August 1996

Seasonal snapshots of nature in close-up

This month's features in our 'sea-side holiday' issue :

• 
• Sun, sea and .... sand
• Sponge spicules
• Seaweed
• Fish scales
• Further reading

  
  

August is the traditional holiday month for many. Whether you're going abroad or just visiting a different area of your own country, there is likely to be plenty of nature around you that is unfamiliar. So don't forget to pack a 10X hand lens to explore the miniature aspects of nature when you're out and about.

This month, in between the sunbathing, we have a stroll around the beach, explore the rock pools and examine fish off-loaded at the harbour.

Please read the important notes on collecting.

Sun, sea and .... sand

While you're on the beach enjoying the sun, there's a potential source of microscopic interest all around you .... the sand, and beaches in general. Keep an eye out for shells, which can have interesting colours and patterns such as the shell (diameter 14mm) at the top of the page.

Depending on the location and other factors, beach sand can be comprised of a variety of constituents, and it is worth taking a sample, sprinkling a little on a piece of black card and examining in good light with a hand lens or stereo microscope. The commonest component is usually quartz, a form of silica, often with smaller amounts of mica, feldspar and other minerals. Of particular interest to the microscopist is the inorganic or fossilised remains of organisms such as foraminifera, sponge spicules and the smaller shells.

Some beaches are famous for their deposits of microscopic interest, and samples of these sands are often available from microscopy clubs and suppliers. The image left above is a sample of foraminifera sand from Dogs' Bay, Connemara, Eire (obtained free from a microscopy club meeting). The largest shell in the image is less than 1mm across. Foraminifera are unicellular organisms with calcareous skeletons which inhabit virtually all marine waters. When the organisms die they sink to form a foraminiferan ooze that covers about 30 per cent of the ocean floor. Limestone and chalk are products over geological time of these bottom deposits. A particularly good place to find the remains of these and other organisms is the white lines between the tide marks on a beach.

STOP PRESS: Coincidentally, the magazine Scientific American this month (August 1996) has a beautifully illustrated article showing sands from around the world.
'Sands of the World' by W N Mack and E A Leistikow, Scientific American, 1996,
August, pages 44-49.

Sponge spicules
The needle-shaped object in the sand shown above is a sponge spicule, and are worth looking for in sand samples. They are delicate glass-like forms that occur in a wide variety of shapes and sizes. A selection of them obtained from a well-known site in New Zealand called Oamaru is shown on the right. They are part of an arrangement on an old microscope slide. You will be lucky to find such a variety as this, but the sand sample from Eire above had a number of spicules similar to the cross-shaped spicule in the image.

Spicules form the skeleton of many sponges and can be either calcareous crystalline forms (eg of calcite) or made of silica. The spicules are either scattered throughout the sponge or united to form fibres. Sponges are primitive multi-cellular organisms of the phylum Porifera and inhabit all seas. Freshwater species also occur. Some sponges form intricate glass-like baskets, whereas others form elastic structures of spongin which were used as a bath sponge before synthetic ones replaced them.

Seaweed
Rock pools will have a wealth of interesting subjects in. The smaller red seaweeds such as Ceramium are very attractive under a lens and a section of the tips of the fronds of this seaweed is shown left under dark-ground illumination using a compound microscope. Seaweeds are algae, and occur in an amazing variety of sizes and forms. Algae span seven orders of magnitude in size from tiny flagellates less than 1 micrometre to giant kelp, a type of seaweed, which can reach a length of 60m in some areas of the world.

Many algae consist of just one cell, others two or more, and the largest have millions of cells. In large macroscopic algae, such as seaweed, groups of cells are specialised for specific functions, such as anchorage, transport, photosynthesis and reproduction.

The importance of algae cannot be overstated, they provide much of the earth's oxygen and they are the food base for almost all aquatic life.

Fish scales
If you are wandering along a harbour where fisherman maybe off-loading their catch, try and obtain a few samples of fish scales. Different fish species have characteristic scales, and after cleaning and drying are interesting to view under a stereo microscope, as well as the compound microscope using dark-ground illumination or cross polarisers. The fish scales shown right are from the sole, a flatfish (family Soleidae).

The fish scale on the left is from the cod (family Gadidae) and is typically 10mm across. This scale does not possess the spines seen in that of the sole above. Fish scales provide protection from the environment and from predators and are formed from bone from the deeper, or dermal, skin layer. There are a variety of types of fish scale. True teeth, for example, are thought to have developed from a type of scale called placoid scales. The typical overlapping fish scale of the cycloid type are large, thin or oval in shape and exhibit growth rings along their free edges. Ctenoid scales resemble cycloid scales but have comb-like teeth on their overlapping edge.

Further reading

The larger encyclopaedias such as Encyclopaedia Britannica should have good descriptions of general seaside life and features, such as sand and beach formation, seaweed, fishes and their scales etc.

A good illustrated field-guide to the plants and animals of seashores in Europe is 'Seashores of Britain and Europe' by A Campbell. Hamlyn, London, 1994. ISBN 0 600 58376 7.

Techniques for preparing slides of foraminifera obtained from chalk etc are often found in the microscopy club magazines.
For example:
Extracting Fossil Foraminifera from Chalk by Andrew Syred, Balsam Post, 1993, no. 21, p25-27. ISSN 0961-043X.
Fossil Forams by Fred Loxton, Balsam Post, 1994, no. 22, p31-32.
Balsam Post is the quarterly newsletter of the Postal Microscopical Society, UK.

Image details

The close-up of the shell and sand were taken with a CCD camera with a 50mm SLR camera lens and extension tubes attached. Camera images were transferred to the PC using a Creative Video Spigot capture card. Image manipulation using Photostyler v2.0 software.

The sponge spicules, fish scales (sole) and seaweed are from prepared microscope slides circulated by the Postal Microscopical Society (PMS) UK, and are credited as follows.
Sponge spicules (a selection from Oamaru) - submitted by R Darby, prepared by R Suter.
Fish scales (sole) - from PMS collection. Prepared by J T Norman in the 19th Century.
Seaweed (Ceramium echinotum) from S. Devon coast, UK - Submitted and prepared by B Darnton.

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The author Dave Walker is a UK based amateur naturalist keen to encourage people to explore nature in close-up.