Changes in metabolic energy use with body sizes within pelagic invertebrate species: new insights from jellyfish

Gelatinous zooplankton ('jellyfish') have a body water content that is proportionately very high, a trait that has evolved in at least 5 planktonic phyla. Many jellyfish are also able to maintain or even increase their metabolic rate per unit of body mass over their development. Such abilities are highly unusual in metazoans, indeed, closely related benthic species typically reduce their metabolic rate use per unit mass during growth. Resolving how and why these patterns occur will provide important insights into the comparative physiology and ecology of marine invertebrates, and in the shifts in energy over ontogeny in animals more generally.

Recent work has shown that much of the variation observed in metabolism-mass scaling across diverse pelagic invertebrates species can be explained by the degree to which they change shape over ontogeny. Many gelatinous organisms show marked body shape elongation or flattening during growth, and are highly reliant upon their external body surface for material exchange (e.g. for oxygen). In this project we will develop new methods to measure surface area over ontogeny for a range of gelatinous taxa, and explore the degree to which the increase in surface area (and hence potential supply) and metabolic rate correlate. Systematic comparisons between these pelagic taxa and their closely related benthic forms will be made (e.g. ctenophores, stauromedusae).

Metabolic theories of ecology have become very prominent and are fiercely debated, yet they commonly fail to explain the variation in metabolism-mass scaling found in aquatic animals. This project will provide new insight into the degree to which the scaling of metabolic rates to mass over ontogeny can be linked with surface area enlargement. This project will also explore why stark differences in such scaling of energy use occurs, in order to better explain these major ecological and evolutionary patterns.