Crabs as a Part of Mangrove Ecosystems

Crabs play important roles in the maintenance, modification and regulation of the benthic environment by influencing both the abiotic and biotic components. Many species of crabs are burrowing in nature altering the surface characteristics of sediments and steering the nutrient cycling (Pandya, 2011). The feeding activity, degradation of mangrove leaf litter and pellet formation by different species of fiddler crabs alters the substratum characteristics and content of organic matter. Furthermore, their biological outputs like faeces contain nitrogen, carbon, phosphorus and trace metals, forming a rich source of food for other consumers (Kuraeuter, 1976).

The bioturbatory processes by crabs on the intertidal area results into variety of biogenic structures and markings controlling an assortment of processes important for an ecosystem. These include facilitation of oxygen to the subsurface depth allowing microbial diversity and sediment oxic-anoxic zoning, feeding activity (scraping the upper organic rich layer of the sediments) regulates organic content, algal covering and by-products from the gut enriches the sediments with minerals (Arya et al., 2014).

In mangrove ecosystems, burrowing activity of crabs increases the porosity of the soil thereby increasing the regeneration of mangrove seedlings (Khan et al., 2005). The burrowing habit assists in oxidizing the sulphide that builds up due to high rate of organic decomposition in mangrove swamps (Diemont et al., 1975). Crabs have been recognized as regulators of the structure of estuarine communities (Dittel et al., 1995; Heck and Coen, 1995). They constitute the food of predatory fishes, terrestrial vertebrates (Siddon & Witman, 2004), and their larvae are also consumed by many carnivores and thus crabs play an important role in the food chain (Macintosh et al., 1984).

Crabs potentially rich in proteins and other nutrients not only sustain the nutritional needs of coastal fishers but also contributes significantly towards sustainable livelihood economies of the local population. As the crabs prey and predate they have potential influence on the behaviour, distribution and abundance of their own as well as neighbouring communities (Seeley, 1986; Trussell & Nicklin, 2002).

In inter tidal areas, these organisms work as a super creatures adapting to the severity of a variety of environmental factors such as dessication stress, temperature, predation, change in salinity, tidal fluctuations, sediment depositions to name a few. These could be the probable causes of spatial and temporal variations in community patterns. Studies on brachyuran crabs are of importance for the formulation of conservation polices (Fransozo et al., 1992; Hebling et al., 1994) as such investigations lead to a better understanding of community structure and ecological processes.