Dimethylsulphide (DMS) is a climate-relevant trace gas derived from the algal secondary metabolite dimethylsulphoniopropionate (DMSP). DMS and DMSP have been shown to act as infochemicals (information-conveying chemicals) for a variety of organisms over a wide range of spatial and temporal scales. Grazing by microzooplankton increases the production of DMS, which in turn may act as an infochemical cue to attract carnivorous copepods that preferentially prey on herbivorous microzooplankton. This extra copepod predation on microzooplankton could release excessive grazing pressure on phytoplankton. Such infochemical-mediated multitrophic interactions are poorly understood in pelagic systems, but may be important for the structuring and functioning of marine food webs. Experimenting with several trophic levels of plankton in laboratory microcosms is challenging and, as a result, empirical data confirming the roles of DMS and DMSP in trophic interactions is lacking. Mathematical models provide a suitable tool to gain insight into such complex interactions. The mathematical models analysed in this thesis show DMS-mediated interactions to have a stabilising effect on food web dynamics and to promote the formation of phytoplankton blooms. Food web models with two species of phytoplankton constituting the first trophic level were analysed. The key result of this analysis was that chemoattractants, which increase the susceptibility of the producer to grazing, enhance the persistence of the producing phytoplankton species by attracting carnivorous copepods to consume microzooplankton grazers. Analysis of a Nutrient-Phytoplankton-Microzooplankton-Zooplankton (NPMZ) model showed the ability of phytoplankton to bloom to be a combination of both top-down (DMS-mediated predation) and bottom-up (nutrient limitation) processes. Analysis of a model simulating these interactions in a vertically heterogeneous environment showed foraging through chemodetection to provide fitness benefits to copepods and to enhance copepod persistence. Overall the results presented indicate that infochemicals have important consequences for the dynamics of marine food webs
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:654526 |
| Date | January 2014 |
| Creators | Lewis, Nicola Dawn |
| Publisher | University of Essex |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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