DENSITY AND DISTRIBUTION OF MEIOFAUNA OF TAMILNADU COAST

The meiofauna inhabiting the different sediment habitat of Tamilnadu was studied. A brief description of the density, sediment characters, total organic carbon and vertical distribution in different sediment habitats. diversity and cluster analysis is given. All the typical meiofauna groups are present. A quantitative estimate of the diverse taxonomic groups encountered is given.The density of total meiofauna individuals in these intertidal sediements ranged from 26 animals/l0 cm2 to 1440 animals/ 10 cm 2 . A list of 101 species identified from Tamilnadu Coast is given. several genera and species regarded as widespread and cosmopolitan were recorded. The evidence that several meiofauna species are widely distributed and any future investigations of the unexplored areas are likely to indicate a closer meiofaunal relationship is supported.The distribution of meiofauna is discussed in relation to the nature of the substratum.


INTRODUCTION
The meiofauna inhabiting the different sediment habitat of Tamilnadu was studied.A brief description of the density, sediment characters, total organic carbon and vertical distribution in different sediment habitats.diversity and cluster analysis is given.All the typical meiofauna groups are present.A quantitative estimate of the diverse taxonomic groups encountered is given.The density of total meiofauna individuals in these intertidal sediements ranged from 26 animals/l0 cm 2 to 1440 animals/ 10 cm 2 .A list of 101 species identified from Tamilnadu Coast is given.several genera and species regarded as widespread and cosmopolitan were recorded.The evidence that several meiofauna species are widely distributed and any future investigations of the unexplored areas are likely to indicate a closer meiofaunal relationship is supported.The distribution of meiofauna is discussed in relation to the nature of the substratum.

ENVIRONMENTAL VARIABLES SEDIMENT CHARACTERISTICS
The median particle size at all stations ranged between 20 (0.250 mm) and 3e (0.125 mm) thereby indicating that it contained median sand (Table la, b).The median particle size of sandy sediment fluctuated between 2.25 and 2.5 Mde, muddy sediment between 2.3 and 2.75 Mde, muddy sediment with seagrass bed between 2.7 and 2.75 Mde and sandy sediment with rocky environment between 2.0 and 2.25 Mde (Table la, b).The Md0 values showed a greater fluctuation in sandy sediments than in muddy sediments.It was also observed that the sediment in stations 4-8, 10-11 had finer sediments than in stations 1-3, 9 and 12 ( The composition of meiofauna in Tamil Nadu coast is mostly related to grain size.The sediment characteristic of muddy sediments with seagrass bed cover had a high silt and clay content with a corresponding higher density of meiofauna.Sediment with higher silt and clay content is mainly inhabited by burrowers such as nematodes and oligochaetes (Table la, b).

TOTAL ORGANIC CARBON CONTENT
The variation in the sediment organic carbon values in the present study, showed considerable similarity at stations 4 to 8, 10 and 11, which had a muddy sediment (Fig. 1), while stations 1 to 3, 9 and 12 (sandy environment) differed from muddy (stations 4 to 8 and 10 to 11) environment (Fig. 1).

StOltlons
The highest value of organic content (9.73 mg C/ g and 9.51 mg C/ g during 2006 and 2007 respectively) was recorded at station 8 in Tuticorin Port (Fig. 1).In general, the total organic carbon content increased with increasing silt and clay content.
Appendix II   Nematodes were the most dominant group of meiofauna at all the sampling stations of Tamil Nadu coast, constituting from 30.25% to 63.60% of total abundance (Figs. 2 a, b).The next important faunal group was the harpacticoid copepods which contributes 10.72 to 26.32% of the total meiofauna.Nematodes and harpacticoid copepods together comprised about 80% of the meiofauna (Figs. 2 a,  b).Ostracods were recorded at all the twelve stations, but their population density was considerably low (1.34 % to 7.14 % at of the total abundance).
The other taxa found were gastrotrichs, turbellarians and isopods which made up only less than 5 % of the total meiofauna.However, at station 3 (Cuddalore) isopods constituted the maximum percentage (13.91%) during 2007 (Figs. 2 a, b).

