5:15 PM - 7:15 PM
[BCG07-P08] Vertical and horizontal distribution of planktonic foraminiferal community and water mass structure in the eastern South Pacific
Keywords:planktonic foraminifera, water mass, community composition, test size
Planktonic foraminifera are calcifying zooplankton that are widely distributed in the surface oceans around the world and play important roles in the marine carbonate cycle. It is also pointed out that planktonic foraminifera respond to various environmental changes sensitively. Recent studies have suggested that due to global warming and ocean acidification, they are at risk of shrinking habitats, changing diversity, and decreasing populations. Consequently, planktonic foraminifera can be used as an indicator organism for understanding changes in marine ecosystems and evaluating the biodiversity shifts in response to multiple stressors.
To address these issues, a working group has been established to create a global database of planktonic foraminiferal communities. Data on planktonic foraminiferal habitats is expected to become a powerful tool for providing the first global spatial distribution of micro-zooplankton in the ocean. Moreover, not only such community data but also quantitative data on their distribution in the modern ocean are required. Currently, there are many blank areas of such data, particularly in the Pacific Ocean. Therefore, we selected the eastern South Pacific for our study, where planktonic foraminiferal habitats are poorly understood. In this study, we investigated the horizontal and vertical community distribution and size variation of planktonic foraminifera, examining their relationships with various environmental parameters that may affect their structure.
We used plankton samples off the coast of Peru collected at five stations between 10-30°S and 90-100°W during the R/V Hakuho Maru KH-19-6 research cruise. Samples were collected using a vertical multiple plankton sampler (VMPS) from seven layers: 0-20 m, 20-50 m, 50-100 m, 100-150 m, 150-200 m, 200-500 m, and 500-1000 m. We picked up all planktonic foraminiferal tests including juveniles, identified the species, separated them into “living” or “dead” based on the presence or absence of cytoplasm, and calculated the number of individuals per cubic meter. Then, we correlated each community with environmental parameters obtained from CTD observations at the same stations. Finally, we measured the test size of all planktonic foraminifera samples and examined their vertical and horizontal distribution.
20,372 individuals, both “living” and “dead”, were identified into 39 species within 19 genera. As a result of classifying the community data by hierarchical cluster analysis, the planktonic foraminiferal communities were divided vertically into surface communities and mid-deep communities. The mid-deep communities were further subdivided horizontally into St1-3 and St4-5. These distributions were closely related to the prevailing water mass structure in this area. The surface community was associated with the distribution of Subtropical Surface Water, which covered the entire area of the sampling stations. The community differences between stations in the mid-deep layer seemed to correspond to the water mass boundaries between Equatorial Subsurface Water with low dissolved oxygen concentration (DO), and Eastern South Pacific Intermediate Waters with relatively higher DO, distributed in the south. These correlations with environmental parameters were also consistent with dbRDA analysis.
The horizontal distribution of test size was similar in St1-4, with a slight trend toward smaller size in St5. Vertically, the smallest individuals were distributed in the surface water, while the larger ones were at deeper depths. This suggests that planktonic foraminifera change their habitat depth through their growth.
In our future research, we plan to study both plankton net samples and annual samples of sediment trap in the eastern North Pacific. To further understand the effects of environmental changes on planktonic foraminiferal community dynamics, we plan to consider not only spatial but also time series changes, e.g., seasonal and annual variations.
To address these issues, a working group has been established to create a global database of planktonic foraminiferal communities. Data on planktonic foraminiferal habitats is expected to become a powerful tool for providing the first global spatial distribution of micro-zooplankton in the ocean. Moreover, not only such community data but also quantitative data on their distribution in the modern ocean are required. Currently, there are many blank areas of such data, particularly in the Pacific Ocean. Therefore, we selected the eastern South Pacific for our study, where planktonic foraminiferal habitats are poorly understood. In this study, we investigated the horizontal and vertical community distribution and size variation of planktonic foraminifera, examining their relationships with various environmental parameters that may affect their structure.
We used plankton samples off the coast of Peru collected at five stations between 10-30°S and 90-100°W during the R/V Hakuho Maru KH-19-6 research cruise. Samples were collected using a vertical multiple plankton sampler (VMPS) from seven layers: 0-20 m, 20-50 m, 50-100 m, 100-150 m, 150-200 m, 200-500 m, and 500-1000 m. We picked up all planktonic foraminiferal tests including juveniles, identified the species, separated them into “living” or “dead” based on the presence or absence of cytoplasm, and calculated the number of individuals per cubic meter. Then, we correlated each community with environmental parameters obtained from CTD observations at the same stations. Finally, we measured the test size of all planktonic foraminifera samples and examined their vertical and horizontal distribution.
20,372 individuals, both “living” and “dead”, were identified into 39 species within 19 genera. As a result of classifying the community data by hierarchical cluster analysis, the planktonic foraminiferal communities were divided vertically into surface communities and mid-deep communities. The mid-deep communities were further subdivided horizontally into St1-3 and St4-5. These distributions were closely related to the prevailing water mass structure in this area. The surface community was associated with the distribution of Subtropical Surface Water, which covered the entire area of the sampling stations. The community differences between stations in the mid-deep layer seemed to correspond to the water mass boundaries between Equatorial Subsurface Water with low dissolved oxygen concentration (DO), and Eastern South Pacific Intermediate Waters with relatively higher DO, distributed in the south. These correlations with environmental parameters were also consistent with dbRDA analysis.
The horizontal distribution of test size was similar in St1-4, with a slight trend toward smaller size in St5. Vertically, the smallest individuals were distributed in the surface water, while the larger ones were at deeper depths. This suggests that planktonic foraminifera change their habitat depth through their growth.
In our future research, we plan to study both plankton net samples and annual samples of sediment trap in the eastern North Pacific. To further understand the effects of environmental changes on planktonic foraminiferal community dynamics, we plan to consider not only spatial but also time series changes, e.g., seasonal and annual variations.