seasonal shifts of meiofauna community structures on sandy beaches ...

SEASONAL SHIFTS OF MEIOFAUNA COMMUNITY STRUCTURES ON SANDY BEACHES ALONG THE CHENNAI COAST, INDIA BY G. MANTHA1,2 ), M. S. N. MOORTHY2 ), K. ALTAFF2 ), H. U. DAHMS3,6 ), W. O. LEE4 ), K. SIVAKUMAR2,5 ) and J. S. HWANG1,7 ) 1 ) Institute of Marine Biology, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung, 20224 Taiwan, R.O.C. 2 ) Unit of Reproductive Biology and Live Feed Culture, The New College, Chennai, India 3 ) Green Life Science Department, College of Convergence, Sangmyung University, 7 Hongij-dong, Jongno-gu, Seoul 110-743, South Korea 4 ) NFRDI, National Fisheries Research and Development Institute, Inland Fisheries Research Institute, Kyunggi-go 114-3, South Korea 5 ) Department of Biotechnology, Karpaga Vinayaga College of Engineering and Technology, Kancheepuram -603308, Tamilnadu, India

ABSTRACT Meiofauna standing stocks and community structures were studied at five sandy beaches along the Chennai coast of the Bay of Bengal, at the SE coast of India from January 2000 to February 2001. Meiofauna densities ranged from 1341.14 ± 1205.76 ind. 10 cm−2 to 3.73 × 106 ± 4.1 × 105 ind. 10 cm−2 . Mean abundance was highest during February 2000 (35 565.85 ± 12 463.03 ind. 10 cm−2 ) and lowest during March 2000 (11 465.85 ± 4250.26 ind. 10 cm−2 ). As for individual stations, the highest abundances were found at Neelangarai (67 058.31 ± 7153.43 ind. 10 cm−2 ) and lowest at Marina (52 517.69 ± 5373.63 ind. m−2 ), respectively. As for taxa, the mean of the highest and lowest meiofauna abundance was observed in Copepoda and Cladocera during different months (109 372.29 ± 10 906.42 ind. 10 cm−2 and 1341.14 ± 241.15 ind. 10 cm−2 ) and at different stations (30 6242.40 ± 3905.26 ind. 10 cm−2 and 3755.20 ± 88.90 ind. 10 cm−2 ), respectively. Cluster analysis and principal component analysis showed that the elements of the meiofauna were separated into three major groups according to their distribution and abundance. Correspondence analysis showed the importance of meiofauna abundance with different months and stations. Ecological indices varied with month, station, and with meiofauna group. Monthly changes in the nematodecopepod index showed that both Ernavoor and Thiruvotriyur were more subjected to pollution, with the highest diversity and evenness values for nematodes among all stations.

ZUSAMMENFASSUNG Meiofaunapopulationen und Gemeinschaftsstrukturen wurden an 5 Stränden entlang der Küste von Chennai und der Bucht von Bengalen, an der Sudostküste Indiens von Januar bis Februar 2001 6 ) Co-corresponding author; e-mail: [email protected] 7 ) Corresponding author; Fax: +886.224629464; e-mail: [email protected]

© Koninklijke Brill NV, Leiden, 2012 Also available online: www.brill.nl/cr

Crustaceana 85 (1): 27-53 DOI:10.1163/156854012X623683

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studiert. Individuendichten der Meiofauna lagen hier zwischen 1341,14 ± 1205,76 ind. 10 cm−2 und 3,73 × 106 ± 4,1 × 105 ind. cm−2 . Durchschnittliche Individuendichten waren im Februar 2000 am hochsten (35 565,85 ± 12 463,03 ind. 10 cm−2 ) und im März 2000 am geringsten (11 465,85 ± 4250,26 ind. 10 cm−2 ). Bei der Betrachtung einzelner Stationen wies Neelangarai die höchsten Meiofauna Abundanzen auf (67 058,31 ± 7153,43 ind. 10 cm−2 ) und Marina die geringsten (52 517,69 ± 5373,63 ind. m−2 ). Bei der Betrachtung der Taxa, wiesen Copepoda und Cladocera die hochsten und niedrigsten Meiofauna Abundanzen auf: monatlich (109 372,29 ± 10 906,42 ind. 10 cm−2 und 1341,14 ± 241,15 ind. 10 cm−2 ) und für die Stationen (306 242,40 ± 3905,26 ind. 10 cm−2 and 3755,20 ± 88,90 ind. 10 cm−2 ). Clusteranalyse und PCA (= principal component analysis) ergaben 3 Meiofaunagruppierungen bei der Berücksichtigung ihrer Verteilung und Abundanz. Eine Korrespondenzanalyse zeigte die Veränderungen der Meiofauna Abundanzen hinsichtlich der Probennahme (Monate und Stationen). Andere ökologische Indizes variierten mit Monat, Station und Meiofaunataxon, Monatliche Änderungen hinsichtlich des Nematoden / Copepoden Indexes zeigten, dass Ernavoor und Thiruvotriyur mehr von Verschmutzungen beeinflusst waren als die anderen Stationen. Hier wiesen die Nematoden auch die höchste Artenzahl und Evenness auf.

