title: From surface to substance : exploring metabolic rates in gelatinous zooplankton
Creators: name: Aylward, Lauren
Publisher: name: University of Liverpool Repository
Year: 2024

description: Metabolism is fundamental to physiology and ecology. Consequently, the limits of an organism's capacity to acquire and use resources have set bounds on size and form over evolution. Metabolic scaling is the general term describing how metabolic rate relates to the size, typically body mass. Theories that aim to explain metabolic scaling have remained contentious for over a century and typically aim to derive a universal set of mechanisms which can predict how metabolic rate scales with body mass in all organisms. However, there are taxonomic and functional groups that routinely outlie the predictions of these theories, with metabolic scaling exponents that are greater, or lower than predictions, or which vary over ontogeny. Gelatinous zooplankton (GZ) are a diverse functional group of taxonomically distinct organisms, which are typically comprised of as much as 95% water by wet mass, and which often achieve metabolic scaling values that exceed predictions of some major metabolic theories. GZ maximise fitness in the pelagic environment by maintaining large, low-density bodies, minimising volume-specific metabolic requirements for maintenance, growth and locomotion, while achieving remarkably high carbon mass-specific rates of growth and feeding. Understanding how the extreme physiologies, morphologies, and distinct life-histories of GZ affect metabolic scaling may shed light on the mechanisms which determine metabolic scaling. To achieve this, Chapter Two presents analysis of relationships between metabolic scaling and ontogenetic changes in growth strategy in the ctenophore Mnemiopsis leidyi, and a general mathematical model to explain the effects of changing relationships between body composition and surface area to mass over ontogeny on respiration rates. We observed changes in log-log respiration to mass relationships consistent with the predictions of the general mathematical model. Chapter Three presents a new 3D reconstruction workflow to estimate the external surface area of soft-bodied marine invertebrates, through the modification of established photogrammetric methods. Morphological reconstruction of the scyphozoan Aurelia aurita as computer graphic 3D models were rendered successfully by applying specific lighting, tissue staining, narcotisation and photography techniques. The resulting 3D models gave surface area values which were plausible and appeared to be an improvement over simple proportional to geometric approximations. Finally, Chapter Four uses concurrently collected respiration, mass, and 3D model data of A. aurita to compare the predictions of established metabolic scaling models when growth is not isomorphic. The models compared have explanatory mechanisms related to internal transport (RTN theories), and exchange surface area (SA theories). The data supported SA over RTN theories in mature A. aurita. Overall, metabolic scaling in GZ appears to be the outcome of multiple morphological and life-history variables which change over ontogeny. This thesis has provided new methods of surface area measurement and modelling of metabolic scaling, with results that. Finally, the results presented within this thesis may inform further research into the mechanisms of metabolic scaling and be useful for metabolic, energy budgeting, and carbon cycling models in GZ.