How do you know you’re a beachcombing geek? When you stop to stare at a kelp holdfast on a beach for so long you arrive late to a meeting--that's a sign. Oh, and if you know what a “holdfast” is, that’s a pretty good sign, too.
For the uninitiated, a holdfast anchors kelp to rocks, similar to how root systems hold plants in place. Unlike roots, however, holdfasts don't take in water and nutrients. Kelp look similar to plants but are a large form of algae (macroalgae).
Phytoplankton are microscopic algae; kelp are macroscopic brown algae. The brown color comes from fucoxanthin, a pigment in kelp chloroplasts that allows for photosynthesis in the poor light beneath the sea. Together, all the algal species of the world's oceans produce more than half the oxygen we breathe.
Simple organisms that evolved in seawater, kelp absorb water and nutrients along their surface instead of through roots, like plants. The stipes of kelp look similar to plant stems but lack the vascular system that plants use to lift water and nutrients from their roots to their leaves. Rubbery stipes allow kelp to sway back and forth, bending with the energy of waves instead of breaking in rigid defiance of the ocean's ebb and flow.
Kelp blades are the equivalent of plant leaves: the flat blades absorb sunlight to power photosynthesis. Plants use solid structures to lift their leaves toward the sun; kelp use gas-filled balls known as pneumatocysts to float their blades toward the ocean's light-filled layers. (The pneumatocysts of beach-cast kelp are fun for kids--and adults--to pop). These buoyant balls allow kelp to stand upright in the water like trees. Some kelp species grow tall enough to reach the ocean's surface, where they spread in dense mats, similar to forest canopies.
Like plants, kelp are primary producers: Kelp eat sunlight; other organisms eat kelp. Kelp support a thriving system we seldom see--a cryptic kingdom concealed by ocean that scatters clues along the shore.
The cameras of divers show towering kelp groves under the sea. Light that penetrates kelp canopies shafts toward a maze of tangled holdfasts, where brightness and shadow trade places like the dappled light on forest floors. Stipes rise more than a hundred feet, swaying like trees in wind. Unlike trees, however, kelp grow phenomenally fast--up to two feet in a day. The fast-growing ocean forests of our planet reach the height of temperate trees and foster the biodiversity and productivity of tropical rainforests.
Kelp's dark surface absorbs thermal energy from the sun, warming chilly ocean water, forming a microclimate for sea creatures. Kelp also creates a separate world within the ocean by absorbing the kinetic energy of waves, making a microhabitat of relatively calm water where thousands of species hide and hunt and graze and breed.
Though kelp forms the foundation of many critically important coastal ecosystems, kelp forests are one of the least appreciated habitats on the planet. Kelp doesn't have the same cachet as coral. Nevertheless, the kelp that breaks free in storms and washes up on beaches hints at a staggering variety of life, from sea slugs to sea otters, from snails to seals, from microscopic diatoms to giant Pacific octopuses.
Small algae and tiny animals attach to every kelp surface, crusting each inch of holdfast, stipe, and blade with rioting life. A holdfast's matrix of spaces provides homes for a whole host of creatures, from crabs to clams. Juvenile fish hide from predators in the shadowed canopies of kelp forests. Sea otters flee orcas in kelp groves and hunt sea urchins that graze on kelp; these absurdly cute mammals tether their babies with kelp strands to keep them from floating away. Whales also shelter their young among swaying blades of kelp, reminiscent of deer hiding their fawns in leafy groves.
Each piece of kelp that washes onto a beach carries with it stories of myriad creatures that teem in unseen worlds beneath the waves.
Kelp deposited on shore after storm swells are dead but continue to support multitudes. Tiny scavengers act as recycling crews, breaking down kelp and returning nutrients to beach ecosystems. The recycled nutrients nourish new algae, plants, and animals.
Beach hoppers are legion along the coast, congregating around beach-cast kelp in such density that the sand itself seems to move, rather than the tiny critters that jump in all directions. At night, when kelp piles thrum with hopper activity, the patter of hard crustacean bodies hitting the dark sand sounds like rain.
The California beach hopper, Megalorchestia californiana, is a handsome crustacean that breaks down dead material. I spot California beach hoppers at night with a headlamp and sometimes see them at dawn and dusk, but rarely do they show themselves during the day.
Bull kelp, Nereocystis luetkeana, grabs the attention of beachcombers with a bullwhip stipe that can stretch more than sixty feet, and a spherical float that can grow as big as a grapefruit. Giant bladder kelp, Macrocystis pyrifera, washes up in ropy piles with many small floats that beachcombers can pop like bubble wrap. Sea palm, Postelsia palmaeformis, resembles a small palm tree and thrives in the harshest surf, where its sturdy stipe bends beneath the largest waves. (Fresh beach-cast sea palm is delicious when brushed with olive oil, sprinkled with sea salt, and broiled to a crispy crunch.)
After many weeks of searching, I found cryptic nudibranchs. This small species is challenging to see because it blends seamlessly with bryozoans that encrust kelp. (Tiffany Boothe of Seaside Aquarium gave me a great cryptic nudibranch hunting tip: Look for the creature's eggs, which are relatively easy to see; then follow the egg clues to the camouflaged quarry.) My eyes are still strained from staring at these little sea slugs that hide in plain sight. Unfortunately my camera wasn't up to the task of photographing tiny, camouflaged creatures in dim light, but the jolt of suddenly finding something I've been seeking for so long left a lasting memory.
I have been late to meetings because I couldn't pull myself away from kelp, but my thoughts are richer for the hours I've spent staring at the many strange lifeforms that inhabit holdfasts. I have explored worlds that fit in the palm of my hand.
After finding cryptic nudibranchs, I knelt down to inspect a bull kelp stipe and saw pelagic gooseneck barnacles moving back and forth, bending their flexible necks as if searching for the sea. I dragged the bull kelp back into the waves, giving the barnacles a reprieve--and robbing hoppers of a meal. Each piece of kelp on the beach harbors a hidden web of connections as intricately tangled as a holdfast.
Along with providing more than half the oxygen we breathe, kelp and other algae serve as a critical carbon sink. These species remove carbon dioxide as a greenhouse gas in the climate system by storing carbon in the solid form of carbohydrates--sugars that support many of the sea creatures we eat.
A holdfast's complex structure is reminiscent of the intricate web that binds our fate to all life in the ocean. Though not as colorful as tropical coral reefs, the kelp forests of cold waters are every bit as important. (And every bit as beautiful, as revealed by Jackie Hildering's stunning underwater kelp photography.)
The great kelp forests of the world's oceans are under siege. Threats range from pollution to climate change to urchin populations that exploded after we slaughtered sea otters. If we continue to abuse the blue lungs of our planet, we could end up like the creatures on a beach-cast holdfast, struggling in a barren world stripped of the resources we need to survive.