Starfish Skeletons

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.

Reference

Barnes, R. D. (1963) Invertebrate Zoology, R. B. Saunders Company, 526-539.

Embroidered Waves

Embroidered silk Chines festive dragon robes from the Qing DynastyA 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.

Jellyfish and Japweed at Studland

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.

Rock Pools at Ferriters Cove

Rock pool with encrusting algae

Location of the rock pools at Ferriters CoveThere 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.

Rock pool with encrusting algae

Rock pool with encrusting algae

Rock pool with encrusting algae

Close-up of rock pool with encrusting algae

Rock pool with calcareous encrusting and foliose algae

Rock pool with calcareous encrusting and foliose algae

 Rock pool with encrusting algae

RocRock pool with encrusting algae

Close-up of rock pool with encrusting algae

Rock pool with encrusting algae

Rock pool with encrusting algae

Rock pool with encrusting algae

Rock pool with encrusting algae

Close-up of rock pool with encrusting algae

Ventry Beach on the Dingle Peninsula

Just a few pictures from my visit to Ventry Beach on the Dingle Peninsula on the west Coast of Ireland yesterday selected from the 480 photographs I took! The weather was amazing for September and I was able to spend five hours on the sand enjoying the sights and sounds as well as the atmosphere of this old pilgrims’ path.

Don’t forget, you can click on any photograph to enlarge the image!

The Barnacle Zone on Waterfront Structures

Barnacles and mussels above the waterline on a wooden pier piling.

Barnacles often settle higher on the shore than most other organisms. They are adapted to live part of their life, sometimes most of it, actually out of water – being able to get by on splashes of water that extend beyond the high-tide line.

The way that animals and plants are distributed across the shore is known as zonation. Zonation is generally accepted as meaning a vertical separation of different groups of organism, often into distinct bands of different colour when living on hard substrates, resulting from the tolerances of individual species to dessication, temperature, and wave action – otherwise termed ‘exposure’. The barnacles and mussels occupy the mid-shore level. Around the world, although the species differ, the same phenomenon is found, with zonation more clearly visible to the casual observer on steep exposed rocky shores.

An extreme example of this zonation can often be seen on the artificial structures of a waterfront harbour where wooden wharf-sides, timber pier pilings, and metal revetments substitute for rock surfaces on which organisms can settle. Many of these artificial substrates are vertical and therefore the zoning of the organisms may be exaggerated and clearer to see.

The pictures in this post show a pale band or stripe, made up almost entirely of cream-coloured sessile or acorn barnacles, naturally cemented onto harbour-side structures, sometimes wholly encircling them. A few common periwinkle gastropod molluscs move around the barnacles, feeding on the bio-film that accumulates on their shells.  Fronds of spiral wrack and sea lettuce type of seaweed, both also fairly tolerant of exposure out of water, are sometimes scattered over the barnacle zone. The barnacles have special adaptations that allow them to survive dehydration at low water but they are none-the-less vulnerable to predating dog whelks at all stages of the changing tides.

Below the barnacle zone, a darker, almost black band, is composed of edible mussels attached by byssus threads. Mussels are less tolerant to air exposure than the barnacles so they survive best lower down where they are not out of the water for so long. They are a sitting target, though, for starfish which use their tube feet to sucker onto these bivalves, forcing them to open, and then everting and inserting their starfish stomach into the mollusc so that they can feed upon the living contents.

All these photographs were taken on the waterfront in Halifax, Nova Scotia. Most of the piers and jetties are still traditionally made of timber because it is such an abundant commodity in Canada. There are generations of timber structures: new; old and decaying; and derelict examples. All of these show the barnacle banding. So do the more recently built rusting metal revetments to the edges of the renovated wharves in the more developed areas.

Interestingly, many modern high-rise buildings in that location have been constructed right on the water’s edge where they are supported by foundations of steel piles driven deep down into the very hard metamorphosed bed-rock. The pilings can be seen projecting below the buildings on the waterside elevations, disappearing into the harbour water. Each white-painted column displays at its base a lower ring of black mussels and a higher ring of paler barnacles – the structures themselves being reflected in the seawater with an odd abstract effect.

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