2:25 PM - 2:45 PM
[O06-03] Complete loss of plants on Nishinoshima Island by volcanic eruptions and new invasion of plants
★Invited Papers
Keywords:volcanic island, vascular plants, Algae, Aerial algae
Nishinoshima is a volcanic island that continues to erupt, and the eruptions from 2013 to 2020 eradicated the vascular plants that had been growing there until now. This means that photosynthetic plants, which produce organic matter through photosynthesis in terrestrial ecosystems, have disappeared from the entire island. In order to understand the ecosystem formation process from such a situation, it is necessary to consider not only large plants such as vascular plants, but also the invasion process of micro-plants such as algae. In this presentation, we will introduce the changes in the flora since 2013, focusing on vascular plants and algae confirmed before and after the eruption.
Before the eruption in 2013, six species of vascular plants lived on Nishinoshima: Eleusine indica, Portulaca oleracea, Echinochloa crus-galli, Ipomoea pes-caprae, Vitex rotundifolia, Tetragonia tetragonoides. However, three species became extinct due to the eruptions since 2013, and only three species, E. indica, P. oleracea, and E. crus-galli, grow on the land that existed before the 2013 eruption (old island part). Furthermore, these plants also became extinct due to the disappearance of the old island part due to eruptions since 2019. On the other hand, in 2019, aerial algae growing on the lava of the old island part were confirmed and collected, and in 2022, algae growing on eruption deposits since 2020 were confirmed and collected. Although no surveys of microscopic plants such as algae had been conducted before 2019, the importance of algae as the earliest plants to invade newly formed volcanic islands was demonstrated.
The collected aerial algae and algae were cultured, and then morphological observations and molecular phylogenetic analysis using 18S rDNA and ITS rDNA sequences were performed. As a result, the aerial algae collected in 2019 was a species belonging to Chloroidium in the Trebouxiophyceae, Watanabeales, and was considered to be an undescribed species. On the other hand, the algae collected in 2022 was identified as Micractinium thermotolerans, a green alga belonging to the Trebouxiophyceae. This species has been found in hot springs in Russia and deserts in China, and is considered to be highly heat-resistant. Since it has been confirmed from such extremely remote and special regions, it is believed that its high dispersal ability and resistance to environmental pressures such as high heat enabled this species to invade Nishinoshima. The undescribed species of the genus Chloroidium may have differentiated on Nishinoshima, but considering the high dispersal ability of aerial algae, it is possible that it was an undiscovered, widely distributed species. In further study, it is necessary to examine the role of wind and seabirds in the dispersal of these algae, the physiological characteristics that allow them to survive in harsh environments, whether they form sustainable populations on Nishinoshima, and whether has the function of forming an ecosystem, such as accumulating organic matter. For this reason, it is important to conduct field surveys, including automatic sampling on Nishinoshima.
Before the eruption in 2013, six species of vascular plants lived on Nishinoshima: Eleusine indica, Portulaca oleracea, Echinochloa crus-galli, Ipomoea pes-caprae, Vitex rotundifolia, Tetragonia tetragonoides. However, three species became extinct due to the eruptions since 2013, and only three species, E. indica, P. oleracea, and E. crus-galli, grow on the land that existed before the 2013 eruption (old island part). Furthermore, these plants also became extinct due to the disappearance of the old island part due to eruptions since 2019. On the other hand, in 2019, aerial algae growing on the lava of the old island part were confirmed and collected, and in 2022, algae growing on eruption deposits since 2020 were confirmed and collected. Although no surveys of microscopic plants such as algae had been conducted before 2019, the importance of algae as the earliest plants to invade newly formed volcanic islands was demonstrated.
The collected aerial algae and algae were cultured, and then morphological observations and molecular phylogenetic analysis using 18S rDNA and ITS rDNA sequences were performed. As a result, the aerial algae collected in 2019 was a species belonging to Chloroidium in the Trebouxiophyceae, Watanabeales, and was considered to be an undescribed species. On the other hand, the algae collected in 2022 was identified as Micractinium thermotolerans, a green alga belonging to the Trebouxiophyceae. This species has been found in hot springs in Russia and deserts in China, and is considered to be highly heat-resistant. Since it has been confirmed from such extremely remote and special regions, it is believed that its high dispersal ability and resistance to environmental pressures such as high heat enabled this species to invade Nishinoshima. The undescribed species of the genus Chloroidium may have differentiated on Nishinoshima, but considering the high dispersal ability of aerial algae, it is possible that it was an undiscovered, widely distributed species. In further study, it is necessary to examine the role of wind and seabirds in the dispersal of these algae, the physiological characteristics that allow them to survive in harsh environments, whether they form sustainable populations on Nishinoshima, and whether has the function of forming an ecosystem, such as accumulating organic matter. For this reason, it is important to conduct field surveys, including automatic sampling on Nishinoshima.