INTRODUCTION

Meiofauna represents the smaller-sized component of the benthos and provides the food for higher consumer levels (Coull et al., 1995; Dahms et al., 2006). Meiofauna production can be equal to or higher than that of macrofauna (Warwick et al., 1979). Meiofauna enhances nutrient mineralization (Montagna, 1995; Fenchel, 1996) and affects biogeochemical cycles (Aller & Aller, 1992; Murray et al., 2002). Meiofauna taxa exhibit high sensitivity to various kinds of disturbance of anthropogenic nature, that make them useful bioindicators for the state of environmental health (Coull & Chandler, 1992; Chandler & Green, 2001; Dahms & Hellio, 2009). Sandy beaches are very much understudied with respect to meiofauna (McLachlan & Brown, 2006). Sandy beaches provide important environments in coastal ecosystems of both tropical and temperate regions, showing a remarkable biodiversity (McLachlan & Brown, 2006), and providing a dynamic environment with variations related to natural abiotic characteristics such as temperature, salinity, desiccation, mean grain size of sediment, sea bottom currents (Coull & Bell, 1979; McLachlan et al., 1996; Coull, 1999; Corgosinho et al., 2003), and community changes that might be mediated by biotic interactions like competition and predation (Snelgrove & Butman, 1994). Equilibrium states are shown by intermediate morphodynamics between organic input and aerobic interstitial conditions (Short & Wright, 1983) that favour meiofauna in such intertidal habitats (Giere, 2009). Rodriguez et al. (2003) found that exposure time, desiccation, availability of food, sediment granulometry, tidal zonation, and interstitial water quality are the physical parameters that regulate the abundance of intertidal meiofauna. Meiofauna plays a major role in pollution monitoring studies (Dahms et al., 2009; Yamanaka et al., 2010). The meiofaunal species are vulnerable to abiotic and hydrodynamic

SEASONALITY OF BEACH MEIOFAUNA

29

disturbance (Davies, 1972; Rodrıguez et al., 2003). Nematodes and foraminiferans are supposed to be the two key groups sensitive to environmental changes and can be used as bioindicators of environmental health (Schafer, 1970; Geetanjali et al., 2002; Chullasorn et al., 2011). To date, there have been several benthic studies made in and around Indian waters. However, most of these were made on macrobenthos. Most meiofaunal studies reported from the seas around the Indian subcontinent conducted in shallow coastal and estuarine waters and mangroves are only of regional importance. The majority of Indian meiofauna studies were done at the west coast (Ansari & Parulekar, 1981; Ansari, 1984; Harkantra, 1984; Harkantra & Parulekar, 1989; Parulekar et al., 1993; Ingole & Parulekar, 1998; Ingole et al., 1999; Ansari et al., 2001; Kumar & Manivannan, 2001; Sajan et al., 2010) and to a lesser extent along the east coast (Aiyar & Alikunhi, 1944; Krishnaswamy, 1957; Pattnaik & Lakshmana Rao, 1990; Moorthy, 2002; Altaff et al., 2004; Altaff et al., 2005). Rao & Ganapati (1968) studied the interstitial fauna of beach sands along the east coast of India. Their study provided the first records of nematodes from the Indian coast. Initial meiofaunal studies reported from the west coast of India were from the Cochin estuary (Kurien, 1972) and the mud bank region of Kerala (Damodaran, 1973). Since then, a few more qualitative and quantitative studies on meiofauna were done on both the east and west coasts of India (Ansari et al., 1980; Harkantra et al., 1980; Ansari & Gauns, 1996; Sultan Ali et al., 1998; Nanajkar & Ingole, 2007). Parulekar et al. (1982) studied the biomass of meiofauna along a depth gradient down to a depth of 75 m at the west coast of India. Ansari et al. (1993) studied the vertical gradients of meiofauna mainly in relation to biochemical changes and microbial abundance in the upper 20 cm of a mangrove mudflat deposit. They also observed that food availability played a supporting role, while physical environmental parameters were more important for meiofaunal dispersion in a mangrove mudflat on the west coast. Rao & Sarma (1994) described the seasonal abundance and the breeding cycle of 15 dominant species of meiobenthic copepods including ovigerous females inhabiting the littoral sediments of the Parikud Islands in Chilika Lagoon. Reddy & Reddeppa Reddi (1994) studied the distribution and abundance of 46 species of Foraminifera in the Araniar River estuary of Pulicat. Sarma & Wilsanand (1994) investigated the littoral meiofauna of the Bhitarkanika mangrove sediments and found 11 major faunal taxa, with nematodes being dominant, and a positive correlation between meiofaunal densities and medium grained sediments with high organic matter. The meiofauna of the outer channel of Chilika Lagoon revealed the presence of 12 major taxa, where nematodes and harpacticoid copepods represented the dominant meiofaunal groups (Sarma & Wilsanand, 1996).

