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Deep seas 2

Black smoker vents amongst deep sea organisms

The deep sea case study overflowed. As hinted at in Deep Seas 1, there are special ecosystems in the sea that draw their energy from a process other than photosynthesis. They need their own story.

Background

Deep sea vents

A vent is a fissure on the sea floor from which flows mineral-rich water. Vents come in two forms - Hydrothermal vents and Cold seeps.

Hydrothermal vents form where there is volcanic activity on or below the ocean floor, such as along the Mid-Ocean Ridge. Water seeps through cracks in the seafloor and is heated by hot rock deep below the ocean crust to as high as 400°C. This hot water is under too much pressure to boil, but it erupts as “smoky fountains” at vents on the sea floor. The hot vents produce unusual chimney-like towers called "black smokers." The hot water contains dissolved metals (including iron, manganese, zinc, copper, sulfur, and others). When they encounter the cold ocean water, the minerals precipitate, making dark plumes of water and irregular deposits (including “chimneys”) on the seabed. The rich supply of nutrients support chemotrophic bacteria which in turn,  support a complete food web of seafloor creatures, including tube worms, mussels, arthropods, fish, and other benthic life forms adapted to these harsh and temporary environments.1

A cold vent/cold seep (sometimes called a white smoker because it vents white plumes of gas and debris ) is an area of the ocean floor where hydrogen sulfide, methane, calcium-rich minerals, and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool. “Cold” does not mean temperature of seepage is lower than surrounding sea water. Actually, its temperature is often slightly higher.2


Chemosynthesis and energy flows

Chemosynthesis  (unlike photosynthesis)  involves the use of energy released by inorganic chemical reactions to produce food.  This process occurs in bacteria and other organisms. All chemosynthetic organisms use energy released by chemical reactions to make a sugar, but different species use different pathways, so there is no single equation to describe all the ways chemosynthesis can occur.

One example of chemosynthesis at hydrothermal vents:  Some bacteria oxidize hydrogen sulfide, add carbon dioxide and oxygen, and produce sugar, sulfur, and water:

chemosynthesis equation
Chemosynthesis equation

 

Vent ecosystems

Chemosynthetic bacteria form the basis of the deep sea vent ecosystems. They are keystone species.

Characteristically, chemosynthetic bacteria grow into a thick mat, covering hydrothermal vents, and this is the start of the food web of the ecosystem. Specialised forms of snails, shrimp, squat lobsters, crabs, tube worms, and fish feed on the bacterial mat and attract larger organisms such as squid and octopuses.

During the initial stage of cold vents, when methane is relatively abundant, dense mussel beds form near the cold seep. These mussels do not directly consume food. Instead, they are nourished by symbiotic bacteria that also produce energy from methane, similar to their relatives that form mats.

Scientists Discover New Ecosystem Underneath Hydrothermal Vents


Services

Nutrient recycling - reservoirs and flows

Hydrothermal vents play an important role in nutrient cycling, including acting as a sink for carbon dioxide and methane, two powerful greenhouse gases.

Activity in deep sea vents is part of the process that cycles carbon around the planet. In the prestigious journal Nature, Arrigo (2005) explains

The way that nutrients cycle through atmospheric, terrestrial, oceanic and associated biotic reservoirs can constrain rates of biological production and help structure ecosystems on land and in the sea. On a global scale, cycling of nutrients also affects the concentration of atmospheric carbon dioxide. Because of their capacity for rapid growth, marine microorganisms are a major component of global nutrient cycles.3

 

diagram representing the movement and storage of carbon in the global ecosystem
diagram representing the movement and storage of carbon in the global ecosystem

Deep sea vent systems reduce flows of methane which is a potent green house gas (GHG) by preventing it reaching the upper water layers where it can escape to the atmosphere and add to global warming.

Because deep sea vent organisms live under conditions of extreme heat and pressure they are termed extremophiles. Their enzymes are uncommon and further study of them might reveal solutions to problems in research, industry and the environment.

Raw materials

The chimneys that form around vents are mineral rich (copper, cobalt, nickel, zinc, lithium). There has been considerable interest in mining these areas to extract these materials for industrial use. This resource can however, only be harvested in such a way as to disrupt vent communities and given that we know so little about the importance of these communities, caution has been urged.

Summary of services provided for us

  • Nutrient recycling
  • Novel chemicals and chemical processes which could be useful in industry and in bioremediation of dangerous materials
  • Raw materials
  • Important scientific insights which are thought to relate to the origin of life

Threats to the services?

Deep sea hydrothermal vent systems that require conservation - map
Deep sea hydrothermal vent systems that require conservation

Recent research has led to 184 deep-sea species being added to the IUCN Red List of Threatened Species.

The relative inaccessibility of these seafloor habitats means they are often not well understood, making it difficult to understand and communicate their ecological significance and their conservation needs.

Hydrothermal vents habitats host a similar density of life as tropical rainforests and coral reefs. There are approximately 600 of these hotspots known worldwide, although there may be many more we do not know about. Vent communities are also distinctly different from the surrounding seafloor, making these highly insular habitats.

There is growing industrial interest in the deep sea, including deep-sea mining for commercially important metals, meaning it is now vital to protect these unique, insular ecosystems and their specialist endemic species.

For an excellent discussion of the issues raised by deep sea mining, see Challenging the Need for Deep Seabed Mining From the Perspective of Metal Demand, Biodiversity, Ecosystems Services, and Benefit Sharing
and/or a less technical article in the Guardian newspaper

Deep sea mining article on Guardian newspaper
Deep sea mining article on Guardian newspaper

The largest threat to the deep sea is, unfortunately, human ignorance- public interest is already lacking for visible, above-sea-level environments where human impact is obvious, so there is little hope that the value of the deep sea will become a public issue.4


What can we do to retain these services?

  • NEW MARCH 2023 Urge politicians to actually practice what they preach - At Last, a New Deal for the High Seas
  • Support petitions such as Protection of deep-ocean ecosystems and biodiversity through a moratorium on seabed mining
  • Become more aware of deep sea research e.g. by visiting reputable web sites like NOAA for information and following the work of research scientists like Sylvia Earle and Diva Amon, quoted below

    So this little deep sea worm that lives, you know, five kilometres down in the Atlantic may have a really important function that ultimately plays a big role in, for instance, locking away carbon for thousands, if not millions of years, for instance. But the problem is, because we've explored so little of it for most of it, we can't answer that fundamental question of what lives there, much less questions about the ecology of these animals. What does it eat? How does it reproduce? What role does it play? And if you can't answer those questions, it's a bit hard to put all the puzzle pieces together to understand these big ecosystem services and not just how important they are, but what's making them function in the way that they are.5


Dig deeper


 

  1. Vents on the ocean floor []
  2. Cold-Seep Ecosystems []
  3. Marine microorganisms and global nutrient cycles []
  4. Shedding Light on Deep-Sea Biodiversity—A Highly Vulnerable Habitat in the Face of Anthropogenic Change []
  5. Diva Amon, marine biologist, veteran of numerous deep sea research expeditions. []
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