Kelp Wrack

Photo: Josie Iselin
Kelp wrack

Washed Ashore

Kelp wrack is how most beachcombers encounter bull kelp, strewn upon the beaches in enormous tangles of knotted stipes and toughened bladders. Sometimes other kelps—feather boa or giant kelp—are caught in the morass, but often enough it is pure bull kelp tangle. When the holdfast comes along and is still attached to the twisted stipe it is clear what a modest anchor it is for so much biomass. These are the great heaps of kelp on winter beaches, the results of storms ripping mature kelp from their watery home toward the end of a healthy growing season.

Baby kelp washed ashore in spring

Baby kelp washed ashore in spring

Photo by Kenan Chan

Another form of bull kelp wrack is found on spring beaches: tiny, baby bull kelp will be found at the water’s edge, bulbs the size of fingernails, with just four golden blades streaming in the sunlight, a thread of stipe and tiny holdfast. These are magical and precious signifiers of the new kelp growth in some unseen bed out beyond the waves and remind us that bull kelp is an annual, growing from microscopic gametophytes to the these delicate tiny sporophytes, to the massive tangles in a matter of months. These months of enormous growth—using the power of sunlight to fuel photosynthesis together with the enormous nutrient availability in cold Pacific Ocean waters—are the spring and summer months of extended sunlight and calmer seas. By late summer the dark brown sori patches in the blades of the mature kelp fall away, the spores dispersing as lipid rich zoospores that can swim about, eventually landing in cracks in the rocky benthos to germinate into the microscopic male or female gametophytes creating egg and sperm—one fertilizing the other and start the cycle anew. In wintertime, the storms and hyperdynamic wave action rip clumps of the majestic bull kelps from their tether to the rocky bottom. Nereocystis often grows with its long, singular line of stipe twisted with other stipes, so that when one holdfast gives way, the entire clump is forced up and at the mercy of the waves. 

Is Kelp a Carbon Sink?

It is suggested that some of this kelp matter might be deposited in the deeper waters, thus sequestering the carbon in its bodies, but this is not recorded or known. It is true that kelp, and especially bull kelp, are remarkably efficient at pulling CO2 out of ocean water and transforming it into biomass. This is the power of photosynthesis. But unlike the trees of a forest on land, kelp is constantly desiccating and degrading, shedding and sloughing. Bull kelp’s biomass is only in existence for a short while before it and its carbon degrade back into the ocean waters to become part of the complex foodweb around it. The carbon sequestration touted by proponents of kelp farming and kelp restoration projects is ephemeral—not a permanent fix—but a reminder of how dynamic the kelp forest is in cycling nutrients and carbon through food webs and shoreline ecologies. Maybe it is not as useful for solving our human dilemmas but extraordinarily important for the health of a panoply of species and their interrelationships.

Blue Carbon

Blue carbon refers to the carbon stored in coastal and marine ecosystems. Mangroves, tidal marshes, and seagrass meadows are known marine ecosystems that sequester carbon. As algae, kelp is more mysterious. Work is being done to figure out if kelp can be calculated to sequester carbon, given its ephemeral nature.

Where Does That Kelp Come From? Can We Tag Kelp?

Wrack can tell many stories. There is a specific nori epiphyte that grows only on bull kelp and can often be seen as a red beard of sorts growing on an old mama bull kelp that has washed ashore, suggesting this kelp has lived well past a full year. Clues to current and tide are revealed by some coves being receptors of massive wrack while others are clean and clear. But most often there is a big question mark about the source of wrack on a given beach. Often there is no clear kelp bed offshore. Wouldn’t it be cool to tag kelp and know where it came from, much like putting a message in a bottle and finding out where it ends up? In fact, there are genetic markers that can identify kelp by region, and these are being used to study the genetic diversity of bull kelp populations all up and down the coastline, in Puget Sound and British Columbia, California and Alaska. As kelp abundance ebbs and flows, its genetics are now being mapped so that genetic variation and health can be gauged. 

Shorebirds in kelp wrack
Photo by Morgan Ball
Photo by Morgan Ball

Kelp Wrack Supports Shorebirds 

All this carboniferous material is a food source for many and a vital part of the kelp forest and near shore food webs. Enormous amounts of bull kelp detritus is caught in coves or on beaches throughout its range, readily attacked and broken down by kelp flies, isopods, amphipods and other insects making a feast of this nutritious kelp mass and in turn becoming a feast for shore birds. These protein-dense scavengers are also critical for migrating birds needing supercharged food sources to complete their journeys. The detrital nutrients are cycling carbon back into the nearshore ecologies, fertilizing wildflowers and feeding shore life.