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Please use this identifier to cite or link to this item: http://hdl.handle.net/2031/4281

Title: Use of artificial reefs and green-lipped mussels (pernal viridis) for removal of nutrients from marine fish farming
Other Titles: Ren gong yu jiao ji fei cui yi bei dui yuan yu hai shui yu yang zhi de fu ying yang hua de qu chu zuo yong de yan jiu
人工魚礁及翡翠貽貝對源於海水魚養殖的富營養化的去除作用的研究
Authors: Gao, Qinfeng (高勤峰)
Department: Dept. of Biology and Chemistry
Degree: Doctor of Philosophy
Issue Date: 2005
Publisher: City University of Hong Kong
Subjects: Artificial reefs
Marine eutrophication
Mussels -- Effect of organic water pollutants on
Restoration ecology
Notes: CityU Call Number: QH91.8.E87 G36 2005
Includes bibliographical references (leaves 154-186)
Thesis (Ph.D.)--City University of Hong Kong, 2005
xviii, 192 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Eutrophication is one of the most serious environmental issues resulting from excessive nutrient addition to the water column. In coastal areas, intensive fish culture activities exert serious eutrophic impacts on the vicinity of the fish raft areas owing to release of uneaten feed residues and excreta from the fish stock. To evaluate the feasibility and capability of artificial reefs (ARs) and transplanted green-lipped mussels (Perna viridis) as biofilters for removal of excessive nutrients induced by fish farming activities, a Before-After-Control-Impact (BACI) study on the sediment nutrient levels and macrobenthic community structure was conducted at a marine fish culture zone in Kau Sai Bay, Hong Kong. From August 2001 to April 2002, a field study was undertaken before the deployment of ARs, so as to obtain baseline data. Bimonthly sediment samples were collected at 6 stations: 2 fish-cage stations under the fish rafts, 2 intermediary stations 100 m away from the boundary of the fish culture area, and 2 reference stations 600 m further away from the culture area. Sediment physico-chemical characteristics in terms of silt/clay fraction, moisture content, total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were analyzed. Macrobenthos (> 0.5 mm) were collected using a 0.05 m2 van Veen grab. At each station, 5 replicate samples were obtained and animals present in the sediment were sorted, identified and enumerated. On average, TOC, TKN and TP levels at the fish-cage stations were 86.5%, 137.1% and 1296.0% higher than those at the reference stations, respectively. Univariate and multivariate statistical analyses revealed that diversity of macrofauna was significantly reduced and community structure differed at the fish-cage stations relative to the reference stations. The intermediary stations near the fish culture area showed a transitional state of disturbance. Faunal diversity was negatively correlated with nutrient levels, reflecting the adverse impacts of nutrient enrichment derived from fish farming activities on the benthic assemblages. In April 2002, 16 sets of ARs together with transplanted green-lipped mussels were deployed at the fish culture zone in Kau Sai Bay. Monitoring of sediment physico-chemical characteristics and macrobenthic communities after AR deployment was continued to investigate the effects of the presence of ARs and transplanted green-lipped mussels on sediment quality and macrobenthic composition. During the post-deployment period, silt/clay fractionation and moisture content of sediments at all the 6 sampling stations did not show significant changes compared with those before AR deployment. Nutrient levels of sediment, however, showed a decreasing trend at the fish-cage and intermediary stations, whereas no significant changes in nutrient levels were detected at the reference stations. As a result of the reduction in nutrient levels in sediments and improvement of the seabed conditions, species diversity of benthic communities showed a gradual increase after ARs were deployed. Colonization of epifaunal organisms on the ARs was studied using settlement plates installed on the AR structure. Epifaunal settlement showed a peak in May 2003 with 53% coverage, but in summer months, higher mortalities and less coverage area were noted owing to decrease in dissolved oxygen level in bottom waters. Dominant epifaunal species included the barnacle Balanus trigonus, bivalve Pseudochama retroversa and tunicate Styela sp.. One year after AR deployment when the epifaunal communities on the AR surface were well developed, metabolic acquisition and expenditure of carbon, nitrogen and phosphorus by the epifauna and transplanted mussels were determined and nutrient budgets in terms of Scope for Growths (SFGs) quantified. On average, SFGs of carbon, nitrogen and phosphorus for epifaunal organisms on the settlement plate surface were 408.4, 108.4 and 17.9 mg h-1 m-2, respectively. The annual assimilation capacities for carbon, nitrogen and phosphorus by epifaunal organisms were 588.1, 156.1 and 25.7 g m-2. For a standardized Perna viridis of 70 mm shell length, the average SFGs of carbon, nitrogen and phosphorus were 1,026.6, 111.3 and 25.4 μg h-1. The annual assimilation capacities for carbon, nitrogen and phosphorus by a 70 mm mussel were 1,477.0, 160.2 and 36.6 mg, respectively. Based on the total surface area of the ARs deployed in this study, the total removal of carbon was estimated at 6.4 kg, nitrogen 1.7 kg and phosphorus 0.3 kg d-1, and the filtration capacity at 8,736 m3 d-1. Translating these figures into annual basis, this was equivalent to nitrogen loss from about 2 tonnes of fish production from literature data. To assess the contribution of various potential food sources from autochthonous particulate organic matter and allochthonous uneaten fish feed and fish faeces derived from fish farming activities, a polyculture system combining cultured fish and mussels was developed by transplantation of mussels into fish cages. The food sources of mussels in the polyculture system were traced and quantified using fatty acid profiles and stable isotopes as trophic markers. Mussels from the same population were simultaneously transplanted to a distant reference site free of effects exerted by fish farming activities and acted as control. After 3-month acclimation, samples of mussel tissue, particulate organic matter, fish feed and fish faeces were collected for measurements of carbon and nitrogen isotopic ratios as well as fatty acid profiles. Enrichment of 13C and 15N in mussel tissue collected inside the fish cages as compared to those at the reference site indicated the uptake and assimilation of isotopically heavier fish feed and fish faeces. Compared with the mussels at the reference site, the pattern of fatty acid profile and single fatty acid species of mussels in fish cages also tended to be closer to the fatty acid profile of fish feed from fish rafts. Based on concentration-weighted isotope mixing model, the proportions of mussel biomass assimilated from particulate organic matter, fish feed and fish faeces were 68.3%, 27.5% and 4.2%, respectively. To conclude, fish farming activities exert adverse impacts on seabed conditions due to release of farming wastes such as uneaten fish feed and fish faeces. The deployment of ARs and transplanted mussels are shown to be effective in removal of nutrients through direct uptake of fish feed and fish faeces or indirect uptake of particulate organic matter from surrounding waters, and can serve as biofilters for improvement of water quality at the fish culture sites. The system has high application potential in the Asia-Pacific region in which trash fish is the major feed for fish farming operations in inshore waters, where dispersion of wastes is limited.
Online Catalog Link: http://lib.cityu.edu.hk/record=b1988743
Appears in Collections:BCH - Doctor of Philosophy

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