Fucus vesiculosus – Bladderwrack

The most common wrack in the Baltic Sea is the bladderwrack, Fucus vesiculosus. Fucus is from the greek phykos, meaning seaweed. The species name vesiculosus refers to the gas filled bladders that are common in the species.
It is belived thet the bladderwrack has been present in the Baltic Sea for about 8000 years, from the period known as the Yoldia Sea. Bladderwrack and serrated wrack (Fucus serratus) are both marine species that have, more or less, adapted to the brackish waters of the Baltic Sea. The best adapted species is bladderwrack, that we can find all along the Swedish coast almost as far north as Umeå.

Bladderwrack can vary very much in shape and size, depending on whether it is living on rocks that are exposed to strong waves or living in sheltered bays. Where it is sheltered it can grow to over one metre in height, with broad thallus and plenty of bladders.
In exposed sites, the bladderwrack often lacks bladders so that the waves cannot tear it away. Both height as well as thallus width is much less on exposed sites.

Bladderwrack has the same lifecycle as humans. The plants are either male or female. They produce eggs and sperm in special organs, called receptacles. The receptacles are located in the tips, with a warty structure.

Receptakler

Eggs and sperm are released into the water column on still nights around full moon. The negatively buoyant eggs sink to the sea floor, followed by actively swimming sperm. New seaweed is made.

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