bladderwrack

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Seaweed on the rocks

It is SUCH an advantage to have access to an ice breaking ship when one works with seaweed.
Mid-March is unfortunately not always full of sun, birdsong and warm spring temperatures.
On March 18th, we wrwe out at the Askö laboratory to do a reading of some experiments that have been out in the sea over winter.

Havet the door

With a lilttle help from the ice breaking R/V AURELIA and skipper Eddie, I could reach one of the sites, located just south of the boathouse.

The seaweed has not suffered from the cold winter, but was in good shape. When I lifted the “weedbeds” up onto the ice, lots and lots of animals swam out. Small crustaceans, gastropods and caddis worms a plenty, all of them have spent the winter in the seaweed.

Tång o is

Allthough the visibility in the water is very good this time of year, and the temperature is, well, shall we say refreshing, I can’t help but longing for summer. It is quite a struggle to move large sheets of ice when one is i the water…

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World Water Day March 22nd

2013 is the International Year of Water Cooperation.
2013logo
Therefore, you can expect a lot of activities on World Water Day, coming up on March 22nd.

At Stockholm University, there will be a series of short, captivating lectures from scientists all working in, on and with water.

Seaweed expert professor Lena Kautsky will give a talk on the reproduction of bladderwrack and why it is important in relation to the management of our coastlines.

A programme in Swedish can be found here.

There will also be a startup to World Water Day at Aquaria Water Museum on the 21st, more information on this will follow.

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Reproduction

Narrow wrack (Fucus radicans) and bladderwrack (Fucus vesiculosus) have separate male and female plants. The reproductive organs are called receptacles and are placed at the tips of the plant. They are easily recognised by their warty structure.

When we try to “sow” seaweed”, we start with collecting ripe plants from the field, determine which sex they have, and cut of the receptacles.

Cut receptacles of bladderwrack

Cut receptacles of bladderwrack

The picture to the left shows a bladderwrack ready to sow. Note that the pile of cut receptacles to the right in the photo is from three plants.

In order to separate between males and females, one has to cut a mm-thin slice of the receptacle and (with a little magnifying help from a loupe or similar) see if there are oogonia (8 eggs in a small sack) or antheridia (64 sperm in an even smaller sack). This can only be done on ripe receptacles, or else it is very hard to see.

Round oogonia contains 8 eggcells. Some are beginning to open up.

Round oogonia contains 8 eggcells. Some are beginning to open up.

Each receptacle consists of several small chambers, conceptacles. The opening pore of these conceptacles are what causes the warty structure of the receptacle. Each conceptacle openes onto the receptacle surface, and this is where oogonia and antheridia (eggs and sperm in bags) are ejected out into the water mass during fertilization. When the oogonia and antheridia have reached the water, the bag keeping them contained, begins to dissolve.

The female oogonia looks like a collection of small green peas, and can be seen with the naked eye if they are very ripe.

It's a girl! Lots of ripe, round oogonia in the receptacles.

It’s a girl! Lots of ripe, round oogonia in the receptacles.


A ripe male, packed full of orange sperm.

A ripe male, packed full of orange sperm.

Antheridia are too small to see, even with a loupe. You need a microscope for them. On a receptacle cut, they give an impression of orange balls along the inside of the receptacle edge (see picture). The colour comes from the eyespot of the sperm, which is orange. With this, the sperm can tell light from dark.

Reproduction occurs around full moon, when it is much darker down towards the bottom than up towards the surface. The sperm “knows” that it should swim towards darkness. The reason for this is that the heavy eggs are sinking in order to attach to the bottom once they become fertilized.

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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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Into the deep

Here is a clip from the “seaweed-bed” at the Askö laboratory, where most of our experiments are going on. This was filmed in january 2012, with the purpose of checking on the bed, change light/temperature sensor and collect some plates for measure of juvenile growth.

The bed holds about 60 ceramic tiles, onto which we have “sown” bladderwrack and some other wrack crosses. We use the non-glazed side of the tiles since it is important that the surface is porous enough for the seaweed eggs to attach. This makes for some interesting conversations when we buy tiles!

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The Baltic Sea

The Baltic Sea is unique because of its low salinity. In the northernmost parts, the water is almost considered freshwater, whilst the salinity at the entrance/exit in Öresund lies around 15 psu (practical salinity unit, roughly equal to ‰ and denotes salinity). The low salinity of the Baltic Sea makes it a stressful environment for both freshwater and marine species, both groups lives on the very edge of their tolerance of either too high or too low salinity.

Salinity and Fucus distribution in the Baltic Sea

Salinity and Fucus distribution in the Baltic Sea

The map show surface water salinity and the distribution of the three species from the genus Fucus that can be found in the baltic Sea.
Green denotes bladderwrack (Fucus vesiculosus)
Orange denotes narrow wrack (Fucus radicans)
Yellow denotes serrated wrack (Fucus serratus) Note that for this species only the distribution along the Swedish coasline is shown, since we have not found any data on its distribution in any other countries along the Baltic Sea.

More information will follow.