Deep-Sea Hydrothermal Vent Communities

Comparison with Other Deep-Sea Benthic Environments Most deep-sea environments are characterized by: Low availability of food No light, no photosynthesis Falling remains of dead organisms, decaying organic matter Low (0-2°C), relatively constant temperature High pressure (400-500 times atmospheric)

Summary of General Biological Characteristics of Deep-Sea Macrofauna Reproduction and Development Late reproductive maturity Slow development Physiology Low metabolic rate and activity level Ecological Long lived species Low population densities, but high species diversity

Hydrothermal Vents Vents are associated with mid-ocean ridges, spreading centers. Cold waters percolate into crust and are geothermally heated before being vented at very high temperatures. Vent waters are not only hot, but low in oxygen and rich in metals and hydrogen sulfide.

Black and White Smokers 2. The seawater continues to seep far below this point in the ocean crust. Energy radiating up from molten rock deep beneath the ocean floor raises the water's temperature to around 350-400°C. As the water heats up, it reacts with the rocks in the ocean crust. These chemical reactions change the water in the following way: All oxygen is removed. It becomes acidic. It picks up dissolved metals, including iron, copper and zinc. It picks up hydrogen sulfide. 3. Hot liquids are less dense and therefore more buoyant than cold liquids. So the hot hydrothermal fluids rise up through the ocean crust just as a hot-air balloon rises into the air. The fluids carry the dissolved metals and hydrogen sulfide with them. 4. The hydrothermal fluids exit the chimney and mix with the cold seawater. The metals carried up in the fluids combine with sulfur to form black minerals called metal sulfides. These tiny mineral particles give the hydrothermal fluid the appearance of smoke. Many factors trigger this reaction. One factor is the cold temperature of the seawater. A second equally important factor is the presence of oxygen in the seawater. Without oxygen, the minerals would never form. In white smokers, the hydrothermal fluids mix with seawater under the seafloor. Therefore, the black minerals form beneath the seafloor before the fluid exits the chimney. Other types of compounds, including silica, remain in the fluid. When the fluid exits the chimney, the silica precipitates out. Another chemical reaction creates a white mineral called anhydrite. Both of these minerals turn the fluids that exit the chimney white Black and White Smokers

Hydrothermal Vent Distribution

Hydrothermal Vent Communites 25 years of exploration have revealed: A new phylum At least 20 new families Over 90 new genera Over 300 new species Over 250 new strains of free-living bacteria Biomass Up to 30 kg/m2 1000 x greater than typical biomass observed on deep-sea floor

Vestimentiferan worms (Riftia pachyptila ) Hydrothermal Vent Macrofauna: Worms Vestimentiferan worms (Riftia pachyptila ) Serpulid polychaete worms

Giant clams (Calyptogena magnifica) Hydrothermal Vent Macrofauna: Bivalves Giant clams (Calyptogena magnifica) Mussels (Bathymodiolus thermophilus)

What supports this abundance of life around hydrothermal vents What supports this abundance of life around hydrothermal vents? What is the energy source for this ecosystem?

Chemosynthesis Basis of life around deep sea hydrothermal vents is chemosynthesis rather than photosynthesis. Chemical energy rather than solar energy supports the ecosystem. Bacteria rather than plants are the primary producers.

Vent Ecosystems Depend on 2 Types of Bacteria: Free-living bacteria Symbiotic bacteria Geol 104/BioES 154

Tube Worm: Riftia pachyptila Unusual animal No mouth No anus No digestive tract Dependent upon bacteria living in its gut Gills extracts hydrogen sulfide, carbon dioxide & oxygen from seawater; blood delivers these to gut In return, bacteria provide nourishment for it

Hydrothermal Vent Macrofauna: Environmental Constraints on Life Cycles and Reproduction Suitable vent environments for these organisms are rare. Individual vents have short life-spans. Volcanic eruptions and earthquakes pose further hazards. These conditions favor rapid growth rates, continuous reproduction.

Geol 104/BioES 154

Geol 104/BioES 154

Geol 104/BioES 154

Geol 104/BioES 154

Geol 104/BioES 154