Wherever ecosystems rich in species develop on the rocky shores of the Baltic Sea, the bladder wrack Fucus vesiculosus has provided perfect groundwork. By colonizing pebbles and rocks, it creates habitats for many other species. Other algae grow on the seaweed to be grazed by snails, isopods and amphipods. Crustaceans, mussels and predatory fish as well as many smaller organisms that are important for the Baltic Sea ecosystem thrive in submarineFucus forests. Fucus vesiculosus is one of the main producers of organic matter in the Baltic and plays a crucial role for its biodiversity and biogeochemical cycles. These functions could be lost due to a series of reactions triggered by climate change.