Spatiotemporal Distribution And Diversity Of Labyrinthulomycetes In Qinhuangdao Coastal Waters

Labyrinthulomycetes,commonly known as fungus-like unicellular heterotrophic protists,are recently considered to play a significant role in nutrient cycling of marine ecosystems.Their distribution pattern,diversity and ecological functions,however,were not systematically studied and thoroughly understood because of the inefficient of traditional detection methods and the limited large-scale field survey in their ecological roles.In this study,we developed a flow cytometric method for rapid quantification in the abundance of Labyrinthulomycetes.Using this method with MiSeq 18 S high-throughput sequencing and bio-statistical analysis,we investigated the spatiotemporal distribution,molecular diversity and community composition of Labyrinthulomycetes along environment gradients in Qinhuangdao coastal waters.Our results showed that Labyrinthulomycetes in Qinhuangdao coastal waters possessed huge biomass and rich diversity,and their abundance and community composition had obvious spatial and temporal heterogeneity.They had significant contribution to marine organic carbon pool and their abundance mainly depended on the chlorophyll-a content,implying their important role in the secondary production with the utilizing of the primary production.The ?-diversity of Labyrinthulomycetes were negatively correlated with chlorophyll-a and particulate nitrogen whereas positively correlated with nitrate and nitrite,and their community structure was shaped principally by the water temperature,pH and phosphorus,suggesting their association with seawater nutrients and other physicochemical factors which could affect them directly or more likely through phytoplankton.Our results also revealed a dual relationship between Labyrinthulomycetes and bacterioplankton showing characteristics of both competition and cooperation,and supported that they shared partially overlapped but distinctive roles in the coastal ecosystems.In addition,Labyrinthulomycetes showed higher average abundance excluding spikes and greater OTU richness in nearshore waters than offshore waters,which somehow reflected impacts of terrigenous nutrient inputs and links with human activities.