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Thesis working title:Degradation of phytoplantkon in fjordic environmentsResearch Summary:Primary production by phytoplankton is the base of the marine food web and is crucial for supporting pelagic and benthic ecosystems. The main pathway for phytoplankton to reach the benthos is either agglomeration and rapid sinking or incorporation into fast sinking faecal pellets of marine invertebrates. Degradation of phytoplankton already begins during the sinking out process and is accompanied by partial recycling in the microbial loop. The mount of degradation at different depths of the water column is likely to vary due to physical (pigments in dead cells are degraded by irradiance), chemical (diatom frustule silica, for example, is recycled lower in the water column) and biological (grazing by invertebrates) drivers, which can vary temporally and spatially. To date the flux and selective loss of phytoplankton groups throughout the water column due to the different factors is not well understood in marine and estuarine systems. Phytoplankton pigments (chlorophylls and arotenoids) are used as biomarkers to determine the selective loss of phytoplankton groups throughout the water column and their incorporation into the sedimentary record. New Zealand fjords, and especially Doubtful Sound with its permanent estuarine circulation, offer a great opportunity to study the flux and selective loss of phytoplankton over a wide range of environmental factors within one ecosystem. The objectives of this study are to(1) understand the grazing pressure on the phytoplankton community, (2) develop a good understanding of the mechanisms influencing the phytoplankton degradation in the upper water column, (3) determine the incorporation of phytoplankton detritus into the surface sediment, (4) develop an understanding of long-term preservation of phytoplankton pigments and (5) use numerical models to model the fate of phytoplankton detritus through the water column.
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