Gracilaria verrucosa seaweed at Studland

Is it Gracilaria verrucosa (Hudson) Papenfuss, or Gracilariopsis longissima (S.G.Gmelin) M.Steentoft, L.M.Irvine & W.F.Farnham – or something else? I’m a bit confused.

To be honest, I am not absolutely certain of the identification of the seaweed in this post. I thought I was – but I have been looking at a lot of books, some of which were published a very long time ago. Now I have looked on-line as well and I am not so certain. This is because science marches on.  Re-evaluation of taxonomic groupings take place in the light of new discoveries. Scientific names change accordingly. Former single species become subdivided into more than one species, or varieties of species, as our knowledge and techniques for investigation improve. Recent developments in DNA can throw light on the complexities in nature. What once seemed fairly simple can turn out to be very complicated. That’s my excuse for uncertainty here.

Although this seaweed found washed ashore at Studland Bay is mostly a light yellow-green, olive-green colour, it is actually a member of the red seaweed group or Rhodophycaea. You can see that some of the fronds are actually pink grading into green (photographs 4-6). Red seaweeds contain red pigment but also have green chlorophyll pigment; and the colour of the alga depends on the conditions of growth.

This genus has separate male and female individuals, and it also reproduces asexually. This is the first time I have seen the seaweed bearing reproductive or fruiting bodies. The small dark pimples or tubercles, on the slender much-branched yellow green fronds of the first three photographs, are the fertile cystocarps of the female seaweed. 

This type of seaweed is an economically important  agar producer. In South Australia during the Second World War large quantities of this abundantly-growing seaweed were harvested for use as a gelatine substitute in tinned meats. In the Sydney area alone, 300 tons of weed, equating to 60 tons of agar, were collected annually (Dickinson, 1963, p 138). At the present time it continues to be grown and harvested for commercial use in the food industry. 

I found the following sources useful in my attempts to identify and understand this type of seaweed.

SOURCE 1

A Popular History of British Seaweeds comprising their structure, fructification, specific characters, arrangement, and general distribution with notices of some of the Freshwater Algae, Rev. D. Landsborough, A.L.S., Third Edition, published in London, by Lovell Reeve, Henrietta Street, Covent Garden, 1857.

SOURCE 2

A  handbook of the British Seaweeds, Lily Newton, Ph.D., F.L.S., Professor of Botany, University College, Aberystwyth, published in London by The Trustees of the British Museum, British Museum (Natural History), Cromwell Road, S.E.7, 1931.

SOURCE 3

British Seaweeds, Carola I. Dickinson, The Kew Series, published in London by Eyre & Spottiswode, 1963.

SOURCE 4

Sea Shore of Britain and Northern Europe, Collins Pocket Guide, Peter Hayward, Tony Nelson-Smith & Chris Shields, published in London by HarperCollins, 1996, ISBN 0 00 219955 6.

SOURCE 5

algaeBASE

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