If you were at the beach in San Diego this weekend, especially off La Jolla Shores, you might have seen streaks of green sea foam. Here’s a stunning photo of the foam off Scripps pier, taken by Eddie Kisfaludy from a small plane 1,500 feet above the ocean.
This foam is the harmless microscopic algae Tetraselmis spp. From the Southern California Coastal Ocean Observing System:
The harmless, green foam has returned yet another year to San Diego County beaches. Researchers at Scripps Institution of Oceanography have determined that the bright green color is caused by a bloom of phytoplankton, Tetraselmis spp. This green flagellate is roughly 10 micrometers in size, and has been found in concentrations as dense as 15 million cells per liter of seawater. The foam has become more prevalent this week, though it has been observed off and on since the first week of July. It’s patchy distribution makes it visible only at some beaches and the foam becomes more apparent in the afternoon when the wind and waves mix the surface waters. Tetraselmis has bloomed each summer since 2009 with blooms lasting from one week to several months. There are no documented health hazards with swimming or fishing in areas of Tetraselmis blooms.