Noctiluca scintillans photgraphed at the surface of a tide pool | Goa
This is the tiny protist organism responsible for most instances of blue bioluminescence in sea water near the coasts. While the blooms are easily noticed by beachgoers at night, the individuals that cause it are not often seen. However, they are quite easily visible in the daytime if you search for them. The individual cells grow quite large when they are in a healthy bloom phase - almost the size of mustard seeds. The ones photographed here seemed to be a small set from a bloom spread across this seashore, every pool had some of them. Unfortunately, I couldn't notice anything at night, probably because the tide had diluted the bloom by then.
Canon 760D, Canon 100mm Macro USM at 1:1
Cropped for detail