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 form FLEXE 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 Energy Reduced chemical (often sulfide, HS - ) Oxidized chemical Chemosynthesis: CO 2 + H 2 O  sugars + O 2 Photosynthesis: Chemical Energy 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 Mouth No Digestive Tract No 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 bacteria per gram of trophosome!! Plume Trophosome Lines of evidence - #1 FLEXE 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 - #2 FLEXE Great Tubeworm Mysteries Rubisco Calvin Cycle INPUT = inorganic carbon OUTPUT = organic carbon Sugar enzymes and chemical reactions CO 2

H 2 S 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 H 2 S, CO 2, and O 2 to make sugars via chemosynthesis 1. Tubeworm takes up hydrogen sulfide (H 2 S), carbon dioxide (CO 2 ) and oxygen (O 2 ) using its plume and shuttles these chemicals to its trophosome CO 2 and O 2 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 plumes 2. 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 Ocean Sulfate in seawater sulfide methane methane Bacteria in the sediment use the energy obtained by oxidizing methane to create sulfide from sulfate Hydrocarbons (Methane) Seep tubeworm community

Plume level: No sulfide (0 µM H 2 S) Sulfide measurements around tubeworms Height of tubeworms = ~ 1 meter Mid-level: Very low sulfide ( µM H 2 S) Sediment level: Low sulfide (0 - 1 µM H 2 S) In the sediment: Very high sulfide levels ( ,000 µM H 2 S) FLEXE Great Tubeworm Mysteries Levels of Sulfide (H 2 S) 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 ( ,000 µM H 2 S)