|MadSci Network: Earth Sciences|
I can't say I'm an expert on that particular lagoon, but the phenomenon of phosphoresence (actually the correct term is "bioluminescence") is quite a common one. The picture to the right is an extreme example (the picture is not enhanced) from "Bioluminescent Bay" in Puerto Rico so it does happen in other places. Quite a few people will have experience with seeing the wake of a boat or waves crashing on a beach "glow" when it is dark out. This is due to planktonic creatures that bioluminesce when disturbed. Many species of dinoflagellates (a type of motile phytoplankton) do this.
Phosphorous (to the best of my knowledge) is only "fluorescent" - that is it must be excited by a wavelength of light to produce light of its own at another wavelength. This is why your shirt might glow with "dots" (from the phosphate in the detergent) under a blacklight. However, you can say phosphorous might be somewhat related because the phytoplankton that are likely causing the glowing may be growing in higher numbers in the bay because of the nutrients.
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