Hydrothermal Vent Communities

Quick links

  1. introduction
  2. lesson objectives
  3. vocabulary
  4. 'story'
  5. summary
  6. vocabulary review
  7. self test
  8. student activity

Introduction

classic hydrothermal vent

This webpage will familiarize students with a hydrothermal vent habitat. Students will learn where vents are likely to form, how they form, and how physical conditions contribute to the development of a living vent community and to its eventual demise.

grade level: 7th thru 10th

for the teacher: Background information on hydrothermal vents may be found at these resource sites:

for everyone:

References for those interested in learning more about plate tectonics:

This webpage uses JavaScript to provide several extra functions.

  1. Words which appear as underlined maroon text (e.g. autotrophs) will pop-up a definition box when you move your mouse over them. Try it!
  2. The pictures on this page are 'thumbnail' images. Click on the picture to the larger version.
  3. Once you've answered the self-test, you can immediately find out the percentage you answered correctly by pressing the 'Score it' button.
  4. The detailed answer sheet shows you your answer and the correct answer for each question. It also provides a link back to the point in the text which discusses the material for the question.

 

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Lesson
Objectives

The objectives of this lesson are:

  1. Students will be able to describe how a vent forms, citing plate tectonics, sea floor spreading, and the roles of magma, water, and minerals.
  2. Students will be able to explain relationships between physical, geological, and biological factors in the development of a vent community.
  3. Students will be able to describe how vent communities survive without photosynthesis at the base of the food web.

 

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Vocabulary
new words

| autotrophs | black smoker | chemosynthesis | chemosynthetic bacteria | crust | decomposition | ecosystem | hydrothermal vent | lithosphere | lithospheric plate | magma | mantle | mid-ocean spreading | ore | oxidize | plate tectonics | precipitate | submersible | symbiotic |


 

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Story

black smoker

black smoker

What is a hydrothermal vent?

Hydrothermal vents are cracks in the ocean floor that emit jets of hot water loaded with minerals and bacteria. The vents range in diameter from less than an inch to mare than six feet. They are usually found at least a mile deep long the mid-ocean ridges. So far, several dozen vent fields have been discovered.

The first hydrothermal vent was discovered in 1977 by geologists on a research expedition in the Galapagos Rift off the coast of South America. The Galapagos Rift is part of the mid-ocean ridge system. To understand vents it is helpful to first have an understanding of these ridges and how new sea floor is formed.

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Plate tectonics and mid-ocean spreading

If the terms plate tectonics and mid-ocean spreading are new to you, don't be put off by them. A brief discussion follows. If you're interested in learning more, references are provided.

The theory of plate tectonics as it relates to vents

The earth's surface is broken up into several large and a few smaller plates. These plates include the crust and the top portion of the mantle. Together these two layers make up the lithosphere, therefore the plates are referred to as lithospheric plates. The plates can consist of ocean crust or continental crust, or more often, a combination of the two. Places where plates meet are called plate boundaries or plate margins. Convergent boundaries are places where plates come together. Divergent boundaries are places where plates pull apart.

How a vent forms

NOAA vent illustration

At the mid-ocean ridges, a 46,000 mile mountain system that circles the globe under the oceans (the longest mountain chain on the planet), the plates move apart during episodes of volcanic activity. Magma rises up from the mantle and adds new sea floor to the separating plates. Fractures develop as the plates are pulled apart. Cold sea water (2o C) seeps into the fractures and is heated by the hot magma (1400o C) contained in shallow chambers under the sea floor. black smoker vent The superheated water is forced back up to the sea floor carrying dissolved minerals leached from the basalt ocean plate. A vent forms when the jet of water shoots through the sea floor and its dissolved minerals begin to precipitate out. The minerals grow into a chimney, or "black smoker". Some vents produce "white smokers". The color depends on the minerals present in the water. Growth continues as long as there is a supply of hydrothermal fluid. Vents have been located at depths varying from 1500 to 4000 meters.

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Life on a hydrothermal vent

Primary producers: the base of the food web

Most living things on earth depend on sunlight as the ultimate source of energy. Green plants use sunlight to make food by the process of photosynthesis. In the darkness of the ocean depths there is no sunlight for photosynthesis. So how do living things survive in such an environment? The answer is found in bacteria that can use another source of energy to make food.

Water coming out of a vent is rich not only in dissolved minerals but also in chemosynthetic bacteria. These bacteria are capable of utilizing sulfur compounds to produce organic material through the process of chemosynthesis. The bacteria are autotrophs that oxidize hydrogen sulfide in vent water to obtain energy, which is used to produce organic material (i.e. grow themselves).

Chemosynthetic bacteria are the primary producers and form the base of vent food webs. All vent animals ultimately depend on the bacteria for food.

How does a vent community develop?

