14:45 〜 15:00
[BPT03-05] Vertical distribution of planktonic foraminifera and its controlling environmental factors in the eastern South Pacific
キーワード：浮遊性有孔虫、水塊、群集組成、鉛直分布
Planktonic foraminifera are calcifying marine zooplankton that are used as a tool for palaeoceanographic study. However, ecological studies on planktonic foraminifera remain insufficient, often making interpretations of reconstructed paleoenvironmental information difficult. For example, planktonic foraminiferal habitat depths have been studied and conceptualized using stable oxygen isotope ratios preserved in their tests, and species were simply categorized into surface dwellers or deeper dwellers for instance. Such categorization is often useful; however, the actual range of their habitat depth is still poorly constrained even in the modern ocean. To address this issue, we focused on planktonic foraminiferal habitat depths, and aimed to reveal the environmental factors controlling the distribution of planktonic foraminifera species. We used statistical analysis using planktonic foraminiferal community data and the corresponding environment parameters.
The samples were collected off the coast of Peru in the eastern South Pacific Ocean during R/V Hakuho-maru Southern Pacific Cruise KH-19-6 using a Vertical Multiple Plankton Sampler. All planktonic foraminifera were picked up from a total of 21 samples, seven layers at each of three stations, St1 (10°S, 100°W), St3 (20°S, 90°W), and St5 (30°S, 90°W), and the number of individuals of each species was recorded. The vertical physicochemical data were obtained from CTD observations at the same stations. Here, water temperature, salinity, dissolved oxygen concentration, chlorophyll concentration, and density were used for the analysis. We considered the species composition per m3 as one community, and then conducted a multivariate statistical analysis (dbRDA) to examine correlations between the environmental parameters and the foraminiferal community.
We picked up 11,931 individuals and identified 39 species in 19 genera. Of the 49 extant planktonic foraminifera species, approximately 80% of the species were found from only three stations, indicating a high diversity. Cluster analysis of the community data showed that planktonic foraminifera communities were divided into four groups: shallower samples of St5 (group I), deeper samples of St5 (group II), shallower samples of St1 and 3 (group III), and deeper samples of St1 and 3 (group IV). The dbRDA results showed that all five parameters significantly affected the vertical distribution of the community, particularly the density of seawater, followed by temperature and salinity. Besides, differences between stations were associated with dissolved oxygen concentrations. Since the water mass structure in this area is characterized mainly by water temperature, salinity, and dissolved oxygen concentration, it suggests that differences in water mass structure may also be reflected in community composition. However, the five environmental parameters examined in this study could not sufficiently explain the differences in community composition. For example, nutrient concentrations and the density of other plankton that may interact with planktonic foraminifera can influence the foraminiferal community. If such biological parameters are considered together with the physicochemical parameters, a more detailed discussion of the factors affecting the foraminiferal community will be possible.
The samples were collected off the coast of Peru in the eastern South Pacific Ocean during R/V Hakuho-maru Southern Pacific Cruise KH-19-6 using a Vertical Multiple Plankton Sampler. All planktonic foraminifera were picked up from a total of 21 samples, seven layers at each of three stations, St1 (10°S, 100°W), St3 (20°S, 90°W), and St5 (30°S, 90°W), and the number of individuals of each species was recorded. The vertical physicochemical data were obtained from CTD observations at the same stations. Here, water temperature, salinity, dissolved oxygen concentration, chlorophyll concentration, and density were used for the analysis. We considered the species composition per m3 as one community, and then conducted a multivariate statistical analysis (dbRDA) to examine correlations between the environmental parameters and the foraminiferal community.
We picked up 11,931 individuals and identified 39 species in 19 genera. Of the 49 extant planktonic foraminifera species, approximately 80% of the species were found from only three stations, indicating a high diversity. Cluster analysis of the community data showed that planktonic foraminifera communities were divided into four groups: shallower samples of St5 (group I), deeper samples of St5 (group II), shallower samples of St1 and 3 (group III), and deeper samples of St1 and 3 (group IV). The dbRDA results showed that all five parameters significantly affected the vertical distribution of the community, particularly the density of seawater, followed by temperature and salinity. Besides, differences between stations were associated with dissolved oxygen concentrations. Since the water mass structure in this area is characterized mainly by water temperature, salinity, and dissolved oxygen concentration, it suggests that differences in water mass structure may also be reflected in community composition. However, the five environmental parameters examined in this study could not sufficiently explain the differences in community composition. For example, nutrient concentrations and the density of other plankton that may interact with planktonic foraminifera can influence the foraminiferal community. If such biological parameters are considered together with the physicochemical parameters, a more detailed discussion of the factors affecting the foraminiferal community will be possible.