11:00 〜 11:15
[BCG05-02] Environmental factors affecting planktonic foraminiferal photosymbiosis: Analysis using ForCens and satellite data
★Invited Papers
キーワード：浮遊性有孔虫、光共生、ForCensデータベース
Paleobiodiversity dynamics of planktonic foraminifera have been suggested to be strongly related to climate change. In recent years, it has been pointed out that the species ecology (photosymbiosis and habitat depth) is also involved in such diversity dynamics. Therefore, further understanding of the interaction between ecology and the environment is required. Photosymbiotic planktonic foraminifera are mainly distributed in subtropical waters, and it is considered that photosymbiosis is adaptive to oligotrophic environments. However, the specific environmental factors that determine photosymbiotic species distribution remain unclear. In this study, to examine the factors regulating photosymbiosis, we conducted statistical modeling using ForCenS (Siccha and Kucera, 2017), a recently published global database of planktonic foraminiferal communities in surface sediments, and environmental data from satellite observations.
We firstly generated a new parameter of photosymbiosis as the objective variable. Here, information on photosymbiosis based on Takagi et al. (2019) was applied, and photosymbiosis-related variables (percentage of photosymbiotic individuals, percentage of photosymbiotic species, and the number of photosymbiotic species) were calculated for each foraminiferal community data of ForCens database. Three variables were integrated as a new parameter through principal component analysis (PCA). Five environmental factors assumed to be related to photosymbiosis were used as explanatory variables: surface water temperature (SST), primary production (NPP), chlorophyll concentration (CHL), mixed layer depth (MLD), and photosynthetically active radiation (PAR). Those were analyzed using a generalized additive model (GAM).
The PCA results showed that 90.4% of the information was explained by the first principal component (PC1), thus we here use PC1 as “photosymbiosis index”. The results of GAM analysis using photosymbiosis index as the objective variable showed that all environmental factors were significantly related to photosymbiosis, and that photosymbiosis index increased at temperatures above approximately 20°C. On the other hand, the positive effect weakened at temperatures above 27°C, suggesting that the fitness of photosymbiosis is slightly reduced at extremely high temperatures. With regard to PAR, a negative effect was observed below about 13 mol m-2 d-1, indicating that the lower the daily irradiance, the lower the photosymbiosis index. The evaluation of the contribution of variables in the model showed the highest contribution of SST, indicating that water temperature is the most important factor in determining photosymbiosis. The relationship between photosymbiosis and environmental factors revealed in this study suggests that planktonic foraminifera community may change to a more photosymbiotic species-dominated one in the future warmer Earth.
We firstly generated a new parameter of photosymbiosis as the objective variable. Here, information on photosymbiosis based on Takagi et al. (2019) was applied, and photosymbiosis-related variables (percentage of photosymbiotic individuals, percentage of photosymbiotic species, and the number of photosymbiotic species) were calculated for each foraminiferal community data of ForCens database. Three variables were integrated as a new parameter through principal component analysis (PCA). Five environmental factors assumed to be related to photosymbiosis were used as explanatory variables: surface water temperature (SST), primary production (NPP), chlorophyll concentration (CHL), mixed layer depth (MLD), and photosynthetically active radiation (PAR). Those were analyzed using a generalized additive model (GAM).
The PCA results showed that 90.4% of the information was explained by the first principal component (PC1), thus we here use PC1 as “photosymbiosis index”. The results of GAM analysis using photosymbiosis index as the objective variable showed that all environmental factors were significantly related to photosymbiosis, and that photosymbiosis index increased at temperatures above approximately 20°C. On the other hand, the positive effect weakened at temperatures above 27°C, suggesting that the fitness of photosymbiosis is slightly reduced at extremely high temperatures. With regard to PAR, a negative effect was observed below about 13 mol m-2 d-1, indicating that the lower the daily irradiance, the lower the photosymbiosis index. The evaluation of the contribution of variables in the model showed the highest contribution of SST, indicating that water temperature is the most important factor in determining photosymbiosis. The relationship between photosymbiosis and environmental factors revealed in this study suggests that planktonic foraminifera community may change to a more photosymbiotic species-dominated one in the future warmer Earth.