Nutrient Transfer Hypothesis for the Fluctuation and Regional Variation of Microbial Diversity in the Pacific Ocean.

Microbial diversity affects marine biogeochemical cycles and sustainability. However, the processes and feedbacks that control the spatial and temporal trends in species diversity and functional gene diversity remain largely unknown at the global marine scale. We analysed 1582 marine metagenomic samples and 19 variables related to marine climate and microbial community dynamics. Over the past 12 years, marine microbial species diversity has significantly decreased across the surface ocean, especially in the Pacific. The greatest decrease reached 24.29% in the central region of the North Pacific Ocean (NPO). We propose a food chain-based nutrient transfer hypothesis in which a decrease in grazing intensity is associated with a decrease in microbial diversity. This hypothesized relationship was further examined using 27 years of independent time series data from a Pacific site. The Pacific Ocean presented high sensitivity to grazing intensity coupled with environmental fluctuations of < 5%, in which species diversity in the NPO and South Pacific Ocean (SPO) regions changed from -9.62% to 13.02% and from -8.38% to 15.03%, respectively. The incorporation of nutrient transfer concepts to reduce the unpredictable uncertainty in marine biogeochemical cycles and ecological stability related to microbial diversity is urgent, especially in the vulnerable Pacific Ocean.