Marine heatwaves effects on urchin reproduction, larval survival, and oceanographic dispersal drive historical collapses in recruitmentExtreme Events

Daniel Okamoto¹, Maya Munstermann¹, Sam Karelitz¹, Nathan Spindel², Dan Swezey⁴, Rachel Simons⁵, Laura Rogers-Bennett⁶, Steve Schroeter⁵

¹University of California, Berkeley, USA - ²Florida State University - ⁴Kashia Band of Pomo Indians, USA - ⁵University of California, Santa Barbara, USA - ⁶University of California, Davis, USA

Marine heatwaves can devastate nearshore ecosystems and affect the viability of populations. While many species experience declines in recruitment during extreme climatic events, attributing causal linkages to specific processes remains a challenge for species with planktonic larvae. For purple sea urchins in southern California, historical collapses in larval supply and declines in recruitment are associated with El Nino events. To understand why such patterns, occur, we experimentally and numerically explored if and at what life stage(s) direct climatic effects can explain such collapses. Specifically, we experimentally simulated marine heatwave effects on gametogenesis and larval survival in the laboratory and paired those results with numerical oceanographic models of larval dispersal. We then linked those results with historical spatial and temporal patterns of larval supply in nature. We show how suppression of adult gametogenesis can help explain historical patterns of settlement, especially when paired with the compounded impacts of reduced larval survival and alteration of current patterns that restrict oceanographic connectivity. Collectively, our results highlight the need for studying multiple stressors, multiple life stages, and compounded effects imposed by extreme climatic events that shape vital rates and dynamics of populations.