Cross-latitude population comparisons of energetic and reproductive investment of purple sea urchins in marine heat wave conditionsExtreme Events

Maya Munstermann¹, Daniel Swezey², Laura Rogers-Bennett¹, Daniel Okamoto¹

¹University of California, USA - ²Kashia Band of Pomo Indians, USA

Marine heatwaves in northern California have resulted in recent explosions in purple urchins (Strongylocentrotus purpuratus), due to a combination of factors including increased larval supply and loss of predators. In contrast, heatwaves and warmer waters in the southern range, where temperatures are often much warmer than northern California, have coincided with reductions in adult densities. Yet how warming and heatwaves shape urchin energetic investment and reproductive capacity across the range remains an unclear. We experimentally compared the influence of five static temperatures from 10-22C and variable heatwave conditions from 18-21C, across Sonoma (northern), Santa Barbara, and San Diego (southern) urchin populations. The two southern populations exhibited similar respiration rates across temperatures and heatwave conditions; however, urchins from the north had significantly higher rates of oxygen consumption. Although gonad sizes did not differ across temperatures and populations, urchins in cooler temperatures across all populations were further along in gametogenesis, with mature gametes, compared to those in warmer temperatures, where gametes were in early stages of development. The increased metabolic costs associated with warmer temperatures may require greater resource consumption, leading to a trade-off between energy storage and maintenance when temperatures exceed optimal thermal windows. Warm (16-22C) temperatures will result in destructive urchin herbivory due to compensatory feeding and varied reproductive potential of urchins under future warming.