Distribution and Diversity of Macrobenthos in Different Mangrove Ecosystems of Tamil Nadu Coast, India

Plants ecosystems are a habitat for a wide variety of species, some occurring in high densities and provide food and shelter for a large number of commercially valuable finfish and shellfishes. They are productive habitats and support coastal fisheries [1]. The mangrove forests are extremely important coastal resources, which are vital for socioeconomic development of the region. As a detritus-based ecosystem, leaf litter from the mangroves provides the basis for adjacent aquatic and terrestrial food webs. It also serves as breeding, feeding, and nursery grounds for most of the commercially important finfish and shellfishes, on which thousands of coastal people depend for their livelihood. It is considered to have physical, chemical, and biological processes which promote the adaptation of inhabiting organisms to tolerate greater amplitude of environmental characters both morphologically and physiologically. Krom MD and Berner RA [2] have reported that the decomposition of organic matter consists of nutrients such as nitrogen and phosphorus, which play a vital role in the establishment of healthy mangroves. However, sediment where the animals inhabit often acts as buffer either as a source or sink of nutrients especially phosphorus by adsorption and desorption reactions [2,3]. Hence, the sediment plays a crucial role on benthic faunal diversity in the mangrove ecosystem. Benthic organisms constitute an important component that influences the productivity of the habitat to a greater extent. Benthos helps in the recycling of nutrients, which in turn promotes primary productivity. A detailed and complete knowledge of the bottom fauna is not only important for the determination of productivity [4] but is also helpful in understanding the diversity of the habitat. Macrofauna are the most widely studied benthic organisms which are retained on 0.5 mm sieve. They reside beneath the sediment surface in burrows and tubes. Thus, seemingly, the bottom of the mangrove substratum habitats forms and a wide array of macrobenthic organisms of various size and taxonomic categories. Indian mangrove ecosystems are known to have a total of 3,985 biological species that include 919 floral species and 3,066 faunal species. Of the biological species, the faunal species occupy about 77%, and the floral species 23%. Thus, the faunal species component is about three times greater than the floral component of the mangrove ecosystem [5,6]. Of these, polychaetes, molluscs, and crustaceans are found to be the major macrobenthic organisms in mangrove environment. Most of the macrobenthos assist in the breakdown of particulate organic material by exposing them to microbes and their waste materials contain rich nutrients forming the food for other consumers. Thus, the macrobenthos plays a major ecological role in the mangrove ecosystem [7]. Mangroves are inhabited by a variety of macrobenthic invertebrates, such as brachyuran crabs, hermit crabs, gastropods, bivalves, barnacles, sponges, tunicates, polychaetes, and sipunculids. The mangrove invertebrates often exhibit marked zonation patterns and colonize a variety of specific micro-environments [8-10]. While some species dwell on the sediment.