Phosphorescence Question

All Questions & Answers

In the Log of Feb 2, 2005, Alex posed the question

The sea is flat greyish blue and it looks diamond clear and there don’t seem to be any little organisms visible – and no phosphorescence at night. What are the necessary conditions for phosphorescence? From my experience, there seem to be at least 2 types – one caused by algal blooms on the surface and one by submerged organisms which spectacularly light up all sorts of odd places like the toilet bowl. Is it as simple as no organisms, no phosphorescence?

Below is the response that he received from Jude Quinn

What causes phosphorescence in the water?

Microscopic single celled (unicellular) algae called Dinoflagellates cause phosphorescence. These are present throughout the ocean, and emit light when they are mechanically disturbed, for example by a boat paddle, the arm of a swimmer or wave action. This leads to a chemical reaction within the organism, resulting in light production.

Dinoflagellates breed all year round, however, there are a number of factors that promote growth and reproduction, these are: light, water quality, temperature, availability of nutrients, and depth or tidal exposure.

 As dinoflagellates depend on photosynthesis to get their energy for growth, light is a major factor in their survival. The intensity of phosphorescence by photosynthetic dinoflagellates is strongly influenced by the intensity of sunlight the previous day, ie. the brighter the sunlight, the brighter the flash.

If the preceding few days are sunny, and the ocean is calm so that the dinoflagellates are not disturbed, this can result in a build up of phosphorescent ‘potential’. This build up when released can look like fireworks in the water.

The other thing that can contribute to such a display could be a concentration of nutrients in the water, most commonly caused by runoff from pollutants, such as sewage. This results in a build up of dinoflagellates.

 Kind regards


Jude Quinn