Understanding species' responses to upwelling may be especially important in light of ongoing environmental change. Upwelling frequency and intensity are expected to increase in the future, while ocean acidification and deoxygenation are expected to decrease the pH and dissolved oxygen (DO) of upwelled waters. However, the acute effects of a single upwelling event and the integrated effects of multiple upwelling events on marine organisms are poorly understood. Here, we use in situ measurements of pH, temperature, and DO to characterize the covariance of environmental conditions within upwelling-dominated kelp forest ecosystems. We then test the effects of acute (0-3 days) and chronic (1-3 months) upwelling on the performance of two species of kelp forest grazers, the echinoderm, Mesocentrotus franciscanus, and the gastropod, Promartynia pulligo. We exposed organisms to static conditions in a regression design to determine the shape of the relationship between upwelling and performance and provide insights into the potential effects in a variable environment. We found that respiration, grazing, growth, and net calcification decline linearly with increasing upwelling intensity for M. francicanus over both acute and chronic timescales. Promartynia pulligo exhibited decreased respiration, grazing, and net calcification with increased upwelling intensity after chronic exposure, but we did not detect an effect over acute timescales or on growth after chronic exposure. Given the highly correlated nature of pH, temperature, and DO in the California Current, our results suggest the relationship between upwelling intensity and growth in the 3-month trial could potentially be used to estimate growth integrated over long-term dynamic oceanographic conditions for M. franciscanus. Together, these results indicate current exposure to upwelling may reduce species performance and predicted future increases in upwelling frequency and intensity could affect ecosystem function by modifying the ecological roles of key species.

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Cabrillo National Monument (CABR) is a unit of the National Park System located on the Point Loma peninsula in San Diego, CA, USA. Despite its small size (0.65 terrestrial km2), the monument attracts 851,000 annual visitors (IRMA SRSS Reports 2011-2020), and acts as an “urban island”, providing habitat for unique algal, plant and animal species in an area of increasing development and urbanization. The coastal area of the park also leads to the rocky intertidal zone, which is regarded by many as the best conserved shorelines in mainland southern California. Due to the high-quality habitat and proximity to an urban area, it is critical to monitor community composition and visitor use of the rocky intertidal area. We leveraged over 30 years of long-term monitoring data of both rocky intertidal communities and visitation to investigate: (1) whether visitation has increased over time, (2) if community composition has changed over time across intertidal management zones. We found that visitation to management Zone I has increased over time. Additionally, we found that visitation doesn’t scale linearly across management zones: 73% of people were observed in Zone I, 19% of people in Zone II, and 4% of people in Zone III. PERMANOVA analyses indicated that community composition differed over time and across management zones for all plot types. Documenting community shifts, rather than changes in populations of single species, allows NPS staff to capture, and respond to, ecological transformation. Using the Resist-Accept-Direct (RAD) framework, we recommend that CABR either accept or direct changes to the rocky intertidal (e.g., directing changes in higher visitation areas by implementing a timed entry or shuttle system, and accepting changes in closed or very low visitation areas). Looking forward, long-term rocky intertidal monitoring will inform the effectiveness of resisting, accepting, or directing actions the park takes to uphold the NPS mission at CABR and other NPS units with rocky intertidal habitat, which span the Pacific coast.