FLEXE Great Tubeworm Mysteries How can animals like the giant tubeworm exist in the cold dark seafloor?
Jan 13, 2016
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)