Dive Dry with Dr. Bill

#277: Wakame... But In Its Place

Last week I was diving on the King Neptune with my friend Mina Leung who was down on Catalina to plan her wedding to fiancee Mark in the fall. The weekend before I had seen an unknown kelp at Pirate's Cove inside Long Point, and asked Captain Bob Kennedy if we could do a dive there so I could film it. We entered the water and dropped down to about 80 feet, then started working our way up to the shallows.

In water shallower than about 40 feet we started seeing the kelp. It was quite prevalent at this site. Individual plants had long, broad blades (the leaf-like part) extending up to about 10 feet in length. Each blade had a well-defined midrib running along the center which terminated in a stipe and small holdfast where the kelp attached to the bottom. Along the edges of the stipe just above the holdfast were frilly extensions on either side that I assumed were the sporophylls, the structures that produce the reproductive spores.

I filmed about 15 min of footage and extracted four representative stills to send up to marine algae specialist Dr. Kathy Ann Miller at UC Berkeley. I asked if it might be a species from the genus Alaria found further north since it resembled some species in that group. In less than an hour, I had an answer from her. No, it wasn't one of the West Coast native Alarias, but the invasive Undaria pinnatifida first observed in Catalina waters in 2001. I hadn't dived the two nearby Catalina sites (Buttonshell Beach and White's Landing) where it was first seen in our waters, and the pictures I was aware of didn't look like the alga I saw in the water. Fortunately it has not spread as disastrously as the Asian invasive Sargassum filicinum which has taken over most of the dive sites on the island's leeward coast in just two years.

Now many of my readers may have encountered Undaria in other locations, as I have myself. In Japan where it is native, it is commonly called wakame and is an additive in the miso soup served in Asian restaurants. It is also known from the cold temperate waters of northern China and Korea, and has been cultivated in those three countries as a food source for centuries. Unfortunately Undaria has begun invading many areas where it is not normally found. It invaded French coastal regions, apparently introduced with imported oysters, and is now cultivated off the coast of Brittany. It has also entered the waters of Great Britain, Spain, Italy, the Netherlands, Argentina, Australia and New Zealand. In fact, it has been called one of the 100 worst invasive marine species in the world.

This kelp disperses because the large sporophyte (spore-producing) plants I saw at Pirate's Cove may each produce 100 million spores that disperse with the currents. Undaria probably arrived in the waters of other continents as spores in the bilge water of large ships, or attached to their hulls. It was first observed on the mainland in 2000 and by the following year was known from Los Angeles and Long Beach Harbors, Catalina and as far north as Monterey. It was reported that an Asian vessel anchored in the vicinity of White's Landing to scrape encrusters off its hull shortly before the kelp appeared here.

I asked Kathy Ann if it was possible to control it. She and Jack Engle worked with the Catalina Conservancy Divers and other dive groups to remove these large plants from Buttonshell Beach and White's Landing. However, it was her assessment that this has really not been effective. The reason probably rests with the fact that there are actually two completely different "generations" of this species: the large sporophytes I filmed, and tiny microscopic gametophytes which would be near impossible to detect and control.

Like our mature giant kelp, Undaria has the large spore producing generation which is an annual plant, observed starting in late winter through early summer. The frilly sporophylls at the base of these plants produce and release the prodigious numbers of spores. This alga is easily to identify based on the sporophylls and the distinct midrib on the blade. These spores then grow into the tiny gametophytes which live hidden on the bottom in the colder months of the year. They produce the sperm and eggs that fertilize to produce the next generation of the large sporophytes.

Undaria in its native regions is largely a shallow water species, found down to depths of about 15 feet. Here off Catalina and in other locations it may be found as deep as 80 feet. This kelp generally avoids areas with much wave action. It tolerates a wide range of temperature and salinity, but not coastal areas with a lot of fresh water influx. It grows best in temperatures below 54 degrees, begins to degrade at 68 degrees and dies above 73 degrees. It readily colonizes new or disturbed surfaces, making it a "good" invasive... and a bad pest. I wonder how many of our southern California species have invaded the waters of cool, temperate Asia.

Although most commonly encountered by westerners like myself in miso soup, the broad blades are also harvested and distributed dried or salted. They have a subtly sweet flavor. Nutritionally they have one of the highest nutrient to calorie ratios of any food, and exceedingly high for a plant. They also contain omega-3 fatty acids, calcium, thiamin, niacin and vitamin B12. It is used in Oriental medicine for blood purification, intestinal strength, skin, hair, reproductive organs and menstrual regulation.

Being a brown seaweed like our own giant kelp, it uses the brown pigment fucoxanthin to help capture sunlight and photosynthesize. Scientific studies have shown that fucoxanthin can assist in burning fatty deposits, and is especially good for eliminating abdominal fat. Hmmm... I guess I should consider harvesting this crop myself so I can trim down the bulge that developed over the winter as I spent hours editing video at my computer instead of diving. I may also invite all my friends who love wakame and miso soup to join me for the nutritional benefits since most of them are already slender!

© 2008 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. Please help me climb out of self-imposed poverty... buy my "Munching and Mating in the Macrocystis," "Great White Sharks of Guadalupe," "Calimari Concupiscence: Mating Squid, " "Playful Pinnipeds: California Sea Lions," "Belize It or Not: Western Caribbean Invertebrates, Fish and Turtles," "Gentle Giants: Giant Sea Bass," "Common Fish and Invertebrates of the Sea of Cortez" or the new "Sharks and Rays of Southern California" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Images of the blades of Undaria showing the distinct midrib; the stipe that connects the blade to the holdfast,
and the frilly, convoluted sporophylls on either side of the base of the stipe.

This document maintained by Dr. Bill Bushing.
Material and images © 2008 Star Thrower Educational Multimedia