Differential response of gametophyte and sporophyte priming to heat stress of Saccharina latissima sporophytes across different age classes

Elevated ocean temperatures increasingly threaten wild and cultivated kelps. Ensuring sustainable seaweed production under future climate scenarios requires resilient kelp strains capable of withstanding thermal stress. Priming serves as a short-term, complementary approach to breeding, by introducing moderate stress to enhance performance under subsequent stress exposure. We hypothesized that thermal priming of Saccharina latissima would induce a physiological ‘stress memory’ enhancing heat tolerance within and across generations. To evaluate transgenerational plasticity, we primed haploid gametophytes (0, 10, 20°C; 3 wk) and assessed the heat tolerance of subsequent diploid sporophytes (microscopic, juvenile, adult) under heat stress. Priming at 20°C increased survival of microscopic sporophytes after 1 wk of heat stress, although this effect was transient and not detectable in juvenile or adult sporophytes. Priming at 20°C showed a trend towards improved regrowth of juvenile sporophytes after a heatwave (10-24°C, 2 wk). To evaluate intragenerational plasticity, we subjected adult sporophytes to a priming trigger (21.5°C; 1 d), with or without prior heatwave exposure (5-20°C, 1 wk) and assessed heat tolerance (20-25°C; 1 wk). Brief exposure of adult sporophytes to 21.5°C enhanced thermal tolerance. When the priming trigger followed a heatwave, thermal tolerance was slightly enhanced compared to priming alone. Our findings demonstrate that warm priming can improve heat tolerance in S. latissima , but effects are transient, stage-dependent, and of limited magnitude. These results highlight the potential of priming for enhancing kelp resilience, but also emphasize the need for further research into the mechanisms, stability, and practical applications of priming for kelps.