Marine Mussel Lab

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Marine Mussel Lab

• Day 1 Introduction to mussels
• Day 2 Mussel dissection and data collection
• Day 3 Deep-sea mussel data analysis

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Day 1 Mussel Introduction
Mussel Taxonomy Phylum Mollusca Class
Bivalvia Order Mytiloida Family Mytilidae
Scientific classification helps us understand
which organisms are closely related to each
other. Evidence suggests that deep-sea seep
mussels are evolved from intertidal mussels and
vent mussels evolved from seep mussels.
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IntertidalMarine Mussels

• Basic Anatomy
• Valve (or shell), two valves left right
• Adductor muscles, posterior anterior
• Mantle, lining the shell
• Gills, two layers on each side
• Siphon
• Foot Byssal threads
• Digestive system (stomach)

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Intertidal mussels are filter feeders.
Seawater in the intertidal mussels environment
is full of plankton, algae and other
photosynthetically derived food particles.
The gills are also involved in respiration.
Extraction of oxygen occurs primarily at the gill
surface.
The mussels gills are involved in filter
feeding. The mussel draws water into its gills
through an incurrent siphon. Mucous on the gills
traps food particles.
Cilia on the gills move the mucous and food
toward the mouth.
Indigestible particles and filtered water leave
the mussel through the excurrent siphon.
Two small labial palps sort the particles
directing edible bits into the mouth.
Click here to see video of the feeding process.
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Intertidal musselsMytilus californianus
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Intertidal Mussels Review Questions

• How do intertidal marine mussels feed?
• Where do the organisms that intertidal marine
  mussel consume get their energy?

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Deep-sea Hydrothermal Vent MusselsBathymodiolus
thermophilus
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Deep-sea Cold Seep MusselsBathymodiolus brooksi
and B. childressi
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Deep-sea Cold Seep MusselsBathymodiolus brooksi
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Think about it
In the deep-sea environment, sunlight does not
penetrate to the seafloor so there is little to
no photosynthetically-created food in either the
seep or vent environment. How do deep-sea
mussels get enough food to survive?
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And not just survive but thrive!
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Hydrothermal vent and cold seep environments
review
Q What is the source of energy at deep-sea seeps
and hydrothermal vents? Q Who are the primary
producers in these deep sea environments? Q
Considering how other animals in the deepsea
extreme environment get their food, where do you
think deep-sea mussels get their food?
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Forming hypotheses
Q Considering that intertidal mussels use their
gills extensively in filter feeding, what kind of
anatomical adaptations would you expect to find
in a deep sea mussel? Make a prediction of what
youd expect to see in a comparison of intertidal
mussels with deep-sea mussels.
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Day 2 - The mussel lab protocol
Scientists studying deep-sea mussels have
carefully examined mussel anatomy, in particular
the gill tissue, and have compiled a dataset on
gills from multiple dissections. To make a valid
comparison we will follow the same protocol used
to collect deep-sea mussel gill data. Q Why is
it important to use the same procedures in the
classroom dissections as the scientists used in
their dissections?
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What will we need?

• Marine mussels
• Dissecting tray
• Two graduated cylinders (one small 10ml, and one
  large 250 ml)
• Small, sharp knife to open mussels
• Dissecting forceps
• Small dissecting scissors
• Plastic weighing dishes
• Calipers
• Water

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Step 1Measure shell length
Measure the length of each mussel shell, in mm.
Record this on the datasheet.
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Step 2Open the Mussels
Open each mussel by cutting through its adductor
muscles.
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Step 3Examine the organs
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Step 4 Remove the Gill tissue (Ctenidia)
Locate the gills. Note the two layers on each
side. Lift the gill tissue up from the mantle
and look for the line where this tissue is
connected to the mantle. Using scissors,
carefully cut along this line to remove the gill
tissue. Be careful to get all of it, while
avoiding the mantle.
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Gill tissue in weighing dish
Place the gill tissue (all pieces, from both
sides) in a plastic weighing dish, and set aside.
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Step 5
Next slide a knife under the mantle. Remove all
visceral tissue (all soft body tissue) from the
shell.
Pull the mantle away from the shell, using the
knife.
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Repeat for the other half of the shell
Scrape all tissue into another plastic weighing
dish. Be sure to scrape all tissue off the shell,
especially the adductor muscle, which is tightly
connected to the shell.
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Heres what you should have

• A tray containing gill tissue
• A tray containing the rest of the body tissue
• A clean shell

