June 1996

Seasonal snapshots of nature in close-up

This month's features in our pond-dipping issue:

Regular readers of Micscape Magazine will know that the contributors are particularly keen to sing the praises of pond-dipping to the amateur microscopist. Youngsters have always had a fascination for ponds, but seem to lose it as they grow older. This is a pity because at any time of year there is a wealth of both macroscopic and microscopic pond organisms for naturalists both young and old to study.
In northern England where the author lives, a spell of cold weather (our second coldest May since records began!) has slowed the progress of early summer, so the author has concentrated this month on some of the plant and animal organisms that can be found in most bodies of freshwater.

Please read the important notes on collecting which also describes some simple precautions when pond-dipping.


For the casual observer of freshwater life, very little equipment is needed to become familiar with some of the commoner pond organisms, either at the pond side with a 10X hand lens or for taking home for closer examination. A more scientific study of the ecology of a habitat and collection of particular organisms requires more systematic techniques and specialist equipment which may be discussed in a later article.

A wealth of subjects to study at home can often be found simply by transferring a small handful of weed and water collected from the pond shallows into a sealed plastic container. It is important to keep the container cool during transport and back at home as well as allowing good aeration.

It is often worth studying the larger invertebrates you may find such as beetles and dragonfly larvae at the pond side and returning them to the pond immediately, as the larger organisms are less likely to survive a journey home, and the carnivorous larvae may eat the smaller organisms of interest! The small white margarine tubs (and lids to examine the larger organisms closely with a lens) are excellent for this. Photographic developing trays are also useful. There are a number of simple guides and keys available which will allow you to identify organisms to the correct family.

The organisms below were all collected from a pond sampled as described above with no special equipment.

Freshwater shrimps

Freshwater shrimps (Gammarus) are commonly found in cleaner ponds and streams where the calcium concentration is high enough to support them. In Yorkshire, England where the author lives Gammarus pulex is not found in water bodies with a calcium content of less than about 10mg per litre.

They are members of the Phylum Crustacea and the order Amphipoda. They can reach 20 mm in length and their habits can easily be observed by eye or 10X hand lens in a shallow dish. They are laterally compressed and swim on their side and typically eat organic debris. Their body and leg structure is worth studying, which are shown in the images heading this and the previous section.

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Algae are single-celled plants and include microscopic forms less than 1 micron long to the giant seaweed called kelp which can reach lengths of 60m. Many algae are very attractive particularly if dark ground illumination is used. Most ponds contain various filamentous algae and the green 'slime' often found in ponds is composed of algae.

A small sample of this apparently unappealing slime when pond-dipping can provide a wealth of microscopic fauna and flora that have attached themselves to the algae or are trapped in the filaments such as the smaller water fleas (see below). The cellular structure of the algae can be examined with modest powers of 100-200X using the traditional 'high power' microscope rather than the low power stereo. One of the general guides on algae may allow identification to genus.

In the sample taken by the author, some of the algal filaments were undergoing conjugation, and is shown on the image on the right above. This is sexual reproduction and involves two filaments lying side by side joining by the formation of outgrowths. The contents of one cell passes into the other and forms a fused cell or zygote which can overwinter while vegetative filaments die.

'Water fleas'

A group of organisms in which the author has a particular interest is the 'water fleas' a popular name for a group that includes Daphnia, which are well known to aquarists as a fish food. Water fleas were formerly grouped in the order Cladocera, although many taxonomists now split them among four groups. However, Cladocera is still a widely used descriptive term for them.

Cladocera are a delight to study under the microscope and have fascinated the author since he received his first microscope at ten years old. A drawing made by the author when he was aged 12 is shown right as proof! Chydorus sphaericus is a very common Cladoceran in most ponds and may be found with similar species in the weed samples described above. The Cladocera shown left above under dark ground illumination is also a member of the Chydoridae family. If mounted in a shallow cavity slide their structure, beating heart and limb movement can be admired while they are alive.

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Suggested reading

Pond-life - Introductory guides.
1) Collins Field Guide to Freshwater Life by R Fitter and R Manuel. Collins, London, 1986. ISBN 0 00 219143-1. A superb guide to the macroscopic and microscopic plant and animal life of Britain and N. Europe and enables organisms to be identified to at least the correct family and many to genus.

2) Freshwater Invertebrates. A Key to the Major Groups. by P S Croft. Field Studies Council, 1986. ISBN 1 85153 181 6. A good pond side guide to allow the macroscopic (> 2mm) invertebrates to be identified to family. Excellent for school students and can complement ref. 1.

3) A beginner's Guide to Freshwater Algae by H Belcher and E Swale. Natural Environment Research Council 1978. ISBN 0 11 881393 5. A good well-illustrated introduction.

Water fleas
4) A Key to the British Species of Freshwater Cladocera by D J Scourfield and J P Harding. Freshwater Biological Association, UK, 1994 reprint. This to the author's knowledge is still the only guide to the British species in print. It became a classic when first published in 1941, but unfortunately the Freshwater Biological Association reprinted in effect the 1958 Edition in 1994 without updating. It is still a useful introduction but is woefully out of date.

5) Crustace Cladoceres by C Amoros. Bulletin de la Societe Linneenne de Lyon, 53e annee, no 3, mars 1984 p72-107. Although an introduction to the French Cladocera, most British species are covered and has a superb diagrammatic key which is a delight to use.

Image details

Macro images of the shrimp were taken using a CCD camera attached to the eyepiece tube of a stereo microscope using a x1 paired objective with no eyepiece. Algae and water flea images were taken using 9x or 20x objective without an eyepiece on a compound microscope.
The pond image was captured from a video by the Microscopy UK Editor Maurice Smith...thanks Maurice!
Camera images were transferred to the PC using a Creative Video Spigot capture card.
Image manipulation using Photostyler v2.0 software.

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

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