Marine Bacteria in a Changing Ocean

‘Starry starry…. oceans?’ These aren’t stars; they’re marine bacteria stained with a fluorescent dye that makes them glow in ultraviolet light. It is estimated that there are 100 million times as many bacteria in the oceans (13 × 10²⁸) as there are stars in the known universe. Image Credit: Linda Rhodes

Bill Nilsson and Linda Rhodes smiling on the deck of the Ronald H. Brown. Photo Credit: Meghan Shea

Linda Rhodes and Bill Nilsson are scientists from the Marine Microbes and Toxins Program at NOAA’s Northwest Fisheries Science Center. Their focus on this cruise is the little guys: the bacteria! Bacteria are single-celled organisms that live almost everywhere; in the crust of our planet, in our forests, in our oceans, and even in our bodies. In the ocean, bacteria have greater collective mass than zooplankton and fishes combined. Bacteria play an important role in global nutrient cycles.

A scanning electron micrograph of marine bacteria (the small balls) attached to chitin (the threads) produced by a diatom (the big cylinders). Credit: NOAA NWFSC

They convert nutrients like carbon, nitrogen, and phosphorus from inorganic forms, in which other organisms cannot use them, to organic forms, which can be processed by other plants and animals in the ocean. This role places bacteria at the bottom of the food chain, which is also known as the lowest trophic level.

Linda and Bill are looking carefully at the species composition of bacteria in the water we are collecting, by measuring and comparing the abundance and types of bacteria, and examining the structure of bacterial communities. Because bacterial communities contribute to the health of the rest of the food web, Linda and Bill are also looking at higher-level production by bacterial communities. Bacterial production provides food for organisms that can’t derive energy from sunlight as plants do, and have to eat organic material (i.e. stuff made by living organisms) instead. Higher-level production by these ‘eaters’ is termed heterotrophic production. By examining production at multiple levels, they can understand how different bacterial communities are affecting the productivity of the rest of the ecosystem.

Linda Rhodes collects water from the CTD. Photo Credit: Meghan Shea

Bill Nilsson filters water collected from the CTD. Photo Credit: Meghan Shea

So how does their research tie into the oceanography goals of this cruise? Physical and chemical ocean properties – such as pH, temperature, and salinity—can have strong effects on the community structure of bacteria. Because bacteria reproduce rapidly, they can quickly adapt to changing environmental conditions. But when the community structure of bacteria changes, there are likely to be effects further up in the food web that relies on them. Once they’re back on shore, Linda and Bill will be using the oceanographic data that other teams onboard are collecting, and looking for correlations among environmental factors, bacterial community structure, and heterotrophic productivity. Understanding how oceanographic conditions affect the bacterial community of the ocean is vital to understanding how our changing ocean conditions are going to affect the organisms that live within it.

Author: Spencer Showalter