Researchers: Warmer oceans threaten clam digging

Spring has sprung, and with it come the seasonal activities we know and love: gardening, outdoor walks, picnics at the park and, for plenty of Pacific Northwest residents, clam digging. However, researchers have identified a big factor that may heighten the risks of this popular activity.

After analyzing two decades of climate data from the Oregon coastal area, researchers have found that in years with higher ocean temperatures, the presence of domoic acid is higher in Pacific razor clams. Domoic acid is a neurotoxin produced by algae. When consumed by humans, it can result in amnesic shellfish poisoning (ASP), a potentially deadly illness that causes diarrhea, seizures, numbness and short-term memory loss.

The researchers found that the five years with the highest ocean temperatures were also the five years with the highest detected levels of domoic acid.

“The biggest takeaway is that the ocean temperatures are changing,” said Matthew Hunter, researcher at the Oregon Department of Fish and Wildlife, in an article. “That has the potential for more frequent and more extreme harmful algal blooms that have significant implications for not only fisheries but also natural resources and human health.”

Clam digging aficionados lamented as domoic acid forced the closure of popular beaches this winter, including Seattle’s Long Beach at Twin Harbors State Park. However, after samples in the area were tested at under 20 parts per million (ppm) for domoic acid, park officials began opening some beaches. The safety threshold designated by the United States Food and Drug Administration is 20 ppm.

Similar restrictions were lifted in New England, as well.

What exactly causes domoic acid to contaminate shellfish?

The toxin is produced by a microscopic algae called Pseudo-nitzschia. Most shellfish are filter feeders, who will ingest the toxin when an algae bloom is produced. Warmer temperatures can create favorable conditions for algae blooms, thereby increasing the possibility for shellfish to be contaminated. While the toxin is not harmful to shellfish themselves, it is unsafe for human consumption, even when cooked. Because most commercially-sold shellfish is privately farmed, generally shellfish is safe to order at a restaurant.

For more information on shellfish poisoning, click here.

Neogen offers rapid tests to screen for domoic acid. For more information, click here.

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