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.

Seaweed at Rocquaine Bay

Seaweeds growing on a mooring rope at low tide

Sand-filled embayments occur among the rocky outcrops on the wide sweep of Rocquaine Bay. This bay is on the west coast of the Channel Island of Guernsey. The embayments are strewn with mooring chains, ropes and buoys that provide good anchorage points for small fishing boats, leisure craft and seaweed.

Velvet Horn Weed (Codium fragile) was growing profusely on one particular mooring rope this autumn. It was also living in rock pools further north on the shore. I was surprised to see it in such abundance because it seems to be one of the less common marine algae on the Dorset coast where I had seen it only a couple of times before. Its dark green branched fronds have an unusual spongy texture due to a thick covering of fine “hairs”. The Velvet Horn dominated for many metres along the rope towards the blue buoy but elsewhere it combined with a wide variety of seaweeds such as Irish Moss (Chondrus crispus), Toothed Wrack (Fucus serratus), and an assortment of filamentous red and green algae to cling in decorative clusters on the rope.

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Seaweeds growing on a mooring rope at low tide

Grapeweed & Toothed Wrack at Osmington

Grapeweed, Mastocarpus stellatus (Stackhouse), on Frenchman's Ledge at Osmington Bay, Dorset, UK, part of the Jurassic Coast (1)

Easily overlooked among the more commonly-occurring seaweeds, Grapeweed, Mastocarpus stellatus (Stackhouse), is an unusual-looking red seaweed. I discovered it for the first time on the rocky promontory called Frenchman’s Ledge at Osmington Bay, Dorset. Initially, the impression is that the ledge has a wide strip of seaweed mostly occupied by a thriving bed of the olive green Toothed Wrack, Fucus serratus Linnaeus – one of the brown seaweeds or Phaeophyceae which I’ve described in earlier posts.

View from Frenchman's Ledge looking west along Osmington Bay, Dorset, UK - part of the Jurassic Coast (2) 

This is a locational shot showing the view from Frenchman’s Ledge looking west across Osmington Bay, Dorset.

Looking south along the length of Frenchman's Ledge at Osmington Bay, Dorset, UK, showing strip of seaweeds, part of Jurassic Coast (3) 

This photograph shows the view looking southwards out across the English Channel, and along the gently curving length of the rocky promontory called Frenchman’s Ledge. You can see a long thin strip of dark seaweed against the lighter coloured rock along its entire length – but restricted to just one side of the ledge.

Strip of mostly bown Fucoid seaweeds on Frenchman's Ledge, Osmington Bay, Dorset, UK, part of the Jurassic Coast (4) 

Getting up closer, it looks as if most of the seaweed is Fucoid or brown seaweed with a few patches of brighter green and red seaweed visible at the edge but possibly extending in small numbers under the brown weed.

Bed of mainly Toothed Wrack, Fucus serratus L., on Frenchman's Ledge, Osmington Bay, Dorset, UK, part of the Jurassic Coast (5) 

Closer still, it is easy to identify the main component of the seaweed bed as Toothed Wrack, Fucus serratus Linnaeus.

Tuft of the red seaweed Grapeweed, Mastocarpus stellatus, at the edge of the Toothed Wrack bed, on Frenchman's Ledge at Osmington Bay, Dorset, UK, part of the Jurassic Coast (6) 

However, at the western edge of the Toothed Wrack individual plants of both red and green seaweeds are visible. The larger red/brown/purple seaweed in the picture above is Grapeweed, with the extremely long Latin name of Mastocarpus stellatus (Stackhouse) Guiry (Gigartina stellata).

Tuft of red Grapeweed, Mastocarpus stellatus, with reproductive bodies mostly absent from the frond tips. Frenchman's Ledge, Osmington Bay, Dorset, UK, part of the Jurassic Coast (7) 

As with the Pepper Dulse described in yesterday’s post, the colour of the Grapeweed varies with shore level, being more purple-brown or even blackish lower down and greener at higher shore levels. The fronds can be up to 13 cm long; and the upper fronds displayed in the above picture are mostly lacking reproductive bodies or these are in the early stages of development.

