Effect Of Filter Feeding Shellfish Mariculture On The Ecosystem And The Evaluation Of Ecology Carrying Capacity

Phytoplankton and particle organic materials are the mainly food of the filter feeding shellfish. The environmental conditions, especially the primary production, hydrodynamic characteristics of the mariculture areas will have directly influence on the growth rate and yields of shellfish, and at some extend, will have directly or indirectly influence on the impact of mariculture on the ecosystem. Because of the differences of mariculture species, density, method and characteristics of mariculture areas, the impact on the ecosystem will be quite different. In this thesis, the bottom culture area—Zhangzi Dao Island and the long-line culture area—Sungo bay were investgated to assess the potential impacts from mariculture, by the methods of in situ monitoring, controlled experiments and numerical model.Mainly results as follows:1. The ecosystemic impact coming from the bottom cultivation of Japanese scallop Patinopecten yessoensis was lower. Non-parameter statistically analysis (symbol test) results showed there were not significant change in the parameters of dissolved inorganic nitrogen (DIN), dissolved reactive phosphorus (DRP) and the mole ratio of N and P between the mariculture and non-mariculture areas. However, the changing trends of the above environmental parameters might have some relationship with the activity of mariculture. For example, the phenomena of ammonia becoming the mainly composition of DIN and the lower concentration of chlorophyll in mariculture areas might have closed link with the excretion and feeding physiological activities of the scallops.In Sungo Bay, environmental parameters existed obviously spatial differences. Except in Spring, the concentration of DIN in control area was significantly higher than the culture area. Comparing with the control area, the concentration of DRP in shellfish cultural area was significant low in spring and winter, and the concentration of SiO₃-Si was significantly high in summer and autumn. The significantly variance frequency for environmental parameters of DIN, DRP and SiO₃-Si at the area of kelp, kelp+shellfish and shellfish were 25%,42% and 50%, respectively. The biodiversity index of plankton, especially the abundance of micro-zooplankton in shellfish area was significant low.2.The impact of large scale shellfish (Crassostrea gigas, Chlamys farreri) and seaweed (Laminaria japaonica) culture on the benthic environment at the Sungo Bay, was assessed using the B-investigation of the MOM (Modelling-Ongrowing fish farms-Monitoring) system. 10 sampling station were set and a total of 66 sediment samples were collected. Seasonal variations in three groups of parameters were compared, but no significant differences were detected between the different culture species sites. The results suggested that the Sungou Bay benthic environment belong to condition 1, which meaned that the effects of long term shellfish and seaweed farming activities on the benthic environment of Sungou Bay were low.3.Through the activity of shellfish and seaweed mariculture, there were nearly 4 million tons carbon being utilized and about 1.4 million tons carbon being taken away from the shallow sea by harvesting, which calculated basing on the data of annual production, the C content of both shellfish and seaweed and the energy budget of shellfish in 2006. From 1995 to 2006, the accumulative total C removed out of the shallow sea by harvested of seaweed and shellfish were 3.65 and 8.93 million tons respectively, and the sum total were 12.58 million tons. The results testify that the mariculture of shellfish and seaweed in the coastal ocean can utilize a great deal of oceanic carbon directly or indirectly and improve the capacity of shallow sea absorbing atmospheric CO2.4. In semi-in situ flowing-through system, the feeding behaviors of scallop Patinopecten yessoensis were measured by biodeposition method. The relationship of clearance rate and water temperature was studied. The results showed that the clearance rate (CR) was highest at 10 oC, and the relationship of water temperature and CR is same as the parabola line:CR=-0.0009T²+0.0188T-0.0306. The relationship between CR and dry tissue weight of scallop could be expressed by CR=aWb, b ranged from 0.45 to 0.65.5.In semi-in situ flowing-through system, the food selectivity of 3 kinds of filter feeding bivalves were measured. The results showed that in natural sea water, particles larger than 4μm, 6μm and 8μm, respectively were cleared with 100% efficiency by mussel Mytilus edulis, Oyster Crassostrea gigas and Scallop Chlamys farreri, repectively. The retention efficiencies by the mussel, oyster and scallop for 2μm (equivalent spherical diameter) particles were 17%, 19% and 8%, respectively. Scallop Chlamys farreri showed more sensitivity to the fluctuation of food concentration and quality. With food concentration increasing, the max-point of retention efficiency for the scallop shifted to the large size particles and the retention efficiency for 2μm particles was lower; with food quality increasing, the max-point of retention efficiency shifted from the particle size of 8μm to 5μm.6. In Zhangzi dao Island, 4 times monitoring results showed that the concentration of chlorophyll ranged from 1.23 to 2.85mg.m^-3, the average value was 1.78±0.57 mg.m^-3. The average primary production was 76.6±41.9 mg C. m^-2.d^-1. The population shell height-frequency distributions of the scallop within the areas were measured at July and October. Basement on the environmental investigated data, annual yields and mariculture areas etc, food limited indexes (clearance efficiency, filtration pressure and regulation ratio) were calculated and the ecological carrying capacity and production carrying capacity were assessed. Both food limited indexes: filtration pressure and regulation ratio were between 0.05 and 1.0, clearance efficiency was lower than 0.05, which mean the current cultured density of the scallop in Zhang zidao Island was at the level of ecological carrying capacity.7. Mathematical model was setup by the STELLA software in Sungo Bay. The response of the concentration of chla, DIN and DRP to the change of scallop and kelp cultivated density were simulated by the model, so as to study the influence of shellfish and seaweed cultivation on the environment. Simulation results shown the concentration of chlorophyll a decreased with increasing of the scallop density. Ecological carrying capacity for the scallop in Sungo Bay was primary assessed. With the scallop at the primary cultivation density, the cultivation area for the scallop could incrase from 1037 ha to 4100 ha without significant change on the concentration of chla.