The potential of kelp holobionts and their microbiomes to provide resilience to their hosts under temperature stress

• Main Author: Yuan, Mengfei
• Publication Date: 2023
• Format: Master thesis
• Language: eng
• Source: Repositórios Científicos de Acesso Aberto de Portugal (RCAAP)
• Download full: http://hdl.handle.net/10400.1/20754
• topic: Brown alga; Gametogenesis; Thermal adaptation; Bacteria; Kelp

Marine ecosystems, particularly kelp forests, are critical habitats for diverse marine organisms and support productive fishing grounds. However, rapid ocean warming due to climate change has imposed physiological stress on kelp, threatening these forests. Heterotrophic bacteria on kelp surfaces play a crucial role in nitrogen fixation and growth promotion, and the microbiome's stability influences the kelp's recovery from environmental disturbances. This study aims to determine if introducing bacterial communities can improve the health and heatwave resistance of Laminaria. ochroleuca. Bacterial inoculation from L. ochroleuca sporophytes and gametophytes is used to manipulate the kelp's microbiome, potentially enhancing its resistance to temperature increases. We specifically examine the physiological responses of L. ochroleuca gametophytes under different temperature treatments (13°C, 23°C, 25°C, and 27°C) and their subsequent recovery capacity, including gametophyte density and reproductive performance. In the recovery period, results indicate that bacterial communities enhance gametophyte density, promoting kelp recovery under the 23°C heatwave treatment but not in the 25°C and 27°C treatments. There was a significant interaction between heat wave temperature on the density of female gametophytes and heat wave temperature x bacterial treatment on the density of male gametes. Bacterial inoculation increases female gametophyte density at 23°C and male gametophyte density at 25°C. The density of gametophytes decreased significantly with time at 27°C treatments compared to other temperatures. Furthermore, bacterial communities reduce male gametophytes in the 13ºC control, 23°C heatwave treatment, and 25°C heatwave treatment. Bacterial intervention facilitates the transition from the vegetative stage to egg production at 23°C treatment. In sporophyte development, bacteria slightly reduce normal sporophytes at 25°C while significantly increasing asexual sporophytes at 23°C.The primary findings of this study reveal that male gametophytes exhibit a higher sensitivity to temperature and are also more responsive to changes in bacterial communities compared to female gametophytes, which differs from previous research. This heightened sensitivity leads to an increase in asexual sporophytes under heatwave conditions. Additionally, it was observed that at the highest temperature allowing gametophyte survival, bacterial communities can, to some extent, aid in the development of female gametophytes. In conclusion, this study underscores the impact of temperature stress on the development and reproduction of L. ochroleuca and sheds light on the effects of bacterial communities as a treatment on the recovery of L. ochroleuca following temperature stress. It highlights the diverse effects of bacterial inoculation, providing crucial insights into complex interactions within kelp forests. These findings are essential for enhancing the resilience of this ecosystem-engineering species in the face of global ocean warming.