A forest vanishes
Off the coast of Shikotan Island, a dramatic ecological shift is underway. Dense underwater forests of kombu kelp (Saccharina japonica) are disappearing, leaving behind rocky plains covered in mostly crustose coralline algae. This widespread phenomenon, known in Japan as "isoyake" or "sea desertification," transforms a productive habitat into a barren landscape. The cause of this change is the sea urchin, specifically species like Mesocentrotus nudus.
Historically, cold water temperatures limited urchin populations and their grazing pressure. Now, warming sea temperatures are altering this balance. The mean water temperature in the East/Japan Sea has risen by nearly 1.7°C over the last half-century. This increase boosts sea urchin metabolism and reproductive success, allowing their populations to expand. These energized urchins consume kelp faster than it can regrow, clearing vast areas of the seafloor. Once the kelp is gone, the urchins can survive in a starved state for long periods, preventing any potential recovery of the kelp forest and maintaining the barren state.