FLEXE Great Tubeworm Mysteries

How can animals like the giant tubeworm exist in the cold dark seafloor?

FLEXE Great Tubeworm Mysteries Tubeworms were first discovered at Mid-Ocean Ridges

(Image from U.S. Geological Survey)

Locations of Mid-Ocean Ridges

(Image from Dive and Discover, WHOI)

FLEXE Great Tubeworm Mysteries Mid-Ocean Ridge Processes

Spreading Centers

Ocean Bottom

FLEXE Great Tubeworm Mysteries Global distribution of known hydrothermal vent sites

(Image from Van Dover et al. 2002)

How hydrothermal vents formFLEXE Great Tubeworm Mysteries

(Image from Dive and Discover, WHOI)

Deep Ocean Seawater

Seafloor

Scientists expected to find very little life at vents

• No light

• Very high pressure

• Low temperatures

• Very little food

• New seafloor

Potential challenges:

FLEXE Great Tubeworm Mysteries

But THIS is what they found instead!FLEXE Great Tubeworm Mysteries

What are these animals eating?

And so began

the Great Tubeworm Mystery…

Before you begin to solve the mystery, let’s look at what scientists did know

about the vent environment.

FLEXE Great Tubeworm Mysteries

Bacteria are everywhere!!

(Image courtesy of Dr. Joe Resing and WHOI)

FLEXE Great Tubeworm Mysteries

Some bacteria can perform chemosynthesis

Photon Photon EnergyEnergy

Reduced chemical (often sulfide, HS-)

Oxidized chemical

Chemosynthesis:

CO2 + H2O sugars + O2 CO2 + H2O sugars + O2

Photosynthesis:

Chemical Chemical EnergyEnergy

FLEXE Great Tubeworm Mysteries

But back to the tubeworms

Mystery:How do the tubeworms obtain nutrition?

Hypothesis #1: Tubeworms are eating free-living bacteria to obtain energy.

FLEXE Great Tubeworm Mysteries

No MouthNo Mouth

No Digestive TractNo Digestive Tract

No AnusNo Anus

Basic Tubeworm Anatomy

But how can they eat with no mouth, gut, or

anus?

FLEXE Great Tubeworm Mysteries

Basic Tubeworm Anatomy Dr. Colleen Cavanaugh used microscopy techniques in 1981 and discovered billions of bacterial cells packed inside the tubeworm’s trophosome.

1011 bacteria per gram of trophosome!!

Plume

Trophosome

Lines of evidence - #1FLEXE Great Tubeworm Mysteries

Also in 1981, Dr. Horst Felbeck discovered Rubisco, the same enzyme plants use in the Calvin Cycle in photosynthesis, in the tubeworm.

Lines of evidence - #2FLEXE Great Tubeworm Mysteries

Rubisco

Calvin Cycle

INPUT = inorganic

carbon

OUTPUT = organic carbon

Sugar

enzymes and

chemical reactions

CO2

H2S from vent fluids

3. Sugars from bacteria are used

as food by tubeworm

Tubeworm + bacteria = Symbiosis!FLEXE Great Tubeworm Mysteries

2. Bacteria in trophosome use

H2S, CO2, and O2 to make sugars via chemosynthesis

1. Tubeworm takes up hydrogen sulfide (H2S),

carbon dioxide (CO2) and oxygen (O2) using its plume

and shuttles these chemicals to its trophosome

CO2 and O2

from seawater

The Mystery Continues …

Mystery:What about tubeworms found at cold seeps?

Hypothesis #2: Seep tubeworms obtain energy in the same way as vent

tubeworms.

FLEXE Great Tubeworm Mysteries

Cold seeps support lush communities

Scientists assumed that seep tubeworms would obtain their energy the same way vent tubeworms do because:

1. Seep tubeworms have plumes2. Seep tubeworms have trophosomes packed full of bacteria that use sulfide as an energy source

FLEXE Great Tubeworm Mysteries

Energy sources in the Gulf of Mexico FLEXE Great Tubeworm Mysteries

Salt layer

Sediment layer

Rock (shale) layer

OceanSulfate in seawater

sulfidesulfide methanemethaneBacteria in the sediment use the energy obtained by oxidizing methanemethane to

create sulfide from sulfate

Hydrocarbons (Methane)

Seep tubeworm community

Plume level: No sulfide(0 µM H2S)

Sulfide measurements around tubeworms

Height of tubeworms =

~ 1 meter

Mid-level: Very low sulfide(0 - 0.5 µM H2S)

Sediment level: Low sulfide(0 - 1 µM H2S)

In the sediment: Very high sulfide levels(100 - 1,000 µM H2S)

FLEXE Great Tubeworm Mysteries

Levels of Sulfide (H2S) at Cold Seeps

The Mystery Continues …

Mystery:How do seep tubeworms take up sulfide?

Hypothesis #3: What do you think???

FLEXE Great Tubeworm Mysteries

Mystery Solved!

These tubeworms have ‘roots’!(well, not true roots, but extensions of their bodies that look and act like roots)

1. Sulfide from the sediment is taken up by

the tubeworm extensions (‘roots’)

2. Sulfide is then transferred to the

symbiotic bacteria in the trophosomes of the

tubeworms

FLEXE Great Tubeworm Mysteries

In the sediment: Very high sulfide levels

(100 - 1,000 µM H2S)