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Dive Dry with Dr. Bill

#343: An "Egregious" Error

Yes, I do realize that the title of this week's column may be very difficult to "fathom" for my readers. Of course that is typical of much of my humor. If I were a stand up comic, I'd probably hear the sound of one hand clapping or one voice laughing! My "egregious" error is the fact that I have yet to write a column about the very "fashionable" kelp known as the feather boa or Egregia. Therefore this week I shall remedy that.

When I first learned of this species it was known as Egregia laevigata, but the currently accepted scientific name is Egregia menziesii. However, there still appears to be some confusion since many sources refer to the two as separate species. Some assigned the common name feather boa to the first and ribbon kelp to the latter. However, the authoritative sources I checked consider it a single species under the name E. menziesii and use both common names for the one taxon.

As you can see in the images accompanying this, the feather boa kelp got its name from its resemblance to... of all things... a feather boa. Although they may date back to the 17th century, these decorative apparel accessories were popular during the Victorian Era, the Roaring Twenties and the 1970s. Think of Mae West, Isadora Duncan, Cher... or Elton John and Hulk Hogan! Wikipedia says they are worn for "erotic seduction purposes," but mating activity will not be a focus of this column (for a change). But I'm not here to write of fashion either, as my readers certainly know from my own personal attire.

The feather boa kelp is a species common along our shores including the world famous Casino Point Dive Park. It is generally found in shallower water shore ward of the inner margin of the giant kelp forest canopy where it can receive enough light. However it may also be found in deeper water, often on sandy bottoms where giant kelp does not usually attach and shade it. Egregia may be found from Alaska (where you can see Russia from your house) to Point Eugenia in Baja California (where the view is much nicer). There are morphological changes or differences in appearance of this species between its northern and southern range. This is referred to as intra-specific variation or variation within a species. Feather boa kelp attaches to rocks from the lower intertidal to depths of more than 60 feet.

The central stipe is substantial but flattened and would look somewhat like a belt if the blades and floats were removed. Oops, there I go on fashion again. The blades extending from the stipe may be fairly long and narrow, almost like pine needles, or broad and flattened. Younger blades tend to be of the flattened type while older ones are usually slender. At the end of each frond is a flattened blade known as the terminal lamina. The feather boa's float bulbs or pneumatocysts are found attached to the stipe as well. Individual fronds may reach lengths of 30 feet or more. They are secured to the substrate by a small holdfast which may vary in shape and structure in response to environmental factors. Thus this kelp may take on a range of different morphological types with varying appearance of the blades and holdfasts.

The stipe or rachis may also take on a different appearance under varying ecological conditions. North of Pt. Conception stipes tend to be rough, thick and resistant to the stronger surge and storm waves there. Blades tend to be smaller, providing less resistance. The nutrient-rich waters there allow for easier uptake of the necessities for growth, and the blades do not need to be large. South of Pt. Conception, the stipes tend to be smooth and thinner since there is less water movement. However, the blades need to be larger in the warmer, nutrient-poor waters.

It is not uncommon for algae to develop different appearance or morphological types in response to environmental conditions. I remember taking my first class on algae while doing my Ph.D. studies at UCSB. Noted phycologist Dr. Mike Neushul required us to collect algae of at least 20 different species and identify them. Wanting to ensure my "A" grade in the course, I collected more than twice that number from the waters around Avalon. Other scientists including Drs. Al Ebeling, Dan Reed and Ray Lewis helped review our collections and verify the identifications we made. I was astounded that a group of experts disagreed on so many of my samples. This was probably a result of the different morphology they expressed here in the calm waters of Catalina's leeward coast compared to the Santa Barbara area. I took their indecision as a signal that it was OK for yours truly not to be able to identify them either!

The feather boa kelp we see along our shores is the sporophyte or spore-producing generation. The tiny spores it produces form microscopic sexual plants or gametophytes whose sperm and egg join to create a new sporophyte. This is very similar to the reproductive pattern of our giant kelp.

Feather boa kelp provides a home to a number of marine invertebrates including amphipods like the caprellid or skeleton shrimp. Notoacmea insessa, a type of snail known as a limpet, is believed to be exclusively found on feather boa and feeds on the central stipe (also called a rachis). This results in oval-shaped pits or scars which may weaken the kelp and cause it to break off in the face of surge or swell. The purple sea urchin feeds primarily on this species of algae, but I have also seen other urchins and abalone munching on it as well. Humans also purchase this alga in various forms from health food outlets. As far as I know, my Xanadusian friends still prefer more crunchy fare... like human beings. I try to avoid asking them their dietary preferences though.

© 2009 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 DVD's (see this link). Yes, take Dr. Bill home with you... we'll both be glad you did!


Occasional dive buddy Sandy modeling the underwater version of the feather boa, the broad blades
of a young Egregia; the stipe and fine blades of the older individuals and
a beached strand showing the float bulb or pneumatocyst.

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