Meeting Abstract
Bull kelp (Nereocystis luetkeana) is the dominant subtidal canopy architect in the Salish Sea, providing important habitat for many species and supplying primary production to food webs within and below the photic zone. Like other kelp, N. luetkeana has a complicated life history, alternating between microscopic (zoospore, gametophyte) and macroscopic stages; unlike many other kelps, it is an annual that must complete its lifecycle within a single year. Focusing primarily on juvenile bull kelp (sporophyte, stipe < 30 cm), we investigated the effects of competition and propagule availability on sporophyte appearance in a factorial-design subtidal field experiment. In the lab, we quantified differences of morphological scaling and material properties as well as the effects of temperature on the microscopic zoospore, gametophyte, and sporophyte stages. Our results indicate that bull kelp are probably not propagule-limited at our study sites and competition from understory species is the most important factor determining where juvenile bull kelp sporophytes grow and persist, with some variability in initiation of growth between plots established in different seasons. We also calculate a “breakpoint” between juvenile and adult morphological scaling. Additionally, we show that increasing temperatures may limit zoospore settlement and transitions between microscopic life stages, which has important implications for the fate of this foundation species, and the communities it structures, as global ocean conditions change. Our findings also highlight the importance of studying organisms with complex life histories across multiple stages because of the different factors that dictate their success across ontogeny.
