Seasonal variations of group-specific phytoplankton cell death in Xiamen Bay, China

The importance of phytoplankton cell death is being increasingly recognized,however,there are still no published reports on this in Xiamen Bay.In this study,the proportion of dead phytoplankton cells associated with environmental factors was assessed at a station in Xiamen Bay from December2012 to December 2013,using a cell digestion assay,which is an effective method to analyze dead/living cells in complex natural phytoplankton communities.The percentages of dead cells(%DC) in the total phytoplankton in summer(16%±6%) were lower than those in winter(27%±16%).Six groups of phytoplankton(G1-G6) were categorized by flow cytometry.These phytoplankton communities with diverse seasonal variations in%DC had different responses to environmental constraints.The main factors affecting mortality were temperature and salinity,while nutrient concentration showed little influence on phytoplankton death.Additionally,our results provide evidence that chlorophyll a concentrations had an inverse relationship with total phytoplankton%DC and viable cell abundance was more meaningful than total cells to explain variations in environmental parameters(such as Chl a).Moreover,the lowest mean%DC in total phytoplankton was 16%±6%at our sample site,which is in a subtropical area with high water temperatures,full solar radiation,and rich nutrients.This indicates that phytoplankton cell death is a process that cannot be ignored.In summary,phytoplankton cell death is important in understanding the dynamics of phytoplankton communities and the functioning of subtropical ecosystems.

The importance of phytoplankton cell death is being increasingly recognized, however, there are still no published reports on this in Xiamen Bay. In this study, the proportion of dead phytoplankton cells associated with environmental factors was assessed at a station in Xiamen Bay from December 2012 to December 2013, using a cell digestion assay, which is an effective method to analyze dead/ living ceils in complex natural phytoplankton communities. The percentages of dead cells （% DC） in the total phytoplankton in summer （16%＋6%） were lower than those in winter （27%q-16%）. Six groups of phytoplankton （G1-G6） were categorized by flow cytometry. These phytoplankton communities with diverse seasonal variations in % DC had different responses to environmental constraints. The main factors affecting mortality were temperature and salinity, while nutrient concentration showed little influence on phytoplankton death. Additio^aally, our results provide evidence that chlorophyll a concentrations had an inverse relationship with total phytoplankton % DC and viable cell abundance was more meaningful than total cells to explain variations in environmental parameters （such as Chl a）. Moreover, the lowest mean % DC in total phytoplankton was 16%q-6% at our sample site, which is in a subtropical area with high water temperatures, full solar radiation, and rich nutrients. This indicates that phytoplankton cell death is a process that cannot be ignored. In summary, phytoplankton cell death is important in understanding the dynamics of phytoplankton communities and the fimctioning of subtropical ecosystems.