Marine diatoms from
Guaratiba Canal,
Rio de Janeiro.

Roland Mortimer,

Guaratiba Canal is a little further north than Ibicui beach on the southern coast of Rio de Janeiro. Although this area has a higher pollution rate than Ibicui, there is still a wide variety of diatom species which proliferate there.

These diatoms were taken from a squeezed seaweed sample which yielded quite a large number of diatoms mainly of the "Sigmoid type" but also contained other nice species.

Pollution of the beaches here in Brazil is a sometimes serious problem and one the local governments tend to turn a 'blind eye' to. I prefer to portray the diatoms in their living condition because most books only show the frustules devoid of the previous owner's contents. Granted, nice pictures showing the frustules and their delicate markings are an essential means of identification, but these books are sometimes very expensive and beyond the means of many who would wish to identify a living example already under observation and who don't have the available chemicals and techniques required to clean the frustules ready for mounting.

Prepared slides are great to look at, but the creatures don't move and there are no colours; much more enjoyment and pleasure can be had by examining these wonderful creatures in a living state. Here are a few of the diatoms I found in my sample from Guaratiba Canal.

I would like to thank Klaus Kemp who identified Isthmia lindigiana for me and also said he found the same diatoms in the sea around Bermuda. I would also like to thank Jan of the Dutch club for his help in identification and for kindly supplying me with the much needed diatom mounting resin. Both Jan Parmentier and Wim van Egmond have written many extremely good articles on diatoms, these can be found in the Micscape Library.

Comments to the author Roland Mortimer welcomed.

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Published in the December 1999 edition of Micscape Magazine.

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