What is kelp?
Kelp are large brown algae, not plants, that grow in cool, nutrient-rich coastal waters. There are about 30 different species of kelp worldwide. Anchored to rocky seafloors by root-like holdfasts, kelp use flexible stems called stipes and leaf-like blades to reach toward sunlight near the ocean’s surface. Many species also have gas-filled bladders, known as pneumatocysts, that help keep their blades suspended in the water column so they can capture sunlight more efficiently.
These marine algae can grow in dense groupings that resemble underwater forests, creating one of the most dynamic and productive ecosystems in the ocean. Kelp forests are found primarily along temperate coasts, including the Pacific shoreline from Alaska to Baja California. Within the National Marine Sanctuary System, kelp forests flourish in places such as Monterey Bay, Channel Islands, Greater Farallones, Chumash Heritage, and Olympic Coast national marine sanctuaries, where they provide food, shelter, and structure for a rich diversity of marine life.
Why are kelp forests important?
Kelp forests support a remarkable diversity of life and are among the most productive ecosystems in sanctuary waters. Their tall blades and dense fronds create a layered habitat that offers food, shelter, nursery grounds, and protection from predators and rough seas for many species. Fish, invertebrates, marine mammals, and seabirds all rely on kelp forests in different ways, from hiding among the blades to feeding in the rich waters they help sustain.
These underwater forests also provide important benefits to people. They support recreational diving, boating, fishing, paddling, and wildlife viewing, and they serve as habitat for commercially and recreationally important fish species. Kelp forests also help cycle nutrients, store carbon, and buffer wave energy along the coast. Because they respond quickly to changes in ocean conditions, kelp ecosystems offer scientists clues about the health of the ocean.
What pressures do kelp forests face?
Kelp forests face a range of pressures, from warming waters and pollution to habitat disturbance and shifts in the balance of predators and grazers. Marine heatwaves, changing ocean temperatures, and El Niño events can reduce kelp growth, reproduction, and survival, especially when stressful conditions last for long periods. Poor water quality and sediment runoff can also limit the sunlight kelp need to grow.
Overgrazing by sea urchins is one of the most serious threats to kelp forests in some areas. In healthy ecosystems, predators such as sea otters and sea stars help keep urchin populations in balance. But when those predators decline, urchin numbers can surge and strip away entire kelp forests, leaving behind rocky areas known as urchin barrens. These dramatic shifts can reduce habitat, biodiversity, and food sources for many species that depend on kelp forests.
National marine sanctuaries help scientists and partners better understand and protect kelp ecosystems through research, long-term monitoring, restoration efforts, and public education that encourages responsible ocean stewardship.
Life in the Kelp Forest
Kelp forests are not just a tangle of seaweed—they have structure. From the floating canopy at the surface to the rocky seafloor below, they create layered habitats that support different kinds of marine life.
Canopy
At the ocean's surface, floating kelp blades form a canopy that shades the water below and provides shelter for fish, invertebrates, and marine mammals. Seabirds may feed around these productive waters, while sea otters often wrap themselves in kelp to rest without drifting away.
Midwater
Beneath the canopy, the kelp forest's stipes and blades create a sheltered midwater zone where fish such as rockfish, kelp bass, and garibaldi can feed and hide. This part of the forest acts like an underwater neighborhood, with animals moving among the fronds in search of food, mates, and refuge.
Seafloor
At the base of the forest, holdfasts anchor kelp to rocky reefs covered in understory algae, creating habitat for sea stars, crabs, snails, sea urchins, anemones, nudibranchs, and many other bottom-dwelling animals. This part of the kelp forest forms an important foundation for the larger ecosystem, and is also where grazing pressures can have the greatest impact.
