In the rough-and-tumble ocean environment, mussels sure show some muscle. Despite crashing waves, these mighty mollusks manage to stay put, thanks to the energy-dissipating byssal threads they use to lash themselves to rocks and other surfaces. Much of these threads’ staying power comes from their outer cuticle, a biological polymer that’s hard and resists abrasion. Now, a team led by Matthew J. Harrington of Max Planck Institute, in Potsdam, Germany, has used in situ resonance Raman spectroscopy to study the byssal cuticle (Science, DOI: 10.1126/science.1181044). The team’s results provide the first direct evidence that the cuticle is a proteinaceous polymeric scaffold stabilized by complexes of iron and the catecholic amino acid 3,4-dihydroxyphenylalanine, or dopa, which is present in one of the cuticle’s proteins. When dopa complexes with iron, it crosslinks the proteins. The density of these iron-clad complexes varies throughout the cuticle, Harrington’s team found. Areas rich in the crosslinks give the cuticle hardness, whereas less crosslinked regions provide extensibility. It’s “an ideal coating for compliant substrates,” the researchers note.