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Hussain et al. (1996) studied ostracod populations in relation to temperature and salinity in waters off Tuticorin, southeast coast of India. Foraminifera were the dominant group in Kayankulam backwaters adjacent to the sea (Prabha Devi et al., 1996). Fine scale vertical and spatial distribution of meiofauna in relation to food abundance in the intertidal sediments at Dias beach, Goa, were observed by Ansari & Guans (1996). Distribution of foraminiferans in Cochin backwaters were studied by Kameswararao & Balasubramanian (1996). Rao & Satapathy (1996) compared the abundance, density, and seasonal fluctuation of two species of Kinorhyncha in Chilika Lagoon. Studies by Goldin et al. (1996) on the meiobenthos of the intertidal zone of mangrove mudflats in Thane creek revealed a dominance of nematodes with little seasonal changes. Ingole & Parulekar (1998) observed the impact of salinity on meiofauna community structure in an estuarine intertidal beach of Siridao, Goa. Ansari & Parulekar (1998) gave an account on the community structure of meiobenthos from the Zuari estuary. Rajesh et al. (1999) showed that ostracod distribution depends on physico-chemical characteristics in the inner shelf sediments off Kasargod. Chinnadurai & Fernando (2003) studied the meiofaunal composition and density from Pichavaram mangrove areas. No meiofauna study has been made as yet on the meiofauna along the Chennai coast. Chennai, being one of the largest metropolitans in India, has a coastal stretch of about 30 km in length, starting from Neelangarai in the south up to Ennore Creek in the north. The majority of the city’s area shows residential and industrial activities, which make the city’s drainage system work at full capacity. The major outlets for these drainage sewage disposals are from the Adyar River (Shanmugam et al., 2007) in the south, the Cuvum River (Ramachandran, 2001) in the central part, the Buckingham Canal (Sreenivasan & Franklin, 1975; Jayaprakash et al., 2005) in the north, and also from small outlets all along the coast. Along the North Chennai coastal region, a number of refineries are located that include thermal power plants and fertilizer industries. Industrial wastes along with residential wastes are finally drained into the coastal waters of Chennai. Since the estuaries of Ennore, Cuvum, and Adyar form the predominant sewage disposal pathways of the city (Shanthi & Gajendran, 2009), these places and their surroundings are heavily polluted (Shanmugam et al., 2007). Along this stretch, five stations were selected based on variations in their hydrodynamic characteristics and their main components of pollutants, with tidal actions reaching a maximum height of 1.23 m during the study period. So far, there is no study that has analysed key environmental factors in structuring the distribution of meiofauna around the eastern coast of India. The present study is the first major investigation into the nature of meiofauna within a study area extending for about 30 km along a stretch of the Chennai coast. The Bay of Bengal is influenced by the northeast monsoon from November through


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April and by the southwest monsoon from June through September with sporadic upwellings in the south. There is marked variation in bottom temperature, salinity, and dissolved oxygen with depth, occurrence of the thermocline, salinity maxima, and oxygen minimum zones in this area (Rodrigues et al., 1982). The width of the continental margin is not uniformly distributed. In the north of the bay region it is wider and in the south of the bay it almost abuts along the coastline, thereby creating gradients in bathymetry (Thakur & Pradeep Kumar, 2007). The objectives of the present study are to (1) provide estimates of the density and biomass of the meiofauna from the eastern continental shelf of India and compare this with similar studies done worldwide, (2) understand the community structure of the major meiofaunal groups, (3) test whether any depth or substratum variations exist for meiofaunal organisms in the study area, and (4) identify key environmental variables controlling meiofaunal standing stocks and communities in the sediments of coastal beaches.

MATERIAL AND METHODS

Description of study sites - Neelangarai: Located at the southern end of Chennai city, representing one of the uninterrupted stretches of sandy beach in and around the Chennai coast, with tourist and fishing activities. - Besant Nagar: Situated in the southern part of Chennai city close to Adyar Creek, from where domestic discharge and offshore waters during storms enter the Bay of Bengal. A sandbar is commonly formed at the river mouth. - Marina: A favourite tourist attraction of Chennai city, is located about 2 km from the southern end of Chennai port, near the Coovum River carrying the majority of treated and untreated domestic sewage waste into the Bay of Bengal. - Thiruvotriyur: Located at the northern end of the Chennai port, with protective artificial boulders on either side. This beach is unique for its heavy wave action, with an open beach that stretches to approximately 200 m. Anthropogenic and industrial activities are pronounced, with minor fishing activity. - Ernavoor: Located at the northern end of Chennai city, very near Ennore Creek, which receives treated and untreated industrial effluents from the Manali industrial area and also fly ash and thermal effluents from the Ennore Thermal Power Station. More dredging activity is seen in this area, with fishing and navigational activities.

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Fig. 1. Location of sampling stations along the Bay of Bengal, SE coast of India.

Sampling Meiofauna samples for the present study were collected monthly, from January 2000 to February 2001, at five stations, situated between 12◦ 56 33.05 and 13◦ 12 10.45 N and 80◦ 15 38.72 to 80◦ 19 21.19 E (fig. 1) along the southeastern coast of India (fig. 1). Samples were taken from the intertidal region at low tide and high tide (2003 to 2005). At each station, sand cores of the top 15 cm layer were taken using plastic corers (3.57 cm inner diameter and 30 cm length). The sediment here comprised coarse sand and silt. The core samples were immediately fixed in buffered seawater formalin at a final concentration of 5%, and taken to the laboratory. Laboratory analyses In the laboratory, extraction of the meiofauna from sediment samples was carried out using the technique described by Warwick & Buchanan (1970). The formalin-fixed sediment sample was washed through a set of 500 μm and 63 μm sieves to extract meiofauna following the method provided by Higgins & Thiel (1988). The sediment retained on the 63 μm sieve was then decanted in to a 250 ml graduated cylinder and filled with filtered seawater to a volume of 280 ml. In order to extract the meiofaunal organisms from the silt/clay sediment, decantation on a 63 mm sieve was used as described in Somerfield & Warwick (1996). The sample was put steady for 60 s, allowing the larger particles to settle. The supernatant with the meiofauna was passed through a 63 μm sieve. This procedure was repeated three times. The meiofaunal organisms were stained with Rose Bengal prior to


