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postgraduate thesis: Effects of hypoxia on marine benthic communities : from bacteria to invertebrates

TitleEffects of hypoxia on marine benthic communities : from bacteria to invertebrates
Authors
Issue Date2013
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Li, L. [李嵐]. (2013). Effects of hypoxia on marine benthic communities : from bacteria to invertebrates. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4979922
AbstractBecause of the eutrophication resulting from increasing anthropogenic activities, hypoxia (i.e. dissolved oxygen < 2.8 mg O2 L-1) is on the rise globally. The objective of this research was to understand more about the effects of hypoxia on the marine benthic communities. Particularly, it focused on the latent effects and indirect effects of hypoxia by investigating how early exposure to hypoxia affect the later life stage of a marine gastropod Crepidula onyx, and how hypoxia alter the bacterial composition of biofilms and the subsequent larval settlement of marine invertebrates. In the first study, the larvae of C. onyx were exposed to 2, 3, and 6 mg O2 l-1. Under low food concentration (Isochrysis galbana at 1 × 105 cells l-1), larvae in both hypoxic treatments (2 and 3 mg O2 l-1) required a longer time to become competent to metamorphose. But when they did, they had a similar size and total lipid content to the control larvae. Moreover, the latent effects of early hypoxic exposure on the juvenile growth were evident. After 2 weeks development in field, the growth rate, mean dry weight and filtration rate of juveniles were significantly reduced in the hypoxic treatments. However, there was no discernible effect on larvae or juveniles when the food concentration during the larval stage was doubled (I. galbana at 2 × 105 cells l-1), suggesting that the latent effects of hypoxia can be offset by larval access to high algal concentration. In the second study, the biofilms were exposed to hypoxia and normoxia in microcosms for up to 7 days, and their bacterial community composition was analysed by terminal-restriction fragment length polymorphism (T-RFLP). The results suggested that hypoxia altered the bacterial community structure within biofilms, and the difference between the hypoxia and normoxia treatments increased through the length of exposure period. The resulting changes in biofilms did not alter the larval settlement response of a model species (i.e. C. onyx) in laboratory assays. Nevertheless, when the biofilms were deployed in the field to allow natural larval settlement and recruitment, biofilms that had been exposed to hypoxia altered the overall larval settlement pattern of different marine invertebrates, potentially leading to a shift in the benthic invertebrate community. This research suggested that periodic hypoxic events and the resulting exposure of organisms to hypoxia during their early development might have effects that persist across the life history. Moreover, it highlighted the possibility that the effects of hypoxia on species composition and structure of benthic invertebrate communities might be mediated through changes in biofilms and subsequently larval settlement and recruitment. To conclude, this research demonstrated that hypoxia could affect the growth in the later life stages of marine invertebrates and the recruitment of the benthic communities.
DegreeMaster of Philosophy
SubjectMarine bacteria
Hypoxia (Water)
Marine invertebrates
Dept/ProgramBiological Sciences
Persistent Identifierhttp://hdl.handle.net/10722/193402

 

DC FieldValueLanguage
dc.contributor.authorLi, Laam-
dc.contributor.author李嵐-
dc.date.accessioned2014-01-03T23:08:33Z-
dc.date.available2014-01-03T23:08:33Z-
dc.date.issued2013-
dc.identifier.citationLi, L. [李嵐]. (2013). Effects of hypoxia on marine benthic communities : from bacteria to invertebrates. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b4979922-
dc.identifier.urihttp://hdl.handle.net/10722/193402-
dc.description.abstractBecause of the eutrophication resulting from increasing anthropogenic activities, hypoxia (i.e. dissolved oxygen < 2.8 mg O2 L-1) is on the rise globally. The objective of this research was to understand more about the effects of hypoxia on the marine benthic communities. Particularly, it focused on the latent effects and indirect effects of hypoxia by investigating how early exposure to hypoxia affect the later life stage of a marine gastropod Crepidula onyx, and how hypoxia alter the bacterial composition of biofilms and the subsequent larval settlement of marine invertebrates. In the first study, the larvae of C. onyx were exposed to 2, 3, and 6 mg O2 l-1. Under low food concentration (Isochrysis galbana at 1 × 105 cells l-1), larvae in both hypoxic treatments (2 and 3 mg O2 l-1) required a longer time to become competent to metamorphose. But when they did, they had a similar size and total lipid content to the control larvae. Moreover, the latent effects of early hypoxic exposure on the juvenile growth were evident. After 2 weeks development in field, the growth rate, mean dry weight and filtration rate of juveniles were significantly reduced in the hypoxic treatments. However, there was no discernible effect on larvae or juveniles when the food concentration during the larval stage was doubled (I. galbana at 2 × 105 cells l-1), suggesting that the latent effects of hypoxia can be offset by larval access to high algal concentration. In the second study, the biofilms were exposed to hypoxia and normoxia in microcosms for up to 7 days, and their bacterial community composition was analysed by terminal-restriction fragment length polymorphism (T-RFLP). The results suggested that hypoxia altered the bacterial community structure within biofilms, and the difference between the hypoxia and normoxia treatments increased through the length of exposure period. The resulting changes in biofilms did not alter the larval settlement response of a model species (i.e. C. onyx) in laboratory assays. Nevertheless, when the biofilms were deployed in the field to allow natural larval settlement and recruitment, biofilms that had been exposed to hypoxia altered the overall larval settlement pattern of different marine invertebrates, potentially leading to a shift in the benthic invertebrate community. This research suggested that periodic hypoxic events and the resulting exposure of organisms to hypoxia during their early development might have effects that persist across the life history. Moreover, it highlighted the possibility that the effects of hypoxia on species composition and structure of benthic invertebrate communities might be mediated through changes in biofilms and subsequently larval settlement and recruitment. To conclude, this research demonstrated that hypoxia could affect the growth in the later life stages of marine invertebrates and the recruitment of the benthic communities.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.subject.lcshMarine bacteria-
dc.subject.lcshHypoxia (Water)-
dc.subject.lcshMarine invertebrates-
dc.titleEffects of hypoxia on marine benthic communities : from bacteria to invertebrates-
dc.typePG_Thesis-
dc.identifier.hkulb4979922-
dc.description.thesisnameMaster of Philosophy-
dc.description.thesislevelMaster-
dc.description.thesisdisciplineBiological Sciences-
dc.description.naturepublished_or_final_version-
dc.identifier.doi10.5353/th_b4979922-
dc.date.hkucongregation2013-

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