Global climate change is transforming ecosystems through changes in the environmental conditions that organisms, populations, and ecological communities encounter. For example, rising temperatures and decreasing levels of pH and dissolved oxygen are expected to affect nearshore organisms within the the California Current Large Marine Ecosystem (CCLME). These effects have been best characterized at the level of individual organisms, but a key challenge is to scale these organism-level responses up to the level of ecological communities in order to understand how environmental drivers will impact the structure and functioning of whole ecosystems.
Sea urchins are an important group of benthic organisms in ecosystems worldwide. In kelp forests within the CCLME, their grazing is known to be a key ecological process that contributes to kelp loss, and can mediate shifts between alternative ecosystem states of kelp forests and urchin barrens. I am interested in exploring how variation in sea urchins' responses to key environmental stressors, such as high temperature and low dissolved oxygen (hypoxia), can be used to predict the effects of these stressors on the structure and function of kelp forest ecosystems, via changes in grazing.
I am characterizing how lethal tolerances to combinations of temperature and hypoxia varies between two common CCLME urchin species (the red sea urchin Mesocentrotus franciscanus and the purple sea urchinStrongylocentrotus purpuratus), and between size classes of each species. I am also examining how grazing rates in sea urchin species and size classes respond to sub-lethal levels of these stressors. By integrating an understanding of this "response diversity" in sea urchins with the existing spatial variation in urchin species composition and population size structure within the CCLME, I hope to generate insights into how climate-driven environmental change can affect tipping points and state changes in kelp forest ecosystems.
Left: Hypoxia tank setup, Right: Differences in grazing by urchins under different dissolved oxygen conditions. Control urchins consumed more kelp (top row) compared to urchins under hypoxia (bottom row).