SEAWEED CLONES

Posted on 2025/03/05 by secret santa

“The clone of bladderwrack in the Baltic Sea was long assumed to be a
separate species, which was called narrow seaweed. Credit: Lena Bergström”

WORLD’s LARGEST SELF-CLONING ORGANISM?
https://onlinelibrary.wiley.com/doi/10.1111/mec.17699
https://phys.org/news/2025-03-giant-clone-seaweed-baltic-sea.html
Giant clone of seaweed discovered in the Baltic Sea
by University of Gothenburg / March 4, 2025

“Researchers at the University of Gothenburg have discovered that what was previously thought to be a unique seaweed species of bladderwrack for the Baltic Sea is in fact a giant clone of common bladderwrack, perhaps the world’s largest clone overall. The discovery has implications for predicting the future of seaweed in a changing ocean. In the brackish waters of the Baltic Sea, bladderwrack is the dominant seaweed species as it is one of the few seaweed species that can tolerate low salinity.

“Bladderwrack is the dominant seaweed species in the Baltic Sea because
it can withstand low salinity in the water. Credit: Kerstin Johannesson”

The seaweed forms large forests from the surface down to a depth of 10 meters. Fish fry, snails and crustaceans thrive here, and the kelp forests also provide an important habitat for larger fish. This makes it an interesting species for researchers to study. Using genetic mapping of marine species is one way to understand how these species should be managed. “The Baltic Sea is entering a period of warmer and probably even fresher seawater. In new conditions, all species must try to adapt in order to survive, including the important bladderwrack,” says Kerstin Johannesson, Professor of Marine Ecology at the University of Gothenburg and one of the lead authors of a new study in the journal Molecular Ecology.

Through DNA sequencing, the researchers have found that a small, bushy form of seaweed in the Baltic Sea that was previously thought to be a separate species (called narrow wrack) is a clone of bladderwrack. The clone has formed new populations by dispersing fragments of an original female plant with the water currents and growing into new individuals of wrack. The clone spreads over more than 500 km of the coast of the Bothnian Sea, from Öregrund in Uppland to just south of Umeå, and may be the world’s largest clone of any organism.

“Genetic ancestry analysis including all individuals from the
55 sampled sites subdivided into K = 12 genetic clusters”

Bladderwrack has separate male and female plants that normally form new individuals after sexual fertilization. “This clone comprises millions of individuals, and in some areas, it is completely dominant, while in other areas it grows alongside sexually propagated individuals of bladderwrack. We have found a few more large clones in the Baltic Sea, but the female clone off the Swedish Gulf of Bothnia is by far the largest clone—a real super female,” says Ricardo Pereyra, researcher in the group who led the genetic analyses.

Seaweed clones face an uncertain future as the Baltic Sea is affected by climate change. Without constant sexual reproduction, there are few genetic changes and adaptations in the genetic material of the stocks. “A clone almost completely lacks the genetic variation that otherwise means that there are individuals in a population that can handle the changes and make the species survive,” says Johannesson. During the survey, the researchers from the University of Gothenburg also identified a new species of seaweed on the Estonian coast which, like the small seaweed clone, is small and bushy, but has both males and females and reproduces only sexually. This seaweed is very closely related to bladderwrack but is currently reproductively isolated from bladderwrack in the area.”

INVASIVE SEAWEED
https://link.springer.com/article/10.1007/s002270000456
https://theguardian.com/world/1999/aug/03/jonhenley
Fifteen years ago it was a small patch of seaweed, now it threatens to ruin the Mediterranean coast
by Jon Henley / 2 Aug 1999

“French marine biologists yesterday admitted that it was probably too late to eradicate a killer Caribbean seaweed that is marching rapidly and relentlessly along the Mediterranean coastline, choking all flora in its path and threatening an environmental catastrophe. “I’m afraid we have lost the battle,” said Thomas Belsher of Ifremer, the national marine research institute. “It is now expanding its cover at about 50% a year. In the current hot weather it’s growing half an inch a day, whereas ordinary seaweed takes a century to cover an extra 10 feet. The situation is desperate.

Last month an association of environmentalists, fishermen and amateur divers lodged a complaint over the government’s failure to respond to the seemingly unstoppable spread of the killer algae, Caulerpa taxifolia, which is found mainly in Caribbean waters and is believed to have been originally imported from Guadeloupe or Martinique by tropical fish fanciers. The president of the national assembly’s sub-aqua club, Pierre Lellouche, has tabled a draft law to be discussed this autumn that would force Paris to take urgent action. “Unless the government takes the necessary steps, it will inevitably face legal action from other Mediterranean countries which are now also being threatened,” he said. “Everyone must be mobilised to fight this threat to our coastline.”

The seaweed or algae, which appears to have grown from a square-yard patch first noticed in the sea off the Monaco oceoanographic institute in 1984, is now rampant along the Cote d’Azur from Toulon to Menton, covering an area equivalent to 6,000 football pitches. Isolated colonies of the weed, whose main fronds can grow to 12ft long, have been spotted as far afield as Sicily and Croatia. By covering the seabed to a depth of 350 feet, the rapacious, fluorescent green Caulerpa taxifolia is starving indigenous marine flora of daylight and gradually killing them off, ecologists say. And with the the gradual disappearance of native seaweeds, the number of species of fish in the Mediterranean – as well as the size of each specimen – is declining.

“What is facing us now is a permanent and radical alteration of the natural balance of the Mediterranean, of a scale and speed which has never been witnessed before,” said Alexandre Meinesz, a professor of marine biology at Nice university. “But I’m afraid most scientists are now agreed that getting rid of the algae completely is impossible. There is too much of it, and we are simply incapable of charting every site it has already colonised.” Laborious and unsuccessful attempts have been made to stop the weed’s spread by ripping it up from the seabed by hand, and by covering it with large plastic sheets to deprive it of light. In a despairing attempt to slow its progress, Mr Meinesz’s team is carrying out laboratory tests with weed-eating slugs imported from the Caribbean and United States. Mystery surrounds the French government’s inaction over the sub-aquatic invasion. Some observers say that at first Paris was keen to avoid a diplomatic incident with Monaco.

Despite a series of DNA tests carried out by Swiss scientists, the principality continues to dispute the most widely accepted theory – that the weed was accidentally dumped into the sea from the tropical fish aquariums of its prestigious oceanographic institute when the undersea explorer Jacques Cousteau was director. Monaco claims instead that the weed is probably a mutant version of a less harmful tropical algae, Caulerpa mexicana, which is found naturally in the Mediterranean having made its way from the Red Sea via the Suez Canal. Others have a different explanation for the government’s failure to respond to the threat. “In the Mediterranean, taxiflora has no natural enemies and is not part of the food chain,” said Mr Meinesz. “Fish don’t eat it because it is poisonous to them but there is no danger to humans whatsoever. What that basically means is that no one has been prepared to spend any money fighting it.”

Mr Lellouche’s draft bill is mainly aimed at slowing the onward march of the weed, which besides growing of its own accord is being spread further along the coastline each summer by yachts and fishing boats. If the measure is passed, merchant ships will have to install filters, and yachts and fishermen will be required to clean their anchors and nets after each voyage. Mr Meinesz is convinced that more urgent preventive action is required. He is calling for the creation of marine sanctuaries, specially protected and regularly patrolled underwater zones where the weed would not be allowed to gain a foothold. But he warned that the investment would be heavy and the commitment permanent. “Unfortunately, this plague is not going to go away. Unless something determined is done right now, within a few years the biologically diverse coastal waters of the Mediterranean as we know them will cease to exist.”

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