I found this tiny hermit crab scrabbling around in the seaweed and seashell debris of a sandy tide pool beneath Rhossili cliffs. I thought at first that it was just a very small, immature, specimen of the common hermit crab (Pagurus bernhardus Linnaeus) but as soon as I picked it up for a closer look I could see that it was something special because it had a large claw (cheliped) on the left instead of the right. There is only one species with this characteristic – the south-claw hermit crab, Diogenes pugilator (Roux). The mature specimens have a greenish carapace no greater than 11 mm in length.
According to Hayward and Ryland (1998) this crab lives in fairly sheltered sandy bottoms from low water spring tide level down to 35 m, on south and west coasts of the British Isles where it is described as common. It also occurs elsewhere from Holland to Angola, Mediterranean, Black Sea, and Red Sea. Mullard (2006) provides more information, saying that D. pugilator is only found in a limited number of places in Britain and Ireland because it is primarily a warm-water species and may be worthy of further study in relation to climate change since there are signs of it extending its range. It was first recorded in Britain “at Worms Head” from specimens provided by L. W. Dillwyn of Sketty Hall in Gower to Spence Bate in 1850 who described it in Annals and Magazine of Natural History.
The crab can quickly bury itself in clean, well-sorted sand on a gently shelving moderately exposed beach facing southwest where conditions are less turbulent than on steeper beaches. This crab has an interesting extra way of gathering food, in addition to scavenging or eating sediment. While mostly buried in the sand, it can sweep its hairy antennae around in an almost circular motion as a net to capture small edible particles from the water.
Hayward, P. J. and Ryland, J. S. (eds) 1995 (revised edition 1998) Handbook of the Marine Fauna of North-West Europe, Oxford University Press, New York, pp 434-437, ISBN 0-19-854055-8.
Mullard, J. 2006 Gower, The New Naturalist Library, Collins, London, pp167-168, ISBN0-00-716066-6.
Starfish, usually Asterias rubens, sometimes get washed ashore in huge numbers on Rhossili beach in Gower, South Wales. Then they disappear again, either washed back out to sea or buried in the sand. Birds peck at them but they do not seem to like to eat them very much. This April, for the first time, I saw ghostly star shapes in the dry sand high on the shore. The long buried stranded starfish were reappearing in skeletal form. You may not have realised that Asteroidean Echinoderms like the Common Starfish had a skeleton. Hidden beneath their often brightly coloured and bumpy skins, bound together by connective tissue, is a lattice network of small calcareous ossicles in the shape of rods, crosses or plates. Spines and tubercles are also part of the skeleton, sometimes separate pieces resting on the deeper dermal ossicles or as extensions of them that project to the outer surface (Barnes 1963).
In these photographs of the dessicated remnants of starfish it is possible to see many small holes in the sand around them. These holes are the places where the scavenging sand hoppers are hiding from the dry hot air and waiting from the tide to return in the cool of the day to recommence cleaning up all the vegetable and animal debris that ends up on the strand-line – like dead starfish.
Barnes, R. D. (1963) Invertebrate Zoology, R. B. Saunders Company, 526-539.
A watery theme in textiles this time. These images show details of the designs on the hems on two Chinese silk embroidered dragon festive robes, worn by an Imperial consort and an Imperial prince during the Qing dynasty (1856-1908). They are displayed in a glass case at the Victoria and Albert Museum in London, England. The hems of the garments depict waves and surf while dragons fly overhead on the main body of the robe. If you look closely at the detail of the churning water, you may see small stalk-eyed crabs, sea snails with coiled shells, leaping blue fish, and strange sea anemones lurking in the foam.
Yesterday on Knoll Beach at Studland Bay in Dorset, the two most common things washed ashore were great clumps of Japweed (Sargassum muticum) and large barrel-mouthed or dustbin-lid jellyfish (Rhizostoma octopus). There were at least a dozen jellyfish on the stretch of sand that I walked. They varied in size from about 20 – 60 cm diameter across the dome. The colours varied from crystal clear to pink and blue. They all seemed very fresh and I think maybe some of them were still alive or just expiring. As they washed to and fro in the waves, sometimes entangled in the Japweed, they turned this way and that, upright then upside down, inside and out. This species is becoming an increasing feature on south-west coasts over the last couple of summers. I first encountered these seashore creature on the Gower Peninsula in South Wales where they have long been a frequent find on the beaches. Click here to learn more about the Rhizostoma octopus jellyfish on Jessica’s Nature Blog.
There are some unusual mini-habitats in the shallow pools that occupy the cracks and crevices between bedding planes of the Silurian strata at Ferriters Cove. Only a few seashore creatures are seen grazing within them. A few common periwinkles (Littorina littorea) and limpets (Patella sp.) are the most frequent inhabitants. The pools have a few isolated branching seaweeds – some miniscule fine branching greens but mostly tiny clumps of Coral Weed (Corallina officinalis).
However, the rock surfaces beneath the water are also covered with a continuous coating, or small individual patches, of a variety of coloured algae such as the chalky red encrusting seaweeds like Pink Paint Weeds (Corallinaceae crusts); dark red non-calcareous encrusting seaweeds (Hildenbrandia rubra and Peyssonnelia sp. are examples in this group but not necessarily present at this location); encrusting brown seaweeds (Aglaozonia sp. and Ralfsia verrucosa would be examples of the type algae in this group); and the commonly occurring bright green algal films. Less obvious to the naked eye but probably also present in this kind of habitat would be the biofilms created by microscopic cyanobacteria, fungi, and lichens.
It is difficult to identify the species or even genera without taking samples to section and examine under the microscope. A complication with the identification or classification of these encrusting seaweeds, particularly the dark reds, is that the crustal form may represent a true species in its own right, or it may simply be only one life stage (tetrasporophyte phase) in the life cycle of a more familiar-looking foliose (branching) seaweed, or even an extensive attachment disc for a foliose alga.