WARNING TO DIVERS ON CHEMICALS ASSOCIATED WITH INVASIVE ALGA!
Many southern California SCUBA enthusiasts who dive the waters of Santa Catalina Island's leeward coast are aware of the appearance of a very aggressive invasive alga, Sargassum filicinum, in our waters last year. Since its first reported occurrence in April of 2006, this alga has spread up and down the leeward coast from near the West End to at least the East End Quarry area. This species is native to the waters of Japan and Korea, where I am told it is a rather uncommon seaweed. Here in our waters it apparently has no ecological controls such as grazing herbivores (snails, etc.). In fact for the first 5-6 months I noted very few of our native species associating with it.
More recently I have observed and filmed events apparently associated with this Sargassum that greatly concern me. The first observation was of male giant kelpfish using this alga to create their nests. Normally these fish establish nests in our native brown and green seaweeds, and defend those nests until the eggs hatch several weeks later. However, eggs I observed in nests created in the invasive Asian alga seemed to "dissolve" well before the embryos could develop and hatch into larvae. Of course this is a very disturbing find, although nests established by giant kelpfish in our native algae do seem to develop normally and hatch successfully.
Within the past month, I have started to observe other native fish including garibaldi, halfmoon, opaleye and kelp surfperch feeding in the dense beds of Sargassum filicinum. Initially I assumed they were browsing on the dense hydroid and bryozoan colonies attached to the alga. However, upon closer observation it appears they are feeding directly on the algal tissues. Then I began noticing that early nests created by male garibaldi were devoid of eggs. Female garibaldi did not seem to be entering the nest and laying. I did see a few females enter the nest of a very dominant male in the Casino Point dive park. However, although they went through the motions of egg laying, none were actually extruded in the process.
I am coming to the conclusion that this intrusive alga possesses some sort of chemical in its tissues that interferes with the reproductive processes of fish that graze upon it, or live in close proximity to it. At first I suspected human estrogen or testosterone from urine in the waste water effluent on the island, but this is an island-wide phenomenon so I ruled that possibility out since there are no significant population centers in many of the areas along the leeward coast, and wastewater from the few that do exist is released through septic fields rather than directly in the ocean.
The presence of this invasive alga alone has been of great concern to me as a kelp forest ecologist. The large-scale loss of giant kelp around Catalina due to the extremely warm water temperatures (readings in the 79-83 F range at times) last summer was probably due to natural causes, although global warming may have played some role. The recovery of the giant kelp was definitely limited due to shading by the very dense "forests" of Sargassum filicinum which preventing the microscopic young stages of kelp from growing due to lack of light. With the observations outlined above, this invasive plant may be far more dangerous to the ecological health of our kelp forests than I initially believed.
I am working with the California Department of Fish and Game to obtain the necessary permits to eradicate this weedy invasive. It will take about six weeks to obtain the permit. I am hoping that divers throughout southern California will volunteer to help eradicate what we can of this threat. The intention is to remove the alga and use it in compost piles on Conservancy lands to assist in the restoration of the native plant life of the island. Please help support this cause.
My college classmate Vice President Al Gore has spoken of the urgency of the global warming crisis. I actually looked forward to the warming of our local waters, and the expansion of southern species including our state salt water fish, the garibaldi. Imagine how appropriate it would be to have the garibaldi's range extend from our southern border with Mexico to our northern border that separates us from the long-haired, Birkenstock-wearing natives of the Duck State. Perhaps we'd even start to see reef-building corals in Catalina's world-famous dive park. The older I get, the more I yearn for warmer waters.
Ultimately global warming may eliminate the threat of Sargassum filicinum from our waters. After all, the kelps are a cool- to cold-water group of algae. It is quite possible that warming waters in our region mat prove inhospitable to it and the threat will disappear. Of course our giant kelp forests will disappear as well, but that's a small price to pay (even for a kelp forest ecologist) to have beautiful coral reefs and 80-degree water in our own background . However, until that happens, I hope divers will avoid contact with the extensive beds of this invasive alga. I would also recommend avoiding sushi made with this kelp... unless you want to effectively stop your own reproductive processes! Happy April Fool's Day.
