About This Species
Seaweed—a workhorse of the ocean—lives around most of the world's coastlines, across all climates. There are more than 13,000 species of seaweed. They provide habitat, food and other important functions in ocean ecosystems and have three basic requirements for survival: seawater, enough light to drive photosynthesis and, for most species, something firm to which to attach.
Many marine species depend on seaweed for food, mating or protection from predators, much like the role that trees play in a forest. In fact, clusters of seaweed are known as seaweed forests. Kelp forests, in particular, are among the most vibrant ecosystems on Earth. Seaweed also plays a vital role in sustaining commercial and recreational fisheries such as abalone and lobsters and others that depend on seaweed for their survival. Seaweed is also edible by humans and is harvested for food and additives.
Seaweeds are incredibly diverse, and many have complex lifecycles that are sensitive to even slight temperature shifts, a problem in the face of warming oceans due to climate change.
As ocean temperatures have risen, some places where seaweed forests have thrived have become inhospitable to them. As those forests die off, they are replaced by turfs, low-lying blankets of algae. The phenomenon is virtually irreversible, and has been affecting seaweed forests for the past several decades. The shift has been observed in western Australia, Tasmania, eastern Canada, southern Norway and northern Spain.
The temperature rise in the ocean off Nova Scotia has been so intense it can no longer support canopy-forming seaweeds. That has led to a 85-99 percent decline in kelp forests, which have been replaced by turf-covered rocky reefs and invasive seaweeds. Similar dramatic shifts have been observed off Norway, Sweden, Denmark and Germany.
Like so many species being affected by Earth's warming, seaweeds are moving to escape the heat. A recent study by scientists from the University of Western Australia found that seaweed species have shifted their range between 16 and 776 miles in recent years. Species in cool water ranges are contracting as the ocean warms, while warm water species are migrating toward the poles.
Since the 1970s, the oceans have absorbed 90 percent of the excess heat that's been generated by global warming, according to the International Union for the Conservation of Nature (IUCN). By the end of the century, the seas are expected to warm by as much as 4 degrees Celsius.
So far, just one seaweed species has been declared globally extinct. Local extinctions can be equally problematic, however. One species of seaweed not expected to go extinct everywhere, for instance, is projected to be extinct in Morocco by the end of the century. When that happens, genetic diversity is reduced, making the species as a whole less able to adapt to future warming.