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Experts declare clams safe as human food
By James Kirley
In an effort to safeguard the multi-million aquaculture industry, clams from the Indian River Lagoon are being regularly checked for a recently discovered natural toxin — and scientists say 18 months of tests have found the clams safe for human consumption.
Poisonous saxitoxin has caused a ban on eating puffer fish caught in five counties that border the lagoon: Martin, St. Lucie, Indian River, Brevard and Volusia.
A species of microscopic algae common in the lagoon and not previously known to be toxic has mysteriously begun to produce saxitoxin, scientists at the Florida Marine Research Institute in St. Petersburg report.
Clams feed by filtering microscopic algae and other marine life from the water.
"When we first heard of the puffer fish poisoning and we thought it might be some kind of toxin, we immediately started sampling clams that are sold for consumption," said Dave Heil of the Florida Department of Agriculture's Division of Aquaculture.
The department is working with the marine institute in St. Petersburg, which has been collecting puffer fish and several species of shellfish from the Indian River Lagoon.
Bill Arnold and Jan Landsberg, research scientists at the institute, said both wild and farm-raised hard clams have been tested — the term "hard clam" being a common name for the genus Merceneria that is harvested and eaten.
"We're closely monitoring hard clams because we know they're eaten by people," Arnold said. "(Saxitoxin) has been detected at very low levels, nowhere near the levels of public health concern — which are very conservative levels to protect public health."
Arnold said other species of clams — wild varieties, typically too small for people to eat — are concentrating the saxitoxin at higher levels. It is thought puffer fish might be absorbing the poison by eating these clams.
Arnold said examination of the stomachs of puffer fish found no clams of the types eaten by people.
More than two dozen human cases of potentially fatal saxitoxin poisoning from eating puffer fish have been reported since 2002.
The toxin is different from one found in Japanese puffer fish that can be made edible with the right preparation. Cleaning and cooking puffer fish can't render saxitoxin harmless.
Also, different species of clams feeding in the same waters will absorb different food — which may account for some types of clams accumulating saxitoxin at higher levels than other species.
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