Kelp forests are composed of rapidly growing large brown algae. This highly productive habitat supports a wide variety of fish, invertebrates, and marine mammals forming the basis for a rich ecosystem. Kelps are found in subtidal regions throughout the world where nutrients, light levels, temperatures and ocean currents permit. Marine grazers such as urchins, fish, and snails can also limit distribution by overgrazing, particularly when predators are removed, which may allow herbivorous populations to boom.
Kelp forests grow predominantly along the Eastern Pacific Coast, from Alaska and Canada to the waters of Baja, California. These kelp forests are found in four of our national marine sanctuaries along the West Coast,and are dominated by two species: giant kelp (Macrocystis pyrifera) and bull kelp (Nereocystis leutkeana). Both of these species are found in California waters, however north along the coast in Washington waters bull kelp is predominant. What makes this macroalgae unique besides the ability to grow to heights of up to 200 feet, is that there are airbladders known as a pneumatocyst that helps the plant float near the surface and gather more light for photosynthesis while shading out competitors. Giant kelp has pneumatocysts on each blade(frond) while bull kelp only has one pnematocyst that supports several blades near the surface.
Along the West Coast, the Pacific Fishery Management Council identified canopy-forming kelp as a Habitat Area of Particular Concern (HAPC) for Pacific Coast groundfish. Canopy-forming kelps are also part of the submerged aquatic vegetation HAPC for Pacific Coast salmon (PDF, 227 pages).
Kelp forests are able to form on top of rocky reefs where few other plants can grow because of their unique holdfast system. Instead of sending roots into the soil, kelp holdfasts attach to submerged rocks. Ocean currents around kelp forests can be very strong. Current speed inside a forest is greatly reduced due to the drag created by the plants. The calmer environment within a forest, coupled with the habitat complexity created by kelp blades (fronds) and holdfasts, provide refuge for many fish, invertebrates, and marine mammals.
Because kelps are primary producers that modify the environment to create suitable habitat for a great diversity of species, they are known as foundational species.
Kelp forests are also among the most productive ecosystems in the world, allowing them to support the diverse assemblage of life that inhibits them. Fish that do not live in the kelp benefit from the animals that grow there as forage items, illustrating the effects of kelp extend beyond the boundaries of the forest. When kelp dislodges from its holdfast, it forms a floating mat known as a kelp paddy. These floating microhabitats provide rare shelter in open water to many fish and invertebrates, often times attracting pelagic fish including sharks and Mola mola, the ocean sunfish.
Kelp forests provide a variety of commercial and ecosystem services to humans. Harvesting kelp began on a large scale during World War I, when it was used as a source of potash to make gunpowder. During that time, removal was unregulated and highly destructive to the surrounding habitat. Currently kelp is harvested in a more sustainable manner by removing only the upper portion of the canopy. The primary resource taken is algin, a product used as a gelling agent in foods, pharmaceuticals, and water and fireproofing fabrics. In addition to algin, kelp is a component in some fertilizers, a healthy ingredient in food, and a potential alternative energy source.
The habitat itself provides humans with many benefits known as ecosystem services. Ocean currents are slowed by drag from the large kelps. Creating a calmer habitat, this current reduction also decreases wave action onshore. By altering the waves, kelp forests reduce erosion, decreasing expensive property protections or replacement. Many outdoor enthusiasts dive or kayak among kelp forests providing important recreational and tourism benefits. Kelp is also an important habitat for a number of recreationally and commercially important fishery species such as kelp bass and various species of rockfish.
Though rapid growth rates help them recover quickly, kelp forests are still threatened by multiple sources. Marine grazers, such as urchins and fishes, can consume enough kelp to remove entire forests. In an undisturbed kelp ecosystem, grazer populations are limited by diversity by predators including marine mammals, fish, and invertebrates. When predator populations are diminished, either through overfishing or other causes, grazer populations increase. Additionally marine grazers will forage less in the presence of predators to avoid becoming prey. Without these predators, kelp forests are at a high risk of destruction.
Commercial harvest is a potential danger to kelp survival, as the demand from pharmaceutical, aquaculture, and food companies has increased with time. However, kelp harvest reached a high level during World War I, and currently does not appear to have major effects on ecosystem health.
Pollution in the form of sewage, industrial waste, inorganic fertilizers, and pesticides carried from freshwater runoff can impair kelp growth and reproduction. Excessive sedimentation from watershed development activities may smother younger kelp and rocky substrate upon which they attach.
Kelp requires cold water for growth, and elevated seawater temperatures from global warming are a major threat to kelp forest survival. Similarly, El Nino southern oscillation events that bring warm water and heavy seas take a heavy toll on kelp forests.