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SECTION-3 SECTION-3 Mangroves and Estuaries
PAPER-1
ESTUARY - A SIGNIFICANT WETLAND
M N Madhyastha, P D Rekha and K C Shashikumar

ABSTRACT
INTRODUCTION
RESULTS, DISCUSSION AND CONCLUSION
REFERENCES
FIGURE-1: THE ESTUARINE MOUTHS OF DAKSHINA KANNADA

ABSTRACT: up | previous | next | last

Estuaries are fragile ecosystems with unique physical, chemical and biological features. These are influenced largely by the annual cycles of land run off from freshwater inputs influenced by human activities and tidal cycles. They form a link between the land, freshwater and seawater. Estuaries are very dynamic and productive, supporting unique but diverse fauna and flora (such as mangroves with high adaptability to the fluctuating water quality). The seasonal variations in the water quality as well as the biological component of these systems are influenced heavily by anthropogenic stress exerted by the developmental activities carried out along the coast (in the form of land discharges, agricultural run-off, domestic and industrial sewage disposals), which alter the health of the ecosystem. Due to these activities the existence of rich biodiversity in this ecosystem is under threat. Strict corrective measures have to be undertaken to safeguard their existence. The monitoring of these wetlands is very essential. Although plankton (phyto and zooplanktons) are the important groups of biological production, the benthic invertebrate community of the unconsolidated sediment is recommended for base line study and to assess the status of the estuaries. This write-up discusses the problems and need for protection of these fragile ecosystems of Malpe and Gangolli estuarine system based on field surveys.

INTRODUCTION: up | previous | next | last

An estuary is a partially enclosed body of water formed by the mixing of freshwater from rivers and streams with the seawater. Estuaries and the surrounding areas are transitory places where the landscape changes from land to sea, and the water quality from fresh to salty. Although influenced by the tides, estuaries are protected from the ocean waves, winds, and storms by reefs, barrier islands, and land, mud, or sand that define an estuary's seaward boundary. They come in all shapes and sizes and go by many different names, often known as bays, lagoons, harbors, inlets, or sounds. The tidal, sheltered waters of estuaries support diverse communities of plants and animals, specially adapted for life at the margin of the sea. Estuarine environments are among the most productive ecosystems on earth, creating renewable organic matter. Diverse habitats that are found in and around estuaries can be grouped as: Shallow open waters, Freshwater and salt marshes, Sandy beaches, Mud and sand flats, Rocky shores, Mangrove forests, River deltas, Tidal ponds and Sea grass beds.

This ecosystem is essential for the survival of many species, which include birds, mammals, fish, and other wildlife dependent on estuarine habitats to live, feed and reproduce. Many species of fish and shellfish rely on the sheltered waters of estuaries as protected places to spawn (as these are the "nurseries of the sea"). Many marine organisms, including commercially valuable fish species, depend on estuaries at some stage during their development. The plants and soils supporting the estuaries act as a natural buffer between the land and ocean, absorbing floodwaters and dissipating pollutants. Examples include salt marsh grasses and other estuarine plants, which prevent erosion, stabilize the shoreline and may also play a role in pollution abatement.

The high levels of productivity linked with these environments are due to the input of nutrients by rivers and the effective recycling between sediment and water mass. The prevailing tidal action results in a rapid circulation of nutrients that might help in removal of nutrients at a rapid rate. The protected coastal waters of estuaries support important public infrastructure, serving as harbors and ports vital for shipping, transportation, and industry. India has a coastal belt of 5686 kms, receiving an enormous amount of fresh water from many rivers all along the stretch from east to west. According to an estimate, the estuaries and backwaters of India occupy 2.6 million hectares of water spread area, of which Karnataka occupies about 0.1 million hectares (Jhingran, et al 1972).

The shoreline of Dakshina Kannada district ranging about 141 km (including the present Udupi district) [Fig.1] has 6 estuarine mouths with several rivers flowing from the Western Ghats region. The Gangolli, Malpe and Mangalore estuaries provide habitat for the west coast's commercial fish catch, and estuarine - dependent fisheries are among the most valuable in this region.

RESULTS, DISCUSSION AND CONCLUSION up | previous | next | last

The physical, chemical, and biological aspects of these estuaries are being monitored over a decade (Maben, 1994; Prince, 1997; Dyavaiah, 1995; Madhyastha et al, 1990). Studies show that Malpe and Gangolli estuaries are very productive at primary and secondary levels and also at benthic productivity level. Gangolli estuary has a water spread of 50 ha with adjoining mangrove vegetation of high fertility compared to Malpe zone. The district faces severe monsoon during June-September.

