THESIS
2014
iii leaves, iv-xvii, 143 pages : illustrations (some color), maps (some color) ; 30 cm
Abstract
Marine coastal hypoxia (dissolved oxygen concentration ≤ 2.0 mg O
2 L
-1), mostly
due to anthropogenic nutrient loading has become a worldwide concern. During
these disturbances, benthic organisms die off, leaving most trophic energy to be
diverted into the microbial food web. Protists, pivotal members of the microbial
food web therefore become key players in nutrient remineralisation and carbon
cycling during hypoxic disturbances. In this thesis, both spatial and temporal
studies from the Gulf of Mexico and Tolo Harbour in Hong Kong were realized
with the goal of further understanding how protist species composition and
structure is affected due to hypoxia. 454 sequencing results revealed an increase
in species diversity in response to hypoxia, and hypoxic protist species
commu...[
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Marine coastal hypoxia (dissolved oxygen concentration ≤ 2.0 mg O
2 L
-1), mostly
due to anthropogenic nutrient loading has become a worldwide concern. During
these disturbances, benthic organisms die off, leaving most trophic energy to be
diverted into the microbial food web. Protists, pivotal members of the microbial
food web therefore become key players in nutrient remineralisation and carbon
cycling during hypoxic disturbances. In this thesis, both spatial and temporal
studies from the Gulf of Mexico and Tolo Harbour in Hong Kong were realized
with the goal of further understanding how protist species composition and
structure is affected due to hypoxia. 454 sequencing results revealed an increase
in species diversity in response to hypoxia, and hypoxic protist species
communities were significantly influenced by nutrients in these hypoxic waters.
Novel clades, as well as parasitic protists were also revealed. Fluorescent in situ
hybridization (FISH) results exhibited lower active cell abundances in Tolo
Harbour hypoxic waters along with a dominance of pigmented protists, also
significantly affected by nutrient concentrations. Ciliate physiology was also studied through isolating three ciliate species from Hong Kong coastal waters.
Controlled hypoxic conditions were simulated in the lab environment, during
which time growth, respiration and grazing rates were measured. Results
indicated that ciliate tolerance to hypoxia is species specific, with overall
metabolism slowing with decreased dissolved oxygen concentration. Overall,
these results suggest that in seasonally marine hypoxic waters, lower protist cell
abundance with high species diversity, as well as trophic shifts from grazing to
parasitism is occurring.
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