Research carried out three years after installation at the Hollandse Kust Zuid offshore wind farm in the North Sea has found that distinct marine communities have developed inside offshore wind turbine foundations equipped with water replenishment holes. The foundations include holes in the walls of the large, hollow steel monopiles—so-called water replenishment holes—that allow seawater to flow through the structure. The findings suggest that water exchange may play an important role in shaping ecological conditions inside the monopiles.