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Mussels at work – filter feeding – made visible with science

With the naked eye, no filter-feeding can be seen. Using a scientific filming method, the fluid flow becomes visible….. and so the mussel’s work, becomes observable



Mussels at Work, is a short 2 minute video, revealing something that you cannot see with just the naked eye – a bivalve mollusc (Common Mussel) doing it’s work of filter feeding.

A bit of science reveals the invisible…. The physics of light, density differentials and fluid flow, along with an adapted Schlieren photography method, captures the visual end results of the mussel….. doing it’s thing….. working hard for it’s living.


See it’s work here in our YouTube vid’.
Mussels at Work – filter feeding – made visible with science.


A quickie on mussels:
Mussels attach themselves most securely to a solid surrounding, a rock, a marine boat pontoon, etc, with self made byssal threads.

They live out there lives in this one place, within the protection of their shells, of which they have two halved sections, hinged together along one edge, allowing the ability to open and close the two halves on the other side.

If on the shore and the tide is out, they close the shells. If under water and are threatened by predators, they also close the shells…. It’s a protection thing.

When under water and under no threats, they open their shells and are then free to suck the surrounding water into themselves, filter any food particles held in the water, then expel the then filtered water out and away… they are filter-feeders.   



A quickie on the sciencey bit:
When an object is observed (go stare at something), you make it out (see it – as you are the observer) from the light that comes from it, heading towards where your eyes are.

The Schlieren photography method gets a precise grip on the light heading to the observer (a camera). The precision is gained from a concave mirror, made with extremely precise engineering standards and end optical quality.

In the video, the Schlieren images seen are all within a circular background…. That background is determined by the mirror size…. only things occurring in front of one of these mirrors, can be observed with this method.

* The mirror used in the video is 150mm diameter and has a long focal length of 1500mm…. the object to be observed must fit within the 150mm diameter, (no problem for a mussel) and must be placed in front of the mirror, but well behind its focal point (the long focal length of 1500mm allows this.
* The camera should be placed beyond the focal point (wherever you get a good and focused view – (will vary according to the camera and lens used).
* The focal point is where the sciencey bit is applying to the image seen in the video.


At the focal point.
place a horizontal ‘edge’ so as to block a little of the total light from continuing to the camera…. the image observed in the camera will dim slightly.
We are now ready for the effects of some physics to be captured in this slightly dimmed image.

The physics to capture:
Light travelling through different densities will be refracted and so change direction.

Back at the focal point:
If any of the focused light has been refracted on route, that light (only that stream of light) will have a slightly altered direction:
* If upwards – It makes it over the blocking ‘edge’… this will be ‘extra’ light to the image and show up as brighter areas
* If downwards – It slams into the blocking ‘edge’… this will be ‘less’ light to the image and show up as darker areas


At the camera.
The camera captures all the light that has travelled through the focal point:
Light that has travelled unaffected by refraction – main lit areas (of this video image)
Light that has travelled effected by refraction – brighter and darker areas (of this video image)

The results. (simplified).
Moving (as videoed) images showing… ummm showing what?

Because the physics is known – light refracts when travelling through areas of different densities – the results show visually that this physics is occurring in certain areas in the image.
Therefore there are certain areas in these images of different densities, each with it’s own boundary edge  – these areas correspond to the exhaled fluid flow streaming from the mussel, into the surrounding fluid medium = a visual result to study of the mussels ‘work’


End Note.
You made it this far?! … Have a badge.
If at any point in the vid or reading this, you “get” how applying a bit of science to the world around us, can be somehow interesting and perhaps even fun… then love science… love the study of nature… pass on your knowledge.

The common mussels that are alive and kicking on this planet, in their environments….. are working today.

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4 Responses to "Mussels at work – filter feeding – made visible with science"

  1. admin says:

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  2. Shona says:

    Very useful for to use in education on popular science group, I will. Very beautiful, the flow and the panpipe music scenes. Nature is pretty. The mussel is hard working (and is tasty hehe).

  3. Sharky says:

    Extraordinary. The little creature, is a creature, as in alive, kicking, and hungry.
    On the shore these are lifeless (apparently). Just fixed to rocks in great numbers.
    After this I can picture them “working”.
    Very interesting article and image creation. Useful to educate. 9/10!!

  4. Jack says:

    Neat project. Revealling what cannot be seen with the naked eye, makes this very interesting.
    Science is very interesting, when presented like this, just for interest and education.

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