Great Blooming Barrier Reef

Created by stuart under Calypso News on Saturday 25th of May 2013

Last Thursday on Thetford Reef, Veteran Diver Stuart Ross and underwater filmmaker Stuart Ireland witness spectacular red tide as it engulfs local Cairns reef. During the second dive, a dark shadow enveloped the reef, as the advancing bloom blocked out the sun. Red tide, or Trichodesmium is a natural occurrence on the Great Barrier Reef, and part of the normal cycle of the reef. Read on for some amazing facts about Trichodesmium!  If you would like to download any of these images please go to

Trichodesmium Red Tide on Great Barrier Reef

Trichodesmium Red Tide on Great Barrier Reef

Trichodesmium is a genus of filamentous cyanobacteria. It is not a red algae as commonly believed.



Trichodesmium forms blooms, which can be extensive on surface waters and led to its widespread recognition as red tide or sea sawdust in northern hemisphere.


'Red' Sea is named after this phenomenon

‘Red’ Sea is named after this phenomenon

The Red Sea gets most of its eponymous colouration from the corresponding pigment in Trichodesmium eryhtraeum.



Trichodesmium blooms are often confused as coral spawn.  The later is usually identifiable using ones nose (say no more) Underwater, coral spawn is also identifiable by it’s rising behavior, however in this still shot its quite difficult to tell the difference

Reef or Sea sawdust

Reef or Sea sawdust?

They are found in nutrient poor tropical and subtropical ocean waters (particularly around Australia and the red sea, where they were first described by Captain Cook)  Cook probably cursed it’s sudden appearance, as the blooms or slicks have the tendency to look like reefs. I know it’s scared me on more than one occasion while traveling to the reef at 30 kts!!


Habitat to many organisms, large and small

Habitat to many organisms, large and small

Colonies of Trichodesmium provide a pseudo benthic substrate (not attached to seafloor) for many small oceanic organisms including bacteria, diatoms, dinoflagellates, protozoa, and copepods (which are its primary predator); in this way, the genus can support complex micro environments. So presence of red tide is natural and found on healthy reefs.



Nitrogen fixer

Interesting Fact,  Trichodesmium is thought to fix nitrogen on such a scale that it accounts for almost half of the nitrogen-fixation within marine systems on a global scale.



Charles Darwin observed during his Beagle voyage

Charles Darwin on his famous voyage on the Beagle observes sea sawdust on a number of occassions.  Upon collecting a sample he made the following observations. “Some of the water placed in a glass was of a pale reddish tint; and, examined under a microscope, was seen to swarm with minute animalcula darting about, and often exploding. Their shape is oval, and contracted in the middle by a ring of vibrating curved ciliae. It was, however, very difficult to examine them with care, for almost the instant motion ceased, even while crossing the field of vision, their bodies burst. Sometimes both ends burst at once, sometimes only one, and a quantity of coarse, brownish, granular matter was ejected. The animal an instant before bursting expanded to half again its natural size; and the explosion took place about fifteen seconds after the rapid progressive motion had ceased: in a few cases it was preceded for a short interval by a rotatory movement on the longer axis. About two minutes after any number were isolated in a drop of water, they thus perished.”



Photographic Delight eeh?

Both Stuart and myself were amazed at the experience.  With over 6000 logged dives combined, neither one of us had witnessed this underwater before.

Special thanks goes out to TUSA dive and their great crew.

For further information on the reef while staying in Cairns, I highly recommend attending REEF TEACH

Camera rental Calypso reef Imagery Centre











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