Tolerance mechanisms and responses of krill species of different latitudes to oxygen minimum zones
Euphausiids (krill) constitute a major part of the macrozooplankton community in terms of total biomass and play a key role in the food webs of the most productive marine ecosystems of the world. From the species found along the Eastern Pacific coastline many do not tolerate hypoxia and they do not...
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| Format: | Thesis |
| Language: | unknown |
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2014
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| Online Access: | https://epic.awi.de/id/eprint/36126/ https://epic.awi.de/id/eprint/36126/1/00103880-1.pdf http://elib.suub.uni-bremen.de/edocs/00103880-1.pdf https://hdl.handle.net/10013/epic.44769 https://hdl.handle.net/10013/epic.44769.d001 |
| Summary: | Euphausiids (krill) constitute a major part of the macrozooplankton community in terms of total biomass and play a key role in the food webs of the most productive marine ecosystems of the world. From the species found along the Eastern Pacific coastline many do not tolerate hypoxia and they do not distribute where shallow oxygen minimum zones (OMZs) prevail. Only very few species are endemic of OMZs. In my thesis, I investigated the physiological strategies and OMZ tolerance mechanisms of euphausiids on a global-scale to explain the current zoogeographical pattern of major species and project it in the future. In a first step, the basal respiration rate of the species investigated was measured. This simple measurement is one of the best proxy to identify the optimal environmental window and the metabolic requirement scale wherein the organism is. A global euphausiid respiration ANN (Artificial Neural Network) model was built with 2479 data sets enclosing 23 of the total 86 species. The model included the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The ANN model indicated a decrease in respiration with increasing LAT and decreasing DLh. For seasonality, a General Additive model (GAM) successfully integrated DLh and DoY effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. For the North Pacific krill, Euphausia pacifica, we found no effect of DLh or DoY and the results for the North Atlantic krill, Meganyctiphanes norvegica were not meaningful, because the seasonal data were insufficient. The activity of the citrate synthase, Krebs cycle enzyme, also seems to be a promising tool for euphausiid respiration prediction and should be further analysed in pair with respiration measurements to develop a model in the future. The results emphasize ... |
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