Symbiosis - Working Together in the Deep Sea

Symbiosis. The name for any kind of a close and long-term interaction between two different organisms. This phenomenon is found in nearly every ecosystem on the planet - allowing organisms to rely on others for food, shelter, or to act as a warning for nearby danger. But nowhere on Earth are creatures more uniquely adapted to relying on others than in the deep sea - a world of darkness, cold, and intense pressure. Let’s dive in, and take a closer look at the incredible role of symbiosis in the deep sea ecosystem.

Image by Zheng Wei Lim

In order to survive the challenging environment of the deep ocean, many organisms have turned to one of nature’s fundamental ecological associations. Symbiosis.


You feed me, i feed you

Perhaps the most common form of symbiosis in any ecosystem is mutualism. In these associations, both creatures benefit from one another in a number of ways. A common example is the case of clownfish, which dwell within anemones in order to be protected from predators. The anemone benefits from the clownfish by gaining nutrients from their excrement.

In the deep sea, mutualism occurs on a much grander scale, and plays a fundamental role in the structure of the entire deep sea ecosystem. This is due to the mutualism that forms at deep sea hydrothermal vents, where chemosynthetic bacteria are the primary producers. Here, the water that wells up from below the sea-floor is rich in minerals for the bacteria to convert into food and energy. To be specific, these compounds are hydrogen sulphide and methane. Both are toxic to animals, but certain specialised bacteria are able to use the chemicals to make the organic matter that animals rely on. This process is known as chemosynthesis. Think of it as an alternative to photosynthesis, but where nutrients are made by converting chemical energy rather than light energy.

Gigantic, odd-looking tube worms grow in clusters around vents and cold seeps; unusual creatures, for they have no stomach, gut, or mouth. This is because they instead contain a trophosome, a large organ containing billions of the chemosynthetic bacteria. The tube worms are specifically adapted to being a symbiont in this relationship; the stable nature of the vents has allowed the worms to evolve over millions of years to possess these important physical characteristics - including a long ‘root’ that collects hydrogen sulphide from the sediment, and ‘plumes’ that collect oxygen from the water. Both the oxygen and the chemicals are transported to the long, central trophosome, where the bacteria use them and carbon dioxide to produce organic molecules. Without the tube worm’s trophosome providing them with a constant supply of these key ingredients, the single-celled bacteria would have a hard time gathering it all in one place.

100% of the tube worm’s nutrition is provided by the bacteria undergoing this process. Symbiosis is so important to these organisms, that they simply would not be able to survive without it. Life needs energy. Without bacteria taking refuge within towering tube worms, the worms would obtain no energy, and life here would be impossible, especially as photosynthesis is not an option down where sunlight cannot reach.

This example of mutualism is not only vital for the survival of the tube worms and mussels. It also supports an abundance of other organisms that rely on the tube worms, and thus form complex communities at vents and cold seeps that simply would not exist if not for the ‘worm-bacteria’ symbiosis. Crabs, eels, isopods, and fishes all use tube worms and mussels as sources of food, or shelter. These animals are called associates.

Hoff Crab

Kiwa tyleri

Found only at hydrothermal vents near Antarctica, this species of squat lobster has been known to feed on the plumes of Giant Tube Worms.

benefitting from harming another

Symbiosis does not just mean that both partners have to benefit. In fact, it describes a variety of close relationships between organisms. Sometimes, one organism benefits from causing harm to the other, like worms, isopods and copepods infecting host species such as crabs and fish. This is parasitism. Let’s take a look.


Parasites often get a bad reputation for their role as blood-suckers and vectors for disease. But parasitism is no less important than mutualism to the deep sea ecosystem. Parasites are key components of food webs, and overall they can be an indicator of a healthy ecosystem. They control populations of dominant species, allowing rarer competitors to thrive. Also, parasitism can lead to mutualism. In shallow reefs, animals with parasites visit ‘cleaner’ stations to have their parasites removed by shrimps and small fish. The small fish get a meal out of eating the parasites, and the host gets some relief by being rid of the parasites.

Sea Lamprey

Petromyzon marinus

The sea lamprey is a parasitic fish of the Atlantic Ocean. It uses a disc-shaped, suction-cup mouth, ringed with sharp, horny teeth, to latch on to an unfortunate fish. The lamprey then uses its rough tongue to scrape away the fish's flesh so it can feed on its host's blood and body fluids.

YOU FEED ME, without gain or loss

Far stranger than both mutualism and parasitism, is commensalism. In commensal relationships, only one symbiont gains anything from the relationship. This could be food, protection, or any other service. But unlike the other two forms of symbiosis, the other symbiont neither benefits or is harmed by the interaction.



Barnacles that attach themselves to whales get a free ride. Being exposed to the currents of the open ocean allows them to access a greater abundance of food as the whale moves around. In return, the whale gets nothing. But it doesn't suffer from their presence.

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