The red tide that has lit San Diego for several weeks is ending in a microscopic bloodbath. The above photo was taken by Linsey Sala, the manager of the Pelagic Invertebrates Collection at Scripps Institution of Oceanography. She writes:

This image was taken from a collection at the SIO pier this [Friday] morning with a 0.120mm net. It illustrates a heterotrophic dinoflagellate (Noctiluca, nearly transparent disks) feasting on the autotrophic red tide dinoflagellate (Lingulodinium polyedrum, orange-red cells).

Noctiluca is a dinoflagellate like Lingulodinium, but it can’t photosynthesize. Instead, it makes a living vacuuming up other single-celled organisms. Some Noctiluca are bioluminescent, but the species here in California is not. According to Dr. Peter Franks: