Diversity of Infaunal Macrobenthic Community in the Intertidal Zone of Vellar Estuary (Southeast Coast of India)  

A Hemalatha , Kapuli Gani Mohamed Thameemul Ansari , R. Rajasekaran , Olivia J. Fernando
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai–608 502, Tamil Nadu, India
Author    Correspondence author
International Journal of Marine Science, 2014, Vol. 4, No. 47   doi: 10.5376/ijms.2014.04.0047
Received: 06 May, 2014    Accepted: 13 Jun., 2014    Published: 11 Aug., 2014
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Hemalatha et al., 2014, Diversity of infaunal macrobenthic community in the intertidal zone of Vellar estuary (Southeast coast of India), International Journal of Marine Science, Vol.4, No.47 1-11 (doi: 10.5376/ijms.2014.04.0047)

Abstract

The diversity and seasonal variations of an intertidal macrobenthic communities link with abiotic variables were investigated in the Vellar estuary, Southeast coast of India. Samples were collected seasonally over a one year period from four different transects based on salinity gradients. Totally twelve infaunal groups were isolated which contained 53 species representing major taxa. Gastropods were the dominant group (81.6%), followed by polychaetes (7.7%), bivalves (5.5%) and amphipods (5.2%). Among these Cerethedia spp. contributed 61% of all gastropods. The macrobenthic community abundance found maximum at transect II (39%) and a minimum at transect IV (15%) while seasonally higher during summer (41%) and lower during monsoon (8%). Diversity (H' log) values varied from 1.859 (transect IV – monsoon) to 2.467 (transect II –summer). Higher diversity and species richness found in transect II due to the artificial mangrove vegetation is playing a major role on this region. Univariate and multivariate statistical analysis clearly define the interaction between biotic and abiotic variables. The results were compared with the early investigations, more or less similar community structure and species composition explained there is no changes on community structure in this estuarine environ, while higher species diversity in the transect II due to the artificial mangrove vegetation.

Keywords
Macrobenthos; Community structure; Seasonal variation; Vellar estuary; India

Coastal waters including estuaries, back waters, salt marshes, mangroves and lagoons plays an important role in exchange of physico-chemical variables in the environment, particularly estuaries are natural buffer zones between marine and freshwater areas. Intertidal benthic organisms are thought to participate an essential diets of many shorebird and fish species and can profoundly influence the abundance and species composition of these tertiary consumers (Alongi, 1990; Skagen and Oman, 1996), while it also plays an integral role in the recycling of nutrients and conservation of water quality within estuarine systems (e.g. Harris, 1999; Peterson and Heck, 1999). Such variability in faunal distribution may be further modified by localized natural and human disturbances of differential magnitude. According to Currie and Parry (1999), defining directional change in the biota of an estuary is inherently unpredictable. An intertidal environment provides the best study area to observe the seasonal changes of physico-chemical process in relation to its inhabitants since a maximum of fluctuation is met in an estuaries. Few important studies have been carried out on the macrobenthic ecology of various estuaries worldwide (e.g. Alongi, 1990; Carvalho et al., 2001; Herman et al., 2001; Warwick et al., 2002; Ysebaert et al., 2002; 2003;; Bosire et al., 2004; McLusky and Elloitt, 2004; Chainho et al., 2006; Sousa et al., 2007) and in India (Harkantra, 1975; Ansari et al., 1977; 1982; 1994; Varshney et al., 1981; Fernando et al., 1984; Fernando, 1987; Vijayakumar et al., 1991; Pillai, 2001; Ajmal Khan et al., 2004; Raut et al., 2005).
Vellar estuary is well studied area in terms of biotic and abiotic variables in last four decades (references?). It is potential and relatively healthy estuary, because no major sources of pollution other than sewage and agricultural run-off compared to the other estuaries of southeast coast of India (Ajmal Khan et al., 2005). An artificial mangrove, seagrass, oyster bed and continuous fresh water flow of Vellar estuary provided nutrient rich sediment layer along the estuarine edges (Kathiresan et al., 1996; Ansari et al., 2014). An artificial mangrove plantation covering an area of 10 ha was established in 1991 on the northern bank of the estuary (Kathiresan et al., 1996; Ajmal Khan et al., 2005). Few studies have been carried out on benthic organisms from this estuary (Ajmal Khan et al., 1975; Chandran et al., 1982; Fernando et al., 1984; Chandran, 1987; Fernando, 1987). After the artificial mangrove plantation, Murugasan et al. (2007) have studied the temporal changes in the benthic community structure in marine zones of the estuary, Ranjitham et al. (2008) have investigated seaweed and seagrass associated fauna, and recently Ansari et al. (2014) have studied the interaction between marine nematodes and mangrove plants. Other than that, there is no much more information regarding the intertidal macrobenthic distribution and diversity of Vellar estuary after mangrove plantation. In this backdrop, the present study objective was designed to detect the seasonal changes of the intertidal macrobenthic community assemblages with relation to abiotic variables in this region and to compare the variabilities in abundance and species composition of macrobenthic community before and after the mangrove vegetation.
1 Materials and Methods
1.1 Study site
The study was undertaken in the Vellar estuary (Figure 1) in the southeast coast of India (Latitude 11°29' N; Longitude 79°46' E). Intertidal sediment samples were collected for one year and formulated to seasonally (July, August and September - premonsoon-2007; October, November and December - monsoon-2007; January, February and March - postmonsoon- 2008 and April, May and June - summer 2008) along four selected transects within the estuary. Transect I was located in marine zone (estuarine mouth) with high amount of sea water entering through tidal action, transects II and III were located in tidal zone (artificial mangroves environment and oyster bed, respectively) with higher nutrient rich environment because of degradation, and transect IV was partially located in freshwater zone with high terrestrial input including organic load from Parangipettai town. The position of the river mouth changes frequently due to sand bar formation. The disappearance of the bar depends upon the amounts of freshwater flow from upstream during the monsoon months (normally this region experiences an annual rainfall between 1200 and 1300 mm).


