Neurotoxin makes California crabs unsafe to eat

By Kim Smiley

California officials have delayed indefinitely both recreational and commercial fishing for Dungeness and Rock crab from the coast north of Santa Barbara all the way to the Oregon border because the crabs have been determined to be a threat to public safety.  Testing has shown that many of the crabs in this region contain potentially unsafe levels of domoic acid, a powerful neurotoxin, that can cause illness in humans if they consume the crabs. Domoic acid poisoning causes vomiting, diarrhea, cramping and can even lead to brain damage and death in severe cases.  Scientists are continuing to test crabs caught off the California coast and the hope is to open crabbing season if/when the crabs are found to be safe for consumption.

A Cause Map, a visual root cause analysis, can be built to help understand the causes that contribute to this issue.  The first step in building a Cause Map is to understand the impacts from the issue being considered.  Obviously this issue has the potential to impact public safety because the crabs have the potential to cause illness, although no cases of domoic acid poisoning in humans have been reported in this year. The economic impact to the fishing industry from the delay in the start of crabbing season is also very significant.  California’s crabbers typically gross about $60 million a year and many families depend on the money made during crab season to live on throughout the year.  This issue also impacts the environment because humans aren’t the only animals that can suffer from domoic acid poisoning and other creatures are continuing to eat the contaminated crabs.  Sea lions in particular have been affected by the neurotoxin and many have died.  Removing large predators has the potential to significantly impact the entire ecosystem.

The Cause Map itself is built by asking “why” questions and laying out the answers to intuitively show the cause-and-effect relationships. So why do the crabs have high levels of domoic acid in their bodies?  This year off the coast of California, warmer than typical ocean temperatures have led to an unusually large and long-lasting algae bloom created by Pseudo-nitzschia. Domoic acid is naturally produced by Pseudo-nitzschia and it can be concentrated into dangerous levels as it moves up the food chain.  Small fish and shellfish such as krill, anchovies and sardines consume the domoic acid along with the algae.  Crabs eat the smaller creatures that have been contaminated with domoic acid.  Crabs can eventually excrete the domoic acid, but the process is slow and takes enough time that the domoic acid can build up to high levels in the bodies of the crabs.  If bigger creatures such as humans and sea lions eat the contaminated crabs, they can be poisoned by the domoic acid that was initially produced by the algal bloom.  There is nothing that can make the contaminated crabs safe for consumption. Neither cooking nor cleaning can eliminate the risk of poisoning from the neurotoxin so the only safe option is to wait until the domoic acid returns to safe levels in the crabs.

To view an Outline that lists the impacted goals and see a high level Cause Map of this issue, click on “Download PDF” above.