Exploratory evaluation of the effects of Kelpak® seaweed extract on cultivated kelp Saccharina spp. exposed to sublethal and lethal temperatures

Kelpak® is a seaweed extract from the phaeophyte, Ecklonia maxima, used to enhance growth and production of terrestrial plants. It is also beneficial for some red and green seaweeds. As such, we assessed if Kelpak® could enhance growth and thermal tolerance of the brown seaweeds, Saccharina latissima and S. angustissima. Juvenile sporophytes were dipped (30 or 60 min) in Kelpak® solutions of different concentrations (0.001, 0.005, 0.05, 1, and 5 ml L−1). These sporophytes were then cultivated in half‐strength PES at different temperatures (12, 16, 19, 23 and 25°C ± 1) for 20 days. The surviving sporophytes were then moved to 18 ± 1°C and cultivated for 14 additional days. Results show that temperature was the main factor driving survival and growth. Both species exposed to the temperatures of 23 and 25°C died during the first 7 days. Furthermore, no significant differences were observed in growth of sporophytes at the temperatures of 12 and 16°C. Results also show that treated sporophytes exposed to 18°C, the sublethal temperature, particularly of S. angustissima showed a higher survival and overall vigor than nontreated sporophytes. These results indicate that Kelpak® may enhance thermal tolerance and growth of S. latissima and S. angustissima exposed to sublethal temperatures.