33

extraction and were sorted and counted under a stereomicroscope (10× and 40× magnification using a Leica digital equipment). The numerical abundance of the meiofauna was expressed as individuals 10 cm−2 . Identification and quantification Dominant groups were identified to higher taxa. Identification of each taxon was carried out by mounting key structures for their identification and comparing them with the descriptions of Aiyar & Alikunhi (1944), Krishnaswamy (1957), Ax (1971), Rao (1972, 1989, 1993), Warwick (1973), Coull (1977), Platt & Warwick (1980), Wells & Rao (1987), and Higgins & Thiel (1988). The identified specimens were grouped according to higher taxa, as Foraminifera, Turbellaria, Polychaeta, Oligochaeta, Archiannelida, Nematoda, Gastrotricha, Rotifera, Ostracoda, Isopoda, Cladocera, Copepoda, and others (all remaining meiofauna elements were grouped together). Physicochemical parameters The physicochemical parameters such as atmospheric temperature (°C), interstitial water temperature (°C), pH, salinity, and dissolved oxygen (mg−1 ) were recorded. Using a syringe, interstitial water taken from the top 5 cm of the sediment and used for analysing pH, salinity, and dissolved oxygen. Interstitial temperature was recorded by inserting a mercury thermometer into the sediment column down to 5 cm depth and keeping it there for a few minutes. Dissolved oxygen was estimated in the field using Winkler’s method, salinity by Mohr’s method, and pH by refractometer. Granulometry Grain size was estimated by following the method of Buchanan (1984). Collected sand samples were air dried for 4-5 days and hand-sieved through a graded series of standard sieves representing intervals of the Wentworth scale (Wentworth, 1922) (table I). The sieves were arranged in decreasing order of the mesh size (2000 → 63 μm). On these stacked sets of sieves, the samples were placed. The stack was closed at the bottom end with a metal pan, and closed with a cover on top, and was agitated for about 15 minutes. After sieving, the material of each individual sieve was weighed. The percentage composition was calculated for further analysis.

1 2 3 4 5 6 7 8

Sta. No.

Sand grain size (in mm) Wentworth scale (1922) >2.000 1.680 0.542 0.425 0.300 0.275 0.147 0.042 Total % WS

Marina

1.90 ± 0.52∗ 2.22 ± 0.69 36.87 ± 4.47 37.64 ± 3.15∗∗ 19.63 ± 1.79 25.25 ± 2.14 20.33 ± 2.51 2.32 ± 0.75 146.16 ± 18.27 20.70**

Neelangarai

1.07 ± 0.43∗ 1.90 ± 0.86 31.28 ± 4.97 37.92 ± 2.68∗∗ 17.13 ± 1.39 23.58 ± 1.71 23.69 ± 3.17 2.80 ± 0.67 139.37 ± 17.42 19.74

0.58 ± 0.11∗ 1.61 ± 0.68 23.97 ± 3.17 33.32 ± 2.68∗∗ 17.74 ± 2.66 27.77 ± 2.54 30.12 ± 3.74 3.89 ± 1.33 139.00 ± 17.37 19.69*

Besant Nagar

0.13 ± 0.77∗ 2.84 ± 0.86 28.46 ± 3.51 34.24 ± 3.14∗∗ 15.71 ± 1.84 24.65 ± 2.89 29.21 ± 3.07 5.07 ± 0.81 140.31 ± 17.53 19.87

Thiruvotriyur

2.15 ± 0.33∗ 3.05 ± 0.87 42.24 ± 2.85∗∗ 38.48 ± 4.11 18.00 ± 1.95 21.25 ± 1.72 13.77 ± 1.54 2.24 ± 0.76 141.18 ± 17.64 20.00

Ernavoor

0.83* 1.65 23.06 25.72** 12.49 17.35 16.59 2.31 100 100

PC%

TABLE I Mean contribution of different sand grain sizes at different sampling stations in: %WS, Percentage of Wet Sand in gm 10 cm−2 ; PC%, Percentage Composition of each grain size; ** = maximum and * = minimum

34 G. MANTHA ET AL.


35

Ecological indices Meiofauna taxon-based indices were calculated: the Shannon-Wiener diversity index as H (Shannon & Weaver, 1949), Simpson’s dominance index as D (Simpson, 1949), Pielou’s evenness index as J (Pielou, 1969), and species richness (SR). The nematode-copepod (N/C) ratio was calculated by dividing the number of nematodes in a sample by the number of copepods. Statistical analysis Parametric ANOVA was used to detect significant differences in meiofauna abundance between months and stations. When the ANOVA showed significant results, Tukey’s HSD test was used to show contrasts. Before analysis, the normality of the data was checked and, when necessary, data were transformed accordingly. The homogeneity of variance was assessed by Cochran’s test. Pearson’s Correlation coefficient analysis was used to show any significant difference between major meiofaunal distribution and environmental variables and sediment size. Single linkage Bray-Curtis cluster dendrograms were constructed following Tseng et al. (2008) and Hwang et al. (2009) to determine the similarity in distribution and abundance between different sampling months, at different stations, and within the meiofauna itself. Scatter plot diagrams for principle component ordination and correspondence analysis were carried out to ascertain the groupings of meiofauna during different sampling months and at different sampling stations. Statistical analyses were carried out using Microsoft-EXCEL (ver. MS-Office 2007), SPSS ver. 15.0, and PAST ver. 2.0.

