Wednesday, March 17, 2010

SEAWEED- BASED INTEGRATED MULTI-TROPHIC AQUACULTURE (IMTA): A POTENT SOLUTFOR SUSTAINABLE AQUACULTURE IN TURKEY

Gamze Turan*, Hatice Tekogul, Edis Koru and Semra Cirik

Ege University, Fisheries Faculty, Aquaculture Department
35100 Bornova, Izmir, TURKEY, gamze.turan@ege.edu.tr Aquaculture in Turkey, most of it on the Mediterranean 8,3333 km coastline, produced 70,000 tons in 2005 at 60 land-based and 229 sea-based farms. According to FAOs most recent tables, in 2006 Turkish aquaculture was the fourth in Europe, behind Norway, Egypt and Spain, in both culture (129,000 tons) and total fisheries (662,000 tons) production, in all water types. The main fish species include seabream, seabass, bluefin tuna and rainbow trout. Sustainability issues have brought Turkish Aquaculture to a crossroad. Recent regulations by the Turkish Ministry of Environment and Forestry, adressing negative ecological impacts, have forced relocation of coastal finfish farms to the land and off-shore. The maintainance and expansion of previous production levels without exceeding the assimilative capacity of the ecosystems is a challenge faced by the Turkish Aquaculture sector.
This is where seaweeds can become important to the industry. Seaweeds can take up nutrients like sponges absorb water. By periodical harvests of the nutrient-rich seaweed biomass, a significant quantity of nutrients is removed from coastal waters and sold, while regrowth of new biomass can continue the nutrient scrubbing process. This is why seaweeds are the centerpiece in Integrated Multi-Trophic Aquaculture (IMTA), which allows environmental sustainability, economic diversification, and social acceptability. Seaweeds can be used as food, fodder, pharmaceutical extractives, fertilizer, and energy. Turkey has many seaweed species with commercial potential and it is rich with the resources required for a very large seaweed culture industry. The country has a total of 24.6 million ha coastal zone, of which 1.5 million ha area is designated economic coastal zone, suitable to grow seaweeds in ecologically-balanced IMTA systems. Additionally, bioremediation by the seaweeds can help the aquaculture sector in Turkey comply with environmental legislative guidlines, standarts, and controls. The species selected for seaweed-based IMTA studies were Gracilaria verrucosa (or, G. Gracilis) and Ulva rigida. The red Gracilaria spp. is edible and useful in agar-agar production. U. rigida is a fast growing edible green algae. The studied species also contain valuable pharmaceutical biochemicals, can feed sea urchin, abalone and sea cucumber, and can serve as a fertilizer and as energy crops.
Cultivation of seaweeds in land-based, sea-based, and semi-locked sea area IMTA systems with marine fish (Sparus aurata, Dicentrarchus labrax, Mugil cephalus), marine aquarium fish (Acanthurus and Zebrasoma spp.) and freshwater fish (Oreochromis niloticus ) were examined. The work took place in our Izmir Bay research centers of Urla Marine and Dalyan Lagoon Units and in a commercial marine fish farm (Hunkar Su Urunleri) in Sigacik Bay. Nutrient concentrations and biomass production of the seaweeds and tissue composition were regularly monitored. Seaweed grew by up to 30% d-1, while diminishing fish effluent ammonia concentrations by 80%. An economic appraisal and a mass balance budget for nitrogen for an integrated seaweed - fish culture system is presented. This indicates that a significant reduction in input nitrogen is realistically achievable through seaweed farms and that the venture is potentially commercially viable.

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