Dive Dry with Dr. Bill

#384: Devil Weed Kills Even After Death

Last weekend was Earth Day here on Catalina and throughout the planet. Hard to believe that 40 years ago I taught on the first Earth Day down at Toyon, and helped plan some events with a group based at the old Ecology Center in Berkeley. I hope this year's event was a great success. Since the Conservancy is doing a good job of tending to the ecological ills of the island itself, I spent the day where it made the most sense to me... under water! After all, about 71% of the planet "Earth's" surface is water, and if we viewed it from outer space like the first astronauts, we'd be calling it the Water Planet instead.

As the Conservancy's former vice president for science, education and ecological restoration, I spent years dealing with the many ecological challenges on our island. Some of the most obvious were the feral pigs and goats, but to the trained eye many of the invasive alien "weeds" also pose a very serious threat to our native species. However, I don't think I've seen a worse ecological menace to Catalina in the 40+ years I've been here than the invasive Sargassum kelp from Japan. Yes, I'm going to write about this nasty stuff one more time before it dies off until next fall. Therefore there will be less humor this week than normal... because it just isn't funny. Despite that, I spent the weekend joyfully filming its death throes. It is fantastic to once again be able to see the bottom in a mere 20-30 ft of water instead of looking down on a virtually impenetrable canopy of the stuff.

First, I thought I'd clarify something. Although I've been calling it Sargassum filicinum since it first arrived here several years, scientists are now referring to it by its more accepted name, Sargassum horneri. One can use either scientific name since they are biological synonyms referring to the same calamitous kelp invader. That extends its known distribution to China in addition to Japan and Korea. I think it is time we come up with a common name for it. Since it is originally from Asia and was not in SoCal until the last decade, we have no common English name for it. I'm going to suggest devil weed or killer weed (no, guys, you can't smoke it... although undoubtedly some moron will try!). It does have one redeeming quality... if eaten, it appears to have cancer fighting chemicals in it and also suppresses herpes simplex. This will be my fifth column on this subject since 2006, but it is of tremendous importance to the health of our local waters.

My dives this past weekend revealed great progress in its disappearance. The ocean floor is now covered in juvenile blades of our native giant kelp (Macrocystis) that have sprouted over the last week as sunlight finally penetrates down to the tiny spores waiting on the bottom. Starting last fall, the Sargassum had effectively out competed them for substrate to attach to, light to photosynthesize and even nutrients to grow. The incredible density of the Sargassum needs to be viewed as a "sink" or trap for many of the nutrients that our giant kelp needed to grow during winter and spring. The Sargassum appears to be more efficient in capturing the "tasty" nitrates, phosphates and other nutrients to build its tissues, leaving less for our native species to utilize.

This means that some of our giant kelp will begin its growth cycle a few months late, and in what is probably a nutrient depleted ocean. Instead of developing into the magnificent forests over the winter and spring as it should, many stands of giant kelp are starting to grow at a time the water is warming up. Giant kelp, like Sargassum, is a cold water species and does not do well in warmer periods. One major reason is that the warm water in late spring, summer and early fall contains fewer nutrients. So our native giant kelp is beginning its life cycle at a very bad time and may not reach its full glory. In addition, plankton blooms usually start in the spring and the phytoplankton or plant plankton also consumes a great deal of nutrients. Our Macrocystis has survived one competitor only to begin a new duel with another.

A second observation also bodes poorly for our own kelp forests. I was surprised to see that many of the very young giant kelp blades have attached to the dying stipes ("stems") of the Sargassum, making them look like an odd terrestrial shrub! Of course the Macrocystis juveniles are looking for any substrate they can attach to, but by adhering to the Sargassum in large numbers they will simply "drift away" (to the tune of Dobie Gray) when the Sargassum finally expires. Thus the nasty Asian kelp keeps tormenting our own giant kelp even in death. To my shock, I spotted a number of juvenile Sargassum on the bottom after the mature ones started dying off. I feel pretty confident that they will die in the warmer water of summer, but if there is the possibility of two "generations" of this nasty stuff in a single year this is not good news.

