Transcript Mussel Lab

Day 1: Exploring Extreme Food Webs
Days 2 & 3: Community Succession in Local
Environments and Cold Seeps
Day 1: Extreme Food Webs
Organisms in any
ecosystem can be
organized into
categories based on
how they get the
energy they need to
survive, grow and
We refer to these
categories as trophic
levels and the flow of
energy as a food web.
(Source: Arctic Climate Impact Assessment, ACIA)
Trophic Levels
= the positions of one or more species in a
food web relative to the initial source of
• Primary producers create biomass using
energy from the initial source (e.g., the sun)
• Primary consumers get their energy from
consuming primary producers
• Secondary consumers get their energy from
consuming primary consumers
• Tertiary consumers get their energy from
consuming secondary consumers
Many organisms can occupy more than one trophic level
What gives you energy?
List some of the items that provided you
with energy yesterday
(e.g., hamburger, salad, fish, rice, bread, fruit, milk)
What’s the source?
For each item, trace the item to its
original energy source
(e.g., milk  cow  hay  sun)
Now, create a Hydrothermal
Vent Food Web!
1. Watch the Chemosynthesis and Hydrothermal
Vent Life video
1. Complete the Chemosynthesis and
Hydrothermal Vent Life multimedia discovery
Day 2: What is Succession?
Succession refers to sequential changes in the
composition of species in an ecosystem over time as
a result of changes in environmental conditions and
interactions between species
Part 1: Thinking locally…
A farmer has agreed to work with a local
conservation group to let one of his fields adjacent
to a forest go fallow (unfarmed) with the intent of
creating more diverse habitat for local wildlife.
Discuss and record:
What changes do you predict will happen to this
site if there is no human intervention during the
next 50 years?
Part 2: Exploring Cold Seep
Community Succession
Communities in the cold seep environment
rely on foundation species such as
tubeworms to provide habitat.
Environmental conditions at cold seeps can
vary considerably over time (e.g., after
several years of flow seepage declines)
Tubeworms can withstand environmental
changes at seep and can live 100-200 years
or more
• The community of other species associated
with the tubeworms, however, undergoes
succession over time.
Let’s look at those changes over time.
Young Tubeworm Community
The community begins when chemicalrich fluids with high levels of sulfide and
methane begin to seep out of the
sediment and into the surrounding water
• Microbes (bacteria and archaea) are the
first organisms to arrive on the scene as
primary producers.
• The microbes use the sulfide and methane
in the sediment for energy to create organic
compounds (e.g., sugars) through the
process of chemosynthesis
0 – 20 years old
Young Tubeworm Community
Deep-sea mussels and tubeworms arrive
early at the seep and act as primary
producers because of their reliance on the
symbiotic bacteria in their tissues
• Most other organisms cannot tolerate the
high concentration of toxic sulfide and
methane at this early stage, so the
mussels and tubeworms enjoy little
competition (other than with each other)
for space and access to the seep fluids
• A few primary consumers are present
during the early life of a seep, including
shrimp, crabs, snails and worms, but the
numbers of secondary and higher-order
consumers are very low
0 – 20 years old
Middle-aged Tubeworm
Over time, seep fluids (e.g., methane and hydrogen sulfide) in
the habitat decreases significantly
• The once abundant mussels have begun to
disappear, along with some species of shrimp
and snails present during the earlier years
Tubeworms, however, continue to thrive
because they have root-like structures that
extend down into the sediments
• Even though the amount of sulfide has
decreased at this stage, there is still sulfide
available in the sediments which the
tubeworm extracts with their root-like
20 – 40 years old
Middle-aged Tubeworm
During this stage of succession the number
of secondary consumers increases for
several reasons:
1) lower toxicity of the habitat due to declines
in seepage and the uptake by tubeworms for
their symbiotic bacteria
1) the presence of enough sulfide and
methane right at the sediment surface makes
the environment more productive than the
surrounding deep sea, and
1) as tubeworms grow, they create additional
habitat for organisms in and around the
tubeworm colonies.
20 – 40 years old
Old Tubeworm Community
Eventually, as seepage declines, methane and sulfide
concentrations above the sediment surface are low and are
essentially the same as the surrounding seawater.
•These conditions support the arrival of
higher-order consumers (e.g, crabs, fish,
sea stars) who are not adapted to survive
in the presence of higher levels of toxic
• It is unknown how long tubeworm
“bushes” in this final stage of succession
can survive at cold seep environments
(although it is likely to be measured in
centuries!), but their persistence indicates
that they must still be able to extract
sulfide from beneath the sediment surface
using their root-like extensions.
40+ years
Challenge Scenario
Your group just collected a
sample from a cold seep
tubeworm community in the
Gulf of Mexico.
• Is this community from an
old tubeworm aggregation OR
from a young tubeworm
aggregation associated with an
early successional stage?
How can you tell??
Comparing Trophic Proportions
You recall learning at a recent
scientific conference that
researchers studying
tubeworm longevity found
interesting patterns in the
community of animals around
young vs. older tubeworms.
They found that the proportion
of organisms within each
trophic level changed as the
tubeworms aged. Because you
can’t tell how old your
tubeworms are, you decide to
sort your sample by trophic
level and see if you can
determine the age of the
community by comparing your
results to the data in Dr.
Cordes’ scientific research
What do you think??