(The results given below are the part of my research in Muthupet mangroves - Dr. Balaji, OMCAR Foundation)
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The Current study has recorded 201 fanual species, including 31 species of Zooplankton, 7 species of amphipods, 10 species of polychaetes, 15 species of crustaceans, 19 species of molluscs, 57 species of fishes, 7 species of reptiles, 49 species of birds and 6 species of mammals.
Krishnamurthy et al.,(1995) found 81 species of zooplankton in Pitchavaram Mangroves, Tamil Nadu. Tintinnids were the dominant mocrozooplankters with 50 species and the most important genera were Tintinopsis and Favella (Godhantaraman, 1994; Krishnamurthy, 1995). They also found 40 rotifer species in 17 genera and the microzooplanktors were most abundant in summer, corresponding with phytoplankton abundance.
Kalidasan (1991) recorded 90 species of zooplankton from Muthupet, which had the domination of copepods, on tintinids and rotifers. The present study recorded the following zooplankters as 1 species from foraminifera, 7 species from ciliata, 2 species from rotifers, 2 species from cladocera, 14 species from copepoda, 2 species from mysidaceae, 1 species from Decapoba, 1 species from doliolids and 1 species from molluscan pteropoda and larval forms of polychaetes, crustaceans and molluscs.
Isias tropica, a calonoid copepod was most abundant species in February, March and April samples collected from station 1. Station 2 and 3 showed no difference in domination of particular species. Oithona sp., are particularly abundant in many studies of mangrove plankton (Kathiresan and Bingham, 2002) but here the abundance of Oithona sp., and Paracalanus parvus were equally observed in April, May, June and July. All the samples collected during the study period, showed the domination of copepods with the peak in May. Osore (1992) also found similar result.
The muddy substratum of mangrove ecosystem may be a favorite place to a variety of epibenthic, in faunal and meiofaunal invertebrates. Because, mangrove sediments generally support higher densities of benthic organisms than adjacent non-vegetated sediments (Edgare 1990; Sasekumar and Chong 1998). The most successful benthic species in mangrove ecosystem are those that can adapt to salinity and temperature stresses that are characteristic of this environment (Ferrari et al., 1994)
Polychaetes are the dominant macrobenthos in mangroves (Guerreiro et al., 1996), there were 10 polychaetes were identified from Muthupet mangroves during this study period. Isopods and amphipods also contributed a major part in benthic samples and 7 species of amphipods were recorded, and the burrowing isopods also do major destruction to mangroves, which significantly affect root growth and development (Ellison and Farnsworth, 1990; Santhakumari, 1991). Commonly found polychaete species in station 1 and station 3 were relatively less in station 2 , which may be due to the absence of mangrove vegetation in station 2.
In crustaceans, 4 species of shrimps 2 species of prawns, 5 species of brachyuran crabs, 2 species of hermit crabs and 2 species of cirripede were identified. Analyses of commercial prawn catches have repeatedly shown strong correlation between abundance and biomass of shrimp and extent of the surrounding mangrove areas (Sasekumar et al., 1992; Kathiresan et al., 1994; Vance et al., 1996). The mangrove waterways directly serve as nursery grounds for juvenile penaeids that move offshore and enter the commercial fishery as they mature (Kathiresan and Bingham, 2002).
The mangrove leaves and other parts were decayed on the substratum. The detritus thus produced may attract the juveniles and larvae of crustaceans. Robertson and Blaber (1992) proposed explanation for this relationship as the organic detritus exported from the mangroves provide food and habitat for juveniles (Daniel and Robertson, 1990), and the creeks receive high levels of terrestrial runoff.
Muthupet mangrove system has Penaeus monodon, Penaeus indicus, Metapenacus dobosonii, Metapenaeus monoceros and prawns like Macrobrachium idae and Macrobrachium rude. The freshwater species were relatively lesser than shrimps in commercial catching. The crabs Scylla serrata, Portunas pelagicus, Calappa lophos, Neoepisesarma brochii, and Sesarma fascianata were recorded. Scylla serrata was found among dense mangroves of waterways and Neoepisesarma brochii was relatively higher in number at mudflat mangroves (near lagoonal mouth) than station 1 and 3.
Baby crabs were observed among the partially submerged pneumatophore meadows of Avicennia marina, which are extending towards creeks. Hermit crabs Clibanarius longitarsus and Clibanarius pedavancis, were occupying the dead mollscan shells, which were commonly seen in station 2 but not in station 1 and 3. It may because, the station 2 is located close to mouth of lagoon, where accidental entry of molluscan shells and hermit crabs may be possible.
Barnacles are the crustaceans under cirripedes which can grow abundantly on mangrove roots and pneumatophores (Foster 1982, Bayliss, 1993). Balanus amphitrite is the most common, abundant in each and every exposed rigid substratum (dead wood, roots etc.,) from water level that is submerged during high tide. Density of barnacles is greater on lower surfaces than upper surfaces of mangroves (Ross and Underwood 1997). The vertical zonation and dense arrangement of barnacles on mangrove roots showed the immense competition for attachment. The recruitment of barnacles and other sessile invertebrates in mangroves is largely controlled by larval abundance, tidal currents, duration of larval life and density of adult populations (Bingham 1992; Young 1995). The partially submerged pneumatophores of Avicennia marina were attached with Balanus amphitrite randomly.
