The topography of the shore near Cape Tribulation varies. At one point it is semi-vegetated with salt-tolerant shrubs. Here the substrate holds water for longer at low tide and the root systems of the plants trap finer sediments and nutrients that are washed down the beach from the nearby forest.
The different composition and consistency of the beach sediments in this place has given rise to a variation on the theme of sand ball patterns made by feeding crabs. The crabs may be the same species or a related species to Scopimera inflata which created the scatters and radiating patterns of drying-out pellets further along the beach (see the previous post). In this location, however, the enriched sand was relatively wet, which meant that the pellets coalesced into discrete linear masses that made very interesting designs on the surface of the beach.
On many sandy beaches along the Queensland coast of eastern Australia there are millions of small sandy balls. Each one is just a few millimetres across. They can form extensive mats or patterns as they cover the shore at low tide. There were many decorating the sand at Cape Tribulation when I visited in 2011. Closer inspection reveals small holes in the sand, usually at the centre of radiating lines of balls. These balls are the result of the feeding activities of small sandy coloured crabs that are themselves rarely seen. The holes are their burrows. They are the “Sand Bubbler” crabs belonging to the genus Scopimera, often S. inflata. The balls are created as the crab feeds on the organic matter attached to the sand grains on the surface around its burrow, and rolls up the cleaned grains into balls before moving on to the next spot.
The patterns vary according to the moisture level of the sand and its organic content, as well as the species concerned, I would imagine. I’ll post some more pictures later showing an interesting variation on the sand ball patterns from the other end of Cape Tribulation beach.
A wide and shallow river flows over the sandy beach at Ventry Bay on the Dingle Peninsula in Ireland. I do not know its name. Characteristic ripple marks are made in the wet sand around the margins of its wandering channels, showing the influence of the freshwater currents modified by the sea water tides. As you walk away from the fast flowing water, the overlapping ‘leaf’ patterns made by the river currents gradually transition into the parallel ridges of wave-induced ripples that are more typical of the intertidal shore .
Patterned Sand 8 – 14: Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this natural abstract art.
Patterned Sand 1-7 – Naturally formed patterns of black sediment on yellow sand were photographed on the beach at Rhossili Bay, Gower, in April 2017. The black sediments were mainly composed of minute pieces of rotten wood, coal dust, and miniscule fish bones, with a small proportion of seeds. The images have been digitally colour-enhanced to emphasise the patterns of this wonderful natural abstract art.
Walking back from Spaniard Rocks now, I took a route closer to the dunes where the character of the shore is quite different from the wet sand and strandlines between high and low tide levels. Here there are pebbles. Rhossili’s pebbles intrigue me. I love scrambling over the banks of stones at the very top of the beach. The colours are lovely pastel shades with pinks and blues and overall reminding me of sugared almonds. A total delight. Many rock types are represented. Some have interesting patterns.
I like the way that the numbers of beach stones seem to increase or decrease depending on how they are pushed around the shore between one visit and the next, and how the sand changes its level and distribution throughout the year and the transition from season to season. This time the wooden ribs and keel of the shipwrecked ketch Anne were only just visible above the sand and pebbles. I like the way that pebbles are arranged partly buried in the damp sand that quickly dries to a different hue and texture. The pebbles underlie the tall sand dunes of the Llangennith Burrows. The dunes have been scooped out by stormy seas and footsteps in many places to demonstrate that even wind-blown sand is stratified; and marram grass roots exposed to air show how deep they penetrate the soft fine sediments to bind them together and stabilise the dunes.
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.