Flat fronds of Grapeweed, Mastocarpus stellatus, showing incurved edges forming a groove or gutter. Frenchman's Ledge, Osmington Bay, Dorset, UK, part of the Jurassic Coast (8) 

The outer edges of the flat fronds tend to roll or curve inwards forming a shallow gutter or groove (see the picture above). As in Channelled Wrack, the fronds lack a midrib. However, Grapeweed is a red alga compared with Channelled Wrack which is a brown seaweed.

On both surfaces of  the tips of most fronds in Grapeweed are numerous small elongate reproductive bodies which superficially resemble grape pips – hence the common name of Grapeweed for this red alga (see the picture below). This feature also differentiates Grapeweed from Channelled Wrack in which the reproductive bodies occupy the entire swollen bifid frond tip.

On an exploitation note, Grapeweed is sometimes used as a substitute for agar production.

Numerous elongated reproductive bodies looking like grape pips on both surfaces of the frond tips in the red alga Grapeweed, Mastocarpus stellataus, on Frenchman's Ledge at Osmington Bay, Dorset, UK, part of the Jurassic Coast (9)

Revision of a post first published 16 June 2009

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved 

Toothed Wrack on Worms Head Causeway

Toothed Wrack seaweed, Fucus serratus Linnaeus, close-up detail showing reproductive conceptacles on the receptacle in transmitted light. Specimen from Worms Head Causeway rocks, Gower, South Wales, UK (1)

Toothed Wrack, Fucus serratus Linnaeus, is a common and familiar British seaweed. It grows on rocks of the lower seashore in the inter-tidal zone. The pictures in this post were taken on the Worms Head Causeway in Gower when the seaweed was exposed at low tide.

This algal plant can reach a length of 2 – 3 feet – that is, up to about a metre. A seaweed is not differentiated into a stem, roots and leaves like the higher plants. However, it does have different parts. The plant body, or thallus, has a branched hapteron or holdfast – a root-like structure at its base – by which it is attached securely to the rocks.  The thin ‘branches’ of the hapteron grow into the cracks and crevices to hold the seaweed into position and make it very difficult for the actions of the sea to dislodge it.

A short cylindrical stalk or stipe connects the hapteron to a flat broad branched blade known as the lamina. In Toothed Wrack the edges of the laminae have an irregular serrated (saw-like or tooth-like) edge from which the seaweed gets its name. 

Reproduction in Toothed Wrack is mainly sexual rather than vegetative. At certain times of the year, the terminal few centimetres of the branched laminae become swollen; and these parts are then called the receptacles. Small cavities named conceptacles sit just below the outer layer of the receptacles and are connected to the surface by minute openings known as ostioles. [Actually, these tiny cavities are found in other places on the seaweed but in these locations they are sterile and only contain hairs. If you look closely at  Picture 4 in this post, you should be able to see regular grouping of these small hairs on some of the laminae.]

However, in the receptacles, the conceptacles are fertile and produce the gametes used in sexual reproduction. Fucus serratus L.  has separate male plants and female plants, each producing gametes that are shed through the ostiole into the sea water where fertilisation and development take place. 

Natural pattern and texture in seaweed: Tooth Wrack, Fucus serratus Linnaeus, detail of the swollen rounded conceptacles containing ripening reproductive products on the terminal receptacles - macro photograph in reflected light showing surface texture. Specimen from Worms Head Causeway, Gower, South Wales, UK (2)

Toothed Wrack, Fucus serratus Linnaeus, showing the branched receptacles bearing the conceptacles at the end of the lamina, blade or frond of the alga. Specimen photographed on Worms Head Causeway, Gower, South Wales. UK (3) 

