Thermal sensitivity of metabolic performance in Squalus acanthias: efficacy of aerobic scope as a predictor of viable thermal habitat

ABSTRACT: Ocean warming due to climate change can affect the metabolism, performance, and survival of ectothermic marine species. On the US Northeast continental shelf (US NES), waters are warming faster than the global average, leading to elevated mean temperatures and an increased risk of marine heatwave exposure in the region. Thus, it is critical to understand the effects of warming on the region’s living marine resources. Here, we quantified the acute temperature sensitivity of metabolic traits to evaluate their role as possible drivers of acute thermal tolerance and viable habitat in the spiny dogfish shark Squalus acanthias on the US NES. From 10-23°C, the standard metabolic rate increased more rapidly than the maximum metabolic rate, resulting in a reduction in factorial aerobic scope at warmer temperatures. However, the oxygen supply capacity increased with temperature in proportion to maximum metabolic rate, and neither metric declined at the warmest temperatures, suggesting oxygen supply capacity does not limit performance within the tested range. Although behavioral observations revealed overt thermal stress via loss of equilibrium at ≥20°C and estimated lethal temperature at ∼24°C, sharks retained the ability to regulate their resting metabolic rate, achieve maximum activity, and peak absolute aerobic scope at warm temperatures. Results suggest that factors other than oxygen supply or aerobic scope are constraining thermal tolerance in S. acanthias and support the notion that aerobic scope cannot be universally applied to determine optimal or viable metabolic habitat.