Sandy sediment with rocky environment
The meiofaunal density varied from 425 to 915 individuals/10 cm-2 (Appendix II, Table 13) and from 438 to 940 individuals/10 cm-2 at station 12 during 2006 and 2007 respectively (Appendix II, Table 13).In general, muddy sediments with seagrass bed had relatively higher densities of meiofauna than those with other sediment types (Fig. 3).The gastrotrichs and turbellarians were totally absent in muddy environment.

DIVERSITY INDEX
The diversity indices were lowest at stations 5 (Nagapattinam) and 8 (Tuticorin), which can be considered as indications of the stress at these sites.These sites were very close to the harbor.Station 7, showed higher diversity in addition to a high density of meiofauna.It must be stated that the sediment here was muddy with seagrass (Table 14).It could also be seen from the similarity matrix (Fig. 4) and the MDS plot (Fig. 5) that the muddy and seagrass bed environment, muddy environment and sandy environment harboured distinct populations.Few sites of muddy stations are closer to those in other zones of sandy sediment stations.Nonetheless in some stations of muddy environment no such distinctness could be recognized, probably because of the impact of pollution (stations 5 (NAG), 8 (TU1) and 11 (RAM)).The densities of meiofauna varied significantly (F = 4.895; P < 0.001) between the stations (Table 15), probably due to the variation in environmental parameters like nature of sediment.The vertical distribution of meiofauna was quite similar in all the twelve stations.Densities were highest near the sediment surface and especially in muddy sediments, where the upper sediment had up 50% of the total fauna (Fig. 6 d, e, h, i, k).
In sandy sediments, total meiofauna fluctuated with depth, and the maximum was found at 2-6 cm.(Fig. 6 a, b, c, 1).In muddy sediment with seagrass bed, again, higher densities occurred in the top portion (Fig. 6f, g  . ., A total of 101 species of meiofauna belonging to 63 families were identified, of which 34 species were nematodes, nine were harpacticoid copepods, 38 were foraminiferans, six each were polychaetes, ostracods and oligochates, one was an isopod and one each of unidentified species of gastrotrichs and turbellarians (Table 16).---- Nine major meiofaunal taxa i.e. nematodes, harpacticoid copepods, foraminiferans, polychaetes, ostracods, oligochaetes, gastrotrichs, turbellarians and isopod were recorded at different sediment nature of Tamil Nadu coast.Nematodes were the most abundant group of meiofauna at all the sampling sites.This is generally the case in marine sediments.The abundance of polychaetes was less, which may be due to predominance of sand fraction in sediments at most of the stations.Oligochaetes were second in abundance to nematodes only at stations 1, 6 and 7 (Chennai, Thondi and Thiruchendur), probably because at station 1, situated near the sewage mixing area and sediment here was very fine.In general, oligochaetes are mainly found in the polluted areas.Among the different sampling sites, areas with seagrass bed cover (stations 6 and 7) sediment contained highest density of meiofauna and also mainly inhabited by burrowers such as nematodes and oligochaetes.Nematodes were the most dominant group in the finer sediments.Meiofauna densities in the seagrass bed were significantly related, with a time log, to change in bacterial standing stock, indicating that microbes may be an important resource.The increase of detritus, which provides the main food for the meiofauna, is suggested to be the reason for the high meiofauna densities observed in the seagrass bed.A lowest density of meiofauna was observed in sandy sediments especially at stations 1 (Chennai), 5 (Nagapattinam), 8 (Tuticorin), 11 (Rameswaram) and 12 (Kanyakumari).Probably because at station 1, situated near the sewage mixing area.

Fig. 1 .
Fig. 1.Variations in total organic carbon content of Tamil Nadu coast during 2006 and 2007.

Fig
Fig. 2a Mean percentage composition of meiofauna communities from intertidal sediments of Tamil Nadu coast during 2006.

Fig. 2b
Fig. 2b Mean percentage of meiofauna communities from intertidal sediments of Tamil Nadu coast during 2007.

Table la .
Percentage composition of sediment texture (%) and mean densities of meiofauna (n/l0 cm2) of Tamil Nadu coast during 2006.

Table lb .
Table la, b).Percentage composition of sediment texture (%) and mean densities of meiofauna (n/l0 cm 2 ) of Tamil Nadu coast during 2007.

Table 15 .
ANOV A for meiofauna density within stations.

Table 16 .
Occurrence and distribution of meiofaunal community in the intertidal region of Tamil Nadu coast during 2006 and 2007.