Dr. Bill
Image caption: Images of Sargassum filicinum off Catalina for identification purposes.
Many southern California SCUBA enthusiasts who dive the waters of Santa Catalina Island's leeward coast are aware of the appearance of a very aggressive invasive alga, Sargassum filicinum, in our waters last year. Since its first reported occurrence in April of 2006, this alga has spread up and down the leeward coast from near the West End to at least the East End Quarry area. This species is native to the waters of Japan and Korea, where I am told it is a rather uncommon seaweed. Here in our waters it apparently has no ecological controls such as grazing herbivores (snails, etc.). In fact for the first 5-6 months I noted very few of our native species associating with it.
More recently I have observed and filmed events apparently associated with this Sargassum that greatly concern me. The first observation was of male giant kelpfish using this alga to create their nests. Normally these fish establish nests in our native brown and green seaweeds, and defend those nests until the eggs hatch several weeks later. However, eggs I observed in nests created in the invasive Asian alga seemed to "dissolve" well before the embryos could develop and hatch into larvae. Of course this is a very disturbing find, although nests established by giant kelpfish in our native algae do seem to develop normally and hatch successfully.
Within the past month, I have started to observe other native fish including garibaldi, halfmoon, opaleye and kelp surfperch feeding in the dense beds of Sargassum filicinum. Initially I assumed they were browsing on the dense hydroid and bryozoan colonies attached to the alga. However, upon closer observation it appears they are feeding directly on the algal tissues. Then I began noticing that early nests created by male garibaldi were devoid of eggs. Female garibaldi did not seem to be entering the nest and laying. I did see a few females enter the nest of a very dominant male in the Casino Point dive park. However, although they went through the motions of egg laying, none were actually extruded in the process.
I am coming to the conclusion that this intrusive alga possesses some sort of chemical in its tissues that interferes with the reproductive processes of fish that graze upon it, or live in close proximity to it. At first I suspected human estrogen or testosterone from urine in the waste water effluent on the island, but this is an island-wide phenomenon so I ruled that possibility out since there are no significant population centers in many of the areas along the leeward coast, and wastewater from the few that do exist is released through septic fields rather than directly in the ocean.
The presence of this invasive alga alone has been of great concern to me as a kelp forest ecologist. The large-scale loss of giant kelp around Catalina due to the extremely warm water temperatures (readings in the 79-83 F range at times) last summer was probably due to natural causes, although global warming may have played some role. The recovery of the giant kelp was definitely limited due to shading by the very dense "forests" of Sargassum filicinum which preventing the microscopic young stages of kelp from growing due to lack of light. With the observations outlined above, this invasive plant may be far more dangerous to the ecological health of our kelp forests than I initially believed.
I am working with the California Department of Fish and Game to obtain the necessary permits to eradicate this weedy invasive. It will take about six weeks to obtain the permit. I am hoping that divers throughout southern California will volunteer to help eradicate what we can of this threat. The intention is to remove the alga and use it in compost piles on Conservancy lands to assist in the restoration of the native plant life of the island. Please help support this cause.
My college classmate Vice President Al Gore has spoken of the urgency of the global warming crisis. I actually looked forward to the warming of our local waters, and the expansion of southern species including our state salt water fish, the garibaldi. Imagine how appropriate it would be to have the garibaldi's range extend from our southern border with Mexico to our northern border that separates us from the long-haired, Birkenstock-wearing natives of the Duck State. Perhaps we'd even start to see reef-building corals in Catalina's world-famous dive park. The older I get, the more I yearn for warmer waters.
Ultimately global warming may eliminate the threat of Sargassum filicinum from our waters. After all, the kelps are a cool- to cold-water group of algae. It is quite possible that warming waters in our region mat prove inhospitable to it and the threat will disappear. Of course our giant kelp forests will disappear as well, but that's a small price to pay (even for a kelp forest ecologist) to have beautiful coral reefs and 80-degree water in our own background . However, until that happens, I hope divers will avoid contact with the extensive beds of this invasive alga. I would also recommend avoiding sushi made with this kelp... unless you want to effectively stop your own reproductive processes! Happy April Fool's Day.
Dr. Bill
Image caption: Images of Sargassum filicinum off Catalina for identification purposes.