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Volume Displacement Measurement Step 1
Next, measure the volume of tissue. First, fill
the small measuring cylinder half full of water.
Record this starting volume on the datasheet.
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Measurement Step 2
Place the gill into the cylinder. Make sure all
the tissue is completely submerged.
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Measurement Step 3
With the gill tissue submerged, note the final
volume (water gill) and record this value on
the datasheet. The volume of gill can be
calculated as this final volume minus the
starting volume.
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Measurement Step 4
Now measure the volume of body tissue using the
large measuring cylinder. You may need the larger
cylinder to measure the volume of rest of the
mussel tissue. Follow the same volume
displacement procedure used to measure gill
tissue. Record your results on the datasheet.
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Calculations
Determine the proportion of gill volume to total
mussel tissue volume. Enter your data into the
class dataset and determine the class average.
Predict how this will compare with deep-sea
mussels. Q Will the deep-sea mussels have the
same proportion of gill tissue? Or will they be
different?
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Day 3 - Deep-sea data comparison
Retrieve the vent and seep mussel data. Calculate
the average proportion of gill to total body
volume for the vent and seep mussels. Read
through the Field Notes to be sure you are
familiar with how these data were obtained.
Compare your class average to the seep and vent
mussel averages. Are they the same or different?
Q What do you think accounts for the
differences? Q Thinking about the protocol that
you followed, are there factors that might cause
variables in your results?
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Deep-sea Field Notes
Excerpts - East Pacific Rise Cruise, May
2005 Collecting mussels from the ocean
floor Although we tried to collect consistent
samples, the number of mussels in each sample
varied because of the uneven distribution of
animals, but also because of the challenges of
working in this environment. Remember, deep-sea
mussels live at the bottom of the ocean, 2500
meters deep, in pitch darkness, and we need a
deep-sea vehicle like Alvin to find and collect
them. Often, the mussels are clumped, held
together by byssal threads, and it's easy to
collect a bunch. Other times, we get only a few.
With each grab, the mussels are placed inside the
Biobox (a heavy-duty plastic box) and brought to
the surface. As soon as Alvin is on deck, the
mussels are removed from the Biobox, placed in
cold seawater and then stored in a walk-in
refrigerator (Temperature 2.8degrees C
/37degrees F) until dissection. Dissections are
typically on the same day as collection. In most
cases, the biologists in Dr. Shank's lab also
sample tissue from these mussels for genetic
analysis.
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Field Notes continued
Location of Vent Sites Locations of vents
where deep-sea mussels were collected are shown
on this bathymetry map. The red areas on the map
are the tallest part of this section of the East
Pacific Rise. Green and blue areas are deeper and
colder.
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Field Notes continued
Deep Sea Mussel Dissection For each mussel, we
measure shell length and then open the mussel to
examine the body cavity. We dissect mussels and
measure gill tissue volume and total body tissue
volume. We then calculate the ratio of gill
volume to total body volume. We use ratios so
that we can make a fair comparison between
individuals of different sizes. By the way, on
nearly all of the deep-sea mussels collected, we
notice a large number of byssal threads covering
the shells. These threads, made of incredibly
strong collagen, serve as a means for the mussels
to attach themselves to the substrate.
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Field Notes continued
Observations Whats this living in here? One
of the first things we notice inside many of the
mussels is an abundance of eggs. So these mussels
are apparently healthy and reproductive. We also
see small polychaete worms in many of the
mussels. This particular species of worm lives
inside mussels and very little is known about it.
As the mussel irrigates its own gills and filters
food by moving sea water in and out of its shell,
the worm likely lives off of the particles
floating around inside. It may also live off of
the mucus formed by the mussel, but scientists
studying these worms are not entirely sure about
this. Polychaete means "many bristles," which is
obvious when you look closely at this worm.
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Putting it all together

• How did your class average compare to the seep
  and vent mussel averages. Were they the same or
  different?
• If different, what accounts for the differences?
• Answer the questions on the Comparing our Data
  handout. These will prepare you for the FLEXE
  Forum.

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NEXT The FLEXE Forum
In March, Dr. Nicole Dubilier, from the Max
Planck Institute of Marine Microbiology, will
host the FLEXE Forum to discuss your findings.
Dr. Dubilier is an expert on symbiosis and has
studied deep-sea marine organisms for many years.
She will also discuss adaptations in general and
the relative importance of symbiosis in deep-sea
ecosystems. Stay tuned!