Dive Dry with Dr. Bill

#267: That's A Lot of Bull... Kelp

In the days when I did almost all my diving right here in the Casino Point dive park, I was frequently amused to hear dive masters and dive instructors refer to species by names which were not correct either scientifically or in common parlance. I remember the day I was filming a giant sea bass heading towards the harbor end of the park and a group of three divers. About 20 minutes later they stormed up the dive park stairs to confront me. "Why did you chase that big shark in our direction?" I wasn't sure what they meant at first, then I realized they were the victims not of a shark... but of mistaken identity. I told them they were very fortunate to have such a close encounter with a big fish slowly making its recovery in our waters.

It was situations like that which led me to create my "Dive Dry with Dr. Bill" cable TV show, DVDs and this newspaper column. I wanted to educate divers so they understood what they were seeing down under (and I don't mean in Australia, although I wouldn't mind being there right now... it's summer). As my educational efforts continued, I realized it was equally, if not more, important to bring the undersea world to those of you landlubbers who don't descend into the depths. I have been an educator all my adult life, and the opportunity to expose you to the world of King Neptune on your television screen is truly a labor of love (although I do still hope to make some money). You get to "dive dry" with me from the comfort of your easy chair... no wetsuit or cold water required.

Now one of the most common errors I hear from divers is when they refer to all that "bull kelp" at depth. I'm sorry folks, but that's just a bunch of bull... unless you are diving north of Point Conception. True bull kelp, known scientifically as Nereocystis luetkeana, doesn't grow south of that biogeographical boundary. What these divers are seeing, and applying the incorrect name to, is elk or elkhorn kelp, Pelagophycus porra. There are some similarities, but anyone with 20/80 vision should be able to tell them apart once they learn the difference.

Elk kelp is a species of brown alga that is usually found in deeper water starting near the outer edge of the giant kelp (Macrocystis) forests. This kelp has a long, thick stipe which grows from the anchoring holdfast. The stipe may be nearly 90 feet long, but is usually much shorter. At the other end is a large float bulb or pneumatocyst. Attached to the pneumatocyst are antler-like branches that bear huge, broad blades designed to capture what little sunlight filters down to these depths. These blades may reach widths of more than three feet, and lengths greater than 65 feet. The blades of the elk kelp often lie along the bottom, but occasionally are buoyed up. However, the relatively short stipes and deep water habitat prevent the blades from reaching the surface where sunlight is brightest. Elk kelp is only found from Point Conception to Baja California.

Bull kelp is also a species of brown alga with a long, thick stipe that grows from the attached holdfast and has a large float bulb. However, that is where the similarity stops, at least in terms of external morphology or appearance. The stipe may be up to 100 feet long, and this kelp's habitat includes shallower waters than the elk kelp's. Therefore the blades of this species may reach near the surface and form a canopy like our own giant kelp (Macrocystis). The blades of this species are attached to the pneumatocyst in two clusters, and may number up to 50, but they are only about 6" wide and no longer than about 15 feet.

Bull kelp is known from the Aleutian Islands of Alaska to the waters off San Luis Obispo County, California. It also differs from elk kelp in that it is an annual, usually surviving only one year (although some live two). They also differ somewhat in reproduction. The spores are produced on the blades near the surface, but need to settle in numbers on the bottom before the next growing season. If they were released individually, the spores would disperse in the currents. To avoid this, the bull kelp spores are released in small packets which fall to the bottom before opening to release the contents.

To confuse the issue a bit, when I first started diving our waters back in the 1960's there was another species of Pelagophycus recognized by scientists. Its scientific name was Pelagophycus giganteus, and was said to differ from the elk kelp in having a much broader holdfast and a shorter stipe. The discovery of the first kelp of this former species was made in Catalina waters, I believe at Long Point. The type location, or site from which the elk kelp was scientifically described, was Catalina. However, most scientists now believed it is the same as the elk kelp.

I have never seen the bull kelp attached in southern California waters. Apparently none of the recognized experts on kelp have either. If divers were seeing it, especially with the frequency it is reported, I'm sure the scientists would have by now. This is not to say I haven't seen this kelp in our waters. In fact, I've seen it twice... but it was as drifting kelp "rafts," not as functioning, attached plants.

My students and I sampled the two drifting bull kelp rafts when we were conducted research with my mentor from Harvard, Dr. H. Barraclough "Barry" Fell, under a National Science Foundation (NSF) grant. I was ecstatic when we found them. Since bull kelp only grows north of Point Conception, these drifting rafts had to originate there too. It was indisputable evidence that these two rafts had drifted distances at least on the order of 100 miles from their point of origin.

Why did that excite me? It meant the living invertebrates (clams, crabs, shrimp, starfish and the like) that were found on the rafts had drifted at least 100 miles as well. This was indisputable confirmation of my hypothesis that marine life could indeed hitch-hike on such rafts and drift into new areas where they might land and colonize. Such mechanisms are especially important for marine species that do not have a dispersal stage such as planktonic larvae that drift in the currents. And that's no bull!

© 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" or "Common Fish and Invertebrates of the Sea of Cortez" DVD's. Yes, take Dr. Bill home with you... we'll both be glad you did!

Two views of bull kelp (Nereocystis luetkeana) on the left and
two of elk kelp (Pelagophycus porra) on the right.

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