UC Santa Barbara

Temperature and body size are two fundamental factors shaping physiological and ecological processes across all levels of biological organization. Understanding the relationship between these two factors is therefore essential to our ability to understand how species are responding to climate change, especially as one response of ectotherms to warming is a decline in body size. Declining body size in fishes can consequently lead to declining economic and recreational fisheries value, declining population productivity, declining food security, and altered size-structure function of communities. My thesis explored the physiological mechanisms and the ecological consequences of body size and life-stage specific vulnerability to warming. First, I used a meta-analysis approach to determine species- and group-specific vulnerability to warming in fishes. I evaluated how aerobic metabolism scales with body mass in fishes across temperature and how these changes in scaling may differ with species ecology and morphology. Further, to better understand the mechanisms behind temperature-modulated scaling of aerobic metabolism, I tested how metabolism and maximum heart rates change with acute temperature change and body size in a model species, barred surfperch (Amphistichus argenteus). I then reviewed aerobic swim performance in adult salmon to determine the potential ecological consequences of shifting body sizes. By combining work both across and within species, and examining ecologically relevant physiological performances and contexts, my thesis demonstrates that relationships between body size and performance can provide a mechanistic platform to identify climate change vulnerability in fishes.