RESULTS

Physicochemical parameters The atmospheric temperature varied between 28.2°C and 32.1°C, the interstitial temperature measured at 5 cm depth varied between 26.4°C and 30.2°C, salinity varied between 29.7 and 33.7 ppt, the pH varied between 7.9 and 8.7, and dissolved oxygen varied between 4.2 and 5.8 mg L−1 (fig. 2), respectively. All physicochemical factors showed similar patterns of increase or decrease across all stations, except for dissolved oxygen, which showed variations across stations during the sampling period. Beach substrata varied considerably with sediment type (table I). Sediments were separated into eight different size groups, measuring >2 mm, >2-1.68 mm, >1.68-0.54 mm, >0.54-0.42 mm, >0.42-0.3 mm, >0.30.28 mm, >0.28-0.15 mm, and >0.15-0.04 mm.

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Fig. 2. Physicochemical parameters at five stations, monthly from January 2000 to February 2001.

Meiofaunal occurrence and density Meiofauna taxa recorded in our study were Foraminifera, Nematoda, Harpacticoida, Ostracoda, Archiannelida, Rotifera, Gastrotricha, Oligochaeta, Turbellaria, Polychaeta, Isopoda, Cladocera, and Copepoda. Meiofauna densities in different months The highest dominance and the least diversity and evenness were observed in May 2000, and the least dominance and the highest diversity and evenness were observed in January 2001 (table II). Even though January 2001 contributed

37


TABLE II Total abundance and ecological indices of meiofauna distributed monthly at pooled sampling stations [RA = Relative Abundance percentage; D = Simpson’s dominance index; H = Shannon’s Diversity index; J = Pielou’s Evenness index; N/C = Nematode/Copepod index; ** = maximum and * = minimum]

Jan 2000 Feb 2000 Mar 2000 Apr 2000 May 2000 Jun 2000 Jul 2000 Aug 2000 Sep 2000 Oct 2000 Nov 2000 Dec 2000 Jan 2001 Feb 2001 Total

Mean ± SD

RA

D

H

J

N/C

12 133.38 ± 3292.86 35 565.84 ± 12 463.03∗∗ 11 465.84 ± 4250.25∗ 17 594.61 ± 4965.97 19 196.30 ± 3696.58 24 032.15 ± 6764.9 15 938.00 ± 3810.90 24 514.92 ± 6277.62 14 115.07 ± 4912.17 15 680.92 ± 4291.55 19 702.46 ± 4400.39 19 289.84 ± 5038.12 28 740.92 ± 11 199.66 29 157.84 ± 9205.19 3 732 666.00 ± 91 718.99

4.23 12.39** 3.99* 6.13 6.69 8.37 5.55 8.54 4.92 5.46 6.86 6.72 10.01 10.15 100

0.2077 0.2949 0.3208 0.2183 0.1427* 0.2176 0.1784 0.1933 0.2919 0.2099 0.1655 0.1980 0.3465** 0.2538

1.898 1.637 1.570 1.919 2.183** 1.959 1.902 1.986 1.619 1.912 2.076 2.067 1.494* 1.798

0.5562 0.3953 0.3697 0.5242 0.6827** 0.5457 0.5153 0.5603 0.3884 0.5206 0.6133 0.6076 0.3427* 0.4646

0.3810 0.2373 0.1452* 0.2864 0.5424 0.2864 0.4612 0.3656 0.2220 0.2099 0.6744** 0.2499 0.1467 0.1856

the third highest abundance of all meiofauna groups together, it showed the highest dominance index, being less evenly distributed throughout the sampling period. The taxa richness in all of the sampled months was observed with thirteen meiofauna groups, except in January 2000, which showed only twelve groups and Cladocera were absent. The monthly mean of total meiofauna density was highest in February 2000 (35 565.84 ± 12 463.03 ind. 10 cm−2 ) and lowest in March 2000 (11 465.84 ± 42 50.25 ind. 10 cm−2 ). The relative percentage composition was the highest in February 2000, contributing about 12.39%, followed by February-2001 (10.15%), and the least in March 2000, contributing only about 3.99% to the total meiofaunal groups (table II). Meiofauna densities at different stations By station, the highest mean meiofauna density was observed at Neelangarai (67 058.30 ± 100 148.08 ind. 10 cm−2 ) and the lowest at Ernavoor (50 188.30 ± 70 788.03 ind. 10 cm−2 ). The relative percentage composition at Neelangari contributed about 23.35%, followed by Thiruvotriyur (21.96%), and the least meiofauna density was found at Ernavoor (17.48%), respectively. The highest dominance and the least diversity and evenness were observed at Thiruvotriyur, and the least dominance and the highest diversity and evenness were observed at Besant Nagar (table III). Thiruvotriyur contributed the second highest

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TABLE III Total abundance and ecological indices of meiofauna distributed at stations during the months sampled [RA = Relative Abundance percentage; D = Simpson’s dominance index; H = Shannon’s Diversity index, J = Pileou’s Evenness index; N/C = Nematode-Copepod index; ** = maximum and * = minimum]

Neelangarai Marina Besant Nagar Thiruvotriyur Ernavoor Total

Mean ± SD

RA

D

H

J

N/C

67 058.30 ± 100 148.08∗∗

23.35**

0.2353 0.2226 0.1990* 0.2391** 0.2182

1.8890 1.8950 1.9840** 1.8520* 1.8860

0.5087 0.5116 0.5592** 0.4900* 0.5072

0.2437 0.3159 0.3175** 0.2410* 0.3079

52 517.69 ± 75 230.73∗ 54 314.46 ± 71 204.58 63 049.38 ± 95 298.4 50 188.30 ± 70 788.03

18.29* 18.92 21.96 17.48

3 732 666.00 ± 6 593 574.00 100.00

Fig. 3. Mean total abundance of meiofauna at five stations, monthly from January 2000 to February 2001.

abundance, next to Neelangari, and it showed the highest dominance index. Taxa richness was similar at all sampling stations, representing all thirteen meiofauna groups. The meiofauna at Neelangarai and Thiruvotriyur contributed more towards the overall abundance with monthly variations, during February 2000, January 2001, and February 2001 (fig. 3).


