Cultured Abalone and the Red Tide

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Warning, this is a biology report on farmed shellfish.

My chef friend, Kurt Grasing who owns Grasing's in Carmel, California asked his abalone supplier about food safety of abalone during these algae blooms. Below is the response.

"Periodically, there is an algae bloom off the coast of California. When is gets out of hand, filter feeding shellfish should not be consumed due to concentrations of toxins. 

Here is some background info on the situation with the algae bloom:

It is caused by a marine diatom in the genus Pseudonitzschia.  The diatom is often present in our waters during spring and summer, and the theory is that it only produces the toxin when it is stressed, which (theoretically) it is right now due to the El Nino which means there are less of the nutrients the diatom needs to grow.  The toxin is called domoic acid, and it causes amnesiac shellfish poisoning.  The toxin is not neutralized by cooking.  During our 23 years of farming abalone, there have been almost annual spikes of domoic acid.  The majority of those spikes have been minor, but this year's is the biggest since 2000 (another El Nino year).

The Shellfish Sanitation Department (CA State Dept. of Health Services) is very concerned about this bloom and is very actively monitoring the commercially grown shellfish produced in CA.  In terms of the risk associated with eating shellfish from the coast of California right now, filter feeding shellfish like oysters, mussels, clams and scallops grown in waters where the bloom is present are the biggest potential threat to human health. They filter out microalgae, like Pseudonitzschia, when they filter feed and the toxins become concentrated in their tissues, mainly the viscera (stomach, gonads, gills, etc) as opposed to the muscles.  Abalone are grazers and eat macro algae - seaweeds - which are not producers of toxins.  In past episodes, we have sent samples of our abalone to be analyzed, and they have come back with either "non-detect", or very low levels of toxins - below the criteria established for protecting human health.  Today, we are sending in more samples for analysis and we should have the results by the end of the week.

Because any toxin in the abalone would most likely be concentrated in the viscera, out of an abundance of caution we are recommending that our customers avoid preparations that include the stomach, gills, gonad, etc.  We believe that the foot muscle, which is the part of the abalone most commonly eaten, is safe to eat."