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Dive Dry with Dr. Bill

#575: Sea "Weeds?"

When I was vice president of the Catalina Conservancy and we were removing feral goats and pigs, I learned a sad lesson. Plants are the Rodney Dangerfields of terrestrial ecosystems... they just don't get no respect. Many wondered why we cared about saving some 50-100 species of plants native to the island and thought we should care more about the introduced mammals that aren't even native to North America (thank you Columbus and other early European explorers).

To a large extent this attitude is mirrored in the marine environment. Many divers are generally unaware of the different species of "seaweed" in our waters. Well, at least our giant kelp (Macrocystis pyrifera) does elicit awe, and there are plenty of divers who are upset about the lack of effort by the California Department of Fish and Wildlife toward controlling the highly invasive Sargassum horneri that has devastated our native ecosystems here on the island and elsewhere. But in general few learn the names of more than a handful of different algae or consider their importance to other marine life.

I've written before that plants... and, by extension, "seaweeds..." are critical components of any ecosystem. They capture energy from the sun through photosynthesis and store it in ways they and animals can use to sustain life. If you don't have healthy populations of native plants or seaweeds, the critters that munch on them (herbivores) will suffer. If these "lower": members of the food chains and food webs don't get enough to eat, the predators that feed on them will likewise be affected. And just in case you slept through high school biology class, we are omnivores and depend directly on plants for our salads and vegetables... and indirectly on them for the herbivores we feed on such as cattle (aka beef) and the tasty predators and omnivores placed on our plates such as pork.

Now I get a bit miffed when people use the word "seaweed" to describe the many species of algae that are present in healthy marine ecosystems. One of my favorite novelists, John Fowles, wrote an interesting article ("Weeds, Bugs and Americans) that was published in, of all places, Sports Illustrated way back in my second year on the island. He wrote that people have a habit of giving labels to things and being satisfied with the label, not learning what the thing labeled is all about. We do that with "weeds" and "bugs."

One can define a weed as a "plant out of place." Human gardeners tend to refer to plants which invade their gardens and crowd out or compete with their lovely geraniums as "weeds." However, these "weeds" are often native plants that invade the well manicured garden from adjacent natural areas (if there are any left!). I imagine Mrs. Ada Wrigley thought the geraniums planted around Mt. Ada were beautiful additions to the island, yet they have become "weeds" in the adjacent natural areas. Her gardener, Albert Conrad, planted the nasty Dyer's greenwold (or genista or Canary Island broom or whatever it is called today) around the gardens of the Hotel St. Catherine in Descanso, yet they escaped into the rest of the island becoming a serious "weed" infestation. Today, about one third of the plants on our island are non-native although not all are invasive threats.

For that reason, I really dislike using the term "seaweed." I prefer the scientific term, alga (plural, algae). Perhaps that is because I was trained as a phycologist (person who studies algae). We are fortunate in that there have been relatively few serious algal invaders in our waters. The primary exception is the Asian Sargassum I've written about frequently. Using the term seaweed is even more politically incorrect than referring to sea "horses," star "fish," sea "cucumbers" or jelly "fish." It suggests the algae referred to are "out of place" when they are actually native to our waters.

Now there is one big problem with algae that one generally does not encounter in fish or invertebrates. Back in graduate school I made a collection of algae from Catalina waters. Our collections were evaluated by some of the top names in the field of marine biology. I was shocked to find that they could not agree on the identification of a high percentage of the species in my collection.

My specimens were collected here on Catalina where environmental conditions often varied significantly from those in the northern Channel Islands or the Santa Barbara coast. These differences were often enough to cause the same species of alga to look significantly different from its relatives up north. We call this "phenotypic plasticity." That simply means that under different conditions of wave action, current, temperature, etc., the same species of alga may develop different structural appearance to accommodate those differences even though their genes are very similar. That's one reason I shy away from algae these days and focus on the critters that I can more easily identify!

I hope more of my readers will understand the critical role plants and algae play in our terrestrial and aquatic ecosystems around the world. Plants deserve not only our respect, but our thanks for providing the food for the majority of the critters we cherish... not to mention a good percentage of the oxygen that makes our atmosphere able to sustain us. We should never refer to them as "weeds" or think them out of place if they are native to the area. Native plant gardens can be beautiful and cut down on water use... a critical issue during times of drought like today.

© 2014 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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Giant kelp converting sunlight to usable energy, green alga Chaetomorpha;
red alga and the highly invasive non-native brown alga Sargassum horneri.

This document maintained by Dr. Bill Bushing.
Material and images © 2014 Star Thrower Educational Multimedia