Dive Dry with Dr. Bill

#379: Die... Die... Die, Evil Weed

I've always said that since I left the Conservancy, I've been a dive bum. Unfortunately with the current economic conditions, it has become especially evident. In years past it was not unusual for me to do 6-8 dives in a single day. However, it wasn't until this past weekend that I did my FOURTH dive of the YEAR (or the decade for that matter). I've got a long way to go to match the 2,200+ dives I did over the last 10 years... and at $6 per tank that will cost me $13,200. Since I never got my investment back from Bernie Madoff, that's more than I can afford! DVD sales have hit rock bottom so until (if?) I can sell my proposed cable TV series, I'll be lucky if I do a dive a weekend. But don't cry for me Avalon (or Argentina), we're all in a pickle.

Speaking of Argentina, Saturday I went down to the dive park to meet up with lovely Argentinean model Paula Marramà, her boyfriend Conrad Julià and his nephew. Conrad's nephew was going to do a Discover SCUBA session with SCUBA Luv. Now Paula is not what you'd "expect" from some of our Stateside supermodels... she's down to Earth and very nice. And the important point is that both Paula and Conrad are avid SCUBA divers. Although I brought all my gear down in the Dr. Bill Mobile and planned to dive, I ended up spending two hours talking to them and other dive friends. After I suited up, I discovered I had left an important video cable at the house and went up to retrieve it. When I returned to the park, I spent another hour talking. By the time I looked out at the water, the winds had kicked up and white caps were breaking not far from the park boundary line so I aborted my plans.

Despite the change to daylight savings time, I was down at the park by 10:00 the next morning. This time I spent no more than an hour chatting before I got into my wetsuit, then set up the video camera, and prepared to descend. My goal was to film short segments of schooling blacksmith and schooling kelp surfperch for two new episodes of my show. Like the best laid plans of most men (and women), I didn't get a chance. That brings me to the other reason I've only done four dives this year, and the primary subject of this week's column... the $%^*%* invasive Asian kelp that has come to dominate Catalina's leeward coast in just a few short years. This infestation is even worse than that of the broom or Dyer's greenwold that escaped from the Hotel St. Catherine and has infected our island.

"Thanks" to this kelp (Sargassum filicinum), I could not even find what I needed to film. This exotic (and highly erotic, if you're another Sargassum) seaweed is an annual, and in the final stages of its relatively short lifespan. As it deteriorates, it breaks up and releases particulates and organic matter into the water that restrict visibility. Now I usually try to see the silver lining in most clouds, and took this as a sign from King Neptune that my task that day was to film the death throes of this alga so I could eventually make a documentary outlining how it has essentially ruined the normal ecological functioning of our waters. OK, so it may not be as dramatic as "Sharkwater" or "The Cove," and I undoubtedly won't win an Oscar (unless the "Oscar" refers to gratitude from the four dominant sheephead we see in the dive park). I still want to depict this evil weed's impacts. Maybe I can wrangle a grant that will fund a dive trip to its native waters off Japan! We could call it the Dr. Bill recovery plan. Heck, my banks and insurance companies got them, and they hardly deserved it (especially with what they charge me).

Last time I dove the park, I was deeply disturbed to see that this invasive species was actually crowding out a number of our native giant kelp plants. Not only can this Sargassum outcompete the Macrocystis for substrate to attach to, it is now overgrowing and shading it, outcompeting the giant kelp for sunlight. This doesn't even take into account the tremendous loss of nutrients for our own kelp forests that are now incorporated in the extremely dense (and increasingly tall) infestations of this noxious weed. I haven't done a formal scientific study, but it does seem that this alga has gotten thicker and taller over the past five years. I had hoped the warmer than normal water temperatures (minimum of 60 degrees F on my dive, and this is only mid-March!) would cause it to die off earlier since it is a cold water species. Fortunately I may be right on that based on my observations last weekend.

I have written previously about how this kelp chokes out almost everything in shallow water above 70 ft with rocky substrate. Our other native seaweeds are affected by this competition. Local invertebrates can't find food as easily in the dense undergrowth (but can readily hide in it... if they survive), and the ability of our own fish to find food and thus their diet are altered. I have never seen an introduced marine alga so dominate our waters to the detriment of our native species.

I spent my entire 65 minute dive filming the Sargassum forests. Heck, it was essentially all I could see. During previous dives this year and earlier, I have observed that very few local fish seem to use this exotic alga for anything other than a hiding place from hungry predators, although I have seen giant kelpfish apparently nesting in it (what other choices did they have?). In my research I learned that this kelp has an effective chemical defense against herbivores that might feed on it. It produces polyphenols which make it unpalatable to fish (and probably humans). However, on this dive, both the opaleye and the kelp surfperch were nibbling enthusiastically on the Sargassum. This gave me some intriguing video to film for my future documentary!

The opaleye were the most active species "feeding" on these foreign forests. Previously, when I've observed fish taking bites out of this kelp, I have assumed they were feeding on the invertebrates that attach to it in its final stages of life. Although opaleye are generally considered herbivores in the southern part of their range such as Baja, scientists have suggested what most divers have already figured out through direct observation. Opaleye seem to feed on giant kelp blades and other seaweed that is heavily encrusted with invertebrates. The researchers suggest that in colder waters, opaleye need to add animal protein to their diet to become more ecologically efficient. Makes sense to me... I was a much more voracious carnivore when I lived in frigid Chicago (although Mom made sure I balanced my plate with vegetables... except for the peas which I passed to my sisters under the table).

On this dive I wondered about a second hypothesis that might explain the observed munching by the opaleye. Since I usually see it happening only late in the Sargassum's annual life cycle, could it be that the alga stops producing the polyphenols that are the basis of their chemical defense? This could also explain why the opaleye and kelp surfperch attack it so readily in spring as opposed to winter. Hmmm... two competing (or mutually reinforcing?) hypotheses to test scientifically. Maybe that grant is a better possibility than I thought. I'll just have to write a letter to marine ecologist Dr. Jane Lubchenco, head of NOAA, to request funding. After all, one of my published scientific papers on designing marine reserves was recommended to her by a group of scientists as the federal government approaches the task of considering such reserves in our nation's waters. Maybe my economic recovery is approaching. Naw, just a pipe(fish) dream. Besides the Sargassum will have died off before I can even get the grant request written. Once a dive bum, always a dive bum.

© 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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Dense forest of the Asian Sargassum filicinum in our dive park, opaleye feeding on the Sargassum or the
invertebrates attached to it, Sargassum outcompeting our native giant kelp (Macrocystis).

Additional images of the Sargassum filicinum forest and senescing individuals.

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