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Mangrove ecosystem is considered to have physical, chemical and biological processes
which promote the adaptation of inhibiting organisms to tolerate greater amplitude of
environmental characters both morphologically and physiologically. However, mangrove ecosystem
is considered as highly productive ecosystem which exports organic matter to the
coastal ecosystem (Ogden and Glatfelter, 1983), the partially decomposed mangrove leaves and
plant materials release the particulate organic matter. The decomposed organic matter is
reported to be rich in nutrients, such as nitrogen and phosphorus, which play a vital role in
the mangrove environment. However, sediment where the animals dwell, often acts as a
buffer either as a source or sink of nutrients especially phosphorus by adsorption-desorption
reactions (Krom and Berner, 1980). More than 500 species of insects and arachnids, 229
species of crustaceans, 212 species of molluscs, 50 species of nematodes and 150 species
of planktonic and benthic organisms are known from Indian mangroves (Gopal
and Krishnamurthy, 1993). Of these, polychaetes, molluscs and crustaceans were found to
be the major macro benthic organisms in mangrove environment. Most of the macro
benthos assist in the breakdown of particulate organic material by exposing them to microbes
and their waste materials contain rich nutrients forming food for other consumers, is the
major ecological role in the mangrove ecosystem. Benthos can be regarded as the efficient tool
to recycle the nutrients and accumulate energy for higher trophic level. Since the
organically rich mangrove sediments abounding a myriad of macro and meiofaunal life, mangrove
fishes depend on them for food which in turn support the subtidal fishery potential of the
mangrove system (Sarma and Wilsanand, 1994). The estimation of benthic production would serve
as a useful index for assessing the fishing production of a particular area (Sultan et al., 1983). The small changes in the environment will have a considerable response on the
benthic community and it avails to measure the degree of pollution (Coull, 1973; and
Fernando, 1987). It is found that for understanding the highly productive nature of mangrove
ecosystem, knowledge of the benthic system is essential. An assessment of the health of a
particular ecosystem can be achieved only through a careful analysis of benthic fauna. In short,
the benthosa dynamic element of marine environment are considered as good tool
for monitoring the interaction pollution and intertidal ecology.
The environmental parameters, such as temperature, salinity, dissolved oxygen and pH
were analyzed following the methods of Strickland and Parsons (1972). The sites were
selected based on their proximities to Open Sea and their levels of anthropogenic pressure. The
two selected sites, namely, Station 1-Open Sea
(10° 20´ N, 79° 30´ E); and Station
2-Sethukuda (10° 20´ N, 79°
32´ E) were chosen (Figure 1). These stations are in the fringe of
mangroves varied in microclimatic niche. The species present on the substratum and vegetation in
the intertidal belt of the vegetated area were recorded in a quadrant measuring 1
m2. Crab burrow density was recorded in three randomly placed 1 sq m quadrates following the method
of Jones (1984). Crabs and other fauna were collected during low tide, and then were
preserved in 5% neutralized formalin. The collected specimens were identified following the works
of Rathburn (1930), Chhapgar (1957), Crane (1975), Williams (1984) and
Sethuramalingam and Ajmalkhan (1991). The general survey involved the collection of various density of
crabs by randomly counting crabs either active on the substrate enclosed within the quadrant
or staying in burrows. |
