4:15 PM - 4:30 PM
[BPT03-09] Effects of the presence or absence of seaweeds on the physiological response of large benthic foraminifera under ocean acidification
Keywords:large benthic foraminifera, ocean acidification, interactions between organisms
Increased CO2 concentrations due to anthropogenic factors are causing ocean acidification (OA). OA reduces the pH and carbonate saturation states of seawater, which can negatively affect the growth of calcifying organisms such as corals and foraminifera. Large benthic foraminifera (LBF) are calcifying protists that inhabit coral reef waters and are more susceptible to OA than reef corals due to their easily soluble high Mg calcite shells. Studies on the response of LBF to OA have been conducted, but only a few studies have used culturing under conditions that mimic LBF habitats. In order to accurately predict the response of LBF under future climate change, it is necessary to conduct experiments under conditions close to their habitat and to study the effects of interactions with other organisms. In this study, LBF were cultured under mesocosms to examine how the presence or absence of seaweeds affects the physiological response of LBF to OA.
Two acidification experiments were carried out. The first experiment (Experiment 1) used Amphisorus kudakajimensis, while the second experiment (Experiment 2) used Amphisorus hemprichii and Calcarina gaudichaudii. One species of seaweed (the family Sargassaceae) was used as a habitat for those foraminifers. A total of four seawater conditions were prepared in both experiments: a control condition and an OA condition with a pH 0.3 lower than the control condition, combined with two conditions with and without seaweeds. In Experiment 1, the foraminifera were cultured for approximately one month from September to October 2023, and in Experiment 2 for approximately two weeks from August to September 2024, to measure seawater environmental parameters and to assess the physiological responses of the foraminifera.
In Experiments 1 and 2, daytime pH was higher in the the algal condition than the non-algal condition, while the nighttime pH was lower in the algal condition than in the non-algal condition. The calcification of Amphisorus kudakajimensis in Experiment 1 showed the mitigation of shell dissolution under the algal condition compared to the non-algal condition. Photosynthetic activity (Fv/Fm) and chlorophyll-a (chl a) contents of symbiotic algae increased in the algal condition compared to the non-algal condition, suggesting that the presence of seaweeds may have reduced the photoinhibition of algal symbionts. As in Experiment 1, the amount of chl a in Experiment 2 tended to increase in both foraminifera species in the algal condition compared to the no-algal condition. In Experiment 2, the propotion of the presence of pseudopodial extrusion as an indicator of the activity of foraminifers were the highest in the control algal condition for both foraminiferal species.
Results of these experiments indicate that seaweeds may alter ambient pH through their metabolism, positively affecting the calcification and metabolism in LBF with algal symbionts, and mitigating their negative effects on OA.
Two acidification experiments were carried out. The first experiment (Experiment 1) used Amphisorus kudakajimensis, while the second experiment (Experiment 2) used Amphisorus hemprichii and Calcarina gaudichaudii. One species of seaweed (the family Sargassaceae) was used as a habitat for those foraminifers. A total of four seawater conditions were prepared in both experiments: a control condition and an OA condition with a pH 0.3 lower than the control condition, combined with two conditions with and without seaweeds. In Experiment 1, the foraminifera were cultured for approximately one month from September to October 2023, and in Experiment 2 for approximately two weeks from August to September 2024, to measure seawater environmental parameters and to assess the physiological responses of the foraminifera.
In Experiments 1 and 2, daytime pH was higher in the the algal condition than the non-algal condition, while the nighttime pH was lower in the algal condition than in the non-algal condition. The calcification of Amphisorus kudakajimensis in Experiment 1 showed the mitigation of shell dissolution under the algal condition compared to the non-algal condition. Photosynthetic activity (Fv/Fm) and chlorophyll-a (chl a) contents of symbiotic algae increased in the algal condition compared to the non-algal condition, suggesting that the presence of seaweeds may have reduced the photoinhibition of algal symbionts. As in Experiment 1, the amount of chl a in Experiment 2 tended to increase in both foraminifera species in the algal condition compared to the no-algal condition. In Experiment 2, the propotion of the presence of pseudopodial extrusion as an indicator of the activity of foraminifers were the highest in the control algal condition for both foraminiferal species.
Results of these experiments indicate that seaweeds may alter ambient pH through their metabolism, positively affecting the calcification and metabolism in LBF with algal symbionts, and mitigating their negative effects on OA.