Aquatic plants are the service providers of marine ecosystems: They provide habitats for fish and other marine life, are food for migratory birds, part of the nutrient cycle – because they absorb CO2, for example – and additionally stabilize the sediment through their roots. By slowing the currents, aquatic plants help prevent soil erosion. Seaweed is also one of these all-rounders that are vital for the ecosystem.
Seagrasses, such as those in Morro Bay, California, are among the most threatened constituents of the coastal environment worldwide. In the past few years, the occurrence of seaweed in Morro Bay has decreased significantly: by as much as 90 percent since 2007. Researchers at California Polytechnic State University have found that the loss of seaweed in this large estuary on the California coast can lead to widespread soil erosion.
After much of the seagrass in Morro Bay had died, erosion also increased in more than 90 percent of the areas previously protected by the aquatic plants. In some places so much sediment was removed that the water depth there increased by up to 50 percent, as the researchers found. Only at the mouth, where seaweed still occurs, sediment still forms as in the past.
“The loss of seaweed in the Morro Bay estuary is comparable to the loss of trees from a rainforest,” explains Ryan Walter of California Polytechnic. “You not only lose the plants, but also all the services that they provide for the whole ecosystem.” At least there is hope: the erosion in Morro Bay could create new opportunities for seagrass reintroduction at least in some places. The removal of the sediment creates the appropriate water depth for the seaweed. The most recent projects of the Morro Bay National Estuary Program have already been successful, as there are indications of a slight recovery of the undersea landscape in parts of the bay.