Dive Dry with Dr. Bill

#534: Epiphytes

Many of my readers are familiar with epiphytes... even if they don't know it. Curious yet? I hope so. The word epiphyte comes from the Greek words "epi" and "phyton" meaning "above" and "plant." Epiphytes are plants that grow on other plants, using the "host" plant for support. They are not parasitic on the host and generally do little damage to it. Why would you know about these? Well, if you ever attended a school dance, you probably bought or received a beautiful epiphyte. Yes, many orchids are epiphytes, growing on other plants but not depending on them for nutrients, moisture or food. I'll bet almost none of you have ever complimented a lady on wearing a beautiful epiphyte corsage! I did... and almost got slapped!

Although epiphytes are most common in tropical or subtropical climates, we have them right here on Catalina. The lichen you see growing on the bark of our scrub oaks and other trees is one type, although technically they are composed of an alga and a fungus. But today I'm not going to dwell on our terrestrial epiphytes like I did in my days as a Conservancy vice president. We have epiphytes in our marine environment as well. At least we've been calling them epiphytes for decades but now I'm not so sure based on the strict definition. Most algae (aka seaweed) are not considered to be true plants.

Depending on whose definition you use, true plants utilize chlorophyll to photosynthesize, have cell walls made of cellulose, utilize sexual reproduction, and store food in the form of starch. Of course I can think of exceptions to all these criteria. Plants were originally separated from animals in a classification of living things into two kingdoms (no relation to the King Dome in Seattle) by Aristotle back in the 300s BC. Later, Linnaeus who is considered the creator of modern scientific classification maintained this distinction in the 1700s AD. However, many modern taxonomists have separated most of the algae from the "true" plants with the exception of the green algae which are believed to be a sister group to the "true" plants.

Scientists believe the other types of algae such as the beautiful reds and the browns (including our own giant kelp) evolved from different ancestral stock and are therefore placed in categories distinct from "true" plants. In fact, current classification systems mostly recognize FIVE kingdoms of living things. True plants are in the Kingdom Plantae. Most algae are grouped with the protozoa in the Kingdom Protista which I find strange from an ecological perspective. Blue-green algae are now grouped with bacteria in the Kingdom Monera. Fungi form the basis for the fifth kingdom, Fungi. Personally, being the democratic American that I am, I see no need for kings, queens and kingdoms. I don't think plants, animals or other critters pay much attention to them either. They really are largely human constructs to help us understand living things by placing labels on them.

So I've taken you on a rather involved explanation of classification just because the definition of epiphyte involves "plants" living on "plants." I'm going to remain "old school" and say that the word may also involve algae growing on other algae. Is that heresy? Probably to rigid taxonomists, but I think most open-minded ecologists will let it slide. So I now feel justified in applying the word epiphyte to what I see in the waters off our island.

When a "plant" or seaweed is growing, it offers a mostly unstable base for another species to attach and grow on it. When kelp blades are new, you see next to nothing attached to them. Only when they have reached a point where growth slows or stops do you see the blades covered with a thick coat of different species like the Jack Frost bryozoan (Membranipora) or tiny tube worms (Spirorbis). Likewise, many of our other seaweeds grow fast when nutrients are more abundant during the cooler part of the year (although reduced daylength affects their growth too) and slow down as the waters warm up. This provides more stable surfaces to attach to.

Given the devastating abundance of the invasive Sargassum from Japan in our waters this year, suitable substrate for an alga (or invertebrate) to attach to may be at a premium. I don't see many epiphytes attaching to the Sargassum as it provides little surface area, and its density blocks light from reaching the rocky reef below its canopy for others to photosynthesize. As it begins to die (senesce), smaller epiphytes may often cover it though. Many of our native seaweeds are beginning to show signs of epiphytic growth... red and smaller brown seaweeds are appearing, attached to mature native algae. By doing so, they obtain easy access to sunlight to sustain their own photosynthesis to power their growth and reproduction. And that's what life is all about... munching to allow the individual to continue, and mating (well, reproduction in the case of seaweeds) to allow the species to continue.

So now you know what an epiphyte is. Remember that next time you buy a corsage for your prom date, kids. Just hope you don't get slapped when you say it. Aren't you glad I clarified for you the present classification of all living things into the five kingdoms? I didn't think so. Just remember, these classification schemes are all based on the human propensity to group and name things. Many times things in the real world don't fit so neatly into our "boxes," although DNA and molecular biology is giving us much better information to base our classification systems on. However, the plants and animals may be laughing at us for our attempts.

Back in 1970 novelist John Fowles wrote a piece in Sports Illustrated entitled "Weeds, Bugs and Americans." He was miffed by our use of "bug" and "weed" to describe a wide variety of living things. In that essay he stated "Any trained biologist will tell you that identification expertise has about as much relation to serious biology as knowing national flags has to do with being an authority on international affairs." Now, I may not entirely agree with that but as the French poet Eluard once said "a fish by any other name would still know the sea."

© 2013 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 29, 10:00 AM weekdays and on Charter Communications Cable channel 33 at 7:30 PM on Tuesdays in the Riverside/Norco area. You can also watch these episodes in iPod format on YouTube through my channel there (drbillbushing). 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!

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Dr. Bill prior to getting slapped for giving his date at the junior prom an "epiphyte," a terrestrial
epiphyte known as a bromeliad; brown and red algal epiphytes growing on brown algae.

This document maintained by Dr. Bill Bushing.
Material and images © 2013 Star Thrower Educational Multimedia