The mangrove molluscs are one of the major populations of marine origin fauna of Muthupet mangroves. Bivalves and snails are the primary representatives of molluscan population. There are 19 species of molluscs were recorded in the present study including bivalves such as Modiolus metcalfei, Perna viridis, Meretrix meretrix, Meretrix casta, Katalysia opima, Anadora granosa, Anadora rhombea. The Oyster Crassostrea madrasensis, Saccostrea cuculata were forming the extensive beds in lagoon.
The Muthupet mangroves provide an ideal environment for production of oyster beds, which are an important part of the habitat (Rajapandian et al., 1990). The dense oyster bed of elevated muddy substratum of lagoon is usually exposed in low tide. Fishermen are avoiding these Oyster beds as they wounded the feet and damaged the nets. So, the oyster beds thus protecting the benthic organisms from human, and serve as the micro hot spots of benthic organisms of the mangrove ecosystem. Teredinids (Shipworms) and Pholads are the burrowing bivalves of Muthupet mangroves, which are destroying submerged roots and branches. Seven species of which were recorded from Pitchavaram mangroves, Tamil Nadu. (Sivakumar and Kathiresan, 1996).
Cecilia Pandian(1996) recorded 73 species of finfishes in Muthupet mangroves but the present study recorded 57 species of finishes. Fish distributions and abundances may also change on dial and seasonal cycles (Chandrasekaran and Natarajan, 1993). Fishes in mangroves are important predators on amphipods, isopods, shrimps, nematodes, insects, gastropods, other fishes and algae. (Erondu 1990, Rooker 1995).
In Muthupet mangroves, fishes like Mugil cephalus, Liza parsia, Terapon jarbua, Oreochrombis mossambica, Chanos chanos were abundant. Terapon puta, Eteroplus suratensis, Leiognathus brevirostris, Platycephalus indicus, Plectorhinchus gibbosus were commonly collected fishes from Muthupet lagoon.
The moving dense school of fish juvenile was observed in lagoon and creeks. So, it is common to find large number of larvae and juvenile fish in net samples from mangrove habitats (Dennis 1992). This high density of fish juvenile may be due to the supply of appropriate food and turbidity of water which may reduce predation and protection from structural complexity of mangroves (Robertson and Blaber, 1992). Another interesting fish to observe on muddy substratum of lagoon shore is the mudskipper Boleophthalmus boddarti. It is a specially adopted fish which has a variety of anatomical, physiological and behavioural adaptations to tolerate environmental stresses (Ogaswaswara et al., 1991).
There are 3 amphibians Rana hexadactyla, Bufo melanostictus and Rhacophoras maculatus were recorded in addition with reptiles Testuda elegans, Naja naja, Bungarus coerulas and Enhydrina schistose. An (Unidentified) Gecko was also observed among the wooden reaper of forest shed, in station 1.
Oswin (1997) reported 160 species of birds including permanent residents, seasonal and local migratory birds. The migratory birds usually come to Muthupet during monsoonal season (September – January) are contributing a major part of the bird population. So, the present study period of summer season did not come across those previously recorded seasonal migratory birds. Local migrants and permanent residents were common among 49 species of recorded birds during this study. Among the birds, the pond heron Ardeola grayii, is commonly found in lower branches of Excoecaria agallocha and Prosopis chilensis along the landward creeks. Pariah kite Milvus migrans, Brahmini kite Haliastur indus, were observed at the upper canopy of the mangroves, the nests of Brrahmini kite Haliastur indus were constructed at the top branches of mangroves. Blue rock pigcon Columba livia, and Indian king dove Streptopelia decaocto and spotted dove Streptopelia chinensis were found at the interior landward mongroves but not frequently. The Lesser pied king fisher Ceryle rudis, Common pied king fisher Alcedo atthis and white breasted pied kingfisher Halcyon symrnensis were seen while they were busy to fish along the creeks of Korayar river
The wholes (nests) of Green bee – eater Merops orientalis were excaved at the sides of small mud elevations, found at the landward sides of the forest. Little cormorant Phalacrocorax niger were usually found at the water surface in wider creeks. Hussain and Acharya (1994) stated that 52 mammals were once lived in Sunderban mangroves. Oswin (1997) reported 13 species of mammals in Muthupet mangrove forest. The present study recorded only 6 species of mammals among which, common jackal Cannis aureus is the major predator on marine and terrestrial origin organisms of Muthupet mangroves. Indian field rat Mus booduga, common house rat Rattus rattus, short nosed fruit bat Cynopterus sphinx were found commonly during night. So the present study recorded higher number of species in fishes (57) and lower number in mammals (6).
