Vertical Distribution of Mesozooplankton in Polar Waters: Evidence for Foray Behaviour and its Implications
The biological carbon pump (BCP) helps regulate the Earth’s carbon cycles through exporting carbon from the ocean surface to the interior, where it may be stored for millennia. Zooplankton play an important role within the BCP, transporting carbon to depth through a combination of their diel and sea...
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| Format: | Thesis |
| Language: | English |
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2020
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| Online Access: | https://ueaeprints.uea.ac.uk/id/eprint/83651/ https://ueaeprints.uea.ac.uk/id/eprint/83651/1/2021FowlerVPhD.pdf |
| Summary: | The biological carbon pump (BCP) helps regulate the Earth’s carbon cycles through exporting carbon from the ocean surface to the interior, where it may be stored for millennia. Zooplankton play an important role within the BCP, transporting carbon to depth through a combination of their diel and seasonal vertical migrations and the rates at which they respire, produce faecal pellets and die. There remains much uncertainty around the timing and extent of these vertical movements. In this thesis, I examine the contribution that copepods (abundant crustacean zooplankton) make to the BCP, focussing on the Polar Regions, where the BCP is especially intense. Most commonly, diel vertical migration (DVM) is considered to comprise zooplankters feeding in surface layers during the night and residing in deeper waters during the day, principally to minimise visual predation. My analysis of depth stratified nets showed that Southern Ocean copepods do not always undertake synchronised DVM, but distribute themselves through the water column both day and night, suggesting the existence of a multitude of different migration patterns. Through deploying a novel motorised upward downward looking net (MUDL), I further revealed that, in populations of copepods such as Oithona spp., both upward and downward migrations take place simultaneously, indicating that individuals make vertical forays regularly over the daily cycle. Beyond visual predator avoidance, DVM may also be advantageous in slowing metabolic rate and reducing energy expenditure when occupying deeper cooler layers during the non-feeding periods. In Arctic Metridia longa, I found that the metabolic response to be sex dependent, with males in the near surface layers having a significantly higher respiration rate than those caught at depth, but females showing no difference between the two strata. Overall, I illustrate that patterns of vertical migration within copepods are complex and need to be considered in more detail to fully assess their contribution to the BCP. |
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