Dive Dry with Dr. Bill

#428: Sargassum... "OUT" in the Cold!

Those of us who swim or dive in the waters off Catalina know that water temperatures last summer and fall were rather cool. For many, this "dampened" their enthusiasm for such recreation, but I saw it as a blessing of sorts. The cool temperatures meant nutrient levels were higher than usual, and our giant kelp (Macrocystis) forests were thick and healthy when they would usually be deteriorating due to the low nutrient levels associated with the normally warm waters. I predicted that these dense stands of kelp would shade out the nasty invasive Asian seaweed, Sargassum horneri (formerly S. filicinum) that has taken over the dive park during winter the previous five years.

However, before I discuss that in detail, I want to clear up some misconceptions I have helped spread about the Sargassum in previous columns. Years ago noted honey bee behavior specialist, Dr. Adrian Wenner, educated me on the principle of FILO. Accountants will quickly understand what I'm referring to... which probably means politicians of neither party will "get it." FILO refers to "First In, Last Out" in the accounting world. However Adrian was referring to information rather than money. He meant that the first thing a person hears on a subject usually sticks with them unless it is driven out rather forcefully by new facts. Scientists are supposed to weigh new information objectively, but even we are subject to this principle. So hopefully you will forget a few things I've written in the past (probably most things for that matter) and let me correct them here.

First, the highly invasive Sargassum horneri is not a kelp. Some people are quick to lump all large brown algae under that label, even people who ought to know better like myself. Sargassum belongs to a completely different group of brown algae than our true kelps like Macrocystis and elkhorn kelp. Second, the Sargassum plants we see crowding out most everything else on our leeward coast is not the spore producing generation of that species like our giant kelps. It reproduces sexually (bet you didn't know many algae do that, did you?). They are precocious, maturing early, and have both male and female reproductive structures on a single individual which makes it very easy for them to disperse and colonize new locations due to the ability to self-fertilize. Third, something others have assumed because it grows during winter is that it is a cold water species. The Sargassum actually likes slightly warmer water than our giant kelp, and dies off in the late spring because it is an annual, completing its life cycle in less than a year.

Now with those clarifications, let's look at what has happened this winter. Initially my predictions (we scientists call them hypotheses) seemed very accurate. There was little to no non-native Sargassum that developed last fall. Light levels beneath the luxuriant giant kelp forests were indeed lower than usual, and it was almost like diving at dusk to be in them. Divers commented on how great it was to have the dive park back in its natural state. The waters remained cool, the giant kelp thick and the Sargassum practically non-existent during much of the early winter. Then temperatures started to creep up a bit. Was it coincidence, or the warmer waters, that resulted in patches of the noxious exotic appearing? Without some good scientific research into this, I'm merely speculating. I'm generally pretty good at that scientifically... but certainly not financially.

Since the Casino Point dive park will soon become an officially recognized marine protected area (MPA), it would seem appropriate... even necessary... to try to do something about this invasive species that can become so dominant during what is usually the best time to dive our waters. When I tried to get a permit to remove it after it first appeared in 2006, I was told it would take 4-5 months to obtain permission (to remove a non-native??? Hmmm...). By that time it would already be well into its reproductive period. Since then it has spread over the entire leeward coast of Catalina and has appeared in the northern Channel Islands and San Clemente Island; along the coast of Los Angeles, Orange and San Diego Counties and even into northern Baja California.

For the past few weeks I've been working on a video to send to the Fish and Game Commissioners outlining the problems this invasive species is causing. It has tremendous impact on our native ecosystems by outcompeting local seaweeds for space, light and nutrients; and limiting suitable habitat and food for our SoCal invertebrates and fish. However, the impacts are not "just" ecological. It has decreased the number of divers who come out to Casino Point during the winter, caused the engines in power boats to overheat by clogging cooling system strainers and filters, become entangled in boat props, and affected habitat for gamefish like the white sea bass that draw anglers to our waters.

I'm hoping this video will trigger a commitment on the part of Fish and Game to address the impact of this invasive species. We will most likely not be able to control it island-wide or throughout southern California. This may be especially true as regional water temperatures increase due to global climate change. However, I have hope that we can at least control it in selected sites like the dive park. Towards that end I am proposing that the Commissioners expedite a permit to remove this species from the dive park at least once a year, preferably in the fall before it becomes reproductive. A mainland dive instructor did clear an area last year, and there was relatively little regrowth despite the fact this species may have overlapping generations in a single season. If we can get the permit, I know plenty of mainland divers willing to volunteer to remove it from the park. I'm hopeful we can also use this project to initiate some real scientific study into this species and its effect on our local ecosystems. Since this project has no current funding, anyone interested in donating for the development of the video or the cost of air and other supplies, please contact me.

© 2011 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. 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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Graph of average August temperatures for the five years (2005-2010) the Sargassum has been present in our waters,
thick growth of Sargassum from previous years; reproductively mature plant and close up of the female receptacles

This document maintained by Dr. Bill Bushing.
Material and images © 2011 Star Thrower Educational Multimedia