A glass of seawater is teeming with life, and a recent expedition revealed more about what ocean water contains. Microscopic creatures in the world’s oceans weigh more than all of the fish in the sea and produce about half of the Earth’s oxygen.

Yet the ecology of marine microbes, which are crucial for everything from absorbing carbon dioxide from the air to regulating the productivity of major fisheries, are only beginning to be understood.

In a step to understanding this hidden world, University of Washington oceanographers have found that diatoms — the intricately patterned single-celled algae that exist throughout the world’s oceans — grow faster in the presence of bacteria that release a growth hormone known to benefit land plants. The study, published online May 27 in Nature, uses genetic and molecular tools to discover what controls marine ecosystems.

“These very small organisms are interacting with their environment, but they’re also interacting with other organisms,” said co-author Ginger Armbrust, a UW professor of oceanography. “In my mind, in order to understand how future ecosystems will work, we need to understand how these organisms that are the basis of the marine food web interact with one another.”