Nerite Shells at Port Douglas

Posted on April 25, 2013 by winderjssc

Nerite Shells are very common inhabitants of rocky shores on the Queensland coast in Australia; and they generally have a wide Indo-Pacific distribution. There are several species but the specimens shown here are Nerita costata Gmelin and were photographed at Port Douglas.

They have a characteristic appearance with thick black rounded ridges spiralling around the shell whorls, with lighter coloured furrows between them. The spire is blunt. The aperture opening is roughly semicircular with a specific arrangement of protruberances or ‘teeth’. The odd-shell-out in pictures 1 and 2 is a Mulberry Shell or Granulated Drupe (Morula granulata Duclos) which has an odd look with spirals of dark rounded bumps vaguely resembling a bunch of grapes or similar.

Wild Oysters on the Queensland Coast Part 2

Posted on April 22, 2013 by winderjssc

The oysters that I found on the rocks at the northern end of Three Mile Beach in Port Douglas were so different from the ones I had seen at Cape Tribulation that I wondered if they were oysters at all.

The identification of Rock Oysters of the Saccostrea Group in the Indo-West Pacific is a fairly hot topic and some very interesting work was completed a few years ago to try and sort out what is what. See the work of Katherine Lam and Brian Morton.

On the basis of shell morphology, I think the oysters illustrated in this post are Saccostrea mordax which are distinct from the other Saccostrea species in having regularly-spaced grooves radiating from the umbone to the ventral margin of the right valve, the triangular shell shape, and finely plicated valve margin (with regular m-shapes). The left valve is completely attached as in the other species of Saccostrea such as cucullata, glomerata, and kegaki which are all morphologically similar to each other with an oval, deeply cupped left valve and a smaller, relatively flat right valve with slightly plicate, raised margins.

The molecular study by Lam and Morton (2006), based on samples obtained from along the whole of the Australian coastline, clarifies what is known about rock oyster biogeography. The identification of the oysters shown here from Port Douglas tallies with the distribution of Saccostrea mordax that is now thought to have a range from the tropical eastern coast of Australia, along the northern coast and throughout Western Australia. S. glomerata only occurs on the south-eastern coast of Australia on temperate shores from southern Queensland to New South Wales while S. cucullata shares the geographical range of S. mordax. One exception, based on someone’s personal observation – and not as a result of inclusion in the mitochondrial DNA work – is that putative S. mordax also occurs, but in much lower numbers, on shores dominated by S. glomerata around Moreton Island and Sydney.

Wild Oysters on the Queensland Coast Part 1

Posted on April 20, 2013 by winderjssc

I have written a lot about the natural variations in oyster shells belonging to the British Native, Flat, or European Oyster, Ostrea edulis Linnaeus. However variable these shells may be, it is always possible to identify the shells as belonging to that species, and to distinguish them from other species.

In Australia and the Far East, the oysters that grow wild and naturally on the tropical shores include several species of Saccostrea which can be difficult to differentiate from one another because of the diversity of their outward appearance. The morphologies of Saccostrea glomerata, Saccostrea cucullata, Saccostrea kegaki, and Saccostrea mordax, are so variable and overlapping that is not always possible to tell them apart by eye. As with so many other groups of organism currently being investigated (marine algae for example), it is only by use of mitochondrial-DNA analysis that true identities and relationships can be established (Lam and Morton 2006).

Which brings me to a discussion of the Rock Oysters that I photographed in several locations on the Queensland Coast. The images shown in this Posting were taken at Cape Tribulation in tropical Far North Queensland. Just going by the external characteristics, I suggest that they may be Saccostrea glomerata – also called the Sydney Rock Oyster. However, the differentiation of that species from Saccostrea cucullata is so problematic at times even for experts that oysters like this are frequently given both names, S. glomerata cucculata.

In following Posts I’ll show oysters growing in Yawarra Bay, Trinity Bay, and Port Douglas for comparison with these from Cape Tribulation. The shells from the rocks at the northern end of Three Mile Bay at Port Douglas look very different from the others and I think that they may be Saccostrea mordax. I’ll also refer in more detail to the Lam and Morton paper:

Lam, K. and Morton B. (2006) Morphological and mitochondrial-DNA analysis of Indo-West Pacific Rock Oysters (Ostreidae: Saccostrea species), Journal of Molluscan Studies (2006) 72: 235 -245, Oxford University Press on behalf of The Malacological Society of London.

