Effects of sori incubation temperature on Nereocystis luetkeana gametophyte and sporophyte development

Abstract

Climate change is affecting marine ecosystems around the world, including those in the Northeastern Pacific Ocean. Warming ocean temperatures have been linked to kelp forest declines, including bull kelp (Nereocystis luetkeana) forests in the Salish Sea. However, the temperature tolerances of different stages of the N. luetkeana life cycle are not well established. This project examined the effects of a short-term marine heatwave on N. luetkeana sori and subsequent life stages, including gametophytes and embryonic sporophytes. We incubated mature sori at temperatures of 18°C, 20°C, and 21°C for 3.75 days, and grew the gametophytes from each sori treatment at both 10°C and 16°C for 40 days. Gametophytes were able to develop normally and produce sporophytes from sori incubated at all temperatures, but gametophyte incubation temperature had significant impacts on the life cycle. Gametophytes grew larger and at a faster rate at 16°C compared to 10°C; however, sporophytes developed more quickly and were more abundant when gametophytes were grown at 10°C. Sorus incubation temperature affected the life cycle as well; when sori were incubated at 21°C, gametophytes were more numerous but fewer sporophytes developed, regardless of gametophyte incubation temperature. Our findings suggest that sori can withstand temporary high temperatures and produce zoospores that develop into gametophytes and sporophytes, completing the life cycle, but if gametophytes experience high temperatures the development of sporophytes may be hindered. A decrease in sporophyte development, i.e. fewer individuals completing their life cycle, could lead to loss of important kelp forest habitat. However, it is important to note that all temperature treatments did produce sporophytes, indicating that it is possible for life cycle completion to occur. Further research should identify the impacts of prolonged temperature stress (>3 days) on sorus development and microscopic life stages.