CONTENTS-
Abstract
Introduction
Discussion
Conclusion
Acknowledgement
References

Chinese aquaculture has employed a balanced ecosystem approach for both fresh and brackish water aquacultures for several thousand years. Utilising species that feed at different levels of the food web has permitted China to have the largest aquaculture production in the world. This production has proved to be sustainable in the long run because there is balance in this system. Chilika lake, situated in the East Coast of Indian peninsula is one of the largest brackish water wet land ecosystem in Asia. The lake covers an area of 917 square kilometre and opens to the Bay of Bengal through a narrow mouth. Chilika has an interesting ecology with several small islands, some of which are inhabited by local people.   Amongst Chilika's various flora and fauna, marine algae forms an interesting group of plants.   During our three years of investigations, we reported 13 species of seaweed's i.e. Enteromorpha compressea , Enteromorpha intestinalis, Ulva fasciata, Ulva lactuca, Chaetomorpha linum, Cladophora glomerata forma. Callicoma, Pithophora oedogonium, Gracilaria verrucosa, Gracilariopsis megaspora, Grateloupia filicina var. luxurians, Ceramium diaphanum var. elegans, Polysiphonia sertularioides, Polysiphonia subtilissima from different parts of the lake, out of which Gracilaria verrucosa, Gracilariopsis megaspora and Grateloupia filicina are of great significance. While the first two taxa are important source of agar, Grateloupia filicina is edible and source of crrageenan.   These phycocolloids have several industrial applications, which includes toothpaste, ice cream, tomato ketchup, chocolate, milk shakes, cosmetics, medicine etc. These seaweeds not only act as a breeding ground for prawns and fish but also remove the extra nitrogen and carbon from parts of the lake, which has damaged the lake ecology to some extent. As a strategy for the sustainable management of the lake we recommend seaweed cultivation at some parts of the lake. Such types of extractive and integrated aquaculture will not only maintain the ecosystem of the lake but will also provide large-scale employment to the local people.

Marine algae are one of the most important living resources of the world. These lower plants are a major source of phycocolloids like agar, carrageenan and alginates, which have several applications in food, pharmaceutical, cosmetic and many other biotechnology related industries. Popularly known as "seaweeds" these plants are also rich in protein, vitamin, carbohydrate, iodine, bromine, mannitol, minerals, trace elements and other bioactive compounds (Sahoo, 2000). Recently, there is an increasing demand for seaweeds and their products in the global market. Thus many species are commercially cultivated through aquaculture. Integrating aquaculture into coastal management has become an important goal throughout the world. Although several aquaculture practices have been used in different countries, Chinese aquaculture practice is quite unique. They have employed a balanced ecosystem approach for fresh, marine and brackish water aquaculture for several thousand years. Utilising species that feed at different levels of the foodweb the Chinese have established the largest aquaculture production system in the world. In this context Chilika Lake has a unique advantage for sustainable aquaculture, which is being discussed in this   paper.

Chilika Lake And Its Marine Algal Flora:

            India having a coastline of 7,680km harbours 770species of seaweeds (Sahoo et al ., 2001). Chilika is a   unique brackish water lagoon situated in the east coast of the country at 19 ° 28' - 19 ° 54' N and 85 ° 05' - 85 ° 38' E. The lake harbours several useful species of seaweeds. The pear shaped lake has   an area of 740sq.km in summer and 1,165sq.km in the rainy season. The lake on one side receives fresh water from nearly 35 rivers (tributaries of river Mahanadi), whereas on the other side gets seawater from the Bay of Bengal through an opening. The lake has several small islands, some of which are inhabited by local people. Thus, Chilika has a unique ecology, which supports many types of flora and fauna.

            In the present study 13species of seaweeds such as Enteromorpha compressa , Enteromorpha intestinalis , Ulva fasciata , Ulva lactuca , Chaetomorpha linum , Cladophora glomerata forma callicoma , Pithophora oedogonia , Gracilaria verrucosa , Gracilariopsis megaspora , Grateloupia filicina var. luxurians , Ceramium diaphanum var. elegans , Polysiphonia sertularoides , Polysiphonia subtilissima   have been found growing at different parts of the lake. Some of these seaweeds can be cultured through integrated aquaculture and exploited for commercial use.

Some Economic Seaweeds And Their Utilization:

Gracilaria verrucosa (Fig. 1A) and Gracilariopsis megaspora are two important red algal species of the lake, which not only produce agar-agar, but also acts as a breeding nest for prawns and fishes. This sulphated polysaccharide has several uses in food, dairy, cosmetic, pharmaceutical, photography, plywood, leather, textile and paper industries. Besides these, agar is   used as a culture media in the laboratories. Demand for agarophytes have increased over the years due to wide application of agar. There are three grades of agar i.e bacteriological, sugar-reactive and food grade. The bacteriological grade agar is most expensive compared to the other two types. The world market value of agar has   been assessed at US$ 200 million (Sahoo, 2000). The major agar producing countries are Japan, Chile, Mexico, South-Korea, China, Thailand, Philippines, Indonesia, and South-Africa. The species of Gracilaria and Gracilariopsis are cultivated in more than 20 different countries to meet the demand of food and industrial grade agar. The life history of these plants   is Polysiphonia type i.e having morphologically identical diploid tetrasporophyte and haploid gametophyte phases, the latter consisting of equal numbers of male and female plants. Experimental cultivation of these two taxa was   undertaken in Chilika lake for production of large biomass through integrated aquaculture.

