Giant kelp is the largest seaweed in the world and one of the fastest growing organisms on earth. Capable of growing upwards of 2 feet a day, these plants can form dense stands of forests near the coasts. If you’ve ever been to the west coast of North America, maybe you’ve seen the canopies of these plants floating at the surface of the water like brown mats. If you’re fortunate enough to dive in one of these forests, you’ll likely encounter a huge diversity of fish, snails, seastars, algae, and other organisms associated with giant kelp.
Photo by Brain Skerry (National Geographic)
To get to towering heights, giant kelp must survive an onslaught of potential stressors and herbivorous animals early in life. Factors like light, burial by sediments, water temperature, and grazing all play a role in survival. As adults, individual plants are capable of releasing millions of spores into the water. However, only a tiny fraction settle onto a surface, germinate into female and male gametophytes, and successfully produce zygotes.
I am most interested in the survival of these plants as young sporophytes under grazing pressure by animals like snails, urchins, and small crustaceans. To perform my experiments, however, I have to first grow giant kelp in the lab in my incubator:
I start off by collecting reproductive leaves by diving in kelp forests in Monterey Bay, CA. In the first picture, you can see those leaves at the base of the plant right above that orange sheephead fish. I induce spore release in the lab and allow the spores to settle on microscope slides. If you give them the right temperature, nutrients, and light cycle, you’ll start to see young sporophytes in 3-4 weeks.
Here’s a series of Foldscope pictures of giant kelp at its different stages:
1. One of one of my microscope slides with an egg extruding out of a female gametophyte (circle emerging from a hollow tube):
2. Once the egg is fertilized by sperm that have been released from male gametophytes, a young sporophyte will grow:
You can see the first several cell divisions, forming a flat layer of cells as the first leaflet. You can also see the remanent female gametophyte at the bottom of the young sporophyte.
3. Once the young sporophyte reaches a large enough size, it will start to grow haptera and form a holdfast, the large conical mass of “roots” that anchor the plant to a surface:
Next to the remanent female gametophyte, the thinner tube coming out of the young sporophyte is a growing haptera.
Eventually, these young sporophytes will become visible to the naked eye (see Manu’s post about one of my cultures here: https://microcosmos.foldscope.com/?p=9165). In nature, it takes just one year for giant kelp to complete its life cycle, starting from spore release all the way to the reproductive stage.
Hopefully next time I can capture a time lapse of one of my cultures starting from the spore stage all the way to the macroscopic leaflet stage!