Download Vent.04 - Cal State LA

The Ecosystem Perspective
• Examines interactions between whole
communities and the physical environment.
• Emphasizes how physical setting influences
trophic structure, energy flow and nutrient
cycling.
• To fully understand the system requires
knowledge from all other perspectives: from
individual adaptation, to population dynamics,
to community processes, to flows of energy
and matter.
An example from the book:
energy flows in a temperate forest
Deep Sea
Hydrothermal Vent Communities:
An Example of the Ecosystems Perspective
A New Age of Exploration
• In the last 30 years, the
development of highly
durable and maneuverable
deep submersible vessels has
opened up the abyss to
exploration.
• Scientists were able to study
the behavior and interactions
of midwater organisms and
the community structure and
physiology of deep water
benthic organisms
• In the late 1970s, the deep
submersible Alvin
descended over oceanic
ridges near the Galapagos
Is. to study hydrothermal
vents > 8,000 ft below the
surface.
• Oceanic ridges are ripples
on the sea bottom at the
sites of sea floor spreading.
• Because the earths crust is
thin at the ridges,
geothermal activity is high.
One type of hydrothermal vent:
a “black smoker”
• Hydrothermal vents
discharge super heated
water, > 4000C. It mixes
with ambient sea (40C)
forming a temperature
gradient away from the
opening of the vent.
• The discharge is laden with
dissolved minerals and
gases, including hydrogen
sulfide, H2S. Minerals
precipitate forming
chimneys and ridges around
the discharging water.
A Startling Discovery
• In the warm waters near
the vents, a unique benthic
community was discovered.
• The most abundant
members were crabs,
limpets, clams, eel-like fish,
and an unusual worm.
• The fauna included species
of gigantic invertebrates
representing previously
unknown taxa.
Galotheid crabs
A hydrothemral vent clam and limpets
• The limpets graze on
free living bacteria on
the.
• The clams, Calyptogena
sp., gain nutrition from
internal bacterial
symbionts.
Riftia is in the phylum Vestimentifera, endemic to the vents.
Large individuals are about 1 meter long. They obtain
nutrition only by digesting bacterial symbionts. The bacteria
derive all their nutrition from oxidizing hydrogen sulfide.
• Riftia has no gut.
• The gills (plume) extract oxygen
and H2S from the sea water.
• Both gases are transported on a
form of hemoglobin through the
circulatory system to the tissues.
The ultimate destination of the
H2S and most of the oxygen is
the trophosome (feeding body)
• Capillary beds in the trophosome
distribute the H2S to symbiotic
bacteria, which oxydize the H2S,
grow and are phagositized
by the tissues of the
trophosome.
A deep-sea respirometer held in
place by the Alvin
• The physiology of these
organisms is remarkable.
• They live at elevated
temperatures, but can
withstand wide temperature
fluctuations.
• Ambient pressure can
exceed 100 atmospheres.
Most vent communities (white dots) have been
found along oceanic ridges, which are zones of
sea floor spreading and hydrothermal actvity.
Convection cells deep within the
earth bring molten magma to the
thin crust at the spreading ridges.
Black smokers and chimneys
Stages of formation and loss of a
hydrothermal vent
Remarkably,
the rock contains life. Bacteria
that may be the direct ancestors
of the earliest life forms respire
chemicals in the rocks.
Stages of vent formation and loss
• At the site of a forming vent the sea floor is thin and
geothermal activity heats the surface rock and water
permeating the rock.
• Two groups of bacteria live below the surface in the
porous rock and sediments: mesophiles which live in the
top few meters in temperature around 500C, and
thermomphiles, which live in deeper layers at
temperatures approaching 1500C.
• An diking event (mini eruption) brings molten magma
near the surface. Through convection, water is drawn
through the sediments, up along the sides of the dike,
and expelled at a fissure, the vent.
• It is estimated that the entire volume of the ocean is
drawn through the vents in the oceanic ridge systems
every 8,000,000 yr.
Marine “Snow”
• The water expelled at
the vent soon after the
diking event carries
high concentrations of
the two types of
bacteria.
• The bacteria
agglomerate into
particles called “snow”
Tropic Structure
• The food web is similar to other marine
ecosystems -- with filter feeders, grazers, and
predators.
• The major difference is that all energy derives
ultimately from inorganic chemicals, rather than
the sun. Chemosynthetic bacteria, either freeliving or symbiotic, take the place of the
photosynthetic autotrophs of other systems.
Succession at a vent site
A. When the vent erupts, marine snow
falls, an initial bounty.
B. After some months, the site is
colonized by dispersive species,
analids, isopods, etc.
C. After several years, Riftia colonies
have taken over the site.
D. Over time, the composition of the
expelled water changes. Additions of
iron oxides sometimes stain the
Riftia tubes.
E. As the concentrations of H2S in the
discharge diminish, so does the
biomass of the Riftia assemblages.
Eventually, the vent fauna becomes
at the site.
A
B
C
D
E
The colonization problem
• Vents are unstable. The appear and disappear
in time courses of a few decades to centuries
at most.
• Therefore, the vent communities must
disperse juveniles to find newly formed vents.
• Most species have dispersing larvae
provisioned with yolky eggs. They swim and
ride bottom currents to colonize new vents.
More than one variation on a theme.
• Since the discovery of the hot vent
communities, cold vent and seepage
communities have been discovered in the
deep sea.
• Any reduced compound appears to provide a
suitable energy source. For example, some
communities thrive on methane that erupts
as organic sediments are subducted under
techtonic plates.
Discovery of the hydrothermal vent fauna
has spawned a new field of study,
“extremophiles”, and transformed our
thinking about extraterrestrial life.
Question: In what major way might
the energy flow diagram of the
hydrothermal vent communities look
different from tha of a deciduous
forest?