Updates From Sea | Cruise 2007
January 21st
By Eric Simms, Education Outreach Coordinator
How Do Your Mussels Measure Up?
SEAS students following this cruise already know that the SEAS program is designed to help students learn about deep-sea science by participating in the research, as much as possible. Of course we can't bring you out here, but we still want to help you understand what it's like here and in the deep-sea, by comparing things in this environment to things in your own environment. That's the reasoning behind the "Classroom to Sea" lab. The lab featured this year is the Mussel Lab. We chose mussels because they are found in so many environments, including the deep-sea.
Clump of deep-sea mussels at EPR. Photo © 2007 DSV Alvin Group
Maybe you've seen them attached to docks or rocks - or in the seafood case at the grocery store - or found their shells washed up on the beach. If you've ever been to the coast, or enjoy eating seafood, chances are you're familiar with mussels. These interesting animals belong to a group known as bivalves, which means that they have two identical hard valves (or shells) connected by a hinge that protects their soft bodies. Mussels live in fresh, salt and brackish (between fresh and salt) waters around the world. Most people are familiar with different types of edible mussels that are found in shallow water along the coast, but some mussels also make a home for themselves at hydrothermal vent communities in the deep sea.
Most mussels are filter feeders - they filter tiny algae, bacteria, and animals from the water by using a siphon to draw water between their shells and trapping the food in a layer of mucous. The mucous is then moved into their gut where the food is digested for energy. It may not sound pleasant to us, but for mussels it's a very energy-efficient and effective way to feed. But what if you're a mussel and you live in the deep sea where there isn't much food to filter from the water? You get some help by having something else make your energy for you.
Collecting a sample. Photo © 2007 DSV Alvin Group
Hydrothermal vent mussels have developed a symbiotic relationship with bacteria that live on their gills. The mussels provide the bacteria with a place to live, and the oxygen, carbon dioxide and sulfur chemicals they need to create energy. In exchange, the bacteria use the chemicals to make sugars that the mussels use for energy. The mussels can also filter feed just like their shallow water cousins, but it appears that the healthiest mussels rely heavily on their bacteria for their energy.
Open mussel showing gill tissue. Photo © 2007 E. Simms
Some of you have already completed dissections on shallow water mussels in the classroom so that you can compare their anatomy to deep-sea mussels. Normally, we would collect mussels during the cruise and dissect them onboard to compare our data with yours. Unfortunately, the recent volcanic eruption on the seafloor here has eliminated most of the sites where mussels were known to live (see the Jan. 14th log). We have found a few here and there that survived the eruption, but they don't appear to be very healthy - that's probably either because the vents they live near aren't putting out enough fluid for their bacteria anymore, or the lava from the eruption moved the mussels away from any vents. In fact, on this cruise scientists located a group of mussels that had been studied before the eruption - but they had been moved by the lava flow almost two football fields (180 yards) away from their original location!
But don't fear - your dissection efforts are not in vain. You can compare your data to deep-sea mussel data that were collected here at the East Pacific Rise in 2005 by clicking SEAS Deep-Sea Mussel Data. Be sure to read the 'Field Notes' before you explore the data to learn how the mussels and data were collected. The Field Notes should help you get a better sense of the at-sea portion of the lab. Also, if you have questions about the "Classroom to Sea" Mussel lab, now is the time to send them in to the Ask-a-Scientist forum. Many of the same folks who helped collect the data in 2005 are back out here on this cruise. And they'd love to hear from you!
Click here for pictures on deep-sea mussels!
Aside
Do mussels have muscles?
Yes, they do. Mussels have very strong adductor muscles that they use to tightly close their shells to protect them from predators. And they have a muscular foot that they use to move and wedge themselves into cracks (click here to see a video clip of deep sea mussels in motion). But muscles aren't the only strong part of mussels - they also produce byssal threads, which are strings of protein that they use like small ropes to attach to surfaces, including each other. These threads have the amazing ability be both elastic and very strong (they can stretch out to 160% of their length while still retaining 5 times the strength of our Achille's tendon). Some scientists are studying the byssal threads of mussels with hopes of creating a material that can be used to make artificial tendons and ligaments for humans (see Intertidal Invertebrate Migration, L. Brentner, Clark University).
