LAUSR

Sea urchins are voracious herbivores that influence the ecological structure and function of nearshore ecosystems throughout the world. Like many species that produce planktonic larvae, their recruitment is thought to be particularly sensitive to climatic fluctuations that directly or indirectly affect adult reproduction and larval transport and survival. Yet how climate alters sea urchin populations in space and time by modifying larval recruitment and year-class strength on the time-scales that regulate populations remains understudied. Using a, spatially replicated weekly-biweekly data set spanning 27 yr and 1100 km of coastline, we characterized seasonal, interannual, and spatial patterns of larval settlement of the purple sea urchin (Strongylocentrotus purpuratus). We show that large spatial differences in temporal patterns of larval settlement were associated with different responses to fluctuations in ocean temperature and climate. Importantly, we found a strong correlation between larval settlement and regional year class strength suggesting that such temporal and spatial variation in settlement plays an important role in controlling population dynamics. These results provide strong evidence over extensive temporal and spatial domains that climatic fluctuations shape broad-scale patterns of larval settlement and subsequent population structure of an important marine herbivore known to control the productivity, community state, and provisioning services of marine ecosystems. Large-scale climate oscillations (e.g., El Niño Southern Oscillation, North Atlantic Oscillation) lead to changes in ocean temperature, biogeochemistry, and the severity and frequency of disruptive events that affect ocean circulation, upwelling, and primary productivity (Mantua et al. 1997; Cai 2014). Such shifts impose wide-reaching ecological impacts, in part by altering animal recruitment and food web structure in space and time (Sydeman et al. 2015). Hence, understanding how climate variability alters the recruitment of marine species is particularly important for effective conservation and management of the ocean’s resources. Climatic fluctuations give rise to shifts in numerous factors that shape both adult reproduction and larval supply, including primary productivity, temperature, and advection and transport. Given these multiple direct and indirect effects of climate on recruitment, significant challenges remain in achieving such understanding for benthic species with planktonic larvae due to the substantial effort needed to characterize spatial and temporal variation in larval settlement and the numerous sensitive vital rates that contribute to it. For benthic species like sea urchins, understanding causes and consequences of recruitment variability has both ecological and economic implications. Sea urchin grazing can alter the structure of some of the world’s most diverse and productive marine ecosystems, including coral reefs (Edmunds and Carpenter 2001), seagrass meadows (reviewed by Valentine and Heck 1999), and kelp forests (reviewed by Filbee-Dexter and Scheibling 2014). In addition, sea urchins form the basis of important nearshore fisheries in many regions of the world (e.g., Kato and Schroeter 1985; Andrew et al. 2003). As a result, climate-driven changes in sea urchin populations have the potential to profoundly affect the ecological structure and functioning of marine ecosystems and the economic value of the fisheries that they support. Much of the research on controls of sea urchin population dynamics has focused on the roles of predation and disease in controlling adult abundance and their cascading influence on community structure (e.g., Estes and Duggins 1995; Lafferty 2004; Filbee-Dexter and Scheibling 2014; Burt et al. 2018). Yet short-term empirical *Correspondence: [email protected] Additional Supporting Information may be found in the online version of this article. Author Contribution Statement: D.K.O., S.C.S., and D.C.R. designed research. D.K.O. designed, built, and conducted analyses and wrote the initial manuscript. D.K.O., D.C.R., and S.C.S. managed data. S.C.S. initiated and oversaw data collection and collaborated on all analyses. All authors contributed to revisions.