Just off the coast of California is the most extensive kelp forest in the world. It is a stunningly productive habitat, busy with life from the ocean bed up to the sunlit surface. Much of the vast Pacific Ocean is a desert, in the sense that it holds little or no life, but the kelp forest is an oasis.
South of Santa Cruz, the dominant species is the gray-green giant kelp, Macrocystis, filling the role of tall tress. These algae are not trees, however, nor even plants. In place of roots they have a holdfast, which looks similar to a root, but draws no nutrition from the sea bed. In place of a stem they have a stipe. It is hung with thick grooved fronds that photosynthesize the way the leaves of plants do. The algae grows fast, 10 inches a day in season, and can reach 150 feet long. There are more than 100 species of seaweed in the forest.
North of Santa Cruz, the community is dominated by the annual bull kelp, Nereocystis luetkeana, whose slender stipes grow straight up to Pneumatocysts, air bladders the size of grapefruits, that keep the algae upright in the swells, and bear a corona of red-brown fronds afloat in the sun. This kelp is uprooted by winter storms, but grows again each year. The underlayer of the northern forest is more open, because the bull kelp bears all its fronds at the top of the stipe.
These are real forests, dense and swarming with life. At the base are found bat stars, starfish that extend their stomachs out of their mouths to eat. They come in reds, golds, and even purples. Abalone cling tightly to rocks, but the cabezon fish harvests them, scraping them off, swallowing them whole, and spitting up the cleaned shell. The gorgeous leopard shark, precisely named for the patterned skin of its back, cruises the bottom too, sucking up worms and other benthic (bottom dwelling) sea life. It can grow to over six feet long, but is harmless to man. Wolf eels hide in crevices and holes, and slither out to eat squid or fish. They can grow up to 8 feet long.
The orange sea cucumber, Parastichopus californicus, lives on the bottom too, eating ocean debris and tiny life. It is related to the spiny purple sea urchin and the sea star. The sea urchin plays a special role in the kelp forest: grazing it. When too many predators of the urchin die, vast populations of urchins can graze the forest down to almost nothing, especially in the northern, annual, forest.
Some of the rockfish, Sebastes species, spend their long lives just above the bottom. They come in gorgeous colors, like the calico,
Sebastes dalli, mottled with orange and black on cream, and the canary, S. pinniger, with touches of yellow gold. Rockfish mature slowly, and may not breed until age 20. They may live to be more than 100, if they are not eaten as California red snapper or rock cod.
The California sheepshead, Semicossyphus pulcher, starts life as a female, and turns male with age. What age depends on the environment and available food. The young females are pink, and the males are black with a white jaw and a broad pink stipe from top to bottom. They eat sea urchins and mollusks. Overfishing has drastically reduced their numbers.
Bright yellow Senorita fish, Oxyjulis californica, clean other fish of parasites and algae, and they also glean from rocks and algae. They range from the ocean surface to its depts., and bury themselves in sand when threatened.
On the fronds of the giant kelp live tiny kelp bryozoans, Membranipora
tuberculata. These are mobile as larva, but then glue themselves to a blade of kelp and build a rectangular casing of chitin and calcium carbonate. They then produce many clones, forming a lacy colony on the frond that may come to number in the millions. They have tentacles that they wave in the turbulent water to gather passing microscopic food. Sea slugs, nudibranchs, in turn feed on them. Jeweled top snails and turban snails also live high on the kelp, avoiding the dangers of the ocean floor.
Near the surface, silvery Pacific sardines dart in shiny schools. They are usually 15 inches or less, and swim in schools that can have millions of members. They are pelagic, that is, they travel the sunlit regions of the open ocean. They feed on plankton, and a variety of birds, fish and mammals feed on them.
Sea otters eat urchins and abalone. They use rocks as tools to crack the shells of the seafood they eat. Once they ranged from Alaska
to Mexico, preferring to live in kelp forests, but now they are found only on the central coast of California, and parts of Russia
and Alaska. They wrap themselves and their offspring in kelp to rest.
Seals and sea lions are pinnipeds, meaning their limbs are flippers. Many kinds of pinnipeds live in or visit the kelp forests, eating its fish and seafood, and sheltering among the weed. The numbers of some kinds of
pinnipeds are declining, and no one is sure why.
Otters, elephant seals, and sea lions exploit the riches of the kelp forest, and so do the hundreds of species of seabirds that fly above it. There is an elegant balance here. The sea urchins and abalone eat kelp and thrive, but too many urchins and abalone can make the forest a barrens. For this reason, and others, the forest needs its predators. Overfishing ultimately kills kelp through over grazing.
It also needs continuing human protection, to be certain that this ecosystem will always remain safe off the coast of crowded California. Visitors can learn more about the kelp forest at the Monterey Bay Aquarium in Monterey, the California Academy of Sciences in San Francisco, or the Seymour Marine Discovery Center in Santa Cruz.
Kelp forests are not confined to the coast of California, of course. Every continent has kelp forests. They are found world wide, in temperate to Polar Regions, bringing hidden life to the depths of the sea.