Agroekosistem

Coastal aquaculture and the environment

((Guidelines for the promotion of environmental management of coastal aquaculture development (based on a review of selected experiences and concepts). FAO Fisheries Technical Paper. No. 328. Rome, FAO. 1992. 122 p. )
Benefits of Coastal aquaculture

Generally, the socio-economic benefits arising from aquaculture expansion include the provision of food, contributing to improved nutrition and health, the generation of income and employment, the diversification of primary production, and, increasingly important for developing countries, foreign exchange earnings through export of high-value products (UNDP/Norway/FAO, 1987; Schmidt, 1982).

1. 
   Aquaculture is also being promoted for its potential to compensate for the low growth rate of capture fisheries. Stocking and release of hatchery-reared organisms into inland and coastal waters support culture-based fisheries (Larkin, 1991).
   
2. 
   Sustainable development of aquaculture can contribute to the prevention and control of aquatic pollution since it relies essentially on good-quality water resources.
   
3. 
   Culture of molluscs and seaweeds may in certain cases counteract processes of nutrient and organic enrichment in eutrophic waters. Conversely, productivity of oligotrophic waters may be enhanced due to the nutrient and organic wastes released from aquaculture farms.
   
4. 
   Aquaculture can contribute to rehabilitation of rural areas through re-use of degraded land.
   

Key areas of ecological concern : Nutrient and organic enrichment
Many aquaculture operations invariably result in the release of metabolic waste products (faeces, pseudo-faeces and excreta) and uneaten food into the aquatic environment. In general, the recipient for soluble waste is the water column and the recipient for the organic waste is the sediment.

The release of soluble inorganic nutrients (nitrogen and phosphorus) has the potential to cause nutrient enrichment (hypernutrification) possibly followed by eutrophication (increase of primary production) of a waterbody. Related changes in phytoplankton ecology may result in algal blooms, which can be harmful to wild and farmed organisms. However, there is no evidence that algal blooms have been caused by coastal aquaculture.

The largest proportion of solid wastes released, which is predominantly organic carbon and nitrogen, settles to the seabed in the immediate vicinity of the farm. Organic enrichment of the benthic ecosystem may result in increased oxygen consumption by the sediment and formation of anoxic sediments, with, in extreme cases, outgassing of carbon dioxide, methane and hydrogen sulphide; enhanced remineralization of organic nitrogen and reduction in macrofauna biomass, abundance and species composition.

There is evidence of very localized effects of reduced concentrations of dissolved oxygen in bottom and surface waters close to farm sites which are due to the considerable biochemical oxygen demand of released organic wastes and the respiratory demands of the cultured stock.

Coastal zones for shrimp culture. I. Intertidal Zone; Mangrove virgin forest (A); Secondary forest (B). II. Supratidal Zone: Rice field (C); Coconut plantation (D). (from Poernomo, 1990). Sumber: http://www.fao.org/docrep/T0697E/t0697e04.htm

Tambak MERUPAKAN kolam buatan, biasanya di daerah pantai, yang diisi air dan dimanfaatkan sebagai sarana budidaya perairan (akuakultur). Hewan yang dibudidayakan adalah hewan air, terutama ikan, udang, serta kerang. Penyebutan "tambak" ini biasanya dihubungkan dengan air payau atau air laut. Kolam yang berisi air tawar biasanya disebut kolam saja atau empang. Kondisi dasar tambak merupakan suatu keadaan fisik dasar tambak beserta proses yang terjadi didalamnya baik yang menyangkut biologi, kimia, fisika maupun ekologi yang secara langsung maupun tidak langsung ikut berpengaruh pada kehidupan udang maupun organisme lainnya dalam suatu keterkaitan ekosistem perairan tambak. Parameter ini dapat dijadikan sebagai salah satu tolok ukur kualitas perairan tambak dengan dasar pemikiran sebagai berikut:

“Dasar tambak” merupakan ruang gerak dan tempat hidup bagi udang dan organisme lainnya dalam kondisi normal seperti habitat alaminya, sehingga kondisi dasar tambak akan mempengaruhi tingkat keamanan dan kenyamanan bagi udang maupun organisme lainnya di dalam perairan tersebut. Dasar tambak juga merupakan tempat akumulasi kotoran tambak baik yang berasal dari treatment budidaya maupun proses metabolisme yang dilakukan oleh organisme yang hidup di perairan tambak tersebut. Dasar tambak merupakan suatu area di dalam tambak yang membentuk suatu sub komunitas tersendiri yang bersifat benthic di dalam tambak dan keberadaannya mempunyai korelasi yang erat dengan ekosistem perairan tambak.