When a vent forms, new lava on the ocean floor around the vent becomes covered with a thick mat of bacteria. Soon tiny animals such as amphipods and copepods come to feed on the bacteria. Gradually, larger animals, including grazers, scavengers and predators join in colonizing the vent.

Scientists studying a field of vents since their formation in 1991 have observed a pattern of colonization. The first organisms to populate the vents are bacteria, then other microorganisms, including amphipods and copepods appear. tube worms at vent opening These are followed by limpets (snails), shrimp, crabs, tube worms, fish, and octopi. Sometime later acorn worms, dandelion-like animals, and other species of shrimp and tube worms add to the expanding community. In their most advanced stages vents are home to mussels, a variety of worms, anemones, and a large population of crabs, as well as many of the earlier colonists.

tube worm 'guts' diagram -->)

 

 

  giant clams in scientist hands

Some vent animals, like limpets, clams, and mussels feed directly on bacteria. Other animals, such as octopi, prey on those that eat bacteria. Vent crabs act as both predator and scavenger. Some of the most successful vent animals, tube worms and giant clams, form symbiotic relationships with chemosynthetic bacteria. The bacteria live within the animals' tissues and provide a built-in food supply. Tube worms have no mouth, gut, or anus. Nutrients are absorbed directly into tissues.

Two species of tube worms inhabit hydrothermal vents. tube worm colony with crabs The smaller of the two, Tevnia jerichonana, which grow at a rate of 30 centimeters per year, are among the first animals to colonize and dominate the vent ecosystem. Riftia pachyptila, which grow much faster (85 centimeters per year) and reach over 2 meters in length, eventually replace Tevnia as the dominant species. Over 300 new species of animals have been discovered at vents. Many are found nowhere else on earth, and could not exist outside the conditions at vents.

Physical conditions at vents

  1. tremendous pressure - 300 atmospheres
  2. extreme temperatures - highest measured vent temperature is 4030C, highest temperature at which living tube worms have been observed is 1000C, sea water is about 20C at depths where vents form, but can be up to 200C near some vents.
  3. chemicals - hydrogen sulfide, the source of energy that fuels vent food webs and the most plentiful compound in vent emissions, is toxic to most living things.
  4. pH - vent fluid is very acidic with a pH as low as 2.8, which is very unhealthy for most living things.

Other strange-but-true findings about vent environments

Scientists have learned that some processes occur very quickly at vents. For example, giant tube worms can grow as fast as 2 meters a year, and "smokers" or chimneys can rise up to 7 feet or more in less than a year. In a couple of years a barren vent can become a bustling community composed of many unusual animals.

Other processes seem to take place very slowly at vents. An example is decomposition. When an accident caused scientists to leave a bologna sandwich behind, they found it in nearly the same condition when they returned to the site a year later. Similarly, dead tube worms they had observed on one expedition were mostly unchanged when the scientists returned the following year.

How long do vents live?

A vent habitat is a very unpredictable place in which to live. Some vents are active for several decades, others may live longer. Some vents may live only a few years or less.

Why do vents die?

Volcanic activity, earthquakes, and other events can extinguish a vent at any time. A chimney may collapse and block the flow of hydrothermal fluid, precipitates may build up, like cholesterol in an artery, choking the vent, or the supply of heat and fluid to the vent may simply become exhausted.


 

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Summary

The 1977 discovery of hydrothermal vents and the spectacular communities living on them was one of the most significant scientific events of the century. Vents are most often found along the mid-ocean ridge and rift system that extends through the oceans at sea floor spreading centers.

Vents form when volcanic activity adds new material to diverging plates and sea water gets into cracks in the plates. The water becomes superheated and loaded with dissolved minerals and metals. It returns to the ocean floor as jets of hydrothermal fluid and cools in contact with cold sea water. Metals precipitate, creating chimneys of ore deposits. These may prove to be of great value in the future if an economically efficient way to mine them can be found.

Chemosynthetic bacteria use sulfur compounds in vent water to produce food for communities of unusual animals, many of which are new species found only around vents. Some of these organisms produce enzymes and carcinogens that could be used to further our understanding of biological processes and improve human health.


 

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Vocabulary
review

| autotrophs | black smoker | chemosynthesis | chemosynthetic bacteria | crust | decomposition | ecosystem | hydrothermal vent | lithosphere | lithospheric plate | magma | mantle | mid-ocean spreading | ore | oxidize | plate tectonics | precipitate | submersible | symbiotic |


 

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Self test

Now that you have read through the material on this page, how about a little quiz to confirm that you've learned the major points about hydrothermal vent communities?

Once you've answered the questions, you can press the 'Score it' button and immediately find out how you did. You can also get a detailed explanation of which questions you answered incorrectly.


 

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Student activity

'Vent' your creativity!.


 

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Additional lessons

If you liked this lesson, be sure to visit the other lessons in the series.

 

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