A Seaweed Divided Against Itself Upsets Oceanic Order

Baltic Sea Offshoot Encroaches on a Vital Counterpart

STOCKHOLM -- Something is happening in the Baltic Sea's underwater forests.

A new kind of seaweed is spreading over hundreds of miles in the north. Scientists call it a "super female clone" because most of the new plants are genetically identical females. Called Fucus radicans, or narrow wrack, it has apparently branched off in the past 400 to 1,000 years from Fucus vesiculosus, or bladder wrack, the tree-like vegetation common in the Baltic and other oceans worldwide.

Researchers are concerned about the ecological implications, since the new species -- or subspecies; some scientists dispute the classification -- is smaller and much less ideal for fish, crustaceans, barnacles and other organisms that populate the sea.

The new seaweed has developed at an "unparalleled speed," according to Lena Kautsky, a marine ecologist based in Stockholm. Kautsky worries that the loss of genetic diversity inherent in the spread of the new species could mean that disease or changing conditions will more easily wipe out large swaths of the older seaweed.

In ecological importance and function, bladder wrack is akin to the sea grass beds in the Chesapeake Bay, whose disappearance has withered the shellfish industry. In addition, Bladder wrack is used widely as fertilizer and in nutritional supplements, since its high iodine content is thought to combat hypothyroidism, and another compound helps reduce heartburn.

Bladder wrack is an indicator of the Baltic's overall health, since it grows well when the water is clear and light gets through. But it is stunted or dies when nutrient-fueled algal blooms block out the light. Kautsky and her brother Hans, also a marine ecologist, have spent years studying the depth at which bladder wrack occurs. (The deeper it grows, the healthier the sea.)

Bladder wrack growth came close to the surface in the 1970s. Since then, the Baltic's Fucus forests have regained some ground in the deep, but with nutrient pollution leading to low-oxygen zones, competition and the unknown ramifications of the narrow wrack clone, their future is still tenuous.

"It's a slowly dying forest," Kautsky said.

Kautsky describes the love lives of bladder wrack in almost poetic terms -- a moonlit ritual not shared by the newcomer. "It's quite romantic," she says.

Male and female bladder wrack reproduce primarily by releasing sperm and eggs into the water twice a month, in the evening, two days before the new and full moons. This precise timing allows sperm to fertilize eggs in the water, then the new embryo sinks, anchors itself to substrate on the sea floor and forms a new plant.

There is virtually no tide in the Baltic, so it is a mystery how the bladder wrack know exactly when to release their gametes. Moonlight and gravity likely play a role.

But narrow wrack shuns this fertilization method. Though it exists in male and female genders and is capable of sexual reproduction, it normally prefers asexual reproduction, spinning off small fragments of seaweed that form new plants.