Piecing together a Most Perplexing Marine Die-off in Sonoma

Cyst forms of a dinoflagellate that is believed to have been the dominant alga during a mass die-off of marine invertebrates in Sonoma County last year. Image: C. O'Kelly, Friday Harbor Labs




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October 12, 2012

October 12, 2012

Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-740-4319

Last year, masses of marine invertebrates washed up dead in Sonoma County during an intense algal bloom. It is presumed that an algal toxin must have been to blame; however, to date, no toxin, not even a candidate, has been found.

In a search for answers, Sea Grant is funding researchers to DNA fingerprint the two strains (morphologies) of algae that were dominant during the 2011 bloom. This approach will let them validate or invalidate two scenarios key to solving the harmful bloom puzzle.

One is that the alga is a new species, closely related to but distinct from others in a dinoflagellate assemblage known in science circles as “the Gonyaulax spinifera species complex.” In supporting evidence for this line of thought, the Sonoma bloom was incredibly luminescent, glowing a netherworldly blue at night (see photo).

2011 Sonoma bloom glowed an eerie blue.
Credit: Sonoma State University

“This is highly unusual,” says Charles O’Kelly of the University of Washington's Friday Harbor Laboratories. “No other Gonyaulax is this brightly blue.”

The alternate theory is that the algae are identical to those common off Washington and elsewhere in northwestern North America and western Europe, and that local conditions somehow elicited toxin production, where it has never before been documented.

In a recent update on their progress thus far, O’Kelly and co-investigator Karina Nielsen of Sonoma State University report some promising early sucess: they have been able to germinate and culture a strain of the dinoflagellate in question.

The images (below) show the transformation of the dinoflagellate from its seed-like cyst form to its free-swimming life stage. The middle image shows the algae shedding its outer shell.

Dinoflagellates are unicellular photosynthetic algae with a complex life cycle that includes a dormant seed-like cyst form. The cyst will rest on the seafloor until conditions are favorable to its free-swimming form. You can barely see in the far right image its thin, tail-like structure, which it whirls for propulsion. Credit: C. O’Kelly


The hope is that scientists can keep these algae alive and multiplying, until there are enough cells to carry out the DNA sequencing work and begin screening for toxins, including new ones that might have been off the radar of earlier tests that turned up nothing.

All lines of evidence suggest that the die-offs were caused by the harmful algal bloom,” Nielsen says. “But we don't have a toxin or a mechanism for the mortalities.

Dinoflagellates in the G. spinifera complex are known to produce compounds called yassotoxins. But these are supposedly of low toxicity, and more to the point, only trace amounts were detected in tissues of afflicted animals. Moreover, no other toxins were detected at levels high enough to explain the die-offs.

This fact intitially led some to speculate that hypoxia (low-oxygen conditions) might have caused the invertebrate deaths, but this was quickly rejected since many of the sickened animals were found along wave-pounded, highly oxygenated stretches of coastline.

Dead sea stars washed up on a beach near Bodega Bay during the 2011 dinoflagellate
bloom. Credit: M. Robart



Yet another unresolved tantalizing detail of the die-off was the oddly selective wipe-out of some but not other marine invertebrates. Notably, bat stars were observed scavenging on marine invertebrate carcasses without any apparent bodily harm.


The bat star may prove an interesting litmus test for any toxin the scientists do isolate later, as the “right” toxin should be lethal to animals as diverse as abalone, urchins, mussels and sea stars but harmless to the steely bat star.

“Algae are doing a whole lot more out there than we think they are,” O’Kelly says. “Just when we think we have a handle on things, along comes an alga that stumps us all.”

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Read More about the Marine Mortality Event in Sonoma in 2011:

Algal Bloom During Marine Mortality Event in Northern California: A Connection? (The Central and Northern California Ocean Observing System)

Toxic Bloom Mystery to Be Answered by Grad Student's Seawater Samples? (Sonoma State University)

Abalone Die-Off Plagues Coast (Press Democrat)