Functional response of the antarctic sea urchin, sterechinus neumayeri, to environmental change and extreme events in the context of a warming climate

Abstract

Gradual increases in mean ocean temperature are one of many broad-scale changes currently experienced in marine systems in response to anthropogenic forcing. Extreme climate events, such as marine heatwaves are forecast to escalate in many areas of the climate system under future global change scenarios. Species will have varying capacities to adapt, persist, and ultimately survive under these scenarios of environmental change. The allocation of energy to fundamental biological functions, in addition to the ability to acclimate to gradual change and recover from acute change, is key to this capacity. In the context of the current climate and that of the future, a better understanding of how organisms allocate energy as a response to environmental drivers is needed.
In this thesis I focus on the common Antarctic sea urchin, Sterechinus neumayeri; a representative species for studying environmental change impacts due to its inherent thermal sensitivity and overall significance as one of the most functionally important Antarctic shallow marine species and the most dominant echinoid in the nearshore benthic community. I explore how S. neumayeri allocates energy, in terms of reproductive investment and key biological functions, in the current climate, as well as during temperature extremes and for the climate predicted for 2100. I use a combination of approaches, including a timeseries of field-based observations and laboratory-based mesocosm experiments to simulate both gradual and acute extreme warming. My results show for the first time that endogenous rhythms against a backdrop of multifactorial shifts in the environment are key drivers of energy allocation in terms of reproduction. In addition, I show that the onset rate of acute warming is more important than absolute temperature in limiting key biological functions, and I provide evidence that a thermally sensitive species like S. neumayeri may have an improved ability to cope with acute warming following acclimation to gradual temperature increases predicted for 2100.
Collectively, these results show that within the boundaries of natural variability, it is likely that species have the energetic capacity to buffer and cope with changes to the environment. However, as our global climate changes over the coming decades, the natural variability range of regional temperatures will shift in conjunction with extreme events, and as such, energetic investment and functional performance will depend on a matrix of factors such as warming onset rate and thermal history. Clearly, even some of the most thermally constrained species have the capacity to acclimate and recover from thermal stress, and although there will always be an energetic cost to this, the ability to acclimate and recover will undoubtedly benefit those who have this capacity in the future.

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