The phenomenon you experienced was caused by something called Noctiluca,
after they were deposited on the beach. The March 2004 issue of the
Tasmanian produced "TAS-REGIONS" has more on these dinoflagellate.
"Noctiluca is an unusually large dinoflagellate, visible to the naked
eye (about 0.5 mm diameter), which feeds on phytoplankton, zooplankton
and fish eggs, capturing them by means of a tiny tentacle. This can be
seen clearly when looking at a live organism down a microscope. When
first described the organism was mistakenly thought to be a tiny
jellyfish or fish egg but they are now known to be unicellular algae."
Like fireflies, and indeed the word Noctiluca turns out to be Latin for
"night light," these "creatures" exhibit bioluminescence. The Biological
Sciences, University of California, Santa Barbara, website has a whole
area, "The Bioluminescence Web Page", that "illuminates" this subject.
"Bioluminescence is simply light produced by a chemical reaction which
originates in an organism."
A subpage of the above site explains the cause of what you saw.
"... the sand will light up sometimes because tiny organisms have been
washed ashore by the waves. When I have seen this phenomenon, it is
mainly in your footprints, but it can also happen in a ring around
where you step. ... The ring of light, though, seems to happen as you
compress the sand, and the disturbance stimulates them. In my experience
a footprint in the sand raises the sand around it and 'dries it out' a
The North Carolina "Free Press" links the glow to the Noctiluca.
"The creature responsible for this bioluminescence is a tiny, single-
celled organism called Noctiluca. Noctiluca ... belongs to a group of
microscopic plants known as dinoflagellates. This group is unique in
having characteristics of both plants and animals.
Light is produced by Noctiluca when the organism is disturbed or
agitated. So, it's no wonder that the breaking waves are bluish-green.
But, what about footprints glowing in the wet sand? The waves coming
on shore deposit Noctiluca on the sand. Our walking disturbs the
Noctiluca and they flash their intense greenish light."
If you need any clarification, please feel free to ask.
Google search on: bioluminescence sand footprints
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