Monterey Bay Aquarium Research Institute
Marine Botany

Gonyaulax Toxicity

dino drawingdino drawingdino drawing

Exotic Toxic Beauty

Gonyaulax toxicity is due to its secretion of a potent neurotoxin called saxitoxin (STX). During the advent of red tides (a great growth of phytoplankton whose pigments cause the discoloration of water), secretion of saxitoxin is especially dangerous. Mussels filter feed on the contaminated water, and although mussels themselves are apparently unafffected by saxitoxin, mussel predators quickly develop the poison symptoms. The high concentration of saxitoxin can cause Paralytic Shellfish Poisoning (PSP), which is dangerous to both humans and marine animals as well. Because of their higher trophic level, these organisms are exposed to the most concentrated levels of STX. PSP symptoms in humans include dizziness, numbing of the lips and the neck, fatigue, difficulty breathing and ultimately possible respiratory paralysis. If artificial respiration is not performed, this paralysis can cause death.

From Poisoning to Chemical Warfare!

  • Saxitoxin is 1,000 times more toxic than the potent nerve gas sarin.
  • Saxitoxin's exotic and illustrious past includes being used by the CIA in the 1950's as suicide pills for its agents.
  • President Nixon ordered the painstakingly collected STX stock of the CIA to be destroyed in concordance with the United Nations Agreement on Biological Weapons.
  • STX is the only natural toxin that, together with ricin, is on the Schedule Chemical Warfare Agents list.
  • Saxitoxin has been reportedly used as a biological weapon.

What is saxitoxin's mechanism of action?

Saxitoxin is a potent neurotoxin that specifically and selectively binds the sodium channels in neural cells. Thus, it physically occludes the opening of the Na+ channel and prevents any sodium molecules from going in or out of the cell. Since neuronal transmittance of impulses and messages depends on the depolarization of the inside of the cell (a sudden and rapid influx of Na+ ions into the cell), action potentials are stopped, impairing a variety of bodily functions, including breathing.

drawing of binding mechanism

STX Binding Mechanism

Why does Gonyaulax secrete STX?

It is not known how or why Gonyaulax secretes this potent neurotoxin. However, several hypotheses have been proposed:

  • One speculation is that the toxin prevents other species of both plants and animals from occupying the same space as the toxic dinoflagellate. This mechanism creates a dinoflagellate niche in the upper level of the phytoplankton. Thus, the photosynthetic requirement of bright light is fulfilled.
  • Some recent studies suggest that STX is actually secreted by a symbiotic bacteria living in Gonyaulax. The bacteria's contribution to its host is providing this deadly mode of protection.

Human pollution is increasing the occurrence of red tides!

Recent studies have shown a correlation between human population growth and an increase in the occur r ence of red tides and PSP. Eutrophication (depletion of oxygen resulting from increased oceanic nutrient levels from pollution) has provided greater nutrient levels for dinoflagellate phytoplankton. The abundance of nitrogen, phosphorus, B12 vitamin and iron (dino feast), have literally skyrocketed the dino population.

| Index | Bioluminescence | Toxicity | Morphology |

| Taxonomy | Human Relevance | Ecology | Chemistry |

© 1999  Allison Arnold and Monica Draghici.     All rights reserved.

Last updated: Feb. 05, 2009