Black Jellyfish
Chrysaora achlyos
After only being spotted around southern California 5 or 6 times in the last 80 years, last summer swarms of 20-30 black jellyfish were bothering San Diego swimmers. Then later that same summer north of San Diego, 10s or thousands of black jellies were reported at the Orange County beaches, a phenomenon that's never been heard of in the history or the California coast. It was thought that they were traveling with and feeding on the red tide.
Black jellies sting as do all Cnidarians. And though one probably won't need a hospital visit, the sting can be quite painful and raise large welts on the skin. These dark burgundy to thick purplish hydrozoa can grow their bell areas to 3' with tentacles ranging from 12' to 25'. Their adult form and size only lasts until the eggs are dispersed and then they die off, leaving a fresh batch for next year!