HYDROTHERMAL VENTS AND CHEMOSYNTHESIS:A HABITAT IN THE DARK

Many of us are familiar with "Old Faithful" in Yellowstone National Park. This famous geyser erupts several times a day. It spouts a column of water heated by volcanic rock deep within the Earth's crust.

A hydrothermal vent is a geyser on the seafloor, where it is very deep and very dark. They are usually found in areas of volcanic activity. They continuously gush super-hot, mineral-rich water that supports a diverse community of organisms. Even though we might consider this to be a harsh environment, hydrothermal vents are abundant with life. In fact, more than 300 species live around the vents and are unique to this type of environment. These creatures include tubeworms taller than you, fish, crabs, shrimp, clams, and chemosynthetic bacteria. These organisms have evolved to survive in the complete darkness, the extremely hot vent water and the tremendous water pressure.

Hydrothermal vents were discovered in 1977 in the Pacific Ocean. Since then, they have been found in the Atlantic, Indian, and most recently, the Arctic Ocean. Most occur at an average depth of about 2,100 meters (7,000 ft) in areas of seafloor spreading along the Mid-Ocean Ridge system — the underwater mountain chain that winds around the globe.

How do hydrothermal vents form? In some areas along the Mid-Ocean Ridge, the huge plates that form the Earth's crust are moving apart, causing deep cracks in the ocean floor. Seawater seeps into these openings and is heated by the molten rock, or magma, beneath the crust. As the water heats up, it rises (hot water is less dense than cold water!).

When this "hot spring" gushes out into the ocean, its temperature may be as high as 360°C (680°F)! Yet this water does not boil because it is under so much pressure from the tremendous weight of the ocean above.

Hydrothermal vents are so deep that light is unable to penetrate. Without light, plants, algae (seaweed) and phytoplankton are unable to perform the process of photosynthesis. Therefore, photoautotrophs are unable to form the basis of the food chain as they do where light is available. Organisms in hydrothermal vents must acquire energy in another way.

Before scientists had the technology to study hydrothermal vents, they believed that only small animals lived at the ocean bottom. They thought that these animals received their food from above, from organisms that depended on sunlight and photosynthesis, just as a food chain on land does. Scientists knew that when plants and animals that live near the ocean’s surface die, they sink to the bottom of the ocean. They assumed that this dead organic material would then feed bottom-dwelling animals.

A hydrothermal vent

Crabs, Worms and Mussels in a Hydrothermal Vent

But this turned out not to be entirely true. With the use of deep-sea submersibles, scientists have now discovered vast communities of fairly large animals in the dark depths! Instead of using light to create organic material to live and grow (photosynthesis), microorganisms at the bottom of the food chain near vents used chemicals such as hydrogen sulfide (chemosynthesis).

At the seafloor, thriving ecosystems receive energy from a source that had never been thought of before - heat and chemicals from the planet itself. The energy to sustain life was not coming down from the sun. It was coming up from the interior of the earth.

Animals at these depths depend on bacteria that are able to use sulfur and other compounds within vent discharge as energy sources to make glucose, a process called chemosynthesis. Larger animals then eat the chemosynthetic bacteria, or eat the animals that eat the bacteria. In some cases, the chemosynthetic bacteria live inside the bodies of vent creatures in a symbiotic relationship. Some organisms, such as tubeworms, that live around the vents do not have a mouth or even a digestive tract as we do. The bacteria actually live inside their bodies and provide nutrients directly to the organism’s tissues.

Adapted From: http://www.onr.navy.mil/focus/ocean/habitats/vents2.htm http://www.divediscover.whoi.edu/vents/index.htmlhttp://www.ceoe.udel.edu/extreme2004/geology/hydrothermalvents/index.html

The Alvin, a deep-sea submersible

HYDROTHEMAL VENTS PRE-READING

Root words Meaning New Vocabulary Definition

hydrohydrothermal

therm

chemo chemosynthesis

photosynthesis

photo

synthesis

autophotoautotroph

troph

symsymbiotic

bio

Unfamiliar term

Sentence Picture Predicted meaning

Definition

geyser The shaken soda can erupted like a geyser when

opened.

diverse Nemo and his coral reef friends represent a diverse

community.

abundant The buffet table was filled with an abundant amount

of dessert.

molten I expect my molten brownie dessert to be hot

and gooey!

submersible A submarine is a submersible ship.

Unfamiliar term

Sentence Picture Predicted meaning

Definition

microorganisms I cannot see the microorganisms living on

my skin.

sustain Hurricane Sandy sustained winds of 45 miles per hour

for 2 days.

compounds Hydrogen and oxygen make the compound water.

nutrient Venus fly traps eat flies for extra nutrients.

HYDROTHEMAL VENTS ANALYSIS: PART I1. Describe the environment around a hydrothermal vent.

2. List six (6) types of organisms that live near hydrothermal vents.

3. How are hydrothermal vents formed?

4. On land, there is usually plenty of sunlight. What organism normally uses this sunlight to produce sugars (food and fuel) for terrestrial food chains?

Why are these organisms unable to survive near hydrothermal vents?

5. At the ocean’s surface, there is also usually plenty of sunlight. What organism(s) normally use(s) this sunlight to produce sugars (food and fuel) for shallow water food chains?

Would you expect to find much of this growing near hydrothermal vents? Why or why not?

6. In the deep ocean near hydrothermal vents, what organism produces sugars (food and fuel) for these deep ocean food chains?

Describe in detail how this organism obtains energy.

7. Describe how organisms higher up the food chain (consumers) in hydrothermal vent communities obtain energy.

Producer Herbivore Carnivore

Producer Herbivore Carnivore

PART II CHEMOSYNTHESIS vs. PHOTOSYNTHESIS

Below is the chemical reaction that occurs during chemosynthesis. Remember that this reaction is happening in the deep, dark ocean near the intense heat of hydrothermal vents.

Chemosynthesis

heat

6 CO2 + 6 H2O + 3 H2S C6H12O6 + 3 H2SO4 carbon dioxide water hydrogen sulfide glucose sulfuric acid

1. What are the REACTANTS in chemosynthesis? ________________________

________________________

________________________

2. What are the PRODUCTS of chemosynthesis? ________________________

________________________

3. What form of ENERGY is used for chemosynthesis? ________________________

Below is the chemical reaction that occurs during photosynthesis. Remember that this reaction requires sunlight.

Photosynthesis

light

6 CO2 + 6 H2O C6H12O6 + 6 O2carbon dioxide water glucose oxygen

4. What are the REACTANTS in photosynthesis? ________________________

________________________

5. What are the PRODUCTS of photosynthesis? ________________________

________________________

6. What form of ENERGY is used for photosynthesis? ________________________

Using the reading and information you compiled in your worksheet answers, complete the Venn diagram below comparing chemosynthesis to photosynthesis.

Chemosynthesis Photosynthesis

Similarities between chemosynthesis and

photosynthesis

Properties unique to

chemosynthesis

Properties unique to

photosynthesis

Items to include in your Venn diagram: reactants products energy sources types of organisms that perform these processes types of environments (aquatic/terrestrial/deep ocean) where these processes occur