Mangrove Ecosystem And Its Importance In Fisheries
by N. Rajendra Naik1, V. Kamalendra1 and Jaya Naik2
Postgraduate Students, 2Research Scholar(UGC)
Karnataka Veterinary, Animal and Fisheries
College of Fisheries, Mangalore, Karnataka.
India has approximately
700,000 ha of area covered by mangroves along the estuaries and major deltas. Mangroves
are salt-tolerant plants of tropical and subtropical inter-tidal regions of the
world. Besides ecological importance in trapping and accreting sediment
material to reduce the erosion, mangrove ecosystem plays a significant role in
Aquaculture. The fishery potential of these areas is tremendous and provide
livelihood to the coastal population as well.
What is a mangrove?
Mangrove is a specialized
marine ecosystem consisting of a group of plants growing in muddy, loose and
wet soils in tropical and sub-tropical areas, comprising of shallow, coastal
waters, deltas and estuaries or lagoons. The specific regions where these
plants occur are termed as 'mangrove ecosystem'. These are highly productive
but extremely sensitive and fragile.
Which mangrove species to grow?
Out of 45 mangrove species occurring in India, some
are true mangrove while others are considered as 'associated' flora. The most
dominant mangrove species found along the east and west coast of India are; Rhizophora
mucronata, R. apiculata, Bruguiera gymnorrhiza, B. parviflora, Sonneratia
alba, S. caseolaris,
Cariops tagal, Heretiera littoralis, Xylocarpus granatum , X. molluscensis,
Excoecaria agallocha, Lumnitzera racemosa, Avicennia officinalis, A. marina.
Common mangrove species in the Florida Keys:
Red mangroves (Rhizophora mangle) characterized by aerial
roots concealed props roots which provide support for soft mud and stabilize
Black mangroves (Avicenia germinans) occurs shoreward to
the red mangrove and is characterized by the presence of small pencil-like
vertical root shots call pneumatophores. These root shots stand in dense arrays
near the high-tide line, enabling the mangrove to obtain oxygen directly from
White mangroves (Laguncularia racemosa) grow on elevated
grounds above the high-tide mark and behind the red and black mangroves. The
leaves are thick and succulent, rounded at both ends, and the same color on
both sides. The root system resembles that of most terrestrial trees and seldom
show breathing roots.
Fishes, shellfishes and crustaceans:
Major constituents of this group in the mangrove environment of India are 105 species of fishes, 20
species of shellfishes and more than 225 species of crustaceans. Among these, commercially important are Meretrixsp., Crassostrea sp., Penaeus sp., Scylla serrata and Mugil cephalis.
Scylla serrata,the large edible
swimming crab, inhabits the muddy bottom of mangrove estuaries, as well
as coastal brackish water. Thalassina anomala, the mud lobster is
also found along estuaries and tidal rivers. Mud skippers are one of the fish
which live on the mud flats associated with mangroves shores.
Birds are a prominent part of most mangrove forests and they are often present in large numbers. The
Royal Bengal Tiger is one of the unique resident species of mangroves of
the Sunderbans. Reptiles are also common in mangroves, which include
snakes, turtles, crocodiles and alligators. The saltwater crocodile, monitor
lizard (Varanus sp.), estuarine crocodile, various species of monkeys,
otters, deer, fishing cats and wild pigs are some of the most common species
of mangrove forests of India.
Flora and Vegetation:
The Indian mangroves comprise approximately 59 species in 41
genera and 29 families. Of these, 34 species belonging to 25 genera and 21
families are present along west coast. There are about 25 mangrove species
which have restricted distribution along the east coast and are not found on
the west coast. Similarly, there are eight species of mangroves like Sonneratia
caseolaris, Suaeda fruticosa, Urochondra setulosa etc. which have been
reported only from the west coast. There are approximately 16 mangrove species
reported from the Gujarat coast, while Maharashtra has about 20 species, Goa 14
species and Karnataka 10 species. There are hardly three to four species
of mangrove which are rarely found along the Kerala coast. The associated
mangrove flora is quite common to both the coasts, with minor variations in
There are different types of faunal communities in mangrove
waters which are dependent on the water component in one way or the other. The
planktonic and benthic animal communities also play a very important role in
the mangrove ecosystem just like the terrestrial animals. There are different
species of crustaceans like Penaeus indicus, P. merguiensis and P. monodon, while the crabs are
represented by Uca sp., Scylla serrata, Thalassina, etc. The fishes are
represented by several species like the mud skippers, carangids, clupeids,
serranids, mullets, hilsa, seabass, milkfish etc.