Winkles on Worms Head Causeway

Posted on April 3, 2013 by winderjssc

The Common Winkles (Littorina littorea (Linnaeus) that live on the rocks of the Worms Head Causeway on the Gower Peninsula have a tough time! It’s an exposed and turbulent environment in which to find a home. There is certainly some shelter in deeper pools and beneath seaweeds on the outer fringing rocks of the causeway – but when the tide comes surging across the jagged strata, most winkles must be stripped from rock and weed to be tossed and battered by waves, currents, and flying debris like stones and pebbles. Winkles don’t have the same ‘sticking power’ as the limpets which can cling on and withstand the battering.

The ebbing tide leaves hundreds of thousands of winkles literally high and dry. A few of these small marine gastropods do manage by chance to remain in the more favourable conditions of temporary tide pools, even if barely covered by a few centimetres of water. Most winkles seem to stay in the open air, approximately where they have rolled by chance, lying loose and unattached in large clusters around the bases of upstanding rocks and amongst the mussel beds. Some cling on to the bare rocks, bone dry in the sun, waiting for the return of the waves.

The life style of the winkles is clearly seen in the dull surface of the rough and pitted thick shells. The shells are more comparable to those of the winkles found at nearby Whiteford Point also on Gower – and contrast markedly with the lovely pristine striped and grooved shells of winkles found among the seaweed on relatively sheltered shores like Ringstead Bay on the South Coast.

Common Winkles

Winkles living on Whiteford wood and stones

Holdfast habitat at Ringstead Bay

Strandline Seashells in situ

Posted on April 2, 2013 by winderjssc

These pictures show natural accumulations of common British seashells on the strandline at Rhossili, Gower, South Wales. They are photographed as found – in situ. The images have a usefulness and significance despite the fact that that they are neither technically brilliant photographs nor what you might call picture postcard shots. They probably wouldn’t win any prizes for beauty or be worthy of framing on the wall.

The pictures show nature as it really is – without re-arrangement, clever angles, or just the right lighting. Their function is to inform rather than visually please. They are a way of recording something both situational and ephemeral, something that may only last a few hours until the next tide, something that may not occur in the same way again for months, if ever. From these jumbled up assortments of shells it is possible, for example, to compile a species list of marine molluscs that until recently lived in the area, not just the shore on which they were deposited, but including a geographically wider variety of habitat substrates, water depths, and degrees of exposure, that have been scoured by the waves, currents and tides.

In the instance of the pictures posted here, the random selections of shells do not represent death assemblages (mass mortalities) which often occur on this and other beaches. Actually, many of the shells, particularly the more robust ones like oysters and limpets, may be decades or even centuries old; the more fragile shells (like those of Banded Wedge Shells) readily break up in a very short time. Thicker, older shells have become incorporated with more delicate shells, from recently dead organisms, all the shells undergoing a cycle of burial and release from the sediments, a process which over time leads to more and more breakages, infestation damage, and burial staining, and general abrasion that leads to the eventual destruction of the shells and incorporation into the finer beach sediments.

This kind of temporary strandline deposit of shells and shell fragments could provide insights into the origins and processes involved in the formation of fossil shell assemblages. It could potentially provide clues to past and changing environments. It might allow understanding and interpretation of archaeological deposits of shells. It is not possible to know every way in which the information might turn out to be useful. So I have recorded it for posterity and future science investigations – just in case.

Just a Common Whelk Shell

Posted on March 6, 2013 by winderjssc

Many seashells, like that of the Common Whelk Buccinum undatum (Linnaeus), show a lot of individual variation in size, shape, growth line patterns, colour, encrustation, and general wear and tear. That’s what makes the shells so interesting and attractive to look at – even if they do not feature bright colours and exotic designs.

So this marks the first in an occasional series of postings – each showing an individual shell from various different view points to demonstrate macroscopic variability in appearance within different species of common British seashells.

Clicking on a photograph will enlarge the image so you can see the details.

Click here for more information and illustrations on whelks and whelk shells in Jessica’s Nature Blog.

Arrangements of Seashells

Posted on March 1, 2013 by winderjssc

I really like to look at shells and have them around me. I often discover the odd shell in my pocket as a souvenir of a trip to the beach. Sometimes I will collect empty shells in larger numbers where this is permitted. The pictures in this post show different assortments and arrangements of common British seashells that have decorated my home from time to time over the last couple of years.

There are many posts on Jessica’s Nature Blog about seashells – sometimes just showing pretty pictures (like here) but often also describing their identifying features and other information. Click here if you would like to browse through more than 60 SEASHELL POSTS.

