Rapid scale growth of intensive mariculture systems can often lead to adverse impacts on the environment. Intensive fish and shrimp farming, being defined as throughput-based systems, have a continuous or pulse release of nutrients that adds to coastal eutrophication. As an alternative treatment solution, seaweeds can be used to clean the dissolved part of this effluent. Two examples of successfully using seaweeds as biofilters in intensive mariculture systems are discussed in this paper. The first example shows that Gracilaria co-cultivated with salmon in a tank system reached production rates as high as 48.9 kg m-2 a-I, and could remove 50% of the dissolved ammonium released by the fish in winter, increasing to 90-95% in spring. In the second example, Gracilaria cultivated on ropes near a 22-t fish cage farm, had up to 40% higher growth rate (specific growth rate of7% d-1 ) compared to controls. Extrapolation of the results showed that a 1 ha Gracilaria culture gave an annual harvest of 34 t (d. wt), and assimilated 6.5% of the released dissolved nitrogen. This production and assimilation was more than twice that of a Gracilaria monoculture. By integrating seaweeds with fish farming the nutrient assimilating capacity of an area increases. With increased carrying capacity it will be possible to increase salmon cage densities before risking negative environmental effects like eutrophication and toxic algal blooms sometimes associated with the release of dissolved nutrients. The potential for using mangroves and/or seaweeds as filters for wastes from intensive shrimp pond farming is also discussed. It is concluded that such techniques, based on ecological engineering, seems promising for mitigating environmental impacts from intensive mariculture; however, continued research on this type of solution is required.
Tank cultivation of Gracilaria using fish effluents has permitted a production of 48 kg m -2 yr -' and can reduce the dissolved nitrogen loads in the seawater. We report the yield, gel strength, gelling and melting point of agar from Gracilaria cultivated in tanks with seawater previously utilized in intensive, land-based salmon cultures and compared to a control using directly pumped seawater, over a study period of 22 months . The results show that the highest agar yield (20 to 22%) was obtained when Gracilaria was cultivated with pure seawater as compared to the fish effluents . The gel strength, gelling and melting point were higher in the agar obtained from algae cultured with fish effluents . During the spring, the gel strength, gelling and melting point increased in tanks with fish effluents and decreased in tanks with a supply of pure seawater.
In Chile, the demand for carrageenophytic algae has increased significantly in recent years. The preferred species is Gigartina skottsbergii, with landings of 26,181 tons in 1998. To avoid a possible overexploitation the development of cultivation technologies is needed. In this study we present a critical view of published and new information to propose the best culture strategy for this species. The results indicate that viable spores are seasonally available only during winter, with tetraspore germination rates of ca. 40%. Germination of carpospospores is lower than 20%. Growth in tanks can be as high as 1% day−1 and high nutrient concentrations (N and P) must be added. Gigartina also present a high and unique regeneration capacity. Field experiments indicate that Gigartina can be cultured in rope systems, where the inoculum can be tissue fragments. These results indicate that vegetative propagation techniques can be used for the massive culture of Gigartina, but selection of a high growing strain remains as one of the future challenges.
In Chile, the demand of edible seaweeds has increased during recent years and Callophyllis variegata is one of the most demanded species. This study summarizes information on phenology, aspects, in vitro culture and vegetative propagation methods for Callophyllis. Results indicate that spore production occurs mainly during winter, and recruitment of new plants appear in nature in the spring. Culture studies indicate that spores presented higher germination and growth rates at 8° C and 10 to 12 μmol m−2 s−1. Furthermore, these results indicate that this species presents a high potential for regeneration from its holdfast. The manipulation of temperature, light and culture medium enhances the regeneration process and growth of Callophyllis in the laboratory.
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