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Meiofauna groups Copepoda were the most abundant meiofauna group, contributing about 41.02%, and outnumbering nematodes at all stations during all samplings, and the least was contributed by Cladocera with about 0.95% (table IV). The highest dominance and the least evenness during months, and the least diversity and evenness at stations, were observed in different meiofaunal groups, whereas the least diversity and the least dominance, the highest diversity and evenness during months, was shown by Cladocera and Turbellaria. At stations, the highest dominance and the least dominance as well as the highest diversity and evenness were shown by rotifers and nematodes, respectively. Taxa richness was similar for all groups, except for Cladocera, which were absent once, in January 2000, during the monthly sampling. The total nematode-copepod index had the highest value (0.6744) in November 2000 and the lowest (0.1452) during March 2000 (fig. 4, table II). Among stations, Besant Nagar showed the highest (0.3175) and Thiruvotriyur the lowest (0.2410) values (fig. 4, table III), respectively. Individual nematode-copepod indices per month and station showed that the most affected areas were the stations Ernavoor and Thiruvotriyur, with maximum values (fig. 4). The single linkage Bray-Curtis cluster analysis of different months (fig. 5a) showed three major groups, likewise at different stations (fig. 5b), demarcating two major meiofauna groups (fig. 5c), and showed three major groups contributing similarly to total meiofauna abundance. In our study, we used eight different types of metal sieves for our soil sediment samples, which showed variations in their distribution at different places during different sampling periods represented by a Wentworth’s scale (Wentworth, 1922) (table I). Pearson’s 2-tailed correlation of meiofauna with different-sized soil sediment showed that Foraminifera, Gastrotricha, Isopoda, Oligochaeta, and Ostracoda correlated negatively with 1.680 mm, 0.3 mm, and 0.042 mm mean soil grain size at the p = 0.05 level. Pearson’s 2-tailed correlation of meiofauna with physicochemical parameters showed that Foraminifera, Turbellaria, Gastrotricha, and Isopoda significantly correlated with atmospheric temperature, that Turbellaria, Isopoda, and Copepoda significantly correlated with interstitial temperature, Polychaeta correlated with mean grain size at the p = 0.05 level, and Turbellaria correlated significantly with pH at a p = 0.01 level, respectively. One-way ANOVA of meiofauna abundance with months and stations showed that Foraminifera, Nematoda, Gastrotricha, Rotifera, Archiannelida, Polychaeta, Isopoda, Cladocera, and Copepoda were significantly different during months at the p 0.05 level, whereas Ostracoda and Isopoda were significantly different by stations at the p 0.05 level.

Total

3 732 666.00 ± 411 337.14

Mean ± SD Foraminifera 5260.42 ± 4263.49 Turbellaria 24 668.71 ± 7097.28 Oligochaeta 40 904.85 ± 20 988.06 Polychaeta 19 128.28 ± 7743.31 Nematoda 30 606.00 ± 12 616.01 Archiannelida 5638.57 ± 4163.28 Rotifera 4657.71 ± 3502.59 Gastrotricha 11 308.00 ± 5510.52 Isopoda 6109.00 ± 3390.89 Cladocera 1341.14 ± 1205.76∗ Copepoda 109 372.28 ± 54 532.08∗∗ Ostracoda 5101.57 ± 3330.62 Others 2522.42 ± 2531.99

D 0.1150 0.0769* 0.0889 0.0823 0.0827 0.1076 0.1089 0.0872 0.0919 0.1250 0.0879 0.0997 0.1383**

Monthwise H 2.3620 2.6010** 2.5130 2.5500 2.5590 2.3630 2.3430 2.5130 2.5020 2.2640* 2.5350 2.4370 2.3340

J 0.7583 0.9622** 0.8813 0.9144 0.9228 0.7586 0.7441 0.8811 0.8720 0.7399 0.9013 0.8170 0.7371* 3 732 666.00 ± 411 337.14

Mean ± SD 14 729.20 ± 2493.04 69 072.40 ± 8734.14 114 533.60 ± 19 552.54 53 559.20 ± 8499.76 85 696.80 ± 4828.84 15 788.00 ± 3141.92 13 041.60 ± 1543.20 31 662.40 ± 6250.38 17 105.20 ± 6322.74 3755.20 ± 1233.27∗ 306 242.40 ± 54 673.65∗∗ 14 284.40 ± 6975.81 7062.80 ± 5540.91 D 0.2046 0.2026 0.2047 0.2040 0.2005* 0.2063 0.2022** 0.2062 0.2219 0.2173 0.2051 0.2382 0.2985

Stationwise H 1.5970 1.6030 1.5980 1.5990 1.6080** 1.5940 1.6040 1.5940 1.5550 1.5670 1.5970 1.5250 1.4070*

J 0.9881 0.9939 0.9886 0.9898 0.9987** 0.9846 0.9945 0.9847 0.9471 0.9589 0.9876 0.9193 0.8165*

100

RA 1.97 9.25 15.34 7.17 11.48 2.11 1.75 4.24 2.29 0.50* 41.02** 1.91 0.95

TABLE IV Meiofauna abundance and ecological indices at stations during the sampling period [RA = Relative Abundance percentage; D = Simpson’s dominance index; H = Shannon’s Diversity index; J = Pielou’s Evenness index; ** = maximum and * = minimum]

40 G. MANTHA ET AL.


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Fig. 4. Nematode : Copepod index at five stations, monthly from January 2000 to February 2001.