The Big Button Shell

Posted on February 20, 2013 by winderjssc

Trochus niloticus Linnaeus is a large heavy Top Shell with a lot of internal mother-of-pearl which has, in the past, been commercially exploited for use in button-making. Hence its common name of Button or Pearly Top Shell. The numbers are reduced now but shells are still found washed ashore. The examples shown here were photographed on Normanby Island near the Great Barrier Reef off the coast of Northern Queensland in Australia.

The island is a nature reserve and nothing can be removed. Whatever lives there, or is found there, stays there – so that it can be enjoyed by all subsequent visitors. Hidden among the trees on the island is a table top covered with some of the unusual or colourful treasures that have been picked up on the beach – comprising clams, cowries, cones, corals, cuttle bones, conchs, helmet and turban shells. The collection also includes several worn and faded specimens of this large Pearly or Button Top Shell – but none as splendid and intact as the ones I found (and left) on the strandline.

Mud Creepers

Posted on February 12, 2013 by winderjssc

Mud Creepers are a common sight on the tidal mud flats at Cairns in Queensland, Australia. Also called Telescope Shells, Mudwhelks, Telescopic Creepers, or Mangrove Mud Whelk. The Latin name is Telescopium telescopium L. They are so emblematic of the place that they have been glorified by a fantastic piece of sculpture by Dominic Johns on the Esplanade.

The reality, however, is that this large gastropod marine mollusc – living on the glutinous muds exposed by the ebbing tide – is not the most attractive of seashore creatures, in fact, a bit creepy. It is dark in colour, about 6 inches long, and the shell is very thick and heavy, The protruding muscular foot and tubular siphon of the animal are hard to distinguish from the mud itself but I believe the flesh is edible.

This sea snail seems to struggle as it drags its weighty shell across the mud in strange irregular movements without the supporting medium of water. The furrows incidentally ploughed by the shells leave networks of trails on the mud. In life the shells are often caked with mud but empty shells washed up on the beach show there is actually a great striped pattern.

Ancient Gower Shells & Raised Beaches

Posted on January 1, 2013 by winderjssc

Britain began to warm up after the first stage of glaciation, between 130,000 and 125,000 years ago, and rising seas caused by the melting of the ice sheets carved wave-cut platforms in coastal bedrocks, and deposited new beaches. In Britain this time is known as the Ipswichian Interglacial period – in geological terms a relatively recent phase of the Pleistocene xx. Subsequently, following various geological stages of ice formation and recession, sea levels dropped again to current day levels – leaving these earlier beaches up to 6 metres above present Chart Datum.

Remnants of these raised beaches have been described from around the coastline of the Gower Peninsula in South Wales. Most of the readily available academic texts refer to the sites at Foxhole, Langland, and at Fall Bay. Despite the focus on a few locations which demonstrate the phenomenon particularly well, there would have to be evidence of this sea level change all around the Gower Peninsula – and I discovered for myself an apparently hitherto un-described location for these ancient shell-bearing deposits right on the tip of the Rhossili Headland where it drops down to the Worms Head Causeway.

Here I found ancient limpet shells (Patella spp.) and winkle shells (Littorina spp.), embedded with minute shelly fragments and pebbles, in a matrix of reddish, iron-stained sediment consolidated by crystalline calcium carbonate. These deposits were located in cracks and crevices of the jagged limestone bed-rock projecting upwards at steep angles from the shore. More significantly, however, the shells were found in distinct, horizontally-aligned strata clearly visible at the base of the softer recent sediments leading down to the present-day beach.

The layers of ancient beach material originally would have spread out and covered all the bedrock which juts up from the upper and middle shore. It has now been mainly washed away but remains in a few places, almost like a coating of conglomerated cement with hard-core, attached to the Carboniferous limestone outcropping on the higher shore. The horizontal layers of raised beach deposits, seen in vertical section at the base of the headland, are often undercut by extreme high-tide wave action and consequently overhang slightly. Above the raised beach levels are solifluction deposits and red soil.

For more information about the raised beaches of Gower, have a look at:

George, G.T. (2008) The Geology of South Wales – A Field Guide, published by gareth@geoserve.co.uk, ISBN 978-0-9559371-0-1, pp 66-89.

Mullard, Jonathan (2006) Gower, Collins New Naturalist Series, Harper Collins Publishers, London, ISBN-13 978-0-00-716067-6, ISBN-10 0-00-716066-6, pp 44-50.

PS Don’t forget that you can click on individual photographs to enlarge them and read a detailed description of the image.