Physical and Physiological Growth Constraints of Key, North Sea Gelatinous Zooplankton

The aim of this thesis was to investigate the physical and physiological growth constraints of gelatinous zooplankton, focusing on under-studied juvenile stages of key North Sea gelatinous zooplankton: the scyphozoan benthic polyp; and the planktonic ephyra stage. The thesis focused on climate-driven factors that are predicted to change due to global warming. We conducted tri-trophic food chain experiments to research the direct and indirect effects of OA and changes of nutrient availability. Polyp growth and carbon content was not affected by CO2, but was significantly negatively affected by P-limitation of the food. The conclusion is that phosphorus can be a limiting factor influencing the fitness of scyphozoan polyps and that phosphorus limited food is of poor nutritional quality. The next step was to investigate the effect of temperature and different levels of CO2. The growth and carbon content of polyps and ephyrae were significantly affected by temperature, but there was no effect either by CO2 or by the interaction between temperature and CO2. To investigate the effect of current, polyps on plates were tested in an annular flow channel under different current velocities. Additionally, two field experiments were conducted to verify the laboratory results and survey the influence of water current and shelter on the survival of scyphozoan polyps. The laboratory and field results demonstrate that current velocity has a negative effect and protection a positive effect on the survival of scyphozoan polyps. The conclusion of this thesis is that the juvenile stages of the species used for this work have a wide range of tolerance for the investigated abiotic factors. This makes them more adaptable to the predicted shift of climate.