Shellfish Biotoxins

Climate change is increasing the prevalence of harmful algal blooms worldwide 


A harmful algal bloom (HAB) is the accumulation of toxin producing algae in marine and fresh water sources that can negatively impact other organisms.  These blooms can be invisible to the eye or alter the color of the water to shades of green, brown, orange, or red.  HABS can be harmful to humans, marine animals, livestock, drinking water, agricultural and marine sources of food for humans and animals, and can have devastating impacts on the economy worldwide.

Increase in nutrients, temperature, ocean currents, and weather events contribute to the occurrence of HABs.  As a result, climate change has been thought to affect the frequency and severity of toxic blooms.  According to the National Oceanic and Atmospheric Administration (NOAA) HABS appear to be increasing along coastlines throughout the US and this is a cause of grave concern for those affected by the shellfish industry including consumers, harvesters and processors, researchers, and government agencies.

There are several algal sources of toxins that can accumulate in shellfish and consequently cause illness and even death in humans.  Some of these toxic algae can cause Paralytic Shellfish Poisoning (PSP), Amnesic Shellfish Poisoning (ASP) and Diarhhetic Shellfish Poisoning (DSP).  Scotia Rapid Testing Ltd. can provide an early warning to those impacted by HABS.

The PSP toxins (e.g. Saxitoxin) which are commonly known as Red Tide are produced by several species of dinoflagellates and cyanobacteria in marine and freshwater systems. The toxins attack the nervous system of humans who consume toxic shellfish and death may result from respiratory paralysis.

The PSP toxin acts within minutes. It is an acute, sometimes fatal form of food poisoning. The syndrome is typically caused by eating bivalve molluscan shellfish (e.g. mussels, clams, oysters, scallop, etc) that have become poisonous from ingesting certain marine dinoflagellates that contain the PSP toxins. Saxitoxin and its numerous analogues are responsible for PSP and are among the most potent natural poisons known. A fatal oral dose for humans is only a few milligrams. Saxitoxin blocks the sodium channel of nerve membranes and thereby inhibits neuronal transmissions. Symptoms of PSP usually begin within 15-90 minutes after ingesting toxic shellfish and most often consist of paresthesia and numbness of the tongue, lips, and fingertips. If the dose is sufficient, this may be followed by loss of muscular coordination and in advanced cases, ascending paralysis. Death may result from diaphragmatic paralysis and respiratory failure within 2-12 hours.

There has been a significant increase in PSP incidences worldwide in the past decades.

The ASP toxin, Domoic acid, is produced by Pseudo-nitzschia algae. It is a potent neurotoxin that causes stomach upset, disorientation and in severe cases, permanent loss of short term memory when ingested.

Global distribution of ASP:





The DSP toxins (e.g. Okadaic Acid) are produced by several marine dinoflagellates. Although non fatal, these toxins cause severe gastrointestinal upset and have one of the greatest impacts on human health and the aquaculture industry because of their frequent occurrence and widespread distribution.


Global distribution of DSP:



Latest News
No News.