Dive Dry with Dr. Bill

#345: (Sea)Weeds: "Plants Out of Place"

Many decades ago the Wrigley family hired Albert Conrad to be their botanist/gardener. He apparently chose to landscape the grounds of the Hotel St. Catherine with an exotic plant from Europe, the Dyer's greenwold or broom. This shrub produces a beautiful yellow inflorescence when the broom blooms. Of course this was in the days when few realized the ecological impacts of introducing non-native plants into a "natural" landscape. Today, this invasive exotic covers the hills in Descanso Canyon and has been transported well into the interior by vehicles, hikers and "natural" dispersal, becoming a major problem for the Conservancy's wildland weed control program.

Those of you with green thumbs (unlike my very brown one) are well aware of the "weeds" that infiltrate your well tended gardens. Back in December of 1970 I was reading the magazines in the former Catalina Island School for Boys (Toyon Bay) library. I encountered an article by John Fowles, my favorite fiction author (The Magus), in (of all places) Sports Illustrated entitled "Weeds, Bugs and Americans." In it he defined a "weed" as a plant out of place. While there are more elegant scientific definitions of the word, Fowles pretty much hit the nail on the head.

For gardeners, who usually grow non-native flowers or vegetables in their home gardens, a "weed" is often a native plant that happens to take root thanks to its seed dispersing to the well-tilled and watered soil in their backyard. While the "weed" is native, it is considered out of place mixed in with the begonias, roses and nasturtiums. Likewise, in a natural landscape full of California sagebrush, St. Catherine's lace or Catalina bedstraw, an introduced geranium becomes the weed (even if Mrs. Wrigley loved them up at Mt. Ada). Of course the Wrigley and Offield families have done much to remediate the unintended effects of these actions through their valuable support of the Conservancy's efforts.

"Weeds" are not restricted to the realm of the landlubber. I'm sure all my readers have heard the term "seaweeds." Actually that refers to the many species of marine algae ranging from the tiny red ones that make up a garibaldi nest to our own giant kelp forests. However, the word "weed" can still refer to an alga or a true vascular plant in the ocean that has invaded a natural underwater landscape. Many of you know about the invasive Asian algae that have invaded our waters including Sargassum filicinum, Sargassum muticum (wireweed) and Undaria pinnatifida (wakame). The chances of these alga dispersing naturally to Catalina are probably even worse than my odds of winning the lottery (and I don't buy tickets). I want to write a follow up on the ecological devastation caused by the rapid invasion of the former species in the waters of Catalina's leeward coast.

I first encountered this alga, a native of Japan and Korea, while diving at the Empire Landing Quarry several years ago. At the time I knew it was "different" and "out of place," but I had no idea of its identity until Drs. Jack Engle of The Tatman Foundation and Kathy Ann Miller of the U. C. Herbarium informed me. Within just two years this highly invasive kelp had spread up and down our coast, and I was seeing large infestations from the West End to the East End. This alga grows so dense during the late fall through early summer that it chokes out not only our native algae, but also those invertebrates that normally attach to the rocky reef... and the fishes that feed on them.

When I first saw it invade our Casino Point Dive Park, I wanted to get permission from the California Department of Fish & Game to remove it with the help of other divers. I was told that I would need a fishing license, and we could only remove ten pounds (wet weight) per diver per day. I was quite puzzled that we were not permitted to remove this highly invasive kelp before it really became a problem. A permit to remove larger quantities might take several months to obtain. Of course the Sargassum filicinum expanded, and the dive park is now choked with it during its annual growing period.

This alga forms patches so dense that it out competes our native algae and invertebrates for substrate or space to attach on the reef. Individual kelp may reach 15 feet in length. In addition to taking over the rocks, it also completely shades out any smaller native kelp and other algae. The spores and other tiny reproductive stages of our natives do not receive enough light to trigger their growth, and either remain dormant or die off. The Sargassum has created a monoculture during its peak growing season, just as an unenlightened farmer might grow nothing but corn in their fields or a gardener nothing but tomatoes. The natural biodiversity of our underwater landscapes is replaced by a nearly continuous stand of this Asian species which I've not seen any of our invertebrates or fish eat.

Fortunately the Sargassum is an annual, and dies off as the water warms up in early summer. When it does, it sheds organic matter and detritus into our waters, causing visibility to drop and making our dive park less appealing as a destination. There are other consequences as well. When this exotic kelp dies, and the last remnants of it fragment off into our waters, the resulting landscape looks like a timber company came through and clear cut all the vegetation. All one sees is the rocky reef and some small algal turf covering it. Slowly the native spores (new and old) respond to the increased light and begin to "sprout." New giant kelp is slowly appearing in these largely barren landscapes.

However, this "resurgence" doesn't occur until summer when temperatures are on the increase and nutrients are diminishing. Giant kelp and our other native cold water algae generally thrive during the winter when temperatures are cold and nutrient levels high. The non-native weed Sargassum has shifted the seasonal cycle of these native "seaweeds," thus altering our Catalina ecosystems both in the winter when they out compete many of the natives, and in the summer when their demise only allows the native algae to grow in less than optimal conditions. CDS staffer Tyson Farley located a web site that talks about methods to control this noxious pest (thanks Tyson). I hope the researchers find an effective means of control both for the sake of the divers who are attracted to our dive park due to its beauty, and for all the native species and ecosystems affected by this alga "out of place."

© 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!

Dense patch of the invasive Sargassum filicinum showing how it can out compete natives for substrate
and light, S. filicinum dying out in early summer and the barren landscapes left
upon completion of its annual life cycle.

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