DIVE DRY WITH DR. BILL #401: DIVER DEVOURED BY DEVIL WEED
For 10 years I have been warning anyone who would listen about the ecological dangers of the highly invasive Asian seaweed Sargassum horneri that first entered southern California waters in 2003 and arrived on Catalina during the winter of 2005-06. I have been diving SoCal waters for nearly 50 years now and this is the worst alien invasion I have ever seen.
Since the species had no English common name, I coined the tem "devil weed" due to its incredible virulence and its devastating impact on our native giant kelp forest ecosystems. During winters following warm water episodes, this species can assume near complete dominance of rocky reefs and is even observed at depths in excess of 100 feet.
Rather than the biodiverse native algal community normally observed in our kelp forests, Sargassum horneri forms a near monoculture, outcompeting not only our smaller native seaweeds, but even preventing the giant kelp (Macrocystis pyrifera) from re-establishing as waters cool in winter.
By preventing giant kelp growth, and severely limiting other native algae, it also affects the herbivores in kelp forest ecosystems. Abalone, top snails, kelp snails, kelp crabs, sea urchins and others have little drift kelp to nourish them and decline in numbers. The rocky reef carnivores that feed on these species have less to survive on and the thick devil weed often makes it difficult for them to find prey.
Unfortunately the California Dept of Fish & Wildlife (CDF&W) did not heed early warnings by scientists including myself and allowed this noxious weed to not only establish here on the protected leeward coast of Catalina, but spread along the more exposed mainland coast to Morro Bay in the north and Guadalupe Island off Baja to the south.
Recently the impact of this devil weed has taken an even more frightening turn. In its native Asian waters, it is strictly herbivorous and is largely controlled by native Asian species of abalone and sea urchins that co-evolved with it over time.
But based on a few recent incidents, I fear the devil weed has evolved along the lines of the carnivorous pitcher plants and Venus' fly traps. Recently I was diving with Simon and Amy in our dive park, friends from Florida that I dove with in Palau last year. On our second dive only Simon and I descended. He swam too close to the top of the Sargassum and it slowly drew him into the dense cover. The last we saw of Simon were the heels of his fins as he was swallowed up by the devil weed. We are still trying to recover his body, but we may have to wait until the thick Sargassum dies out in a month or two.
Divers, please exercise extreme caution when swimming close to this evil alga. The life you save may be your own. Maybe now CDF&W will actually do something about this threat to our region.
© 2016 Dr. Bill Bushing. For the entire archived set of nearly a bazillion "Dive Dry" columns, visit my website http://www.starthrower.org/
Image caption: Last view of Simon as he is engulfed by the devil weed.
For 10 years I have been warning anyone who would listen about the ecological dangers of the highly invasive Asian seaweed Sargassum horneri that first entered southern California waters in 2003 and arrived on Catalina during the winter of 2005-06. I have been diving SoCal waters for nearly 50 years now and this is the worst alien invasion I have ever seen.
Since the species had no English common name, I coined the tem "devil weed" due to its incredible virulence and its devastating impact on our native giant kelp forest ecosystems. During winters following warm water episodes, this species can assume near complete dominance of rocky reefs and is even observed at depths in excess of 100 feet.
Rather than the biodiverse native algal community normally observed in our kelp forests, Sargassum horneri forms a near monoculture, outcompeting not only our smaller native seaweeds, but even preventing the giant kelp (Macrocystis pyrifera) from re-establishing as waters cool in winter.
By preventing giant kelp growth, and severely limiting other native algae, it also affects the herbivores in kelp forest ecosystems. Abalone, top snails, kelp snails, kelp crabs, sea urchins and others have little drift kelp to nourish them and decline in numbers. The rocky reef carnivores that feed on these species have less to survive on and the thick devil weed often makes it difficult for them to find prey.
Unfortunately the California Dept of Fish & Wildlife (CDF&W) did not heed early warnings by scientists including myself and allowed this noxious weed to not only establish here on the protected leeward coast of Catalina, but spread along the more exposed mainland coast to Morro Bay in the north and Guadalupe Island off Baja to the south.
Recently the impact of this devil weed has taken an even more frightening turn. In its native Asian waters, it is strictly herbivorous and is largely controlled by native Asian species of abalone and sea urchins that co-evolved with it over time.
But based on a few recent incidents, I fear the devil weed has evolved along the lines of the carnivorous pitcher plants and Venus' fly traps. Recently I was diving with Simon and Amy in our dive park, friends from Florida that I dove with in Palau last year. On our second dive only Simon and I descended. He swam too close to the top of the Sargassum and it slowly drew him into the dense cover. The last we saw of Simon were the heels of his fins as he was swallowed up by the devil weed. We are still trying to recover his body, but we may have to wait until the thick Sargassum dies out in a month or two.
Divers, please exercise extreme caution when swimming close to this evil alga. The life you save may be your own. Maybe now CDF&W will actually do something about this threat to our region.
© 2016 Dr. Bill Bushing. For the entire archived set of nearly a bazillion "Dive Dry" columns, visit my website http://www.starthrower.org/
Image caption: Last view of Simon as he is engulfed by the devil weed.
