The Collection and Mounting of Foraminifera.

Images by Jan Parmentier (NL)

Text By Brian Darnton (GB)

Introduction.

The Foraminifera have been known to microscopists since the time of van Leeuwenhoek, but very few people actually seem to collect them. In the study of geology and within the petroleum industry in particular, fossil deposits have become familiar markers of time periods and allied climate in the earth's crust. Living creatures are to be found in marine conditions from the ooze of the deepest ocean to the seaweed's of the littoral zone. They can also exist in hyposaline estuarine situations. There is even one non marine environment where they can be encountered in brackish pools of the eastern shore Neusiedlersee which divides Austria from Hungary. Some claim that this is a residue from the Miocene period sea which existed here 10 Million years before the Present time.

Greenhouse effect.

If the "greenhouse effect" does become more than a theory, then it would be important to record the content of the seas around us before the sea conditions begin to change. Although the Mediterranean Sea and the North Sea share one or two species each has a very distinctive "assemblage" of types.

Education.

Foraminifera and the Shelly remains of other calcareous marine creatures would be an ideal component of the School Curriculum: The empty "Shells" have considerable aesthetic appeal. Material from shore gatherings does not require to be killed or fixed, nor would their collection affect the environment in any significant manner. Investigation would be quite suitable for low magnification, low cost microscopes.

Collection.

Soundings or dredgings from the sea bed are beyond the means of the amateur, but beach gatherings are very useful indicators of foram associations. They are to be found amongst the debris of the upper tide marks of sheltered bays. Open storm beaches are not fruitful sites for investigation.

The bays of the Irish and Scottish Atlantic coast like Dogs Bay (Ireland) and Calgary Bay (Isle of Mull) are excellent sites where the forams are blown into dunes. Pure cultures can discovered growing on seaweed in the early summer. The common Foram Elphidium crispum enjoys the Sargassum muticum fronds along the Southern English coast. In the Netherlands there can be some confusion. In tidal lagoons like at Het Zwin, and broad estuaries like the WesterSchelde, fossil Forams may be found alongside recent ones as much of the Zeeland landscape consists of covered or exposed tertiary beds. The United Kingdom also has a few similar sites: Bracklesham Bay is a good example of an area where Tertiary beds have an input into the marine debris.

 

In the bay situation the spread of Foraminifera is confined to a very limited deposition zone which is to be found towards the headland from which the tidal flow originates. Local newspapers usually indicate which local harbours have the earlier high tide times. Frequently the sample is marred by particles of discarded coal or natural lignite but the black and white banding is a useful indicator at the deposition zones. In the Mediterranean Sea the Foraminifera are numerous but because of the lack of strong tides, the deposition zone extends to most of the sandy coastline with large numbers to be found to the lee of headlands. In the open sea, depressions in the sand near submerged rocks can reveal pockets of "Shells" In gathering from the shore a good X10 hand lens is a useful tool and material is best scraped from the sand with a flat children's spade. Do not forget to label samples in a plastic bag.

Cleaning.

Its a good idea to tip the sample into a bucket of water for the salt must be removed. A certain amount of separation from the sand can be achieved by stirring vigorously with a wooden spoon. If the suspension is observed in bright light, after almost one second most of the heavier sand will have sunk to the bottom but the white calcareous remains will still have some buoyancy.

 

 

This suspension may be decanted off into a 50 micron sieve or a fine sieve may be used to fish for forams in the suspension. If the bucket is carefully emptied and filled with a tap water at pressure some of the forams will fill with air and float on the surface for a while and may be captured. The Mediterranean types float well. The physical separation from sand can become the most challenging part of the business. When a fairly pure mixture of Forams has been cleaned then sieves can be used to separate species. Each seems to have a well defined size.

 

 

 

Mounting.

Smaller "Shells" less than 100 microns may be strewn in water and when dry mounted in Numount or a similar mountant. Its always a good idea to smear the slide first with a trace of gum tragacanth paste in order to prevent the "Shells "moving after mounting. Bubbles emerge after mounting in Numount for about five days and can spoil the mount. It is best not to use any heat for a week. The larger faction will probably have to be dry mounted. A fine oooo art brush is a good tool for manual selection. Here again Gum tragacanth is a suitable adhesive because it tends to leave no unsightly smear. At first, a simple 1 mm deep cell with a black background is very suitable but when one becomes familiar with species then some form of numbered grid is a good idea. NBS do produce some plastic cell slides which are very useful for this work.

Gum Tragacanth.

This is a traditional substance for dry mounting but it should be prepared at least 2 days before use. The key to its use is to dilute it as thinly as possible so that there is little or no trace on the slide surface when dry. NBS now produce a dry mount adhesive which works very well.

Conclusion.

Mounted Foraminifera from home or distant oceans were a familiar attraction of the Victorian microscope cabinet. World travel is now open to a much larger portion of the community, therefore there is no reason why an interest in these fascinating creatures should not be rejuvenated. Our own European seaside will provide a very good introduction to the subject.

Comments to the author Comments to the author sent via our contacts page quoting page url plus : ('bdarnton','')">Brian Darnton welcomed.

References.

J.W.Murray. "An Atlas of Recent Foraminifera" 1971, ISBN 0 435 62430 X, Heinemann Press with 96 ESM plates

R.W.Jones "The Challenger Foraminifera" 1994, ISBN 19 854096 5, Oxford University Scientific Press

J.A.Cushman " Foraminifera" 1980 fifth printing, SBN 674 30802 8, Harvard University Press.

Tregouboff G an Rose M. 1957 "Manuel de Planctonologie de Mediterraneenne" (2 volumes).

Faber Dr.F.J "Geologie van Nederland" Deel 3 Nederlandsche Landschappen.

 

Editor's note: to read other Micscape articles on Foraminifera by Brian Darnton enter 'Foraminifera' into our Library Search engine.

 

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Published in November 1998 Micscape Magazine.

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