The mangrove water, usually rich in detritus are highly
suitable for fishing. The major fishery resources found in these waters are
detritivorous species of fishes, crabs, crustaceans and molluscs. Roughly about
60% of India's coastal marine fish species is dependent on the mangrove
estuarine complex. Some of the most common fishes in Indian mangrove waters are
Liza, Mugil, Lates, Polynemus, Sciaena, Setipinna, Pangasium, Hilsa, Ilisha
Prawns are represented by the species of Penaeus and Metapenaeus while the crabs are
represented mainly by Scylla serrata. The molluscans of mangrove waters are mainly
represented by Crassostrea spp., Mytilus and clams. In the
upstream regions, giant prawns like Macrobrachium rosenbergii are also found in large
In India, mangrove trees are used for house building,
furniture and certain household items. Mangrove trees have been the source of
firewood in India since ancient time. Tannin is extracted from the bark of some
mangrove species like Rhizophora mucronata, Bruguiera gymnorrhiza and
Indian mangrove trees have 35% tannin in their bark which is higher compared to
other countries. Extracts from mangrove bark are used by Indian fishermen to
dye their fishing net and enhance its durability. Honey collection from the
mangrove forest is a promising business in India. It has been estimated that
Sundarbans mangrove alone produce 111 tons of honey annually. Bark and roots of
Aegicera corniculatum and Derris heterophylla are used as mild fish
poison. Avicennia spp;
Phoenix paludosa and Sonneratia caseolaris are used for human consumption and as
cattle feed. Nypa fruticans is tapped for an alcoholic drink.
Mangroves shed and drop about seven and a half tons of leaf
litter per acre per year. The constantly-shed leaves are quickly broken down by
bacteria and fungi and released into the water, providing food for sea-life.
Mangroves are the nesting grounds for mammals, amphibians, reptiles, countless
unique plants, juvenile fish and invertebrates, sponges, barnacles, oysters,
mussels, crabs, shrimps, oysters and many water birds such as the great white
heron, reddish egrets, roseate spoonbills, etc.. Mangroves are also recharge
underground water supplies by collecting rainwater and slowly releasing it.
The fishes lay their eggs in tangled roots of mangrove trees
and later hatch and grow with needed nutrients available. Thus mangroves act as
natural nursery grounds. Mangroves offer shelter to the juveniles of a wide variety
of marine organisms, notable among them being certain species of penaeid
shrimps. A linear relationship exists between shrimp production and the size of
the mangrove forest area. Mangroves give recreation to hunters, fishermen,
bird-watchers, photographers and others who treasure natural areas.
swamps and other low-lying areas along the estuaries are generally preferred
for brackishwater fish farming. The species cultivated are Liza parsia, L. tade,
Mugil cephalus, Chanos chanos, Penaeus monodon and Fenneropenaeus indicus. Mangroves trap debris and silt, stabilizing the near
shore environment and clarifying adjacent open water, which facilitates
photosynthesis in marine plants. The fringing network on mangrove buffers
natural forces such as hurricanes, wave action, tidal change and run-off,
preventing soil loss with its firm, flexible barrier. Beyond serving as a
refuge for juvenile marine organisms, mangroves filter sediment and buffer
coastlines against erosion and storm surge. The major ecological role of
mangroves is the stabilization of the shoreline and prevention of shore
erosion. The dense network of prop roots, pneumatophores and stilt roots not
only give mechanical support to the plant, but also trap the sediments. The
important ecological role of the mangroves is the detritus, which help in
feeding and provides breeding and nursery grounds for the juveniles of many
commercially important shrimps and fishes.
Threats to mangroves:
Large hurricanes: Hurricane Donna, in 1960, damaged an area of
100,000 acres of the Mangrove zone of South Florida. Loss of trees ranged from
25% to 100% from shearing the trunks above ground, complete over wash of
islands and prop root damage from marl and fine organic matter coating the
Shoreline development has replaced mangroves
with marinas, dredged channels, airports, seawalls and other commercial and
residential construction. Other threats are illegal dumping, beach
renourishment, and oil spill, agricultural run-off that contains herbicides,
pesticides and sugarcane wastes. Globally mangrove forests are disappearing at
a rate of 1-2 percent per year, a pace that surpasses the destruction of
adjacent ecosystems, coral reefs and tropical rainforests. The U.N. Food and
Agriculture Organization estimates that mangroves are critically endangered or
approaching extinction in 26 out of the 120 countries in which they are found. Indian mangroves have been deforested and
reclaimed to such an extent that the mangroves along the west coast are very
much degraded. This has not only affected the coastline but also the fisheries
to a large extent.
serve as a critical nursery for young marine life and therefore play an
important role in the health of fisheries and the economic well-being of fishermen.
The ecosystem is also considered as most productive and biodiversity providing
significant functions in the coastal zones as buffer against erosion, storm
surge and tsunamis. Afforestation of mangrove areas on a large scale is the
most urgent need of today, if the coastal environment is to be brought back
again to its earlier pristine glory.
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