Study On Marine Cage Culture And Carrying Capacity In Sandu Bay

The study of cage culture carrying capacity of Sandu Bay, Fujian was carried out during 2005 and 2007. The environment paremeters including dissolved inorganic phosphorus (DIP), dissolved inorganic nitrogen (DIN) in the water and sulfide, organic carbon of surface sediment, species, biomass and density of macrobenthos were measured. Meanwhile, the volumn, historic and present status of cage culture areas were also surveyed. According to the results, the parameter which has remarkable relation to carrying capacity of cage culture is selected. Based on pertinent standards, carrying capacity of cage culture in Sandu Bay and output which is suitable for the environment were calculated. The results were as following,1. DIN and DIP in the cage culture areas are ranges of 0.413～0.754 mg/L and 0.036～0.082 mg/L. Both of them are higher than means of DIN and DIP in Sandu Bay respectively, which are 0.347 mg/L and 0.027 mg/L. The result shows the concentration of DIN and DIP in the cage culture areas of Sandu Bay were accumulated by cage culture. DIN and DIP in the cage culture areas are higher than the standard for Class II seawater, even higher than the standard for Class IV seawater. It is seriously eutrophicated at cage culture areas.The results of water sampling in cage culture area show that there are water mass of high concentration of DIN and DIP near cage culture areas which flow with the tide. Both DIN and DIP change with the the tide. The tide has significant effect on the concentration of DIN and DIP at the cage culture areas. The maximum and minimum of DIN and DIP will lag behind flood slack and ebb slack.2. There is a decline of sulfide content distribution from the central area to the outside of cage culture. The contents of sulfide are 399～1377 mg/kg at the central areas, which are higher than standard of Calss I (300 mg/kg) of sulfide for marine sediment, the contents of sulfide at marginal areas are 30～439 mg/kg, which are as much as the sulfide standard, contents of sulfide in the controlling areas are only 22～246 mg/kg, which are lower than the standard. 3. It is the same trend of organic carbon content from the central area to the outside. The organic carbon contents are 1.01～1.27% in the central areas, 0.94～1.34% in the marginal areas, and 0.90～1.25% in the controlling areas. All organic carbon contents are lower than the standard of Class II for sedimental quality (2.0 %).4. Densities of macrobenthos in the central areas are higher than those in the marginal areas, and densities of macrobenthos in the controlling areas are lower than those in the marginal areas. Biomass in the central areas is lower than those in the marginal areas, and biomass in the controlling areas is higher than those in the marginal areas. Diversity indexes in the central areas are lower than those in the marginal areas, and diversity indexes in the controlling areas are higher than those in the marginal areas. Dominance in the central areas is higher than that in the marginal areas, and dominance in the controlling areas is lower than that in the marginal areas. Diversity and dominance in the marginal areas are between those in the central areas and controlling areas mentioned above.The results show that the aquatic environment and sedimentary environment are affected by the cage culture. It is seriously affected at the central areas, slightly in the marginal areas and normally in the controlling areas which are 500 m far away from cage culture.5. Based on the survey data, there is a well relationship between breed densities and sedimental sulfide concentrations. By using the equation between breed densities and sulfide concentration, cage carrying capacity is calculated with 1.26 kg/m~3 at Sandu Bay. And the fish carrying capacity in different cage areas are as following, 1.44×10~5t for Sandu Island, 0.67×10~5t for Baiji Gulf, 0.64×10~5t for Dongan Island, 1.59×10~5t for Changyao Island and 4.75×10~5t for Qingshan.