Marine Microbiology: meet the microbes in the sea!

Mira Okshevsky
2 October 2017

Above: Image © stockakia,

Picture this: a white sandy beach, palm trees and the warm blue ocean lapping at the sand. Who could resist going for a dip in that inviting water?

Perhaps you’ve been swimming in the ocean, or perhaps you’ve imagined it, like we just did. But either way, did you know that when you swim in the ocean, you’re actually bathing in a sea of microorganisms?

Just a single drop of seawater contains millions of marine microorganisms! But don’t worry, most of them won’t make you sick. Most of them are actually a good thing. They play useful roles in oxygen production, marine food chains, and more!

Where is oxygen produced?

When you read this question, what do you think of? Maybe you’re imagining rainforests or other places with lots of plants. Trees and other plants take in carbon dioxide and release oxygen in the process of photosynthesis.

However, only half of the oxygen in Earth’s atmosphere is produced by plants on land! The rest of it is produced in the oceans by billions of photosynthetic microbes called phytoplankton. Here’s another way to think of this: marine microorganisms have produced the oxygen in every second breath you take!

Food chains in the ocean

A food chain describes the relationship between organisms that eat other organisms. For example, cows eat grass, and many of us people eat cows. Just like plants are the base of land food chains, phytoplankton are the base of ocean food chains

Did you know? Algae are an example of phytoplankton.

Phytoplankton get their energy from the sun. They are eaten by the creatures on the next level of the food chain, zooplankton. These tiny critters include krill, larval forms of crabs and fish, and other tiny non-photosynthetic creatures that drift with the currents.

Zooplankton is then eaten by bigger animals such as fish and whales. That means that without phytoplankton, there would be no life in the oceans!

What else do marine microorganisms do?

All kinds of other useful things! For example, they break down oil after an oil spill, and decompose marine animals after they die. Imagine if there were no marine microorganisms around to do those things. The oceans would be a mess!

Did you know? Ocean water has sulfur in it. One kind, sulfate, can be “breathed” by some marine bacteria, just like you and I breathe oxygen. This process can produce sulfide, the compound responsible for giving rotten eggs and even some beaches their awful smell!!

Some animals, like the Hawaiian Bobtail Squid, have special relationships with marine bacteria.

Where do marine microorganisms live?

In the oceans, microorganisms don’t only swim. They also live in the sand on beaches, in the sediment at the very bottom of the ocean, and in close relationships with marine animals.

For example, the Hawaiian Bobtail Squid has a unique organ that it uses to hold a marine bacterium with a very special ability. This bacterium makes light, which the squid shines onto the seafloor to mask its shadow! This helps the little squid avoid being spotted by its predators. Relationships like these, where each organism helps the other, are called symbiotic relationships. Marine bacteria also live in other kinds of symbiotic relationships with fish, worms and corals.

How do scientists study marine microorganisms?

They don’t have an easy time of it! A 1995 study stated that less than 1% of marine bacteria can be taken out of the ocean and grown in a laboratory. That’s why scientists mostly rely on the information that they can get from the DNA of marine bacteria.

Did you know? When scientists grow bacteria in the lab, they call it a bacterial culture.

Scientists can extract this DNA directly from ocean water or sediment, which means they don’t have to grow bacteria in the laboratory at all. Scientists can then read the sequence of this DNA to find out which bacteria are present where the sample was taken, and what those bacteria are able to do.

Did you know? Learning about bacteria by extracting DNA directly from an environmental sample is called metagenomics.

Next time you’re at the ocean, remember that it is full of marine bacteria that are too tiny to see. They help all the different life forms beneath the waves survive. And by producing the oxygen you breathe, they help you survive, too!

Learn more!

Source of Half Earth's Oxygen Gets Little Credit (2004)
J. Roach, National Geographic News

A Drop in the Ocean is Teeming with Life
J. Becker, MIT-WHOI

Max Planck Institute for Marine Microbiology - Research
Max Planck Institute for Marine Microbiology

Mira Okshevsky

Mira has a Master of Science in Marine Microbiology and a PhD in Nanoscience. She is currently a postdoctoral research fellow at McGill University, where she studies how bacteria stick together is communities called biofilms. In her free time, Mira enjoys exploring the coves and beaches of her home province of Newfoundland.