UC Santa Barbara

Marine heatwaves (MHWs) are persisting and increasing in frequency and duration, and they are occurring with greater severity than in past decades. MHWs are a widespread occurrence, and events can span thousands of miles. As anthropogenic climate change worsens, we will be experiencing more intense marine heatwave events, so investigation into their biological impacts is necessary. My research focus was centered on the impacts of marine heatwaves, on the purple sea urchin, Strongylocentrotus purpuratus. S. purpuratus is an important sedentary herbivore in Santa Barbara Coastal kelp forests. Previous research identifies transgenerational plasticity in urchins, where the environment of the adults impacted the phenotype of offspring. Specifically, maternal and paternal provisioning in eggs and offspring assist with successful fertilization and offspring physiology. In my dissertation, I had three aims: 1) investigate how exposure to fluctuating MHWs during gametogenesis in adults impacts egg quality and fertilization success, 2) utilize SBC LTER data to investigate MHW patterns and how they correlate with S. purpuratus abundance, size, and larval settlement, and 3) probe for local adaptation between populations of S. purpuratus across their biogeographic distributions along the California Current Large Marine Ecosystem. In my first aim, I discovered that exposure to MHW conditions during gametogenesis led to larger eggs with greater protein content. If adults are exposed to adverse conditions during gametogenesis, they may provision greater biomolecules in eggs to help with growth and development. In my second aim, I discovered decreases in urchin abundance over time and an impact of urchin abundance on kelp detritus. This is consistent with the phase shift from healthy kelp forests to urchin barrens that we have seen during periods of ecological stress. In my third aim, I discovered egg and gonad differences in urchins from Mohawk reef, the southernmost site. Eggs were smaller, but gonad weight was greater in Mohawk urchins. This suggests the potential for local adaptation, but further research is necessary, such as a common garden experiment, to further investigate population level differences. Overall, marine heatwaves are occurring regularly and can cause adverse organismal impacts, but tolerance mechanisms may allow organisms to survive or thrive in future climate scenarios.