorus sp 1, Cerithidea cingulate, Strombus sp 1, Strombus sp 2, Natica sp 1, Chicoreus capucinues, Cantharus tranquebaricus, Bullia sp., Cassidula rugata, Ellobium aurisjuda, Ophicardelus sp1, Ophicardelus sp2 and two species are unidentified. While the bivalve species was Saccostrea glamerata.
The dominant molluscs in Batang Kayan are Nerita lineata and littorina fasciata. This two species can be found at line transect, along the batang kayan river as well at the tree trunks. In term of individual Batillaria cumingi was the most abundance compare to all the species but this species only be found at line transect. The least molluscs species found in Batang Kayan were Strombus 1 with 1 individual (Appendix 1: Table of summary molluscs).
The molluscs community can be influenced by several factors such as types of substrate, biological factors, habitat and availability of food source and nutrient. According to Haven, 1971 the changes of substrate influenced the distribution of molluscs such as the Cerithidea rhizophararum usually found at the muddy substrate. The biological factosr such as wave, predation and competition on food influence the distribution of molluscs community in certain area (Ahmad Affendy, 2000). The predation and competition on food give arise of dominant species in the area.
Besides that, the molluscs were subjected to expose under the sun with no covered by the sea during the low tide at mangrove ecosystem. Due of this most of marine animals dry out and cannot respire in air but certain molluscs especially epifauna are semi-aquatica organisms that have impervious exoskeletons and shells to restrict water loss by heat, so that they can withstand above the water for a longer period (Shabdin & Hidir, 2008). At the high and middle tide zone there are less number of species found due to the area are covered by mangrove tress and the penetration of light was less (Figure 13 and Figure 18). The light intensity and dissolved air are contributed to influencing the distribution of animals at mangrove area (Barnes et al, 1982).
Gastropod communities in batang kayan
Mostly in this study, gastropoda is the dominated class. From the results, show that the gastropod belongs to 10 families with 22 species where 2 of the species unidentified (Table 13). The gastropod is abundance at the lower zone which is at low tide zone. This low tide zone area often floods by saline water when compare with middle and high tide zone. One of the factorS that contribute to the abundance of gastropod at lower zone is due to the soil sediment which mostly silt and clay at mangrove area. This mangrove was exposed with several of environment parameters such as temperature, sedimentation and tidal current (Shanmugan & Vairamani, 1994). Thus the molluscs have the ability to withstand the change of the water parameters everyday in their daily. Besides that, another factor is the influenced by a variety factory such as light that act as a main factor to determine the algal growth and the influencing humidity (Nagelkerken et al., 2007). According to Wan Zaidi (2010), the tidal exposure, salinity and substrate type can influence the distribution of molluscs. While some of the mollusc can be found on soil surface or wet soil on the pneumatophores of mangrove s tree such as Avicennia spp.and Sonnerita spp.
Bivalve communities in batang kayan
In this study, the class of bivalve is the less class we found which only one species belongs to the family Osteridae (Table 13). The species mostly found attached at the root of the mangrove trees such as Avicennia spp.and Sonnerita spp. The reason of this less class we found might be due to the bivalve species are buried in the sediment. They can bury in the sediment due to the its characteristic which have a substantial capacity for anaerobic respiration where it has a bacterial symbiont in its gill tissue that using nitrate instead of oxygen as a terminal electron acceptor. This existing of this characteristic helps the bivalve species to survive temporary burial on beaches and in estuaries (Hentschel & Felbeck, 1995). The bivalve buried them self in the sediment due to avoid low salinities condition and also predation. According to Newell (1979) stated that the bivalve burrowing deeper into the soil to avoid from the desiccation and thermal stress. Besdies that, in this study only focus on the epifauna molluscs which are on the surface of the sediment. There are no activities of digging inside quadrate at line transect which give strong evidence there are no bivalve species was found at the line transect. Most of bivalve can be found inside the sediment (Wan Zabidi, 2010). Besides that, according to Shabdin (1998) the availability of class bivalve might due to the excess exploitation for commercial by the local people in the area.
From the results of correlation (Table 14), there are differences between chlorophyll a in line transect 1 and 2. In line transect 2 there are strong correlation with the species diversity, richness and evenness while in transect 1 the correlation were weak especially for species diversity. This differences might be due to the types of sediment at each line transect where in this study the sand fraction (%) was not analyzed. From the observation during the fieldwork at line transect 1 there sediment or soil substrate was muddy mixing with sand. These give the structure more compact and easy to walk especially at high tide zone (Quadrate 1). While in Line transect 2 the sediment or soil substrate more to muddy. Thus the muddy substrate contain more algae in the sediment which contribute to stronger correlation in line transect 2. Mangrove sediments which are more to silt or clay suitable and can enhance the growth of benthic microalgae and macroalgae. According to Mohd Nasaruddin (2006), algae community can be found different from high to low tide zone in term of distribution. These algae provide food for certain gastropod which gastropods are herbivorous that feed on small algae (Wan Zabidi, 2010). As for the correlation with Total organic matter are weak and negative correlation might due to the rapid movement of water during the tide which causes the organic matter cannot settle down at the sediment (Ettin, S.S, 2007). Thus at batang kayan the correlation between chlorophyll a and Total organic matter with the species composition and distribution did not give much impact where as the types of sediment or soil substrate may give more impact due from the differences of sediment between the transect. Accorfing to Nyabbaken (1993), the richness of species was influenced by the substrate whereas the muddy substrate has lower value for species richness compare to substrate with sand. This was proven (Table 8 and Table 11) the highest value of species richness was in the line transect 1 (1.8205) compare to line transect 2 (1.2511).