Weather Watch

A kelp-ful primer on coastal seaweed

Marine biologist Jim Kelly holds giant kelp in his hands.
Marine biologist Jim Kelly holds giant kelp in his hands.

Giant kelp can grow at the unbelievable rate of 1 to 2 feet per day under the right conditions along the Central Coast, ultimately reaching well over 150 feet in length. From a boat on a sunny day, you could almost watch it grow.

Giant kelp is one type of marine algae or seaweed among thousands that exist in the oceans. Seaweed is divided into three color varieties: green, red and brown.

Green seaweeds are generally found in the region between the tides, also known as the intertidal zone. As you can imagine, this zone can experience a great amount of wave action and the greens need to be very resilient, but they get plenty of light to grow.

In deeper water, the red seaweeds are the most abundant. They are more adapted to lower light levels for photosynthesis and have been found at depths of more than 600 feet. However, in shaded areas, reds can also be found in the intertidal zone.

Between the tide pools and the deeper water depths where the reds reside, lie the brown seaweeds or kelp. Giant kelp (Macrocystis) and the closely related bull kelp (Nereocystis) are large kelp species that thrive along the Central Coast. Both grow best in water 5 to 60 feet deep.

They can be identified by air-filled bladders that look like small balloons at the end of their stipes (similar to stems of terrestrial plants). These bladders help the plant to grow straight up to the sun’s light. Along our coast, giant kelp and bull kelp often compete with each other for the same light and form large canopies waving back and forth in the swells across the ocean’s surface. Sea otters often wrap themselves up in kelp to keep from drifting away. In fact, a host of invertebrates, fish and marine mammals flourish in this ecosystem.

Although kelp resembles a tree, kelp has no roots but anchors itself to the bottom of the rocky ocean floor by holdfasts. Unlike roots, holdfasts do not take in nutrients for the rest of the plant.

Kelp loves nutrient-rich, cold and clear water, all of which can become abundant during heavy upwelling events. As the northwesterly winds blow parallel to our coastline, the friction of the wind causes the ocean surface water to move. The Coriolis force turns the surface water to the right, or offshore, causing upwelling along the coast as cold and nutrient-rich subsurface water rises to the surface along the shoreline. Usually the peak growing season for giant kelp occurs in April and May, during the height of the upwelling season.

Over the years, kelp has been harvested for a variety of uses. During World War I, kelp was used to produce potash, which was a necessary ingredient for gunpowder.

Along our coastline, kelp is harvested for use in aquaculture — food for cultured mollusks at the abalone farm in Cayucos, for example. Kelp is also harvested for algin, a binding and emulsifying agent used in ice cream, toothpaste, cereals, cosmetics and pharmaceuticals.

Even more intriguing is its use as a biofuel. It turns out kelp is very efficient in using the sun’s energy to produce sugars by photosynthesis. The kelp’s soluble sugars and energy-dense carbohydrates can be turned into ethanol and may one day prove to be a viable biofuel.

Today’s forecast

This morning’s northeasterly (offshore) winds will produce another gorgeous day with clear skies and temperatures reaching the 70s throughout San Luis Obispo County.

A major change in the weather pattern will develop Monday as the nearly stationary high-pressure ridge that has dominated West Coast weather slowly degrades and a 987-millibar low-pressure system, with an associated cold front, approaches the California coast.

Increasing southerly winds and mid- to high-level clouds will develop Monday morning and afternoon, with a few rain showers reaching the Central Coast by Monday night.

The associated cold front will pass the Central Coast on Tuesday morning with strong to gale-force (25 to 38 mph) southeasterly winds and periods of moderate rain. Rainfall amounts should range between 0.5 and 1 inch, with larger amounts in the mountains.

Cold and unstable air behind this front will produce scattered rain showers Tuesday afternoon through Tuesday night.

Fair weather should return by Wednesday. Thursday and Friday appear to be fair and slightly warmer. Next weekend, there will be chances for more precipitation.

Preliminary extended weather analysis: A change to wetter and cooler conditions across the Central Coast is anticipated late in February, and these conditions should persist into early April.

Today’s surf report

Today’s 6- to 8-foot northwesterly (295-degree deep-water) swell (with a 13- to 15-second period) will remain at this height and period through Monday morning. This swell will decrease to 3 to 5 feet (with an 11- to 13-second period) Monday afternoon.

Strong to gale-force (25 to 38 mph) southeasterly winds Monday night into Tuesday morning will generate 8- to10-foot southerly (190-degree shallow-water) seas (with 4- to 8-second period) late Monday night through Tuesday morning.

A 9- to 11-foot westerly (270-degree deep-water) swell (with an 11- to 17-second period) will follow Tuesday afternoon and night, building to 10 to 12 feet (with a 14- to 17-second period) Wednesday.

A 7- to 9-foot west-northwesterly (285-degree deep-water) swell (with an 11- to 15-second period) is forecast along our coastline Thursday, decreasing to 6 to 8 feet Friday.

Preliminary extended surf analysis: An 11- to 13-foot west-northwesterly (285-degree deep-water) swell (with an 18- to 20-second period) is expected along the Pecho Coast on Feb. 15.

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John Lindsey is a media relations representative for PG&E. He is also a local weather expert and has lived along the Central Coast for more than 25 years. If you would like to subscribe to his daily weather forecast or ask him a question, send him an e-mail at