Spore priming by coastal upwelling in the intertidal kelp <i>Lessonia spicata</i>

The kelp populations of two cryptic species of Lessonia inhabiting the intertidal zone of the southeastern Pacific are vulnerable to local extinction and range contraction by being exposed to large-scale thermal extremes and strong harvesting by artisanal fisheries. Our study explored the effect of variable ocean temperature conditions on the germination of spores, a critical stage for post-disturbance persistence of local populations, including harvesting. Over a 15-month experimental period, we collected reproductive tissues from 10 tagged sporophytes of a wild local population of L. spicata in Central Chile (~33.5° S) and measured germination success. Reproductive activity closely tracked the presence of low (<14°C) ocean temperatures at the study site. Mean spore germination was over 80% from late Austral fall to late spring and sharply declined and became more variable under the warmer ocean conditions of summer and early fall. Unexpectedly, a mid-summer mesoscale upwelling event cooled seawater below 14°C, and spore germination success increased from <50% to up to 90%. Across the study period, germination showed a significant negative correlation with seawater temperature, down to a lag of 4 days prior to the collection of reproductive tissue. These results suggest both a temperature threshold and a temporal scale for spore priming in L. spicata, providing support to earlier hypotheses positing spatial heterogeneity in the upwelling regime as the leading driver of speciation in the Lessonia complex. Together, our results provide an important evolutionary insight for the conservation, restocking, and management of the Lessonia complex.