Annual changes in the microeukaryotic community in intertidal sediments, Qingdao, China

Microeukaryotic communities in intertidal sediments play an important role in maintaining ecosystem health and resilience, as they are involved in ecosystem services such as nutrient cycling, organic matter breakdown and the support of diverse marine food webs. However, the seasonal variations in these communities and the differences between communities in muddy and sandy sediments are poorly understood. To address these gaps, surface sediments from both muddy and sandy sediments were collected monthly over a year (4 seasons, 10 months). Microeukaryotic community structure was analyzed using 18S rRNA sequencing, focusing on alpha-diversity, OTU composition, community composition, network structure, and trophic functional group structure. Results show that there were significant monthly changes in community composition, which were closely linked to changes in environmental factors such as temperature, dissolved oxygen (DO) and salinity. Species co-occurrence network analysis showed that interaction numbers and network density peaked in summer and declined in autumn and winter. This study also highlights the different characteristics of eukaryotic communities of muddy versus sandy sediments. Mantel tests show that temperature, DO and chlorophyll a (chl a) have a significant influence on eukaryotic communities in muddy environments, while DO, chl a and particulate organic carbon (POC) are important in sandy environments. This suggests that eukaryotic communities in muddy sediments are susceptible to ocean warming and hypoxia, while those in sandy sediments are more vulnerable to hypoxia and pollution. It was also found that autotrophs, heterotrophs, and mixotrophs react differently to seasonal climate shifts and different sediment types, with notable peaks in abundance for autotrophs in June, heterotrophs in December, and mixotrophs from September to November. These results will provide an important baseline on the microeukaryotic communities in intertidal sediments, essential for forecasting changes in community structure and ecosystem functions resulting from environmental changes.