SUMMARYThere are dramatic and physiologically relevant changes in both skylight color and intensity during evening twilight as the pathlength of direct sunlight through the atmosphere increases, ozone increasingly absorbs long wavelengths and skylight becomes increasingly blue shifted. The moon is above the horizon at sunset during the waxing phase of the lunar cycle, on the horizon at sunset on the night of the full moon and below the horizon during the waning phase. Moonlight is red shifted compared with daylight, so the presence, phase and position of the moon in the sky could modulate the blue shifts during twilight. Therefore, the influence of the moon on twilight color is likely to differ somewhat each night of the lunar cycle, and to vary especially rapidly around the full moon, as the moon transitions from above to below the horizon during twilight. Many important light-mediated biological processes occur during twilight, and this lunar effect may play a role. One particularly intriguing biological event tightly correlated with these twilight processes is the occurrence of mass spawning events on coral reefs. Therefore, we measured downwelling underwater hyperspectral irradiance on a coral reef during twilight for several nights before and after the full moon. We demonstrate that shifts in twilight color and intensity on nights both within and between evenings, immediately before and after the full moon, are correlated with the observed times of synchronized mass spawning, and that these optical phenomena are a biologically plausible cue for the synchronization of these mass spawning events.

The changing global climate is having profound effects on coastal marine ecosystems around the world. Structure, functioning, and resilience, however, can vary geographically, depending on species composition, local oceanographic forcing, and other pressures from human activities and use. Understanding ecological responses to environmental change and predicting changes in the structure and functioning of whole ecosystems require large-scale, long-term studies, yet most studies trade spatial extent for temporal duration. We address this shortfall by integrating multiple long-term kelp forest monitoring datasets to evaluate biogeographic patterns and rates of change of key functional groups (FG) along the west coast of North America. Analysis of data from 469 sites spanning Alaska, USA, to Baja California, Mexico, and 373 species (assigned to 18 FG) reveals regional variation in responses to both long-term (2006-2016) change and a recent marine heatwave (2014-2016) associated with two atmospheric and oceanographic anomalies, the "Blob" and extreme El Niño Southern Oscillation (ENSO). Canopy-forming kelps appeared most

Sea Grant. She studies dynamics of marine systems and how we can manage ecosystems for long term sustainability. This work was completed as a postdoctoral researcher at Stanford University's Hopkins Marine Station. 2 Fiorenza Micheli is a Professor at Hopkins Marine Station of Stanford University and a Senior Fellow at Stanford's Woods Institute for the Environment. Her research focuses on the ecology and conservation of coastal marine ecosystems. 3 Laura Airoldi is a marine ecologist at the University of Bologna She studies what factors facilitate the recovery and restoration of damaged marine ecosystems. 4 Charles Boch is a postdoctoral fellow at the Monterey Bay Aquarium Research Institute. He studies biological response to global and local environmental drivers. 5 Giulio De Leo is a Professor at Hopkins Marine Station of Stanford University and a Senior Fellow at Stanford's Woods Institute for the Environment. He studies theoretical ecology focused on disease ecology, marine conservation, and public health. 6 Robin Elahi is an ecologist at Hopkins Marine Station of Stanford University. He studies the drivers of biodiversity change in marine ecosystems. 7 Francesco Ferretti is a quantitative and computational marine ecologist at Hopkins Marine Station of Stanford University. He studies ecosystem baselines and the effect of human impact on marine ecosystems.

Main Points ‐Responses to climate change and large‐scale forcing can vary widely at local scales creating marine microclimates. ‐Microclimates are robust even under extreme large‐scale forcing events (ENSO, climate change) potentially creating spatial refuges or ‘safe spaces’ for important species. ‐Small/medium no‐take zones, artificial reefs, and other possible spatial management can be placed to harness local variability as an adaptation or conservation measure in the face of climate change.