Hill End to Spaniard Rocks & Back: Step-by-Step Part 6

As my walk continued from Hill End northwards on Rhossili beach, the dark drift patterns and fine strandline debris covering the sand eventually faded away to be replaced by dry sand ripple and swash/backwash patterns before arriving at the extreme north-east corner of Rhossili beach. This is the place where much of the flotsam ends up. It is not that Gower visitors are careless with their trash. Most of this stuff comes from far afield – sometimes as far away as South America. It does get periodically cleared away but is difficult to manage because the rubbish arrives and leaves with each tide, and can get buried or revealed from one high water to the next. Bicycle wheels, brightly coloured plastic pieces, fishing net and ropes, toothbrushes, balloon stoppers, and flip flops are common items along with the driftwood. The pile of organic and plastic rubbish lies adjacent to Spaniard Rocks which connect the tidal island of Burry Holms to Llangennith Burrows.

The geology here is interesting but on this occasion I focussed on the seaweeds which attach to the rocks along the water-filled channel between Burry Holm and Spaniard Rocks. There are many types intermingled. They include amongst others the brown Fucoid algae such as Toothed Wrack (Fucus serratus) , Spiral or Flat Wrack (Fucus spiralis), and Egg or Knotted Wrack (Ascophyllum nodosum). Bladder Wrack or Pop Weed (Fucus vesiculosus) was also present but not in its typical form. The numerous small, paired, almost spherical air bladders typical of the species were few and far between on specimens in the area where I was looking – so that there is confusion in my mind as to the identity of some of the weed I have named as Spiral Wrack.

There were also some red algae of the thin bladed type that dry out between tides into blackened streaks on the rocks (of the kind to which the lavabread seaweed belongs). Another red alga was the Sand Binder seaweed (Rhodothamniella floridula) which forms small humps of fine filaments trapping sand grains on rocks low on the shore; it is often found beneath the taller stalked fucoids. Finely branching red Polysiphonia lanosa was epiphytically attached to the Egg Wrack.

Of special interest this visit was the fact that the seaweeds were getting ready to reproduce. The Spiral Wrack had swollen receptacles on the forked frond tips that were not fully ripened yet. However, the Egg Wrack was ready to go. It has separate males and females. The male receptacles are bright golden green studded with orange pustules (conceptacles) that release a colourful fluid containing the sperms. I had seen these and reported on them before. This time I also saw the female receptacles which were dull green and covered with minute darker almost black blisters (conceptacles) containing the eggs. It almost seems as if you can see the eggs when you zoom in on the picture – actually just the light bouncing off the ripe eggs within the pustule.

Egg Wrack at Ringstead

Egg or Knotted Wrack, Ascophyllum nodosum (Linnaeus) Jolie, with attached tufts of the red seaweed, Polysiphonia lanosa (Linnaeus) Tandy, at Ringstead Bay, Dorset, UK - part of the Jurassic Coast (1) 

This colourful and interesting pattern of seaweeds was growing as an extensive mat on the flat rock outcrop called Perry Ledge at Ringstead Bay, Dorset. It mostly shows the brown seaweed known as Egg or Knotted Wrack, Latin name Ascophyllum nodosum (Linnaeus) Jolie.

Egg Wrack typically is a robust, leathery, olive green alga with no midrib to the blade. Large egg-shaped air bladders that act as floats are spaced at intervals along the blades. The bright yellow objects (resembling sultanas on stalks) are the reproductive bodies that release the spores into the water.

I particularly like the way the weed is apparently artfully arranged (actually that is just how I found it – I did not rearrange this for effect); also the contrasting colours of dark green, bright yellow and deep red; and the combination of textures from leathery, to granular, and moss-like.

The photographs show the Egg Wrack living in association with the red seaweed Polysiphonia lanosa (Linnaeus) Tandy. This short red tufted alga is usually attached – sometimes in great numbers as in the pictures – around the stalk of the reproductive bodies of the Egg Wrack.

Egg or Knotted Wrack, Ascopyllum nodosum (Linnaeus) Le Jolis, with attached tufts of the red seaweed Polysiphonia lanosa (Linnaeus) Tandy at Ringstead Bay, Dorset, UK - part of the Jurassic Coast (2)

Revision of a post first published 21 April 2009

COPYRIGHT JESSICA WINDER 2011

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Egg Wrack reproduction

Egg Wrack or Knotted Wrack: Ripe receptacles on Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at Spaniards Rocks, Rhossili, Gower, West Glamorgan, UK (1) 

Sometimes you are just in the right place at the right time to witness and record natural phenomena that are rarely seen. This happened one morning in early April at Spaniard Rocks, Rhossili Bay in Gower. I had photographed the dark olive green Egg Wrack on the rocks of the causeway last year and noticed the yellowy-green, raisin-like, fruiting bodies hanging down on short stalks.  However, this spring, after just over a year on the plant, they were ripe and ready for their big moment.

