Dive Dry with Dr. Bill

#362: See "Weeds..." and Not Much Else

Readers of my column are aware that I've been doing almost all of my dives after sunset the past two months. I've been gathering footage for my cable TV show episode on "The Night Shift." However that is now drawing to a close for this year. No, water temperatures are still warm enough (64 F at maximum depth) to dive in my easily donned 3/2mm wetsuit. Other than wanting my evening glass of merlot a little earlier, the reason for stopping this extremely enjoyable activity has to do with my preference for stereo equipment, camcorders and high definition TV sets coming largely from Japan.

No, I'm not staying home at night to listen to music or watch the glut of nonsense found on television these days. My reason is related to the container ships and other vessels that bring these goods to Los Angeles' ports so I can purchase them. It appears that these vessels carried with them some highly undesirable cargo... the spores of the pernicious, highly invasive Asian kelp known as Sargassum filicinum. This species invaded the Long Beach area back in 2003, and quickly found its way to Catalina. A few short years later and it has come to dominate nearly every dive site on the island's leeward coast including Casino Point. To add insult to injury, any of us who buy anything transported from Japan or Korea (where it is native) have contributed indirectly to this nasty introduction, including myself! I've often wondered how many of our SoCal seaweeds have been transported to Asian waters and caused problems there.

I have written about the impact of the extremely dense populations of this kelp on our native species which are out competed on our reefs for both space and, in the case of algae, sunlight. Why would this atrocious alga cause me to stop night diving? The answer is simple. It almost completely obscures the subjects I'm trying to film at night... the lobster racing along the bottom, the kelp bass and morays trying to munch blacksmith and kelp surfperch, or those prey species as they seek shelter from the onslaught. Even if I find a subject to film, the darned stuff moves about in the surge and ends up in front of my camera obscuring the stars of my show.

Of course my irritation with this errant and egregious exotic is minor compared to its impact on our local ecosystem. The fact it excludes so many of our native algae and encrusters by outcompeting them is a major issue. So far I have only seen three local species use this alien invader. Giant kelpfish have taken to sheltering in it since our native smaller kelp and other seaweeds can't grow in its presence. Kelp surfperch will feed on the small crustaceans, hydroids, bryozoa and other invertebrates that grow on it as it starts to age or senesce. And I did film one tiny, white sea anemone that had attached near the tip of one frond, looking almost as if the Sargassum was in flower rather than producing spores.

So very few of our local species benefit from the overwhelming presence of this kelp. In addition to crowding out our local invertebrates and algae, how else has this disastrous demon impact our native ecosystems? When a single species dominates a landscape to such an extent, it greatly reduces the local system's biodiversity and creates a near monoculture. This results in a decrease in the system's ecological stability, and its ability to weather environmental changes. It alters food webs, habitat availability and even reproduction for our natives. Fortunately this alga does not grow high enough to shade out our adult giant kelp, but it can delay the growth of the microscopic spores on the reef. We are also lucky that this is an annual species, growing from late fall to late spring, then disappearing during the warmer summer months.

Based on my night dives, I have observed several apparent impacts on my species of interest. Some snails come out at night to feed on algae since one of their primary predators, the sheephead, is sleeping in the rocks. I don't remember seeing any of our snails feeding on the Sargassum. If they can't find enough native seaweed to munch on, their numbers may decline reducing food for our sheephead and other predators... no more escargot!

Over the past few weeks I have filmed many large calico or kelp bass hunting blacksmith at night. The blacksmith shelter near the base of the reef or in crevices. When the Sargassum is thick, the kelp bass have more trouble finding their prey. This can affect growth, and therefore reproduction since larger fish contribute more eggs and sperm for reproduction. Therefore, when these impacts continue over several years, it can impact population size and health.

I had previously reported not seeing many large lobster at Casino Point shortly after bug season began. The bug hunters I observed undoubtedly had an impact at least on those of legal size. Some believe lobbies can read calendars, and know that when the hunt commences, they need to flee to deeper waters. On my "last dive," I noticed very few lobster out on the bottom where the Sargassum was thick. Its density forced me into shallower water. There I started seeing clusters of lobster hanging on the vertical faces of the boulders in areas free from the pesky exotic weed. Perhaps they, too, had been forced off the ocean floor into clear areas like I was.

Casino Point and the waters off Catalina are considered world class dive destinations. I have met divers from all over the globe there. When I travel internationally, many SCUBA enthusiasts from Asia, Europe and elsewhere know of Casino Point and Catalina. It is a travesty that this seaweed has spread so rapidly and affected the beauty and diversity of our island waters.

© 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!

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The evil villain Sargassum filicinum, kelp and top snails feeding on native kelp at night;
giant kelpfish sheltering in Sargassum and lobster cluster on vertical wall
out of reach of the Sargassum.

This document maintained by Dr. Bill Bushing.
Material and images © 2009 Star Thrower Educational Multimedia