Award: OCE-1630474

How is the abundance of animals without backbones influenced by unpredictable ocean conditions? In a 3 year study in Southern California, with funding from an NSF RAPID proposal in the last year, we observed the development of the ?Blob?? and El Niño, two disturbances that affected large sections of the US West coast and beyond. During the back-to-back events, spanning from fall 2014 to spring 2016, waters warmed, and the sea level rose a few centimeters before returning to normal conditions. Through our study, we counted barnacle larvae from samples of water taken near the shore (at stations from 4 to 12 m water depth), and we followed the number of larvae settling in the shore, where adults live. We also measured water temperature, wave height, and currents. During the Blob and El Niño, the abundance of larvae in the water and those settling at the shore decreased significantly relative to normal conditions. Importantly, we discovered that the temperature depth-gradient, the temperature difference from surface to bottom also known as ?thermal stratification?, also decreased during these events. Changes in thermal stratification may have impacted the abundance of larvae near the shore by scrambling the physical mechanisms barnacle larvae use to transport to the shore. Elevated water temperatures might also have affected the number of larvae spawned at the shore. Overall, this research suggests that thermal stratification is a key variable to study the effects of changing ocean conditions on the distribution and abundance of coastal animals. Individuals involved in this study had a chance to learn about the broad interdisciplinary research topic, including the importance in considering marine animal distribution and abundance in the context of hydrodynamic processes, as well as the opportunity to train in various laboratory and field techniques. This included three undergraduate students (USD), one graduate student (USD), and four technicians (3 from USD and 1 from WHOI). More broadly, our findings provides strong evidence that thermal stratification is an important tool to evaluate how varying ocean conditions influence the dynamics of marine animals, and thus offers a way to look toward comprehending marine population change in the face of changing environmental conditions. Last Modified: 01/23/2019 Submitted by: Nathalie Reyns