Clam Research Sheds New Light On Red Tide

"I was shocked to hear that the paper was so popular. It's had more than 60,000 downloads since November, and it's still going," Connell said with enthusiasm. "I'm not sure what made it so popular, but is does have a very broad appeal."

Connell's report, Sodium channel mutation leads to saxitoxin resistance in clams increases risk of PSP, was the culmination of more than eight years of intensive research by an international team of scientists aimed at achieving a better understanding of a notorious and potentially deadly compound known at saxitoxin. Saxitoxin is the primary culprit in cases of Paralytic Shellfish Poisoning, or PSP, the always dangerous, sometimes-deadly consequence of the coastal phenomenon known as red tide.

Filter feeders like clams accumulate saxitoxin in their tissues as they dine on the algae that carry the poison, passing along a concentrated dose to their mammalian predators. The first research to take a comprehensive look at the affects of saxitoxin on clams, Connell and her team, including retired UMaine researcher Betty Twarog, found that the mollusks suffer many of the same symptoms as human PSP victims.

Well, at least some of them do.

Connell discovered is that not all clams are created equal when it come to fighting off the affects of PSP, and has begun to unravel a microscopic mystery that speaks to the very nature of the nervous system itself.

Thanks to a mutation in their genetic code, red tide resistant clams were able to survive and reproduce despite the presence of saxitoxin, eventually becoming the dominant strain in clam populations that are frequently exposed to red tide.

In fact, Connell and her team of specialists found that the mutant clams were more than 1000 time more resistant to the affects of red tide than their unmutated brethren, a surprising discovery that has significant implications in both clam management and medical research.

Because of its power over the nerve impulse, saxitoxin has been used extensively by medical researchers to study the function of the nervous system and its associated diseases. Connell's comprehensive approach opens new doors to future research by connecting sodium channel function to specific control sites in the organism's DNA.

The discovery that some clam populations were genetically much more resistant to red tide poisoning than others could open up new directions for managing the soft-shell clam fishery.

"The ability of individual populations to resist the affects of saxitoxin could be used to determine how long clam beds would have to remain closed after a red tide event," said Connell. "Genetically resistant clams are able to continue feeding much longer, accumulating more toxins in their tissues which take longer to purge. Knowledge of the genetic susceptibility of clams to red tide could help managers make better decisions on what clams to use in seeding programs, how long to close clam beds, and other issues."

The project's implications don't stop there. Connell's discoveries have been of interest to marine ecologists, public health officials, bioengineers, fishermen: the list goes on and on. The significance of the research in such a broad range of disciplines certainly speaks to its popularity in Nature.