Black dots on water surface

[stanleyc]

My daphnia culture has a bit of what looks like ground black pepper on the surface of the water. What are these?

 

[Azhael]

If the dots are about 1mm and slightly triangular, then they are ephippia (resistance eggs).

 

[Jennewt]

Yes, these are the "seed" form of the daphnia. In the future, the way to avoid this is to always harvest enough daphnia from the culture to keep their population under control. They form ephippia when their population density becomes too high.