Perhaps I should recap for a bit. Egg Wrack or Knotted Wrack, Ascophyllum nodosum (Linnaeus) La Jolie, belongs to the same group of brown seaweeds or Phaeophyceae as Bladder Wrack and Toothed Wrack but, unlike these other Fucoids, it has no midrib and it has male and female plants – it is dioecious

Egg Wrack attaches to rocks around the mid tide level by means of a many-fingered holdfast or hapteron. A short rounded stalk develops from this into the flattish, irregularly serrated, frond along the sides of which are notches or axils every 2 to 5 cm. The axils are growing points from which either another ordinary branch of frond arises or a bunch of thin stalks about 1 to 5 cm long with an oval or ellipsoid fruiting body on the end: the receptacles. The receptacles about 1 to 2.5 cm long. On male plants they are said to be a golden yellow colour while on the female plant they are yellowish olive. In reality, it is a bit difficult to distinguish them on this basis. There is a shape difference too.

Each receptacle contains a large number of small superficial cavities called the conceptacles and each of these opens outwards through a minute pore or ostiole. The gametes or sex cells are produced in these special cavities. The gametes are produced by a type of cell division known as meiosis which results in cells with half the full complement of genetic material – they are haploid. The plant itself is diploid and has a full complement of chromosomal material.

The female gametes, the eggs, are produced by oogonia developing in the female conceptacles on the female Egg Wrack plant. The male gametes,  antherozoids or sperm, are produced by antheridia in the male conceptacles on the male plant.

Sexual reproduction in Egg Wrack and other Fucoids is oogamous, meaning that the eggs are released from the parent plant before fertilisation. Fertilisation takes place in the surrounding seawater. The eggs and the antherozoids are released into the water at the same time. The activity is synchronised. The antherozoids can swim. They have two minute flagellae attached to the side of the cell that move the cell along by a whip-like action. The egg is non-motile but has enough buoyancy to remain suspended in the water rather than sinking to the sea bed.

Release of the gametes is triggered by the number of daylight hours and exposure of the ripe receptacles to air overnight. The first gametes are released in April and the last in June. After fertilisation, the zygote settles within 10 days. The spent receptacles are shed in June. 

Once the gametes are released, the antherozoids are attracted to the egg cell by a chemical it contains and they swim along a gradient of the chemical concentration in the water until huge masses of antherozoids surround each egg and spin it around in their attempts to penetrate it. Finally, one male gamete fertilises the egg, joining the two haploid chromosomal halves, and produces a  zygote, that settles down on a rock surface into a new diploid plant. 

What I was fortunate enough to witness was the moment immediately prior to the synchronised release of the reproductive products from the mature specimens of Egg Wrack (plants  reach maturity over a five year period and can live from 10 to 20 years). The receptacles take from 12 to 14 months to ripen. The photographs here show the small swollen yellow conceptacles glistening on the surface of the receptacles – resembling minute yellow blisters. These burst when touched. The yellow liquid containing the gametes formed a wet coating over some of the plants and stained my hands like nicotin where I had handled the fronds. The incoming tide was just seconds away as I took these shots, my outstreched feet behind me getting wet as I positioned myself low enough to capture the moment that the pustules started to burst.

More information?

Click here for more pictures and posts on Egg Wrack in Jessica’s Nature Blog.

More Egg Wrack information online at the Marine Life Information Network

Ascophyllum nodosum and its harvesting in Eastern Canada

Lowson’s Textbook of Botany (Revised by Simon, Dormer, and Hartshorne), 1977, University Tutorial Press, London, ISBN 0 7231 0614 2, pp 513-516.

British Seaweeds, Carola I Dickinson, The Kew Series, Eyre & Spottiswoode, 1963, Catalogue no, 6/2372/1, pp 108-109.

A handbook of British Seaweeds, Lily Newton, The Trustees of the British Museum, London, 1931, pp 219 – 222. 