Figure 1 Map of Vellar estuary showing sampling stations (T1 – marine zone; T2 – tidal zone (artificial mangroves); T3 – tidal zone (oyster bed) and T4 – partially freshwater zone)


1.2 Sample processing
Physico-chemical variables from sediment overlying water were measured by standard methods. Temperature was measured with thermometer with ± 0.5? accuracy, salinity with refractometer (manufacturer and model?), pH with pH meter (Elico Ltd), and dissolved oxygen concentrations were measured using Winkler’s method following Strickland andParsons (1972). Textural analysis of the surface sediments was made by the pipette method (Krumbein and Pettijohn, 1938). The total organic carbon content was measured by the chromic acid oxidation method followed by titration with ammonium ferrous sulfate (Walkley Black method) modified by Gaudette et al. (1974). Sediment samples of 1 m2were collected for faunal observation during low tide using a quadrate method (Alongi, 1990). In the order to ensure precision, three duplicate samples were collected at each transect. The sediment samples were sieved through a set of sieves (1 mm and 0.5 mm). The organisms retained on the sieve were preserved by 4% neutral formalin and stained with Rose Bengal (0.1 g in 100 ml of distilled water) to facilitate further sorting and identification in the laboratory using the standard taxonomic keys (e.g. Polychaeta: Fauvel (1953), Day (1967); Mollusca: Abott and Dance (1982), Pinn (1990); Subba Rao et al. (1991; 1992), Subba Rao and Dey (2000); Amphipods: Lincoln (1979); Lyla et al. (1999)). The data were compared with earlier investigations of this estuary in 1974 by Ajmal Khan et al. (1975), in 1977 (Chandran et al., 1982), in 1977-78 (Fernando, 1987), as well as with recent study in the marine zone in 2000 between transects I and II of the present study (Murugasan et al., 2007). The above investigations were based on monthly collections for a period of one year.
1.3 Data analysis
Biodiversity measures (Shannon Wiener diversity - H′log2, Margalef’s species richness - d, Pielou’s evenness - J′ and Simpson dominance index - l-Lambda′) were calculated, and the multivariate analysis consisted of estimating Bray-Curtis similarity of sample abundance data. The similarity matrix was subjected to both clustering (hierarchical agglomerative method using group-average linking) and ordination (non-metric multidimensional scaling, MDS). Seasonal variation of physico-chemical variables were analysed using Principal Component Analysis (PCA). The relationship between the distribution of macrobenthos and physico-chemical variables were analysed using comparative (Mantel-type) tests on similarity matrices and rank correlations between the similarity matrix derived from the species abundance data and matrix derive from subset of environmental variables to define suites of variables which best explain the biotic structure. Analysis of uni- and multivariate statistics were performed using the PC software packages PRIMER version 6 (Clarke and Gorley, 2006) and PAST version 1.93 (Hammer et al., 2001).
2 Results
 
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