Principal component analysis (fig. 6) also confirmed the results obtained by the cluster analysis, that there are three different groups that contributed differently to meiofauna abundance. The scatter plot diagram of Correspondence analysis of both months (fig. 7a) and stations (fig. 7b), showed the contribution of different meiofauna groups as a part of total abundance. Environmental correlates of meiofauna Among the hydrographical parameters, dissolved oxygen showed a positive correlation with biomass and density for all meiofaunal groups, while temperature had a positive correlation with biomass of total meiofauna and diversity. Salinity was found to negatively correlate with copepods, biomass of total meiofauna, and diversity. Bulk organic matter showed a negative correlation with copepods and biomass of total meiofauna. Nematode biomass, nematode abundance, and total meiofauna abundance were negatively correlated with coarse sediment (sand) and positively correlated with finer sediment (clay). Correlation of different parameters with fauna indicates their impact on the distribution and abundance of meiofauna. Dissolved oxygen and temperature were the most relevant parameters for the density of meiofauna. Meiofauna communities were most affected by depth and temperature.

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Fig. 5. Cluster dendrograms of: A, meiofaunal groups; B, meiofaunal abundance during different months (January 2000 to February 2001); C, meiofaunal abundance at different stations.

Spatial and substratum variation in meiofauna Meiofauna species abundance decreased with pollution. Neelangarai being a clean, undisturbed station showed the highest abundance (67 058.30 ± 100 148.08 ind. 10 cm−2 ). The most polluted station, Ernavoor, showed the lowest with 50 188.30 ± 70 788.03 ind. 10 cm−2 . In general, average biomass and abundance of nematodes were found to increase from coarse to fine sediment, while copepods showed an opposite trend. The biomass of other groups was higher in sandy substrata. Slightly higher species numbers were recorded in sandy sediments (7) compared to sand–silt/clay (6) and silt/clay (5) substrata. Species numbers showed no variation (13 species groups at all stations) and diversity indices showed little variation with substratum.


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Fig. 6. Principal Component Ordination of meiofauna taxa [A = Foraminifera, B = Turbellaria, C = Oligochaeta, D = Polychaeta, E = Nematoda, F = Archiannelida, G = Rotifera, H = Gastrotricha, I = Isopoda, J = Cladocera, K = Copepoda, L = Ostracoda, M = others]. DISCUSSION

Meiofauna taxa recorded in our study were Foraminifera, Nematoda, Harpacticoida, Ostracoda, Archiannelida, Rotifera, Gastrotricha, Oligochaeta, Turbellaria, Polychaeta, Isopoda, Cladocera, and Copepoda (table IV). A similar faunal composition has been reported earlier from tropical mangrove regions and other parts of India. Sarma & Wilsanand (1994) reported Nematoda, Harpacticoida, Polychaeta, Kinorhyncha, Foraminifera, Ostracoda, Oligochaeta, Bivalvia, and Tanaidacea in Bhitarkanika mangroves of the east coast of India. Likewise, Kondalarao & Ramanamurty (1988) studied similar faunal assemblages in Kakinada Bay, Gautami, the Godavari estuarine system at the east coast of India. Similar reports are also provided by Ingole et al. (1987) for the Saphala salt marsh of India and by Ingole & Parulekar (1998) for the Siridao Beach, from the west coast of India. The total meiofauna abundance in our present study ranged about 3.7 × 106 ± 4.1 × 105 ind. 10 cm−2 , which is within the range recorded by McIntyre (1969), who mentioned that densities of overall meiofauna in the intertidal zone can range from 11 × 103 ind. 10 cm−2 to 16 × 106 ind. 10 cm−2 . Although our results

Fig. 7. Correspondence analysis showing the contribution of meiofaunal abundance: A, during different months [1 = Jan 2000, 2 = Feb 2000, 3 = Mar 2000, 4 = Apr 2000, 5 = May 2000, 6 = Jun 2000, 7 = Jul 2000, 8 = Aug 2000, 9 = Sep 2000, 10 = Oct 2000, 11 = Nov 2000, 12 = Dec 2000, 13 = Jan 2001, 14 = Feb 2001]; and B, at different stations [1 = Neelangarai, 2 = Marina, 3 = Besant Nagar, 4 = Thiruvotriyur, 5 = Ernavoor].

