Drivers of kelp recruitment across a reef landscapeMacroecology

Billie Beckley¹, Tom Bell², Kate Cavanaugh³, Max Castorani⁴, Kyle Cavanaugh³, Frankie Puerzer¹, Robert Miller¹

¹University of California Santa Barbara, USA, ²Woods Hole Oceanographic Institute, USA, ³University of California Los Angeles, USA, ⁴University of Virginia, USA

Understanding how and why populations vary in space and time is a fundamental goal in ecology. Water temperature, nutrients, and wave disturbance are known regional drivers of giant kelp, Macrocystis pyrifera, populations. However, drivers of kelp recruitment on local scales (< 2 km) remain elusive, as recruitment often exhibits uncorrelated spatial dynamics due to environmental and biotic factors, such as substrate and light availability, herbivory, and competition, that can vary at small scales and influence recruitment success. To address this gap, we carried out a field survey campaign with high spatial (55 5x5 m2 plots) and temporal (10 consecutive months) resolution, which included quantifying giant kelp recruitment and hypothesized abiotic and biotic drivers across a reef off Santa Barbara, CA, USA. Our findings reveal a strong positive correlation between kelp recruits (<1 m tall) and benthic light availability. As kelp plants grew larger (>1m tall) their presence was linked to substrate characteristics, particularly percent cover of silt-covered substrate. These results increase our understanding of how small-scale variation in resource availability and biotic interactions can influence giant kelp recruitment location and success across a reefscape.