The luminescence of the sea is caused by certain organisms that are sometimes present in
the water in large quantities, often due to similar conditions to those that cause discoloration of
seawater by plankton bloom.
The luminescence itself is produced in two ways:
- By the luminescent organisms
themselves, such as the (single-cell) Noctiluca, that are
around 1 mm in diameter and the Pyrosoma, that are many centimetres long, and
- Indirectly because the
luminescent organisms use for the luminescence colonies of
luminescent bacteria, that are accumulated at certain points in their body.
It is thought possible that sea waves in a field of these organisms take on a smoother surface
as a result of an oily excretion from these organisms.
The luminescence may sometimes take on certain specific forms. For example the name
'milk sea' from the phenomenon where the sea spreads an equal light over a great area, that
often contrasts considerably with the darker air above it. Milk sea is apparently only or virtually
only observed in certain parts of the Indian Ocean and the Indonesian seas, e.g. east of Cape
Guardafui and south of Java. Especially in the months of July, August and September, milk
sea is observed there a lot.
Another phenomenon is that where the luminescent phenomenon looks like exploding bubbles
or spots rapidly increasing in size. This phenomenon is chiefly limited to the Indian Ocean and
especially the Arabian Sea.