The Dance of the Mussel

Natural systems have a remarkable ability to generate all sorts of spatial patterns, a process called spatial self-organization. Although we have many examples of such patterns, it is often unclear how they have formed, as it often takes years if not many decades for these patterned lands to develop.

Young mussels, however, are happy to give you a demonstration of how this works in just a  day. Mussels like to live in clusters, were they are safe(r) from predators and the danger of dislodgement by waves. If they would live in one big cluster spanning many meters, however, the ones in the middle have nothing to eat. How they solve this, is shown in the following movie:

This experiment has been published in:

Van de Koppel, J., Gascoigne, J.C., Theraulaz, G., Rietkerk, M., Mooij W.M., & Herman, P.M.J. 2008 Experimental evidence for spatial self-organization and its emergent effects in mussel beds. Science 322:739-742. Link to Journal.

A unique think about pattern formation in mussels is that you can just do it in a very simple laboratory setup, or even in front of a school class. You just need a container of sea water, a webcam hooked to a laptop, and an aquarium pump to supply air. That is, as long as you keep the experiment short (else you need running seawater).

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To do the “dance” that you can see in the above video, mussels do a specialized “stepping pattern”, called a Lévy walk. This Lévy walk, in which they alternate small steps with large leaps, is the optimal walk to quickly embed yourself in a safe pattern.

Monique de Jager has study this process, and has published a neat paper about it. The reference is:

De Jager, M., Weissing, F.J., Herman, P.M.J., Nolet, B., & Van de Koppel, J. 2011  Lévy walks evolve through feedback between movement strategies and environmental complexity. Science 332, no. 6037:1551-1553. Link to Journal.

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