Another interesting conclusion from my dives this weekend relates to the fact that I am seeing lots of late season algae growing on the rocks left largely bare by the death of the Sargassum. These are species that I normally don't see until summer. They are often much better at utilizing the low nutrient levels common when the water is warmer. Their presence this early in the year seems to establish additional evidence that our waters are currently somewhat nutrient poor. If my hypothesis is correct, the Sargassum has altered the normal seasonal cycle of both nutrients and of the native algae that depend on them. By shifting much of the giant kelp growth to later in the year, and creating conditions suitable for normally late summer species to appear in spring, the devil weed has radically altered our marine environment not only during the eight months it is actually present, but also in the four months it is not.

I realize that some who read this may not be as concerned as I am about the ecological impact of this devil weed on our island's waters. However, they may be more responsive to the economic impacts and the effect on recreational activities pursued off Catalina. I have heard countless mainland SCUBA instructors say that the presence of the Sargassum has caused them to stop trying to teach, or greatly reduced the frequency of their visits, here in our waters during the cooler months. SCUBA divers are a user group that brings repeat business to the island. In better economic and ecological times, mainland dive shops often brought at least one SCUBA class over each month so they provide repeat business that also introduces potential first time visitors to our island. Many recreational divers loved to come to Catalina on a repeat basis to dive our clearer and calmer waters, but are now faced with the monoculture of Sargassum in the cooler months when we really need them. Visitor groups that make repeated trips to the island over the years are very important to our economy.

A few weeks ago I asked J.J. Poindexter if the Harbor Dept. received any complaints of Sargassum fragments clogging the cooling systems on visitor's boats. He said no, but mentioned that Oren was working on a patrol boat that had overheated. The next day J.J. told me that the cause had indeed been due to the Asian kelp clogging the strainer. I've been wondering if other boaters in our waters have had similar issues since this could add to the economic problems associated with the devil weed. Another potential impact on recreation and our local economy is to angling. If fishers are getting their lines or anchors tangled up in the devil weed, this could also be a problem. Of course the Sargassum will be gone by our peak summer season.

I've decided that in view of the relative inaction by the California Dept. of Fish & Game on this invasion, I'm going to create an educational video about its impacts to share with the CDF&G commissioners and state legislators, as well as federal legislators who control trans-Pacific shipping. We have had several invasions in our waters most likely from ballast water or specimens attached to the hulls of Asian cargo ships. My guess is that their waters have been invaded by some of our species as well. We run the risk of "homogenizing" our temperate water ecosystems by transporting such non-native species across the huge barrier of the Pacific Ocean which they would not cross without human "assistance."

Of course this will be yet another effort that will end up costing me $$$ rather than adding income to my imbalanced balance sheet. I'm hoping to partner with an officially recognized non-profit so that folks can donate to this project, and to my desire to organize diver events next fall to temporarily eradicate this noxious pest in the dive park and possibly Lover's Cove. Although after doing my 2009 income taxes, I'm without question "non-profit," the IRS has not recognized me officially... yet! Other ways that people can contribute to this effort include giving "testimony" on camera about the effect of this evil weed on their recreational activities be it diving, boating or angling. Although I doubt we will ever eradicate it completely... at least not until global climate change causes reef-building coral to grow in the dive park rather than cold water kelps, hopefully we can make a dent in it next fall and make Avalon's waters more conducive to the types of activities we and our visitors enjoy. As I warned you, not much funny in this week's column, so I'll try to make up for it in future ones.

© 2010 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!

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Mature Sargassum thinning out as it dies, nearly barren rock surface after death of Sargassum;
juvenile giant kelp (Macrocystis) growing on bottom, and small juvenile giant kelp blades
attached to the stipes ("stems") of the dying Sargassum.

This document maintained by Dr. Bill Bushing.
Material and images © 2010 Star Thrower Educational Multimedia