Test identifies potent toxin in Los Angeles fish die-off

Scientists continue to investigate the mass die-off of fish in Southern California last week.  The LA Times reported over the weekend that some early claims of no evidence of toxic exposure were in error.  

In fact, some of the million or so dead fish have tested positive for domoic acid, which is a naturally occurring toxin produced by algal blooms.  The Times quoted USC scientist, David Caron:  "It is possible that high levels of domoic acid in the sardines in King Harbor may have exacerbated physiological stress of the fish brought on by oxygen depletion of the water, or may have been a contributing explanation for them congregating in the harbor at very high abundances, but this has not been confirmed."  Domoic acid has caused other big die-offs, as the American College of Veterinary Pathologists and others have noted. 

Last week, I blogged about this mystery, wondering about the role of urban runoff over time.   The Times itself noted the possible connections to unusually heavy early winter rains and other environmental factors.   While domoic acid is natural and produced by algae, the amount of algae in ocean waters is influenced by a range of factors.  Some have suggested a connection with runoff pollution, which can be rich in nutrients, in increasing the incidence and seriousness of algal blooms.

The results of more tests are due later this week.  The exact causality here may never be perfectly established, but as scientists investigate this and similar situations the pollution connection deserves especially careful scrutiny.