August 7, 2026 – Bi-weekly Report

Evolving Meta-Ecosystems (EVOME) researchers are making excellent progress as data is collected, analyses begin, and anecdotal evidence in the field begins to evoke new questions. This is exactly what is happening now for graduate students Matthew Zimmerman and Shira Berkelhammer, assisted by REU Lily Downing, as they study CTmax. CTMax stands for the Critical Thermal Maximum, which is representative of the temperature maximum that an organism could no longer maintain or survive at long-term. In this study, it is an acute exposure to a temperature where the study’s focal fish, Arctic grayling, begin to display some level of stress. This stress documentation is documented in a form of maintaining equilibrium. A fish’s balance is naturally upside-down due to their swim bladder, but as they swim they hold themselves right-side up. The fish are heated very slowly until individuals reach a temperature where they can no longer maintain their balance, and their swim bladder pulls their belly up. The fish start at ambient temperature, which is typically around eight to twelve degrees Celsius, depending on the water that the fish were sourced from. This water is then heated 0.1 degrees Celsius per minute, or 6 degrees an hour, until the fish hit their CTMax. This temperature is noted as the fish are very quickly pulled out of the warm water and placed into a bucket of medium-temperature water to recover. Once the fish are recovered, researchers measure their weight and length – keeping these measurements tied to their CTmax, and lastly clipping their adipose fins to identify them if re-caught. Fish of varying sizes are included in the experiment from each site, representing different life stages. The experiment shows comparisons across seasons and live stages, illustrating how tolerance changes throughout an individual’s life.

On a larger scale, this experiment is run along a latitudinal gradient by comparing CTmax across all EVOME sites to identify a genetic component across the landscape, if southern populations might have higher temperatures where they hit that CT max where they can’t maintain balance anymore. The team expected a natural temperature gradient along the latitudinal gradient, but have noticed from the 2025 data that the northern sites have significantly more temperature swings. Anecdotally, the northern sites tend to have colder colds in the winter, warmer warms in the summer, and more direct UV light from the lack of canopy shade. So far it appears fish from the northern sites acclimatize, not acclimate, faster likely because of the more variable conditions, as observed in the summer last year.