The mussels have provided all three. Their plankton-stripping ability has dramatically increased the depths to which sunlight can penetrate. Their shells provide a surface on which the seaweed can grow and the mussels’ phosphorus-rich excrement fuels the plant’s growth. The result is an endless forest of brilliantly green, hair-like tendrils swaying in the current, invisible to anyone on shore—until relatively small amounts of it break off, wash ashore and, along with the mussels it has attached to, rot.
