Adam Spencer, The Triplicate

Shellfish gathered from Del Norte County coasts this fall have been found to contain the highest level ever detected here of a dangerous toxin produced by red algal blooms, often called red tide.

The red algal blooms are so intense this year that they have been visible to the naked eye on many stretches of Del Norte coasts, including the images on this page of Crescent City's South Beach taken by an aerial photographer Monday.

The findings have prompted state health officials to extend and expand a quarantine on shellfish gathered here, and to warn consumers to avoid consuming the internal organs of crabs.

The meat of crabs is safe to eat, officials said.

Every year, starting in May, California state officials impose a quarantine on mussels gathered in all of California due to dangerous levels of biotoxins that accumulate in shellfish.

The toxins recently detected in Del Norte mussels, known as paralytic shellfish poisoning (PSP) toxins, can affect the central nervous system and have been linked to 542 reported illnesses and 39 deaths in California since 1927. Two particularly problematic years, 1933 and 1943, produced four deaths and 33 cases of PSP-related illnesses in Del Norte and Humboldt counties.

"Early symptoms include tingling of the lips and tongue, which may begin within minutes of eating toxic shellfish or may take an hour or two to develop. Symptoms may progress to tingling of fingers and toes and then loss of control of arms and legs, followed by difficulty in breathing," according to the California Department of Public Health's website. "Death from PSP has occurred in less than 30 minutes."

Typically the statewide quarantine is lifted Oct. 31, but this year, sampling of mussels from Humboldt and Del Norte counties prompted the CDPH to keep the quarantine in place for those two counties indefinitely.

The levels of PSP toxins detected in mussels collected from Wilson Creek beach on Oct. 29 were 6,000 micrograms per 100 grams of tissue, well above the federal alert level of 80 micrograms/100 g. The previous record for the highest concentration found in Del Norte was 370 micrograms/100 g in October 2009.

A Nov. 5 sample taken in Crescent City detected 1,763 micrograms/100 g.Del Norte samples were taken by officials from the Yurok Tribe Environmental Program.

On Tuesday, CDPH added sport-harvested clams and scallops to the list of Del Norte Countyshellfish that people should avoid, because toxin levels spiked significantly after the Oct. 31 quarantine extension. Cooking does not destroy the toxin, the CDPH said.

"The toxin levels detected in samples from Humboldt County so far are considerably lower (450 micrograms per 100 grams of tissue) and consistent with concentrations that are detected in most years," CDPH said in an email.

With dozens of recreational fishermen catching Dungeness crab since the season opened last weekend, consumers are being advised to avoid eating the crab's internal organs, also known as crab guts or "crab butter," where PSP toxins can accumulate.

CDPH officials said that there is no evidence that toxins move into the meat, as the department has tested crabs for toxins after cooking.

"By cleaning the crab thoroughly and discarding the internal organs, eating only the white meat, the risk is eliminated," according to the email from CDPH officials. "Cooking the crabs live is fine; however the crab should be cleaned after cooking (regardless of whether it is cooked live or dead)."

CDPH could not predict how long the quarantine will last.

"Often a change in environmental conditions (wind, rain and/or water temperature) will cause the toxin-producing phytoplankton to die off or be transported away from the coastline," the CDPH email said.

The CDPH plans to continue to track the toxins by collecting shellfish and phytoplankton samples, working with the California Department of Fish and Game, the Yurok Tribe, the Del Norte and Humboldt County Environmental Health departments, and a volunteer network of samplers.

Community members interested in becoming a volunteer sampler should leave a message on CDPH's toll-free "Shellfish Information Line" at (800) 553-4133. All training, materials for sampling and shipping, including shipping costs, is provided.

Reach Adam Spencer at .