Climate variability hypothesis is partially supported in thermal limits of juvenile Northwest Atlantic coastal fishes

As ocean warming continues to impact marine species globally, there is a need to understand the mechanisms underlying shifts in abundance and distribution. There is growing evidence that upper and lower temperature tolerances rather than mean preferences explain range shifts, but the full thermal niche is unknown for many marine species and observational data are often ill-suited to estimate the upper and lower thermal tolerances. We quantified critical thermal maximum (CT_max ) and critical thermal minimum (CT_min ) using standard methods to quantify temperature limits and thermal ranges of 14 economically and ecologically important juvenile fish species on the US Atlantic coast. We then tested the climate variability hypothesis (CVH), which states that higher-latitude species should have a wider temperature tolerance due to higher climatic variability closer to the poles. Our findings generally support the CVH in the juvenile fishes that we evaluated. However, low-latitude species were not uniformly stenothermal. Rather, species with median occurrences across a wide range of latitudes had wide temperature tolerances, but only the tropical species we tested had more narrow ranges. These findings suggest that quantifying temperature tolerances may be used to predict which low-latitude species are most likely to shift in response to warming water and those that may be more sensitive to climate change in this region.