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.
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.
The majorpart 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.
Revision of a post first published 7 February 2010
Extensive fresh growths of the small pink calcareous seaweed Corallina officinalis Linnaeus were everywhere on the low seashore at Kimmeridge in March. Attached to the bedrock in shallow pools seeming very decorative and unusual. If you have a look at my previous Post of 19th February 2009 (Flat periwinkles and calcareous seaweed at Kimmeridge Bay), you can see the interesting white chalky beaded appearance of this Coral Weed when found dead and dried on the strandline.
Huge rafts of detached, mostly red, seaweeds including Corallina were accumulating at the water’s edge at the western edge of the bay and much of this will no doubt get left high and dry on the strandline eventually.
Also growing rapidly at the western end of the bay were extensive beds of the Toothed Wrack Fucus serratus Linnaeus. You can see from the close up picture above that it is olive green in colour although it belongs to the brown seaweed group. It is a fairly small, short alga with branched fronds with a midrib. The edges of the blades are serrated or toothed and they do not have either gas bladders or noticeably swollen reproductive bodies at the tips of the fronds.
In the picture below you can see how the whole bed of Toothed Wrack looked on the lower shore as the tide was going out.