Bull kelp is a buoy of the ecosystem

One of the things we do when still waters takes people out on short educational ecocruises in Appletree Cove and Puget Sound is look at examples of the seaweed and seagrasses that grow in these waters…

One of the most amazing plants is… the kelp. They are big, rubbery and amazing. They also tell an interesting story about the human effects on the Puget Sound ecosystem.

Kelp is large macroalgae — seaweed — that grows along the coasts. Macroalgae are grouped generally by color: reds, greens, browns, and coraline.

Kelp is brown algae.  There are several kinds of macro — large, visible by the eye — algae that grow in our area. The kelp I have seen most commonly are sugar kelp (Saccharina latissima), a giant kelp (a macrosistis species) and bull kelp (Nereocyctis luetkeana). Each has different kinds of large blades, or fronds, but they all have two attributes in common that make them very unique — their holdfast and stipe.

The holdfast is the fascinating way these plants hold themselves in place. They don’t grow roots down to fasten themselves but rather grow multiple finger-like structures called haptera, to grasp whatever they find on the sea floor to hold themselves down — holding fast. Typically in Puget Sound it will be rocks, but it can be anything that they find. If what they choose is not heavy enough, the plant can be picked up and moved with a big wave.

As they grow larger, kelp can grow additional haptera and grab additional rocks to hold tight as the plant grows larger. These holdfasts create such a superstructure that they become home to other organisms while doing their anchoring job for the plant. These extra residents can include kelp fish, anemones, brittle stars, snails, and crabs.

The stipe is a stalk that grows between the holdfast and the blades of kelp.  While some kelp’s stipes are short and non-descript, the bull kelp stipe is  long, thick, and rope-like. It can be many feet long. The stipe is used by the plant to hold its blades up in the water column to get light. However, we humans use the stipe in other ways.

Some cultures cut the stipe into pieces and pickle it or use it in soups. Still others have fun with it, using the dried stipe in decoration, or cutting the tubular stipe and use it as a horn, blowing into one end. The horn sounds a bit like a moose.

At the end of the stipe is a bulbous knob from which the long, thick blades grow. This knob is what you can see bobbing in the water in kelp beds, like the one you can see looking just south in the water as you walk of the ferry ramp in Edmonds.  These knobs are flotation that keeps the kelp blades at the surface so that they can get the maximum sunlight. These plants, as all macroalgae, take the sunlight and convert carbon dioxide and nutrients from the water into plant material and oxygen.

Bull kelp grow multiple long blades, 5-10 feet long. Some times of the year, a blade can grow a foot a day. Paul Dorn, fisheries scientist from the Suquamish Tribe, shared on a recent cruise that this rapid growth rate used to mean that portions of the Puget Sound had very dense kelp beds. He is in involved trying to restore the kelp bed that was formerly south of Jefferson Head.

Efforts to regain kelp beds are challenged by several factors, one of which is wave energy. As we all notice when we’re out in a kayak or even the ferry, when big boats go by, we have to ride wake waves. For a plant holding on to a rock on the bottom with a bunch of long flat blades at the surface, those wake waves cause  a wiping motion, back and forth. While kelp actually need water movement to help them grow, they need to stay in relative close proximity to each other to reproduce and to create the dense “kelp forest” habitat that supports the other marine life typically found with them.

We hope this kelp project can be successful so that some of the dense kelp forests seen by Capt. Vancouver when he came to Puget Sound can be restored.


Photo caption: Bull kelp floats just off the shore of Bainbridge Island, near Wing Point.— Image Credit: Paul Dorn / Contributed

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