Gracilaria verrucosa seaweed at Studland

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Studland Bay seaweed: Gracilaria verrucosa seaweed with reproductive cystocarps on the fronds, on the strandline at Studland Bay, Dorset, UK, on the Jurassic Coast (1) 

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. 

Studland seaweed close-up: Gracilaria verrucosa seaweed - close-up showing reproductive cystocarps on the fronds, from the strandline at Studland Bay, Dorset, UK, on the Jurassic Coast (2)

Cystocarps on seaweed at Studland: Gracilaria verrucosa seaweed - close-up showing reproductive cystocarps on the fronds, from the strandline at Studland Bay, Dorset, UK, on the Jurassic Coast (3)

Common British seaweeds: Gracilaria verrucosa seaweed with no reproductive cystocarps on the fronds, washed up on the strandline at Studland Bay, Dorset, UK, on the Jurassic Coast (4)

Green and pink filamentous seaweed at Studland: Gracilaria verrucosa seaweed with no reproductive cystocarps on the fronds, washed up on the strandline at Studland Bay, Dorset, UK, on the Jurassic Coast (5)

Yellow-green seaweed with many branches: Gracilaria verrucosa seaweed close-up without reproductive cystocarps on the fronds, washed up on the strandline at Studland Bay, Dorset, UK, on the Jurassic Coast (6)

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

SOURCE 1

19th Century seaweed picture: Illustration of Gracilaria confervoides seaweed (shown on far right of the page) from the book "Popular History of British Seaweeds" by the Rev. Landsborough published in1857 (7)

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

Botanical drawing of seaweed Gracillaria confervoides: Illustration of Gracilaria confervoides (verrucosa) from the book "Handbook of the British Seaweeds" by Lily Newton published in 1931 (8)

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

COPYRIGHT JESSICA WINDER 2011

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3 Replies to “Gracilaria verrucosa seaweed at Studland”

  1. Your readers might be interested to know that the Latin adjective verrucosa means ‘warty’, presumably a reference to the dark protuberances that your first two close-up photographs show so well.

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