Everyone knows that our waters have a tendency to develop bioluminescence, especially in the spring and fall. But what is it and why isn't it always present?

The bioluminescence is caused by a group of organisms called dinoflagellates. They are unicellular members of the microalge. The dinoflagellates are widely distributed in fresh, estuarine and marine waters and not all are bioluminescent.. They have two flagella; one is longitudinal and the other is wrapped around the centre. The longitudinal flagellum pushes water away and the transverse flagellum causes rotation and forward movement. For this reason they earned the name dinoflagellate which translates from Latin to "terrible spinner".

So why don't they luminesce all the time? Well, in the summer, the water column becomes layered and lighter, warmer water sits on top of denser colder water. Of course you know this, it's why sometimes you can be sitting in the middle of Howe Sound in what you know to be 300' of water yet your depth sounder throws a reading of 10' back at you (you of course rush to check your charts in a panic). This thermocline blocks the denser colder water from mixing with the surface waters. So? Well,it's that cold water that contains all the good stuff that plankton need. Stuff like nitrogen, phosphorus, copper, manganese, etc. In the spring the sun starts warming things up and helps the phytoplankton get going on photosynthesis and blooms can happen. As the water warms up, that thermocline starts to form and get larger. It blocks all the good stuff from getting to the surface so the plankton start to run out of food and begin to die off. They also get munched on by zooplankton populations that get a kick start by the phytoplankton. The whole things usually comes to a crashing halt (well, maybe not quite that abrupt) by mid summer. There aren't strong winds to turn the water over and that thermocline sets up residence. It isn't until fall winds return and start kicking up a bit of turbulence that the thermocline starts to break down and those nutrients become available again. At that time you can see another bloom.

And for interest sake, dinoflagellates are also responsible for many of the red tides that threaten our coasts. "Terrible Spinners indeed! "

Want more information? Check out the Dinoflagellate site at the University of Calgary

Last growth spurt on February 12, 2008