Mysterious green foam returns to La Jolla beaches


A harmless, iridescent green foam is once again washing ashore on San Diego County beaches.

Researchers at Scripps Institution of Oceanography in La Jolla have determined that the bright green color is caused by a bloom of phytoplankton,

Tetraselmis spp

  1. 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.

On July 23, green particulate matter (

Tetraselmis sp

.) was found floating in the water in La Jolla. The foam grew more prevalent last 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, though it 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. Whereas the bloom looks rather ominous, it is harmless in nature. Conditions that may attribute to a bloom such as this would be temperature, surf conditions, or light. Which are the contributing factors exactly, and why? It is a question researchers at Scripps Institution of Oceanography are working to discover.

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--Staff Reports