Bull kelp is so beautiful, especially now in the early spring when the young “sporophyte” stage is growing at an insanely fast rate. The stipe (stem-like structure) of this kelp species, Nereocystis luetkeana, can grow to be up to 36 m long. The stipe would have to grow an average of 17 cm a day to reach this length in the 210-day growing period (source: Druel). If you include the growth of the fronds (the leaf-like structures), the maximum growth rate has been documented to be at least 25 cm per day (source: Duncan).
It is at this early stage of growth too that bull kelp is an intense colour green unlike anything else I know. When older, the colour darkens to an olive green.
Kelp is an alga, not a plant but, like plants, algae also photosynthesize, converting the sun’s energy into food. However algae have simpler structures and different chemical pathways.
Young bull kelp grows so fast to allow the leaf-like parts, called “fronds”, to be closer to the sun so that more food can be made.
The round, floating part of the kelp, is the “pneumatocyst”. This bladder-like structure is completely hollow and is filled with carbon monoxide (NOT carbon dioxide), allowing the long fronds to drift at the surface to catch the sun’s rays.
Apparently, there is enough carbon monoxide in bull kelp to kill a chicken! Now that’s valuable information. See my blog “Enough Carbon Dioxide to Kill a Chicken” at this link.
The stem-like part is called the “stipe” and it is also hollow. I’m sure it is not what Nature had intended, but this allows we humans to play the stipe of bull kelp like a trumpet or didgeridoo!
Bull kelp does not have roots. Rather a “holdfast”, a tangle of woody structures, anchors bull kelp onto rocks. However, if rocks are too light to counter the floatation of the pneumatocyst, the kelp will actually change the ocean bottom by carrying away smaller rocks, likely ending up washed onto the shore.
The stipe gets thinner and whip-like near the holdfast which is why bull kelp likely got its name; because the stipe is shaped like a “bull whip”.
And bull kelp always grows in patches, truly forming an underwater forest that is life-giving for the same reasons as terrestrial forests: kelp forests buffer the climate change gas carbon dioxide; produce oxygen; and provide food and habitat for so many other organisms. Bull kelp forests are, in fact, estimated to provide habitat for some 750 species of fish and invertebrates (animals without backbones).
Sea urchins are one of those invertebrates, living in the forest and grazing on a lot of bull kelp. If otters, mink, wolf eels and other predators of urchins did not keep urchins in check, there would be further reduced kelp forests.
Kelp forests are not what they used to be for reasons far beyond our foolishness in over-harvesting sea otters. There used to be such dense forests that it is theorized “Ancient humans from Asia may have entered the Americas following an ocean highway made of dense kelp.“
All coastal boaters still benefit from kelp. It is a navigational aid since, where it grows, you know you there is shallower water.
We divers have yet an additional reason to value kelp. Since it is so strong, we can hold onto it if we need to during our safety stop (3 minutes at 5 metres depth) or if needing to gradually pull ourselves down into the depths or back to the surface.
Oh – and you can eat it. (I love pickled young bull kelp!)
And yes, you could do puppet shows with bull kelp, cutting a face into the bladder like you would into a jack-o-lantern. The fronds even look like two pig-tails!
There will be more on bull kelp here in the future. Wait till you find out how bull kelp reproduces! The “alternation of generations” is mind-blowing with the offspring look nothing like the adults.
But for now, come underwater with me. Come into the forest, breath in, breath out and worship the kelp!
For more on the natural history of bull kelp see this link.
For more information on algae – click here for my blog “Every Breath You Take . . .”
- Duncan, M. J. 1973. In situ studies of growth and pigmentation of the phaeophycean Nereocystis luetkeana. Helgolander Meere- € sun. 24:510–25.
- Druehl, Louis and Clarkston, Bridgette. 2000. Pacific Seaweeds – a guide to common seaweeds of the west coast.