Duration vs. severity: understanding invertebrate herbivory under varying warming events

As oceans warm, organisms are experiencing increased thermal stress. Marine thermal anomalies occur in both short-term heatwaves and long-term increases to mean temperatures, but direct comparative studies looking at the impacts of multiple types of thermal anomalies are rare. In ectothermic organisms, studies examining metabolic change after heatwaves show conflicting results to long-term climate change studies, leaving questions as to how species will be impacted across timescales. We tested the hypothesis that moderate experimental warming would increase herbivory rates over time, with a more pronounced increase occurring during long-term warming in comparison to short-term heatwaves. After simulating warming events on red sea urchins Mesocentrotus franciscanus and purple sea urchins Strongylocentrotus purpuratus , the dominant eastern Pacific kelp forest herbivores, we found that feeding rates and thermal maxima varied by species and length of warming. While short-term heatwave events caused no increase in herbivory, longer-term warming led to increased herbivory by both species. This increase in herbivory could be especially impactful to ecosystems due to the capacity of these species for overgrazing. This study provides valuable insights into the differences in species interaction strength under varying global change scenarios in a comparative framework highlighting variation in physiological response to thermal stress across time.