The physico-chemical studies revealed that the water characteristics show these ecosystems to be healthy. These waters support a vast assemblage of varied life from primary producers to consumers and are listed in Table 1. A total of 52 phytoplankton and 45 zooplankton species belonging to different groups were recorded from these estuaries. The areas are productive in terms of fisheries during pre and post monsoons. The Macrofauna belonging to different groups comprised of 130 species and are listed in Table 2.

TABLE 1: BIOLOGICAL PRODUCTION IN MALPE AND GANGOLLI

PHYTOPLANKTON

Bacillariophyceae

(30-35 species)

Cyanophyceae

(10-15 species)

Chlorophyceae

(8-10 species)

Chrysophyceae

(2-4 species)

ZOOPLANKTON

Protozoa

(6 genus)

Coelenterata

(3 genus)

Chaetognaths

(1 genera)

Annelida

(2 genus)

Cladocera

(3-5 genus)

Ostracoda

(2-4 genus)

Copepoda

(15-18)

Others

(11-12)

TABLE 2: MACRO AND MICRO FAUNA AT MALPE AND GANGOLLI

BENTHOS

MACRO FAUNA

MICRO FAUNA

Annelida (62%)

Nematoda (8%)

Mollusca (19%)

Rhynocoela (4%)

Arthropoda (9%)

Ostracoda (3%)

Rhynchoela (7%)

Bivalves (2%)

Sipuncula (2%)

Polychaeta (2%)

Echinodermata (1%)

Others (3%)

Others (0.5%)

  

The backwaters of Gangolli estuarine support a rich vegetation of mangroves (50 ha), which include Rhizophora, Avicennia, Acanthus, Bruguiera, Sonneratia, Kandelia, Clerodendron and Acrostichum, Derris. These mangroves provide niche for birds and also support the local human population in providing food, fodder and fuel wood. The economy of many coastal areas is based primarily on the natural beauty and bounty of estuaries. When these natural resources are imperiled, the livelihoods of the people living and working in and around them are at a risk.

Aquaculture involving prawn cultivation is posing severe threat to this vegetation. The Malpe and Gangolli are the most important marine fish landing centers on this coast. The major fish catch composition includes

  • Sharks, Ray and Skates
  • Oil Sardine* and other sardines
  • Clupeids*
  • Mackerel*
  • Seer fish
  • Tuna, Lactarius
  • Lady fish, Crangids
  • Pomfrets, Silver bellies
  • Scianids*, Ribbon fish
  • Fat fish, Soles, Anchoviella*
  • Prawns, Crabs, Squids, Squilla, etc.

    • * ---->abundant
    60 % of the fish catch takes place during the post-monsoon period.

    There are many anthropogenic activities coupled with burgeoning population exerting pressure on the estuary. The shell removal is extensively carried out along the Gangolli estuary, and the resultant disturbances caused will definitely affect the migratory fishes. Hence care has to be taken to cut down the shell and sand removal from the estuary. Stony embankments are required to control waste dumping [from tile factories and aquaculture farm, coir industries (retting of coir in the mangroves), etc.], apart from initiation of proper management plan for city domestic waste disposal.

    Commercial exploitation of fish involves the operation of mechanised boats and trawlers, which use petroleum and other synthetic products, which when leaked pollute the water body. The other activities, like shorelines being reconstructed to accommodate human housing and transportation, pollute the water further. Estuaries are an irreplaceable natural resource that must be managed carefully for ecological sustenance.

    REFERENCES up | previous | next | last

  • Dyavaiah, C.D. 1995. Studies on afforestation and regeneration of mangroves of the Dakshina Kannada Coast. Ph.D thesis, Mangalore University, India.
  • Jhingran, V.G., Gopalakrishnan, V., Ray, P. and Ghosh, A. 1972. Methodology for Survey of Brackish water areas in India for coastal aquaculture. Indo. Pacific Fish Comm. Occasional paper., pp. 72.
  • Maben, S.S. 1994. Hydrographical studies of Shambhavi (Mulki) river with reference to its faunal composition. M.Phil Dissertation, Mangalore University, India.
  • Madhyastha, M.N., Honnegowda, H., Ramalingaiah, D. and Shyamala, I.V. 1990. A survey on the shell removal along the estuaries of Dakshina Kannada. The Second Indian Fisheries Forum Proceedings, May 27-31, Mangalore, India pp. 231-232.
  • Natural Resource Valuation: A report by the Nation's Estuary Programs, August, 1997 (Web source).
  • Prince, J.P.J. 1997. Metallic profile of biosystems along the coastal waters of Dakshina Kannada. Ph.D Thesis, Mangalore University, India.

    • FIGURE-1: THE ESTUARINE MOUTHS OF DAKSHINA KANNADA up | previous | next | last


    FIGURE-1

    Address: up | previous

    1.) Department of Biosciences,
    Mangalore University,
    Mangalagangotri 574 199,
    India

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