Mussel beds are “as strong as steel”

Mussel beds are not a random clustering of mussels, but they contain patterns that resemble the arrangement of molecules and atoms in materials like bronze, steel or polymers. PhD student Quan-Xing Liu, myself, and a team of ecologists and mathematicians revealed their findings in the journal Proceedings of the National Academy of Science (PNAS) of July 1st.

Direct link:

“In our study we discovered that mussels form a pattern based on the mathematical principle behind phase separation, a process unknown within ecology,” highlights drs. Quan-Xing Liu of the NIOZ, currently working at the University of Amsterdam. Phase separation, where molecules and atoms of different types separate out to form spatial patterns, is an important physical process explaining the strength of alloys like bronze or steel, or polymers like polystyrene.

Until now, ecological models explain regular, self-organized spatial patterns, based on spatial differences in birth and mortality rates of organisms. The phase separation principle is solely based on movement and therefore deals with animal behaviour. “This is therefore a fundamentally different process of ecological pattern formation,” Liu adds.

Classroom experiment
“This discovery was made with a very simple experiment that can be done in any school classroom,” says prof. dr. Johan van de Koppel of the NIOZ, who is the supervising author of this article. “We spread out mussels in an aquarium and using a camera, we watched them move around to form strings that become regularly spaced on the aquarium bottom. The strings then form a net shape, very similar to that found in the field. In these strings, local mussel density is high enough for the mussels to attach to each other together using byssus threads. Because of the net-shaped patterns, the mussels are well protected against the pounding of waves and the snatching by predators such as gulls that threaten them in the real world.”

Quan-Xing Liu then made a mathematical description of the movement of mussels that he integrated into a model. To his surprise, this model was very similar to the classical model for phase separation developed by John Cahn and John Hilliard in 1958. Phase separation leads to the formation of honeycomb-shaped structures within materials that make polymers and alloys such as bronze and steel very strong. These results highlight that the same process makes mussel beds robust. Mussel beds are, so to say, ‘as strong as steel’.

A unifying principle
The results of this study extend well beyond the ecology of mussels. Aggregation and pattern formation is common to many animals. By demonstrating in their analysis the potential of applying phase separation models to ecological systems, they alert colleagues in their field to the possibility of using the results and models from the physics community in applications to ecological phenomena. Potential applications include aggregation in foraging birds, and mound building in social insects.

Moreover, it highlights that even in the 21st century, scientists can discover unifying principles that explain common phenomena in seemingly unrelated fields such as material science and ecology.

This study was financially supported by The Netherlands Organisation for Scientific Research (NWO) through the National Programme Sea and Coastal Research: the Project WaddenEngine, and by the Mosselwad Project, funded by the Waddenfonds and the Dutch Ministry of Infrastructure and the Environment.

Quan-Xing Liu, Arjen Doelman, Vivi Rottschäfer, Monique de Jager, Peter M.J. Herman, Max Rietkerk, Johan van de Koppel. Phase separation explains a new class of self-organized spatial patterns in ecological systems. PNAS July 1 2013.


A paper on Early Warning Signs in Science as coauthor with Marten Scheffer

Anticipating Critical Transitions
Marten Scheffer, Stephen R. Carpenter, Timothy M. Lenton, Jordi Bascompte, William Brock, Vasilis Dakos, Johan van de Koppel, Ingrid A. van de Leemput, Simon A. Levin, Egbert H. van Nes, Mercedes Pascual, John Vandermeer

Tipping points in complex systems may imply risks of unwanted collapse, but also opportunities for positive change. Our capacity to navigate such risks and opportunities can be boosted by combining emerging insights from two unconnected fields of research. One line of work is revealing fundamental architectural features that may cause ecological networks, financial markets, and other complex systems to have tipping points. Another field of research is uncovering generic empirical indicators of the proximity to such critical thresholds. Although sudden shifts in complex systems will inevitably continue to surprise us, work at the crossroads of these emerging fields offers new approaches for anticipating critical transitions.

You can find more at the Sciencemag website:

Oil spill triggers cliff erosion on southern US marshes

The BP Deepwater Horizon oil spill temporarily worsened existing manmade problems in Louisiana’s salt marshes such as erosion, but there may be cause for optimism, according to a new study.

A study appearing online Monday in the Proceedings of the National Academy of Sciences found the 2010 spill killed off salt marsh plants 15 to 30 feet from the shoreline and this plant die off resulted in a more-than-doubled rate of erosion along the marsh edge and subsequent permanent marsh habitat loss. Vegetation farther from shore was relatively untouched by the incoming oil.

“Louisiana is already losing about a football field worth of wetlands every hour, and that was before the spill,” said Brian Silliman, a University of Florida biologist and lead author of the study. “When grasses die from heavy oiling, their roots, that hold the marsh sediment together, also often die. By killing grasses on the marsh shoreline, the spill pushed erosion rates on the marsh edge to more than double what they were before. Because Louisiana was already experiencing significant erosive marsh loss due to the channelization of the Mississippi, this is a big example of how multiple human stressors can have additive effects.”

(From the University of Florida Press release)

For the paper, look here:

For the English press release, see:

For the Dutch press release, see:

For a US newspaper article about our work, see:

For some Dutch newspaper article, see:

See also vroege vogels:

Tjisse van der Heide’s paper on the symbiosis between seagrass, loripes and sulfide-reducing bacteria has appeared in Science!

About a year ago Tjisse came to me with a brilliant experiment and a even more birllian idea. I helped him to shape it up for Science. And it worked!

See here the abstract:

Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis, a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve–sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters and offer new prospects for seagrass ecosystem conservation.

and the Issue Highlight:

Ellen’s paper on spatial patterns as indicator appeared in Ecology!

Ellen Weerman (former PhD-student with Peter and Johan) her paper on spatial patterns as indicator of degradation appeared in Ecology!

Do you know that with this publication she published all (relevant) chapters of her PhD-thesis… she worked at Groningen University last two years… she works at HAS (university of applied biological science) ‘s Hertogenbosch since April 1 (this is no joke! 🙂 )…

Do you know that current SE members Peter, Johan and Jim are co-authors on this paper.

Do you know that this is Jim’s first publication in a peer reviewed journal (as second author)!

So, this means he will have to bring some cake…

You can find the article here:

There is no alternative for Sergio

Everything you ever want to know about salt marsh modelling

There is no alternative for Sergio
Sergio Fagherazzi from Boston University

About two and a half year ago, I participated in a workshop on salt marsh modelling just before the AGU meeting in San Francisco. Over there, we came up with the idea to write a review paper on salt marshes. This idea has been lingering on until Sergio Fagherazzi of Boston University put it in motion and wrote a paper that we submitted to Review of Geophysics. I came out as the first thing this year!

You are warned! The rumor is that Sergio fell asleep while proofreading the manuscript!