Marine ecosystems are among the largest and the most productive of the Earth’s aquatic ecosystems, comprising salt marshes, intertidal zones, estuaries, lagoons, mangroves, coral reefs, the deep sea, and the sea floor. Marine ecosystems provide services at the global scale (oxygen production, nutrient cycles, carbon capture through photosynthesis and carbon sequestration) and at regional and local scales (stabilising coastlines, bioremediation of waste and pollutants, and a variety of aesthetic and cultural values).
Deteriorating biodiversity weakens a marine ecosystem’s capacity to provide food, maintain water quality, and recover from perturbations (Worm et al., 2006). Hence, awareness on the status of marine ecosystems is important for a country like India, which boasts a coastline of 7,517 km, and an exclusive economic zone (EEZ) of 2.02 million square km comprising 0.86 on the west coast, 0.56 on the east coast and 0.6 million square km around the Andaman and Nicobar Islands (Ramakrishnappa, 2000).
While India’s west coast is generally exposed with heavy surf and rocky shores and headlands, the east coast is lined with beaches, lagoons, deltas and marshes. The west coast is a region of intense upwelling associated with the southwest monsoon (May-September) whereas the east coast experiences a weak upwelling associated with the northeast monsoon (October-January). Islands on the east coast are continental, whereas the major island formations in the west coast are oceanic atolls, resulting in marked differences in the qualitative and quantitative patterns of fisheries.
Fisheries and dominant faunal biodiversity
Fish fauna: Fish comprise about half the total number of vertebrates. The number of estimated living fish species in the world is close to 28,000. Francis Day (1889) described 1418 species of fish from the British India, while P K Talwar (1991) enumerated 2546 species. The distribution of marine fish is rather wide and some are common to the Indo-Pacific and Atlantic regions. Around 57 per cent Indian marine fish species are common to the Indian, Atlantic and Mediterranean Oceans.
The exact number of species associated with Indian coral reefs is still to be established; however, coastal and marine ecosystems in India have 2618 species, of which Chondrichthyes (cartilaginous fish) comprise over 154 species, bony fish (Actinopterygii) another 2275 and others. Recent studies claim an increase of species to 2629 (Ramakrishnappa, 2000).
The categories of fish occurring in India’s coral reef ecosystems includes various species of damselfish (76), butterfly fish (40), parrot fish (24), sea basses, groupers and fairy bassets (57), cardinal fishes (45), jacks and kingfishes (46), wrasses (64), combtooth blennies (58), gobies (110), surgeon fish, tangs, unicorn fishes (40). Another 20 per cent are composed of cryptic and nocturnal species that are confined to caverns and reef crevices in the daylight.
Crustaceans (Crab, Lobster & Prawn): Global estimate of crustacean diversity is 150,000 of which, 50,588 species have been discovered so far. Of the 4,258 native species of crustacea reported by the Zoological Survey of India (ZSI) so far, there are as many as 4 species of cladocerans (water flea), 541 of copepods, 332 of hermit crabs, 167 of amphipods, 319 of isopods and 1655 of decopods. Crustaceans play an important role in marine and terrestrial food chains. Smaller crustaceans recycle nutrients as filter feeders, while larger ones can act as food for aquatic mammals.
Crustacean fisheries could be broadly grouped under prawns, lobsters and crabs. Of these, prawns are the most important accounting for about 98 per cent of marine crustaceans landed. Crustaceans are landed in all the maritime states of India, but the amount of landings vary. Annual total crustacean resources range from 3.62 to 5.32 lakh tonne with a mean at 4.36, and its contribution to total marine landings range from 13.9 per cent to 18.9 per cent (Maheswaradu and Vinetha, 2013). The east coast accounts for 26.4 per cent of the total landings, while the balance 73.1 per cent is accounted for by the west coast, with Gujarat and Maharashtra making up for the major share.
India is endowed with a rich diversity of crustaceans, with as many as 150 species forming the major focus of all commercial catches. However, intensive fishing pressure for prawn over the past several years has led to over-exploitation. Similarly, crabs of the species, Scylla serrata and Scylla tranquebarica are fished exclusively in estuarine regions. With the development of live-crab export, there is heavy exploitation and dwindling of this resource in brackish waters.
Besides fish, crabs and other crustaceans, there are several lesser known marine floral and faunal species which are of great significance.
Seaweeds: There are 936 species of marine algae documented from all over India (ZSI, 2015b). The maximum number of seaweeds has been recorded in Tamil Nadu (302), followed by Gujarat (202), Maharashtra (159), Lakshadweep (89), Andhra Pradesh (79) and Goa (75). The scanty records in other maritime states, especially the Andaman and Nicobar Islands, may not necessarily mean a rarity of algal species but may rather reflect a lack of concentrated surveys.
Seaweeds are mainly harvested for use as raw material for production of agar, alginates and seaweed liquid fertilizer. The estimated total standing crop of seaweeds in intertidal and shallow waters of India is 91,345 tonnes wet weight and 75,373 tonnes in deep water, which consists of 6000 tonnes of agar yielding seaweeds. Red algae (Gelidiella acerosa, Gracilaria edulis, G. crassa, G. foliifera and G. verrucosa) are used for manufacture of agar and brown algae (Sargassum spp., Turbinaria spp. and Cystoseira trinodis), for alginates and seaweed liquid fertilizers.