Pada dasar tambak terjadi proses-proses biologi, kimia, fisika dan ekologi yang sangat tergantung pada kestabilan ekosistem perairan. Pada kondisi tertentu, dasar tambak dapat bersifat an aerob karena tidak terjadinya proses oksidasi sehingga dapat membahayakan bagi kondisi dan kualitas udang di dalam tambak. Kondisi dasar tambak mempunyai keterkaitan secara langsung dengan kondisi dan kualitas udang serta kualitas perairan tambak, yaitu jika perairan tambak berada pada keseimbangan ekosistem dan bersifat stabil serta kondisi dan kualitas udang bagus maka kondisi dasar tambak akan terjaga dengan sendirinya. Salah satu faktor yang juga ikut menentukan kondisi dasar tambak adalah penempatan posisi kincir air yang dioperasikan pada saat kegiatan budidaya berlangsung. Posisi kincir yang sesuai dan dapat mengarahkan kotoran dasar tambak ke arah sentral pembuangan dapat meminimalkan terjadinya penyebaran akumulasi kotoran tersebut di dasar tambak, sehingga pada saat dilakukan pembuangan air tambak kotoran tersebut dapat ikut terbawa.

Pada dasarnya setiap petakan tambak yang sedang dioperasikan selalu dijumpai adanya kotoran dan hal yang perlu diperhatikan adalah tingkat keberadaan dan tingkat penyebarannya di dasar tambak dibandingkan dengan tolok ukur dari hasil pengamatan terhadap kondisi dan kualitas udang serta kualitas perairan tambak. Beberapa faktor penyebab yang dapat mengakibatkan terjadinya akumulasi kotoran di dasar tambak adalah (http://id.wikipedia.org/wiki/Tambak_Ikan):

1. 
   Desain dan kontruksi dasar tambak yang tidak dirancang dengan tingkat kesesuaian terkonsentrasinya kotoran ke arah sentral pembuangan, sehingga menyebabkan kotoran di dasar tambak tersebut menyebar di beberapa titik konsentrasi.
   
2. 
   Penempatan posisi kincir air yang kurang tepat, sehingga tidak dapat mengarahkan kotoran tersebut ke arah sentral pembuangan.
   
3. 
   Program pakan yang over feeding jika dibandingkan dengan tingkat kebutuhan udang. Sisa pakan yang berlebihan tersebut tidak terkonsumsi oleh udang dan membusuk serta terakumulasi di dasar tambak menjadi kotoran.
   
4. 
   Teknik pemberian pakan yang tidak merata ke seluruh area pakan di dalam petakan tambak, sehingga pakan terakumulasi di satu titik dan tidak terkonsumsi merata sehingga membusuk di dasar tambak.
   
5. 
   Tingkat populasi udang di dalam tambak. Pada tambak dengan populasi udang yang relatif padat, kondisi dasar tambak akan relatif bersih karena kotoran di dasar tambak akan terdorong dengan sendirinya ke sentral pembuangan yang diakibatkan oleh aktifitas udang di dasar tambak.
   
6. 
   Kurangnya pengecekkan dasar tambak dengan melakukan penyelaman secara berkala.
   
7. 
   Kurangnya intensitas dan frekuensi sirkulasi air yang dapat mendorong kotoran dasar tambak ke arah sentral pembuangan.
   

Berkembangnya system budidaya perairan (akua-kultur) dianggap sebagai era “Revolusi Biru” karena mendatangkan berbagai manfaat bagi kehidupan manusia dan ramah lingkungan

(Jeremy Elton Jacquot, Technology / Clean Technology, June 19, 2007 )

Jeffrey Sachs, the director of the Earth Institute at Columbia University and world-renowned anti-poverty crusader, has turned his prodigious attention to an issue dear to many of us in the TreeHugger community: environmental sustainability.
Aquaculture, could support rising consumption of seafood while reducing anthropogenic pressures on oceanic ecosystems. This "Blue Revolution" has come at a critical time because, as he put it:
"Between 1950 and today the total landed catch from open- and inland-sea fishing almost quintupled, from around 20 million to about 95 million metric tons. Both higher demand from rising world incomes and higher supply from more powerful fishing vessels contributed to the surge. So, too, did large and misguided subsidies to fishing fleets, reflecting the political power of geographically concentrated fishing communities and industries. The world put itself on a course to gut ocean ecosystems, with devastating consequences."

Sumber: http://www.treehugger.com/clean-technology/discussing-the-merits-of-aquaculture.html

Sumber: http://www.feedingminds.org/fmfh/fisheries-aquaculture/wonders-of-the-oceans/from-the-sea-to-your-plate/lesson-9-farming-fish/en/

Sistem akuakultur terpadu (budidaya udang, ikan, dan mangrove) di Kenya



Photographer: Max Troell . Sumber: http://www.azote.se/index.asp?q=vattenbruk&id=14138&p=40&lang=eng


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