Abalone Recruitment in Low-Density and Aggregated Populations Facing Climatic Stress

Understanding spatial and temporal patterns in the recruitment of marine invertebrates with complex life histories remains a critical knowledge gap in marine ecology and fisheries. As marine invertebrates are facing multiple stressors from overfishing and climatic stress, it is important to evaluate the conditions that facilitate recruitment in low-density populations. The red abalone Haliotis rufescens historically supported an economically important fishery in California, but the fishery was sequentially closed as stocks declined, and the last fished area was closed in 2018 following the collapse of the kelp forests in Northern California. Here, red abalone recruitment was evaluated annually from 2012 to 2016 and monthly from 2016 to 2017 in Central California where red abalone naturally occur in highly aggregated but low-density populations because of sea otter predation. Trends in wind-driven upwelling, temperature, wave forces, and food resources (kelp) were evaluated over the same time period as factors that could affect recruitment patterns. Recruitment was annually consistent except in 2015, when recruitment declined by 76%, likely because of reproductive failure during the second year of the North Pacific marine heat wave. The monthly recruitment assessment was the first field assessment of red abalone recruitment over a full year, and it showed that red abalone can recruit year-round. There were no clear recruitment patterns associated with seasonal wind-driven upwelling or relaxation patterns, and kelp density was constant over the study period; however, conditions at the study sites included three key features that may provide optimal conditions for consistent recruitment: (1) spatial abalone aggregation, (2) a sheltered embayment that may retain larvae, and (3) persistent algal food resources. These results can inform statewide and global abalone recovery and management programs.