Temporal niche partitioning of Skeletonema: seasonal succession of the community composition in surface water of Tokyo Bay

Abstract

The diatom Skeletonema spp. frequently blooms in both the winter and summer seasons of coastal waters worldwide and consists of several cryptic species. However, their seasonal pattern of species occurrence is not yet well understood in Tokyo Bay, Japan, where Skeletonema spp. frequently cause blooms. The species composition and cell density of Skeletonema spp. were investigated monthly from March 2016 to February 2020 in the bay using a PCR and environmental variables. In total, 6 Skeletonema spp. (S. marinoi-dohrnii complex, S. potamos, S. menzelii, S. japonicum, S. ardens, and S. costatum sensu stricto [s.s.]) were identified. Logistic regression analysis revealed that the occurrence of the S. marinoi-dohrnii complex had a significant negative relationship with the square of temperature; the species frequently occurred at <25°C. The occurrence of S. japonicum was frequently found at <15°C. In contrast, S. potamos, S. menzelii, and S. ardens tended to occur at >25°C but did not occur at <13°C in most cases. Skeletonema spp. cell density showed a bimodal seasonal changing pattern, and the species composition of Skeletonema spp. was also divided into winter/spring and summer/autumn communities by distance-based redundancy analysis. The first peak in cell density occurred between January and May (103-104 cells ml-1) and consisted of the S. marinoi-dohrnii complex and S. japonicum. The second peak was found between June and September (>104 cells ml-1) and consisted of S. potamos, S. ardens, and S. costatum s.s. The present study demonstrated that the Skeletonema spp. community changed with the seasons, depending on the temperature.