Day 1: Introduction to mussels
Day 2: Mussel dissection and data collection
Day 3: Deep-sea mussel data & analysis
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.
Intertidal
Marine
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)
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.
Indigestible
particles and
filtered water
leave the mussel
through the
excurrent
siphon.
The mussel’s 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.
Two small labial palps sort the
particles directing edible bits into
the mouth.
Click here to see video of the feeding process.
Intertidal mussels
Mytilus californianus
Intertidal Mussels
Review Questions
• How do intertidal marine mussels feed?
• Where do the organisms that intertidal
marine mussel consume get their energy?
Deep-sea Hydrothermal Vent Mussels
Bathymodiolus thermophilus
Deep-sea Cold Seep Mussels
Bathymodiolus brooksi and B. childressi
Deep-sea Cold Seep Mussels
Bathymodiolus brooksi
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?
And not just survive but thrive!
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 deep–sea
extreme environment get their food, where do you
think deep-sea mussels get their food?
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 you’d expect to see in
a comparison of intertidal mussels with deepsea mussels.
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?
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
Step 1:
Measure
shell length
Measure the length of each mussel shell, in mm.
Record this on the datasheet.
Step 2:
Open the
Mussels
Open each mussel by cutting through its adductor muscles.
Step 3:
Examine
the
organs
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.
Gill tissue in weighing dish
Place the gill tissue (all pieces, from both sides) in a
plastic weighing dish, and set aside.
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.
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.
Here’s what you should have:
1. A tray containing
gill tissue
2. A tray containing
the rest of the
body tissue
3. A clean shell
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.
Measurement: Step 2
Place the gill into the cylinder.
Make sure all the tissue is
completely submerged.
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.
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.
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?
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?
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.
“Field Notes”
continued
Location of Vent Sites:
Locations of vents where deepsea 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.
“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.
“Field Notes”
continued
Observations:
What’s 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.
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.
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 deepsea marine organisms for many years. She will
also discuss adaptations in general and the
relative importance of symbiosis in deep-sea
ecosystems.
Stay tuned!