11:15 〜 11:30
[BCG07-09] 飼育実験から探る光共生性浮遊性有孔虫の地球温暖化応答
キーワード：浮遊性有孔虫、飼育実験、光共生、地球温暖化
Photosymbiosis, the intracellular symbiosis with microalgae, is an important trophic strategy for various marine organisms living in warm, oligotrophic waters. Recently, concerns have been raised about the negative impacts of global warming on photosymbiosis, particularly the bleaching phenomenon observed in reef-building corals. In contrast, there have been no reports of bleaching in planktonic foraminifera, although some species within this group also host symbiotic algae similar to corals. In fact, during past global warming events, such as the Paleocene/Eocene thermal maximum (PETM), the photosymbiotic group of foraminifera rather thrived and contributed to diversity increase. This suggests that foraminifera may have adapted well to global warming through their photosymbiotic ecology. However, it remains unclear how modern photosymbiotic planktonic foraminifera respond to elevated water temperatures. In this study, we conducted culturing experiments with foraminifera and their symbiotic algae to investigate their potential for adaptation to high temperatures (thermotolerance) and to assess changes in their physiological state (photophysiology) under increased temperature conditions.
The experiments were conducted at three different temperatures: 19.5°C (low-temperature group), 24.5°C (control group), and 32°C (high-temperature group) using a photosymbiotic species Trilobatus sacculifer in association with dinoflagellate (Pelagodinium béii). In addition to observing the condition of the organisms under a microscope, we evaluated the response to each temperature condition using photophysiological parameters as indices. Unexpectedly, no significant differences were observed in photophysiology among the groups. The highest temperature set (32°C) is an extreme temperature for natural marine environments and is typically associated with coral bleaching; however, the foraminifera exhibited normal growth, and the chlorophyll concentration per individual—indicative of symbiotic algal biomass—actually increased. These results suggest that foraminifera exhibit a high tolerance to high temperatures.
We also examined the temperature responses of P. béii’s isolate (in free-living state), and in contrast to the above results, they ceased to grow even at 30°C and demonstrated low photosynthetic activity. This indicates that P. béii inside foraminifera is more resilient to high-temperature stress compared to its free-living state. This finding suggests that the host may protect the symbiotic algae from temperature-related stress through some mechanism. Further studies are necessary, but our research indicates that the photosymbiotic relationship serves not only as a nutritional strategy but may also provide shelter for symbiotic algae during periods of high water temperature stress.
The experiments were conducted at three different temperatures: 19.5°C (low-temperature group), 24.5°C (control group), and 32°C (high-temperature group) using a photosymbiotic species Trilobatus sacculifer in association with dinoflagellate (Pelagodinium béii). In addition to observing the condition of the organisms under a microscope, we evaluated the response to each temperature condition using photophysiological parameters as indices. Unexpectedly, no significant differences were observed in photophysiology among the groups. The highest temperature set (32°C) is an extreme temperature for natural marine environments and is typically associated with coral bleaching; however, the foraminifera exhibited normal growth, and the chlorophyll concentration per individual—indicative of symbiotic algal biomass—actually increased. These results suggest that foraminifera exhibit a high tolerance to high temperatures.
We also examined the temperature responses of P. béii’s isolate (in free-living state), and in contrast to the above results, they ceased to grow even at 30°C and demonstrated low photosynthetic activity. This indicates that P. béii inside foraminifera is more resilient to high-temperature stress compared to its free-living state. This finding suggests that the host may protect the symbiotic algae from temperature-related stress through some mechanism. Further studies are necessary, but our research indicates that the photosymbiotic relationship serves not only as a nutritional strategy but may also provide shelter for symbiotic algae during periods of high water temperature stress.