Toothed Wrack, Fucus serratus Linnaeus, showing branched reproductive receptacles at the end of a flat, tooth-edged lamina. Growing specimen exposed at low tide on Worms Head Causeway, Gower, South Wales, UK (4)

Seaweed of the Gower Peninsula: Toothed Wrack, Fucus serratus Linnaeus, showing branched reproductive receptacles at the end of a flat, tooth-edged lamina. Growing specimen exposed at low tide on Worms Head Causeway, Gower, South Wales, UK (5)

Toothed Wrack and Coral Weed growing together: Olive-green Toothed Wrack, Fucus serratus Linnaeus, growing among purple Coral Weed, Corallina officinalis Linnaeus, exposed at low tide on the lower shore at Worms Head Causeway, Gower, South Wales, UK (6)

Common British seaweeds of the lower rocky shore: Toothed or Serrated Wrack, Fucus serratus Linnaeus, on the lower rocky shore with other common British seaweeds, exposed by a very low tide at Worms Head Causeway, Gower, South Wales, UK (7)

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

Seaweeds on rocks at Eype

seaweeds at Eype: Abstract patterns made by different coloured seaweeds on flat rocks at Eype, Dorset, UK - part of the Jurassic Coast (1) 

The major part of the beach at Eype is made up from small size shingle and pebble with scattered large boulders that have rolled across the beach from landslips along the cliffs. However, if you walk westwards along the seashore, the number of boulders increases until the far point is entirely rocky shore from the base of the cliff down into the sea. It is on these rocks and boulders between the extremes of tide that the seaweeds grow.

Strangely, not all of the rocks in the intertidal zone are colonised by algae. Seaweed seems to have definite attachment preferences. The large flat rocky surfaces are the most likely habitat to be occupied – as are large boulders that are constantly splashed and frequently submerged at lower levels of the shore. The seaweeds of different types that cover the flat-topped rocks make interesting patchworks of diverse colour and varying textures.

The most common seaweed is the olive-green Toothed Wrack, Fucus serratus, which is actually a member of the brown seaweed group or Phaeophyceae. Bright splashes of colour are provided by shapeless masses of soft green seaweed, probably Gut Weed Enteromorpha intestinalis, which belongs to the Chlorophyceae group. Pepper Dulse, Laurencia pinnatifida, is easily recognised by its wonderful golden hue, although it is actually a red seaweed belonging to the Rhodophyceae. Soft filamentous red seaweeds that are difficult to individually identify are responsible for extensive areas of pink or purple-brown colour; these provide a counterpoint and contrast to the other types of basically green to yellow algae. 

Seaweeds on rock: A strange shaped rock draped with seaweed just offshore at Eype, Dorset, UK - part of the Jurassic Coast (2) 

Seaweeds growing on rock: A natural arrangement of seaweeds on a circular flat stone at the waters' edge at Eype, Dorset, UK - part of the Jurassic Coast (3) 

Living Toothed Wrack (Fucus serratus Linnaeus): A rock in the water festooned with bunches of Toothed Wrack at Eype, Dorset, UK - part of the Jurassic Coast (4) 

Seaweeds on the Dorset coast: Toothed Wrack and Gutweed on a pointed water-worn rock at Eype, Dorset, UK - part of the Jurassic Coast (5) 

Common British seaweeds: Detail of the edge of a zone of olive green Toothed Wrack over-lapping a contrasting neighbouring zone of filamentous purple-brown red algae on rocks at Eype, Dorset, UK - part of the Jurassic Coast (6) 

Seaweed natural pattern: Detail of Toothed Wrack (Fucus serratus) naturally arranged in over-lapping layers on an intertidal rock at Eype, Dorset, UK - part of the Jurassic Coast (7) 

The beach at Eype: A view looking west towards the rocky end of the beach at Eype, Dorset, UK - part of the Jurassic Coast - showing boulders amongst the shingle and in the shallow sea at the water's edge (8) 

Revision of a post first published 7 February 2010

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved