Walking along the coast at low tide, one often comes across shallow pools of water where the receding sea has left behind many interesting creatures. Crabs and small fish hide between sea grass, anemones, and stones, along with urchins and snails. What is a relaxing environment for human beachgoers poses a great challenge for the inhabitants of the tide pools, however. Exposed to the sun and predators like birds, they must endure low oxygen and increasing water temperature for hours, and they also need the ability to cling very tightly to the rocks when the returning tide hits them hard with crushing waves. The starfish, one of the most famous inhabitants of the tide pools, has developed a fascinating strategy: it uses its tube feet, specialized adhesive organs with discs at the end, in order to attach temporarily to surfaces. The feet secrete several substances from different glands with different purposes, forming a bi-layered glue. One type of secretion forms a thin film in direct contact with the substratum; the second forms a thick meshwork on top of it. This layer effects the cohesion between the lower layer and the disc. In order to detach the tube foot, the starfish secretes yet another substance that weakens the bond between the adhesive layer and the disc surface. The starfish can now move on, leaving behind only its footprint. The picture was painted in acrylics.
Sources: M. Algrain et al., “In the footsteps of sea stars: deciphering the catalogue of proteins involved in underwater temporary adhesion”, Open Biology, vol. 12, issue. 8, (2022).https://royalsocietypublishing.org/doi/10.1098/rsob.220103