Growth and energy storage responses vary seasonally in the Australasian snapper Chrysophrys auratus with only modest changes in aerobic scope

Abstract

Many temperate marine species cope with profound seasonal changes in temperature. One way in which these species have adapted to these conditions is by adopting life-history traits that employ seasonally dependent growth, maximising growth in the warmer summer period before experiencing a period of negligible growth and maintenance in the cooler winter period. This strategy is considered to ensure that temperate species survive the unproductive winter period. However, in the field of eco-physiology, the inability to grow in low temperature environments is considered to result from physiological limitations on growth and digestion imposed by low aerobic scope (AS) at low temperatures. In this study, we investigate the seasonal growth, bioenergetic changes and metabolic oxygen requirements (including AS) of the Australasian snapper (Sparidae: Chrysophrys auratus) over natural seasonal cycles. We demonstrate that snapper undergo marked growth over a 7 mo period spanning spring, summer and autumn, then negligible (or even negative) growth in the winter. These growth responses coincide with marked changes in physiological character, including changes in energy storage, body composition, gonadal development and haematological variation. The biological changes observed occur in combination with a broad AS curve that was relatively insensitive to the seasonal temperatures experienced in their natural range. Within this broad AS curve, variations in growth rate could not be explained by changes in AS, and vastly different rates of biological activity were observed despite only modest change in AS availability. The relevance of the oxygen capacity-limited thermal tolerance framework to the seasonal responses of snapper is discussed.