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showed that harpacticoid copepods dominated the total meiofauna community, most other meiofauna studies reported that Harpacticoida are second in abundance, next to nematodes (Capstick, 1959; Platt & Warwick, 1980; Hicks & Coull, 1983; Heip et al., 1985; Dahms et al., 2007). According to Houge (1978) and Alongi (1987), occasionally other groups like Harpacticoida, Turbellaria, and Gastrotricha may dominate meiofauna assemblages. This holds particularly true for sandy beaches where Tardigrada dominated the Marambaia Restinga at the southeast coast of Rio de Janeiro, Brazil with around 71.35% of total meiofauna individuals (Albuquerque et al., 2007). McIntyre (1969) reported that the distribution of meiofauna is influenced by temperature, salinity, and also by grain size, which affects the interstitial space between sand grains and the availability of food and oxygen within those interstitial spaces. Our study showed that dissolved oxygen and salinity did not influence any of the meiofauna taxa. However, atmospheric temperature, interstitial temperature, and pH influenced the distribution of Turbellaria greatly. Copepod distribution and abundance were influenced by interstitial temperature rather than by any other factor. Moreover, at sandy shores, soil size is the main component determining the distribution of organisms. Other factors, such as the level of pollution, the organic load, and food availability are also known to affect meiofauna abundance and diversity. Sandy shores are most vulnerable to hydrodynamics, tidal changes, wind, erosion of sand, and of nutrients during monsoons, with heavy loads of nutrient enrichment via sewage disposals (McIntyre, 1968; Coull & Bell, 1979; McLachlan et al., 1996; Coull, 1999; Rodriguez et al., 2003; McLachlan & Brown, 2006; Shanmugam et al., 2007) and the animals living within these sandy shores also get affected. The degree may vary according to their selectivity and tolerance to that particular environment (Giere, 2009). Sediment grain size is one of the important factors affecting the distribution of meiofauna (Ansari & Parulekar, 1998). In the present study, average biomass and density of Harpacticoida were higher in silt/clay substrata than in sandy and mixed sand substrata. In general, sediment was more silty at the beaches of the Bay of Bengal. This indicates that if many species are characteristically associated with a given sediment habitat, their distribution is rarely confined to that environment. Food supply is considered to be very important for meiofauna (Giere, 2009). High benthic biomass and density in nearshore areas can be due to the rich primary production in nearshore waters. It has been argued that bulk organic matter measurements may not accurately reflect the amount of organic matter that may actually be utilized by an organism (Mayer & Rice, 1992). However, BIO-ENV has shown the importance of organic matter, which indicates that this factor is vital in shallow areas where the labile form is adequately available to the fauna. Strong

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correlations between meiofauna and chloroplastic pigments have been reported, indicating that meiofauna biomass relies on the availability of food supply (Liu et al., 2007; Tseng et al., 2008). According to Achyuthan & Richardmohan (2002), heavy metal concentrations like nickel and chromium at Muttukadu (near to our collection site Neelangari) are lower than at Adyar and Ennore (near the main outlets of Chennai City). This might be one of the possible reasons for the greater abundance and diversity at Neelangari. It is commonly agreed that nematodes dominate polluted, organically enriched, and deoxygenated areas (Sutherland et al., 2007). However, in the present study, harpacticoid copepods were highly abundant at all sampling stations. The Nematode-copepod ratio was first used by Raffaeli & Mason (1981) as a fast and reliable tool in monitoring the level of organic pollution, as nematodes commonly show a higher tolerance to pollution than do copepods (Moore & Bett, 1989). Even though there were several critiques on this oversimplified but complex relationship (Coull et al., 1981; Lambshead, 1984; Gee et al., 1985; Danovaro et al., 1995), considering its easy, fast, and handy nature, several researchers (Amjad & Gray, 1983; Sutherland et al., 2007; Moreno et al., 2008; Veiga et al., 2010) still use this nematode-copepode ratio in assessing and identifying eutrophically enriched and/or polluted sediments. Our results showed that at individual levels this index was higher at Ernavoor. At mean total values, Besant Nagar and Marina showed higher values than Ernavoor. A cluster dendrogram showed three major meiofauna groups (fig. 6a), five major monthly groups during different months (fig. 6b), and two major station groups at different stations (fig. 6c) among meiofauna communities that contributed to the total abundance of meiofauna in the study period. Scatter plot diagrams of the principal component ordination confirmed the cluster dendrogram, with three major groups of meiofauna contributing to total abundance during the study period. A scatter plot diagram of the correspondence analysis showed the degree of contribution of different meiofaunal groups during different months (fig. 7a) and at different stations (fig. 7b) during the period of study. Thus, the abundance of meiofauna, with harpacticoid copepods being dominant during the study period, showed that even though the sandy shores of the Chennai coast are affected by pollution and hydrodynamic disturbance, their faunal diversity and abundance were well-balanced with variations and modifications in their faunal groups. For example, Ostracoda showed differences by stations and all other groups except Turbellaria, Nematoda, and Oligochaeta were influenced by monthly variations. The lack of nematode dominance can be attributed to sampling only the top 15 cm layer, which carries a higher amount of medium and fine sand. This might have contributed towards the higher abundance of Copepoda and Oligochaeta, rather than to an increased abundance of nematodes. Enhanced


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nematode abundance is commonly observed when the vertical sampling gradient is increased. A higher abundance of harpacticoids can be attributed to their crawling and digging mode of life, inhabiting larger interstitial spaces between the sand grains of these shores, and their high tolerance towards pollutants and hydrodynamic disturbance (Giere, 2009). Harpacticoid copepods represented the most abundant taxon (41.02%), followed by Oligochaeta (15.34%), and the remaining taxa contributed only 43.64%. Other taxa included Nematoda, Turbellaria, Ostracoda, Polychaeta, Rotifera, Gastrotricha, Archiannelida, and other, less abundant groups. The highest meiofauna densities reported from Goa (Ansari et al., 1980) and the Bay of Bengal (Rodrigues et al., 1982) were