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Sequoias of the Sea

Photo Courtesy by Douglas Klug | National Science Foundation

There is a plant that is not really a plant. It photosynthesizes, but has no roots. Some people eat it deliberately. Most of us eat it without knowing it. It can be farmed or harvested naturally. It is incredible to explore, and provides food and shelter to a vast diversity of animals, but you probably don’t want to sit next to it on the beach. It forms huge forests that have been compared in height and awe to the Giant Sequoias of Northern California. It is seaweed. More precisely, it is Kelp.

There are two main types of kelp that grow along the California coast. North of Point Conception, the dominant species is bull kelp, or Nereocystis luetkeana. Here in Southern California, we have Macrocystis pyrifera, or giant kelp. Both of these species are fast-growing marine algae that form large “forests” off the coast. However, unlike trees, seaweeds are not plants. They are part of an entirely separate kingdom called protists. They are considered plant-like protists, along with other algae because they contain chloroplasts, an organelle that enables them to photosynthesize. Multicellular algae, or seaweed, can have plant-like structures like roots and stems. These roots, though, are different from plant roots. Plants absorb nutrients and water from the soil through their roots, whereas kelp absorbs nutrients directly from the water around it. The “roots” of kelp are called holdfasts, and their job is to anchor the kelp to the rocky substrate on which it grows.

Kelp's Holdfast. Photo Courtesy by Jackie Hildering with dive buddy Natasha Dickinson | The Marine Detective

Kelp has some very interesting adaptations to living in its marine environment. Rooted to the bottom, the seaweed grows up towards the light with the help of gas-filled pods, known as pneumatocysts, that float at the base of each blade. Giant kelp is one of the fastest-growing organisms on the planet. Under ideal conditions, kelp can grow up to and occasionally exceed 2 feet per day. That is one inch per hour! Its brown color is the result of the brown pigment fucoxanthin, which absorbs light in the blue-green part of the spectrum. This pigment, along with chlorophyll, allows the kelp to harvest light at depths up to 100 meters.

Kelp is quite important to humans. It contributes beneficial ecosystem services such as carbon sequestration, providing habitat for numerous economically significant species, and reducing shoreline erosion by absorbing wave energy as it flows towards the shore. We use it in many household products, such as salad dressing, toothpaste, and hand cream. Brown algae is the source of alginate, which is used as a binding and thickening agent in foods, cosmetics, and medicines. Also, new research in Hawaii is looking into adding seaweed to cattle feed to reduce methane emissions resulting from the cows’ digestion (Maui News). You may not have realized that seaweed is a part of your daily life.

Sunflower Star. Photo Courtesy by Monterey Bay Aquarium

The problem is that our kelp forests are in trouble. A “perfect storm” of conditions has caused the kelp in California to decline drastically. In Northern California, it is estimated that 95% of the bull kelp forests have disappeared. In Southern California, the story is not so bleak, but could follow the same pattern. The initial problem was an event known as “the Blob” that brought warm, nutrient-poor water down the coast of Alaska from 2014 to 2018. This warm-water event wreaked havoc on the coastal ecosystems of the Pacific Northwest, and all along the Eastern Pacific. At the start of 2011, there was a catastrophic collapse of the Sea Star populations in the same area. One particular species of sea star, the Sunflower Star (Pycnopodia helianthoides), is a significant predator of purple urchins, which in turn, feed on kelp. Areas where the sea stars have disappeared have become what is known as an “urchin barren.”

Urchin Barren. Photo Courtesy by Katie Davis | UCSB Current

There are several groups working on bringing our kelp forests back, but the biggest threat to these “Sequoias of the Sea” is climate change. Pollution of coastal waterways, including chemicals, fertilizers, and sedimentation also play a role in the health of these ecosystems, which provide us with oxygen, food, and peace of mind. Our coastal areas are to be treasured, not trashed. If we want to feed the world and feed our souls, we need to carefully manage our precious coastal resources.

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