The Why Files The Why Files --

Tonic toxins

Red tide at night, shellfisher take flight
A red tide of toxic algae is moving south along the New England coast. As the poison accumulates inside clams, oysters, mussels and scallops, shellfishers are leaving the water, Ocean waves crest in orange color as small boat floatsand shellfisheaters are growing leery of those clams on the half-shell.

A harmful algal bloom heads toward shore. Hope someone warns that boat.... Photo:NOAA

The algae, Alexandrium fundyense, is a single-celled, cold-water plant that makes a toxin called saxitoxin. Experts say a cold spring hastened its unusual movement south from the Gulf of Maine, and the harmful algae is already widespread along the Massachusetts coast.

Shellfish can concentrate pollutants and natural toxins while filtering nutrients from the water. Eating saxitoxin can cause paralytic shellfish poisoning, with symptoms that range from annoying -- tingling lips -- to deadly -- respiratory failure.

Shellfish are immune to saxitoxin. The poison does not accumulate in fish, or in crabs or lobsters, which are not filter-feeders. Unlike two toxic algaes found further south, saxitoxin does not become an airborne poison.

Map of locations of sampling for bacteria cells
Alexandrium fundyense cell concentrations in the Gulf of Maine, in cells per liter of seawater. Dots show sampling locations. The bottom map shows counts taken May 17-18, in a survey around Cape Ann. Cell counts in Massachusetts Bay and just north of it doubled in a few days. Map: Woods Hole Oceanographic Institution

Red tide in morning, shellfisher take warning
What we call the red tides are known to scientists under the dreary moniker, harmful algal blooms. HABs "occur in virtually all oceans, in virtually all climates, Two men stand over batch of harvested oystersand they are all different organisms," says Daniel Baden, a professor of marine science at the University of North Carolina at Wilmington. "You have specific organisms that develop to bloom proportions, in specific geographic areas, each produces a different kind of toxin, which confers different characteristics."

Scientists examine freshly harvested oysters. In the lab, they will check if these oysters carry toxin from a harmful algal. Photo: Stephen Ausmus, USDA

HABs aren't only a salt-water problem. New research indicates that as artificial fertilizer continues to gather, freshwater lakes could breed their own toxic soups.

The root of the problem is the biological toxin -- a molecule that attaches to a specific structure, called a receptor, on cells. The specific effect on the target organism depends on the function of the receptor. "Each marine toxin I work with has a specific receptor site that deals with some essential cell function," says Baden. "And when they interact, that causes aberrant cell behavior, and that causes the lethal action."

Two cells stained in yellow and redThe smaller cell (about 35 microns in diameter) is probably Alexandrium fundyense, from a bloom near Casco Bay, Maine in 1998. The red color comes from a stain used to identify the organism. Image: Kristin Gribble, © Woods Hole Oceanographic Institution

Toxins are widespread in biology. Microbes use them for offense and defense. Dangerous bacteria like Staphylococcus aureus use toxins to injure or kill their hosts -- us. Spiders and snakes use toxins in venom to immobilize or kill prey before dinner. Plants make toxins to poison animals that would otherwise devour them. And people have used biological toxins as weapons since ancient times.

But because toxins target individual biological structures, they also help unravel the signaling systems that underlie biological interactions, and that makes them first-class research tools.

Our toxin tour starts with the powerhouse poison: botulinum toxin.


Megan Anderson, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David Tenenbaum, feature writer; Amy Toburen, content development executive

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