Disentangling marine microbial networks across space

Although microbial interactions underpin ocean ecosystem functions, they remain barely known. Different studies have analyzed microbial interactions using static association networks based on omics-data. However, microbial associations are dynamic and can change across physicochemical gradients and spatial scales, which needs to be considered to understand the ocean ecosystem better. We explored associations between archaea, bacteria, and picoeukaryotes along the water column from the surface to the deep ocean across the northern subtropical to the southern temperate ocean and the Mediterranean Sea by defining sample-specific subnetworks. Quantifying spatial association recurrence, we found the lowest fraction of global associations in the bathypelagic zone, while associations endemic of certain regions increased with depth. Overall, our results highlight the need to study the dynamic nature of plankton networks and our approach represents a step forward towards a better comprehension of the biogeography of microbial interactions across ocean regions and depth layers.

Introduction

The introduction highlights the distinctiveness of the Atlantic as the least-navigated temperate ocean in the medieval and early modern period. When Europeans first crossed the Atlantic in the eleventh century, they faced no deep-water competition from indigenous Americans or Africans, but maritime supremacy did not easily translate into power on land. The introduction examines the Norse colonization of Greenland and attempted colonization of Newfoundland to illustrate the military challenges Europeans faced across the Atlantic. Compared to subsequent colonists, the Norse were unusually isolated. After encountering indigenous American military resistance, they abandoned their colony on Newfoundland. The Europeans who crossed the ocean in the late fifteenth and sixteenth century had larger ships to ferry and supply people and maintain communications, but even with these advantages, colonists depended on indigenous American trading partners and military allies in order to survive.