Posted by: Rob Viens | March 31, 2012

It’s Not Easy Being Blue-Green

Survey work done, the last day of March found the Beagle heading towards Rio.  Darwin’s only comment today:

“A fine rattling breeze.” (Mar 31)

A simple statement, but I sort of like the poetry of it – not just a wind, but a “fine rattling breeze” (there I got to say it again). I wonder if the rattling comes from the sound of he rigging?

The last week or so has shown Darwin’s interest in the “small” details of the ocean’s surface. He seems to have a soft spot for the “little critters” on land, too.  Before leaving the ship for a few months, Darwin describes a couple more interesting ocean floaters – two species of cyanobacteria. (Cyanobacteria are a type of bacteria that are also known as blue-green algae.  Yes – algae is actually a type of “bacteria”.)

“A few days afterwards, when not far distant from the Abrolhos Islets, my attention was called to a reddish-brown appearance in the sea. The whole surface of the water, as it appeared under a weak lens, seemed as if covered by chopped bits of hay, with their ends jagged. These are minute cylindrical confervæ, in bundles or rafts of from twenty to sixty in each. Mr. Berkeley informs me that they are the same species (Trichodesmium erythræum) with that found over large spaces in the Red Sea, and whence its name of Red Sea is derived. Their numbers must be infinite: the ship passed through several bands of them, one of which was about ten yards wide, and, judging from the mud-like colour of the water, at least two and a half miles long.” (Voyage of the Beagle)

Trichodesium magnified 1000x (from Purdue Cyanobacterial Image Gallery)

This type of algal blooms is quite common in warm waters around the world, and it has been described by other ocean explorers throughout history:

“In almost every long voyage some account is given of these confervæ. They appear especially common in the sea near Australia; and off Cape Leeuwin I found an allied, but smaller and apparently different species. Captain Cook, in his third voyage, remarks, that the sailors gave to this appearance the name of sea-sawdust.” (Voyage of the Beagle)

Image of a “bloom” of Trichodesium (From Oregon State University)

See a related article on Angel White’s research on Trichodesium from the Oregon State University.

Trichodesium is a type of cyanobacteria that is significant because of the fact that it “fixes” nitrogen in the world’s oceans.  Nitrogen is an essential element for living things, however, most forms of life cannot access the nitrogen (in the form N2) that makes up over 75% of the Earth’s atmosphere. So most living things (including humans) are dependant on those special few species (a few select types of bacteria) that have the ability to convert atmospheric nitrogen into a form that we can process.  These organisms are called “nitrogen fixers”. Since all life in the ocean requires usable nitrogen, all life in the ocean depends on well-being of these microbes. Darwin is right to be interested in the “little things” – sometimes they are the most important part of the picture.

It is also worth noting that all agriculture until the 20th century was dependant on these nitrogen fixers in order to fertilize the soil we grow our crops on.  However, in 1909 a German scientist by the name of Fritz Haber figured out how to artificially fix nitrogen from the atmosphere, and today humans fix as much (or more) nitrogen the sum total of all natural nitrogen fixers. (Sadly, Haber was also instrumental in the business of chemical warfare during WWI.)

In his Zoological Notebook, Darwin also describes another white-colored cyanobacteria that also grows into long filaments – Oscillatoria erythraea. (Since Darwin’s species names are sometimes not accurate by current classification systems, I have to wonder if he is describing the same cyanobacteria in two different sources.  For the purpose of this post, I will assume they are different.)

Oscillaotia sp. images (from Purdue Cyanobacterial Image Gallery)

Darwin writes:

“My attention was called by Mr Chaffers observing that the sea was in places discoloured…it was owing to the presence of numberless minute whitish particles: These when examined under a lens whose focal distance was under above 1/10 of inch appeared like bits of chopped rag, the ligneous fibres of which projected beyond the end.” (Zoological Notebook) [FYI – Edward Chaffers was the Master on the Beagle.]


“These particles seen under a higher power consisted of about 20 fibrils adhering side by side & forming either a flat or a nearly cylindrical bit of mat.— These cylin fibrils or stalks were in length from .02 to .03 of inch; in diameter 1/2000: extremities round, rather broarder, transparent; internally a tube containing concentric layer of greenish brown granules. Hence appearing jointed: these layers are close to numerous. The external tube was marked by fine circular rings.” (Zoological Notebook)

Oscillaotia have the interesting characteristic that they reproduce by “breaking” – each individual piece will grow into a new filament.

Time for Darwin to go to sleep, but not for long – April Fools’ Day is coming… (RJV)


  1. Oh my… Charles was a prankster?

    • Probably fair to say that he was more of a prankee 🙂

  2. […] If you recall from a couple of days ago, the moorlands are one of the four main biogeographic regions of Tierra del Fuego. They tend to dominate the southwestern coast, growing in areas that have high rainfall (coming in off the Pacific). In these regions, the high winds, lower temperatures, and poorly drained soils make it more difficult of the Southern beech to take hold, so the water-loving “peat moss” quickly takes over. Tierra del Fuego is actually just the southern margin of these Magellanic moorlands – they extend all they up to 42°S latitude. (By the way – Confervae are a type of blue-green algae. For more info see It’s not Easy Being Blue-Green.) […]

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