Ripe receptacles on Egg Wrack: Ripe receptacles on Egg Wrack or Knotted Wrack, Ascophyllum nodosum (L.) La Jolie, on Spaniard Rocks, Rhossili bay, Gower, South Wales, U.K. (2) 

Ripe receptacles on Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at Spaniard Rocks, Rhossili, Gower, West Glamorgan, UK (3)

Ripe receptacles with burst conceptacles on Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at Spaniard Rocks, Rhossili, Gower, West Glamorgan, UK (4)

Knotted Wrack receptacles and conceptacles: Close-up of ripe receptacles dotted with conceptacles on Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at Spaniard Rocks, Rhossili, Gower, West Glamorgan, UK (5)

Close-up of ripe receptacles dotted with conceptacles on Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at Spaniard Rocks, Rhossili, Gower, West Glamorgan, UK (6)

A single yellow-green ripe receptacle covered with small deep yellow conceptacles on Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at the moment before the release of the reproductive products into the sea - at Spaniard Rocks, Rhossili, Gower, West Glamorgan, UK (7)

Detail of the small yellow conceptacles containing the reproductive products, swollen and about to burst and release the contents into the sea, on a receptacle of the seaweed called Egg Wrack, Ascophyllum nodosum (L.) La Jolie, at Spaniard Rocks, Rhossili, Gower, West Glamorgan, UK (8) 

Revision of a post first published 17 May 2009

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

Egg, Bladder & Channelled Wrack at Rhossili

Ascophyllum nodosum: Egg or Knotted Wrack, Ascophyllum nodosum (Linnaeus) Le Jolis, on Spaniard Rocks, Rhossili Bay, Gower, showing yellowy pendant reproductive bodies looking like sultanas on short stalks (1) 

Looking like bunches of flattened yellow sultanas hanging down on stalks, the reproductive bodies of the Egg or Knotted Wrack, Ascophyllum nodosum ( Linnaeus) La Jolis, were a very noticeable feature of the weed in April. This picture was taken of the seaweed attached to the limestone of Spaniard Rocks, adjacent to the causeway separating the mainland from Burry Holms, on Rhossili Bay.

Egg Wrack with reproductive bodies: Frond of Egg or Knotted Wrack, Ascophyllum nodosum (Linnaeus) La Jolis, washed in by the tide at Rhossili Bay, Gower, South Wales - showing the large egg-shaped air bladders along the olive coloured stem and yellow reproductive bodies attached to the stem by short stalks (2) 

Here a detached frond of egg wrack has been washed up onto the sandy beach. You can clearly see the large egg-shaped air bladders spaced along the central olive-coloured frond which lacks a mid-rib.

It is interesting to note the way the Egg Wrack at Rhossili differs in its appearance from the same weed at Ringstead in the same month. The plant and fruiting bodies photographed in Rhossili are larger, more robust, and lacking the attached red seaweed – at least when growing on rocks by the causeway to Burry Holms. Although the Egg Wrack occupied the same approximate tidal position on the shore in both places, the main distinction between the two habitats is the greater exposure to wave action at Rhossili. It looks like the Rhossili Egg Wrack thrived where the sea was rough.

Common British seaweeds: Bladder Wrack or Popweed, Fucus vesiculosus Linnaeus, growing on Spaniard Rocks, Rhossili Bay, Gower, South Wales - showing small bean-sized air bladders along the fronds and swollen reproductive bodies at the tips (3) 

Bladder wrack or Popweed, Fucus vesiculosus Linnaeus, was growing on the limestone Spaniard Rocks right next to the Egg Wrack (there is a small bit of Ascophyllum gate-crashing top left corner of the picture above). You can tell the two seaweeds apart by the mid-rib to the frond and much smaller bean-sized air bladders positioned lower on the blade in Bladder Wrack, and the reproductive bodies are confined to the lighter coloured swollen tips. Bladder Wrack tends not to grow so large as Egg Wrack.

Olive green seaweed: Channelled Wrack, Pelvetia canaliculata (Linnaeus) Decaisne and Thuret, growing on Spaniard Rocks, Rhossili, Gower, South Wales (4) 

Channelled Wrack, Pelvetia canaliculata (Linnaeus) Decaisne and Thuret,  is a much smaller seaweed than the previous two described. It grows in short dense tufts upto 15 cm high attached to rocks just above high water level of neap tides. It is frequently seen dried up and blackened. Black Pygmy Lichen is often mistaken for very small tufts of Channel Wrack.

Pelvetia does not have a midrib or gas bladders; the edges of the fronds tend to curl inwards – creating the groove or channel from which it gets its name – but this is not a reliable feature for identification. The fruiting bodies are irregular shaped, swollen, forked ends to the fronds.

Egg, Bladder and Channelled Wrack are all brown seaweeds belonging to the Class Phaeophyceae.

You can find more information about these seaweeds on the marLIN  or British Isles Seaweed Images web sites.

Channelled Wrack, Pelvetia canaliculata (Linnaeus) Decaisne and Thuret, growing on Spaniard Rocks at Rhossili Bay, Gower, South Wales. 

Revision of a post first published 2 May 2009

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved