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

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The abundance of gelatinous zooplankters is increasing in many marine systems with unknown trophodynamic consequences due to a lack of controlled experiments examining growth physiology. This proposed research explores the bioenergetics (metabolism: anabolism and catabolism) of four, key gelatinous predators in the North Sea: Aurelia aurita, Cyanea capillata, Pleurobrachia pileus and Mnemiopsis leidyi. During bloom conditions, each of these two scyphozoan and two ctenophore species can exert top-down control on zooplankton resources, limiting the flow of energy to other primary consumers. Moreover, they can directly prey upon early larval stages of key marine fish species. Predation pressure by these gelatinous predators is particularly intense at hydrodynamic convergence zones such as fronts: trophodynamic “hot spots” in the North Sea. The research planned in this proposal should allow the quantification of energetic and nutrient demands of these key predators, and measure and model the interactive effects of food quantity and food quality (expressed as changes in elemental ratios) on growth and reproduction in the four gelatinous zooplankters. The research expands upon previous results suggesting fundamental differences in how changes in nutrient stoichiometry of food affect the productivity of jellyfish compared to other secondary consumers (e.g., larval fish). Our experiments test fundamental hypotheses regarding ecological stoichiometry and resource-limited growth in key predators in marine systems. Knowledge gained from our physiological experiments will be used to create dynamic energy budgets and individual-based models (IBMs) of foraging and growth for gelatinous zooplankton, and it is to our knowledge the first time that not only energy, but also food quality is taken into account in such models. These laboratory and modelling activities are essential if we hope to understand growth dynamics and resource limitation in jellyfish and are a perquisite for gaining robust projections of the trophodynamic impacts of these predators in the North Sea and elsewhere.