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Title: Fatty acid profile in green-lipped mussel perna viridis as environmental marker in marine ecosystems
Other Titles: Li yong fei cui yi bei de zhi fang suan wei hai yang sheng tai xi tong de huan jing zhi biao de yan jiu
Authors: Yip, Ka Man (葉嘉文)
Department: Dept. of Biology and Chemistry
Degree: Master of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Fatty acids
Indicators (Biology) -- China -- Hong Kong
Marine ecology -- China -- Hong Kong
Mussels -- China -- Hong Kong
Notes: CityU Call Number: QL430.7.M95 Y56 2006
Includes bibliographical references (leaves 234-255)
Thesis (M.Phil.)--City University of Hong Kong, 2006
xxix, 255 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Fatty acids, including saturated fatty acids (SFAs), monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs), constitute the main part of the lipids, which are important for metabolism and cell membrane formation in aquatic organisms. They can remain unchanged when they are transferred from the lower to higher trophic level. Thus, they can be used as markers to provide information about the dietary intake, food constituents and trophic relationships among organisms in an ecosystem. In order to examine how fatty acids can be used as markers in the marine environment, three investigations were conducted to 1) study the trophic relationship in a simple food chain consisting of phytoplankton, zooplankton and green-lipped mussels, 2) demonstrate adaptation of green-lipped mussels to changes of environmental/food quality in the field, and 3) compare inter-site differences and seasonal pattern of fatty acid profiles in green-lipped mussels over a study period of one year. For Investigation 1, green-lipped mussels Perna viridis, collected from Peng Chau, were allotted to two treatment groups. The first treatment group comprised mussels fed with diatom Thalassiosira pseudonana only, whereas the second treatment group contained mussels fed with marine rotifer Brachionus plicatilis, which was in turn fed with diatom T. pseudonana. The mussels were fed two times each day over the experimental period of 14 days. On Day 4, Day 7 and Day 14, 3 mussels were collected from each tank of each treatment group and treated as a single replicate. Fatty acid profiles of diatoms, marine rotifers and the three organs (digestive gland, mantle margin and adductor muscle) of the two mussel groups were analyzed. Results showed that MUFA 16:1n7 was conserved along the food chain among diatoms, marine rotifers and green-lipped mussels. This suggested that MUFA 16:1n7 or the ratio of MUFA 16:1n7 to SFA 16:0 can be a good marker for diatom Thalassiosira pseudonana and elevated amounts of MUFA 16:1n7 in mussels can reflect the dominance of diatoms in the environment. The present results also showed that rotifers could accumulate MUFA 18:1n7 and PUFA 20:4n6 which were transferred up to mussels, especially MUFA 18:1n7, as zooplankton have the ability to synthesize or actively accumulate certain fatty acids that they need for growth or reproduction. There was an increase in the amount of MUFA 18:1n7 in the digestive gland of mussels fed with rotifers but the level of this fatty acid remained unchanged in those fed with diatoms, further confirming that MUFA 18:1n7 can be used as a marker for the presence of rotifers in trophic relationship studies. For Investigation 2, a reciprocal transplantation experiment was conducted, in which a batch of green-lipped mussels from Kat O was transplanted to Ma Wan and vice versa over a study period of 12 weeks. Mussels from the transplanted groups and the non-transplanted (native) groups were collected in weeks 2, 4, 8 and 12 respectively for analysis of fatty acid profiles in the digestive gland, gonad, gill, mantle margin and adductor muscle. Results showed that the fatty acid profiles of the digestive gland of the two transplanted mussel groups registered the fastest acclimation and were relatively similar to those of the native mussel groups within four weeks of exposure. The acclimation rate of the transplanted mussels from Kat O to Ma Wan was also found slower than that of those transplanted from Ma Wan to Kat O. By analyzing the similarity of fatty acid profiles of the five organs of the transplanted and the native mussels, results demonstrated that in general the transplanted mussels from Ma Wan to Kat O could adapt to the new environment within four weeks of exposure whereas those transplanted from Kat O to Ma Wan could not show such adaptations even after twelve weeks of exposure except for the digestive gland. This could be explained by the high food quality in the water body of Kat O, in which the transplanted mussels could accumulate essential fatty acids through filter feeding. However, owing to high turbidity in Ma Wan, the food quality is relatively poor and the transplanted mussels could minimize food uptake from the water column and use their fatty acid reserve to support growth. The present findings implied that green-lipped mussels may be able to accumulate or reserve fatty acids in their tissues when they are exposed to environments with different food conditions. For Investigation 3, green-lipped mussels and sub-surface water samples were collected from six locations, Peng Chau (PC), Central (C), Tsim Sha Tsui (TST), North Point (NP), Kwun Tong (KT) and Tung Lung Chau (TLC), at bi-monthly intervals over a study period of one year. At each site, the gonad and somatic tissues of mussels were separated to determine the gonado-somatic index (GSI) and fatty acid profiles. In the water samples, fatty acid profiles of the total particulate matter and physico-chemical parameters, including pH, temperature, salinity, dissolved oxygen, chlorophyll a, ammonia, nitrate and phosphate, were determined. Results showed that the gonad and somatic tissues of mussels from the six sites exhibited similar inter-site differences and seasonal changes in fatty acid profiles. For inter-site differences, levels of SFA 16:0, MUFAs 16:1n7 and 18:1n7 and PUFA 20:5n3, which are indicative of presence of phytoplankton, were significantly higher at TLC and PC than C, TST and NP, except for KT, whereas amounts of MUFAs 18:1n9, 20:1n9 and PUFA 18:2n6, which are indicative of presence of zooplankton and marine fungi, were higher at C, TST, NP and KT than TLC and PC. For seasonal changes, levels of MUFA 18:1n9 and PUFA 18:2n6, were significantly higher in the cool, winter months (15 – 18ºC) than the hot, summer months (23 – 30ºC). The fatty acid profiles of total particulate matter in the water samples were also positively correlated with those of gonad and somatic tissues of mussels, especially SFAs 14:0, 16:0, MUFAs 16:1n7, 18:1n9 and PUFA 18:2n6. This reflected that the fatty acid profiles of mussels were affected by their food sources. Other physico-chemical parameters in the water samples were positively or negatively correlated with the fatty acid profiles of total particulate matter. This indicated that the change of physico-chemical parameters can affect the fatty acid profiles of TPMs in the water column. However, a negative correlation was noted between PUFAs 18:3n3 and 22:6n3 and the GSI of mussels collected at TLC. The present findings demonstrated that fatty acids can be used to indicate the food sources of marine organisms and their trophic relationships. In particular, the fatty acid profiles of green-lipped mussels can reflect their physiological state as well as the food quality in the marine environment. This study further confirmed the applicability of fatty acid profiles as a marker in an organism to reflect the pertinent environmental conditions.
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