Grateloupia filicina var. luxurians is an edible seaweed as well as an important source of high quality polysaccharide known as carrageenan (Fig. 1B). Recently, the structure and reproduction of the species has been studied (Baweja and Sahoo, 2002). This species also provides a breeding ground for the prawns in the lake. The demand for carrageenophytes has increased throughout the world, due to the wide application of carrageenan. (Table-I). This   sulphated polysaccharides differ from agar in having high sulphate concentration. Carrageenan has greater reactivities and synergies compared to agar as it forms interesting gel textures. Further more, its price is much lower than that of agar (Armisen, 1995). Pure carrageenan costs US$ 15,000 per tonne whereas semi-refined carrageenan costs US$ 7,000 per tonne. Thus cultivation of Grateloupia filicina var. luxurians will be an important step to augment the income of the local population.

Application of Carrageenan

Food Industry                         Crystallisation inhibitor                         Ice cream, syrups.

                        Film former                                           Sausage,casings, coating.

                        Foam stabilizer                         Topping.

                        Gelling agents                                            Pudding, desert , aspics.

                        Stabilizer                         Mayonnaise.

                        Suspending agent                         Chocolate, milk.

                        Thickening agent                                      Jams, sauces, gravies.

Non food industry                         Water stable binder and solid gel formation                         Palletized prawn feed and                                                 air freshener gel.

                        Thickening agent                         Textile printing.

                        Emulsifier and stabilizer                         Toothpaste, dental                                                                filling and hair shampoo.

                        Gelling agent                         Culture media.

                        Fungicide                         Fungicide stabilizer.

                        Fertilizer                         Rice cultivation.

                        Absorbent                         Napkins.

             Ulva and Enteromorpha are two important green seaweeds, which help the lake from eutrophication (Fig. 1C,D). These plants not only act as a breeding ground for prawns and fishes but also remove the extra nitrogen, ammonia and carbon from its environment. Both the seaweeds are edible as   they have nutritional value. Ulva lactuca and Enteromorpha intestinalis are used as seaweed liquid fertiliser for many crops (Arunkumar et al .,2002; Gandhiyappan and Perumal,2001) .

The rapid expansion of intensive aquaculture systems and the concern for negative effects on the environment from such practices have renewed and increased the development of seaweed based integrated techniques (Vandermeulen and Gordin, 1990; Cohen and Neori,1991 ; Haglund and Pedersén, 1993; Troell et al ., 1997; Neori and Shpigel, 1999; Chopin et al ., 1999). All these studies demonstrate that waste water from intensive and semi-intensive aquaculture are suitable as a nutrient source for the production of seaweeds, reducing the discharge of dissolved nutrients to the environment.

            Chilika is presently under threat from both natural and anthropogenic pressures. The problems of siltation, drastic changes in saline   concentrations, eutrophication, excessive use of bioresources and overall loss of biodiversity are quite apparent. Large scale prawn culture has been in practice in several parts of the lake which has damaged the lake ecology to some extent. As a strategy for the sustainable management of the lake, seaweed cultivation should be undertaken in different parts of the lake. The potential of   integrated aquaculture approach may gain both direct and indirect benefits   by improving the water quality and the lake ecosystem. Integration of aquaculture with seaweeds is both practical and profitable viable solution (Chopin et al ., 2001).

            Recent reviews on integrated aquaculture research include a focus on seaweed utilisation (Troell et al ., 1999). Integrated aquaculture has been classified into three major groups – i) Tank Culture, ii) Pond culture and iii) Open-water cultures. Current researches have shown that the dissolved nutrients from fish cultures can be used as an input for the seaweed growth. This has been a successful implementation of the integrated aquaculture. Tank or pond culture has been attempted with a view to commercialise the cultivation of Gracilaria in Namibia (Rotmann, 1987) and Chile (Edding et al ., 1987). In Taiwan pond cultivation is extensively practised on a commercial scale (Chiang, 1981). Haglund and Pedersén demonstrated that outdoor pond cultivation of Gracilaria   (1993) helps in removal of nitrogen and phosphorous when co-cultivated with Oncorhynchus mykiss (Rainbow trout).

It has been successfully demonstrated that integrated aquaculture not only helps in maintaining   a balance in an ecosystem but also increases the productivity. Culture of prawns and fish along with seaweeds cultivation will be not only economically but also be an ecologically profitable proposition for Chilika lake. The oxygen evolved during photosynthesis by seaweeds help the aerobic bacteria to accumulate the degradation of complex organic substance to simple elements.   Ammonia , Urea and other nutrients present in the excreta of animals can be utilised by the seaweeds for it's productivity thereby reducing the nutrient loading and protecting the lake from eutrophication. Integrated aquaculture will lead to   enhancement of the quality of polysaccharides and other commercial products obtained from seaweeds. Seaweed culture will give an alternate source of income to the fisher folks and provide new employment opportunities to the women. Different types of cottage industries based on seaweed utilisation can be established. Thus it will not only improve the socio-economic condition of the local communities, but also earn valuable foreign exchange for the state.

   We are grateful to Department of Science and Technology, Govt. of India, New Delhi for the financial assistance to carryout the research work.

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Legends

Fig. 1 (A-D) – Economic Seaweeds of Chilika Lake.

            A :             Gracilaria verrucosa (Hudson) Papenfuss .

            B :             Grateloupia filicina var. luxurians (Lamouroux) C.Agardh.

            C :             Ulva fasciata Delile.

            D :             Enteromorpha intestinalis (Linnaeus) Nees.

Marine Biotechnology Laboratory,
Department of Botany,
University of Delhi,
Delhi – 110 007.India.
Phone No: 91-11-7666792.
E-Mail: nivedita_sahu@rediffmail.com