Domoic Acid Poisoning – Oceans of Fun
Integrated Science
Name:
Date:
Pd.
Understanding Domoic Acid
Domoic acid toxicity was first discovered in the late 1980’s. Since this discovery, domoic acid
poisoning has been responsible for several unusual mortality events involving seabirds and marine
mammals and also has caused detrimental effects to humans who consume the toxin through shellfish
consumption. The impacts of domoic acid poisoning range from nausea and headaches to more severe
symptoms including neurological damage, seizures and even death.
Domoic acid is a naturally occurring biotoxin that does not present danger in small quantities. It
becomes dangerous when it is present in large quantities. While we are uncertain of the causes of the
influx of domoic acid in our oceans, scientists are researching possible causes for the increased levels.
Possible contributing factors include global climate change, eutrophication from fertilizers, agricultural
and urban runoff, aquaculture activity, coastal development and consequently the increased exposure to
waters and foods contaminated by domoic acid.
Domoic acid is often associated with “Red Tide”. Red Tide occurs when certain phytoplankton
species with reddish pigments bloom, resulting in water that appears to be colored red. Not every algae
bloom is harmful, but a small number of algae species produce neurotoxins, which present many
challenges for animals in the wild and the ecosystems where they occur.
Harmful Algae Blooms
Harmful algae blooms (HABs) can occur when conditions cause specific types of algae to grow
quickly forming visible patches of algae at the surface of the water. HABs can occur in all water sources
from lakes, rivers, estuaries and oceans. These harmful algae blooms can cause various problems for
humans, animals, plants and the environment. Algae blooms often occur in the spring, after winter storms
have caused nutrients from deeper water to rise to the surface, where sunlight is present, producing
favorable conditions for the growth of thousands of species of phytoplankton. Excessive algal growth can
deplete oxygen and block sunlight that is vital for the survival for many aquatic species. Some of these
algae blooms produce toxins that can affect the health of animals and humans.
A Harmful Toxin
Domoic acid is a neurotoxin produced by a few specific types of harmful algae blooms. The
diatom, Psuedonitzschia australis, is a phytoplankton that causes detrimental effects in the marine
environment. The alga is not detrimental to its primary consumers but becomes harmful when it is
consumed by another organism. Many shellfish and other small fish consume this alga when it is
blooming and then it accumulates in their bodies. The problem occurs when another member of the food
chain consumes this contaminated prey source. The toxin is then biomagnified through the food chain
resulting in health concerns for the animals or humans who have consumed the toxin.
Biomagnification is the increase in concentration of a pollutant from one link in a food chain to
another. Many of the most dangerous toxins settle to the seafloor and then are taken in by organisms that
live or feed on bottom sediments. Because these compounds aren't digested, they accumulate within the
animals that ingest them, and become more and more concentrated as they pass along the food chain. Top
predators will have the highest concentrations of the toxin because they have eaten the most prey that has
been contaminated.
Domoic Acid and Its Effects
Domoic acid poisoning affects the brain and causes lethargy, disorientation, seizures, and may
even result in death. This toxin attacks a portion of the brain called the hippocampus. The hippocampus is
part of the limbic system that is responsible for emotion, behavior and long-term memory. The role of the
hippocampus is to consolidate and organize new memories, connect emotions and senses to memories,
and aide in navigation and spatial orientation. Damage to this structure affects the ability to form new
memories, may cause problems with memory recall and impairs the sense of navigation with similar
effects in animals as seen in humans.
Left: Normal hippocampus Right: Shrunken hippocampus caused by domoic acid toxicity
In humans, domoic acid causes a syndrome known as Amnesic Shellfish Poisoning (ASP), which
is transferred through the consumption of contaminated shellfish. ASP results in nausea and vomiting
while extreme cases may result in neurological symptoms including short-term memory loss,
hallucinations, seizures and possible death. Most cases experience minor symptoms within 24 hours of
consumption.
It has been found that sea lions are the most common pinniped exposed to domoic acid poisoning
due to their habitat and location of foraging sites. Sea lions are impacted by domoic acid when they
consume contaminated prey sources. Sea lion pups are at risk as pregnant mothers pass the toxin onto
their developing fetuses and through nursing after giving birth. The results of domoic acid toxicity are
very detrimental to the infected animals.
Sea lions with domoic acid poisoning often beach themselves and undergo head bobbing,
disorientation and seizures. Local marine mammal rescue crews work to safely rescue and rehabilitate as
many animals as possible. In most cases, rescued animals are given an electrolyte solution and
medications to help control seizures. If the sick animal stabilizes, meaning the seizures stop, they begin
eating consistently, their physical abilities return and blood work is normal, the animal will be cleared for
release. The unfortunate truth is that though every effort is made to rehabilitate and release every rescued
animal, some will survive the toxicity and others will not win the fight against the poison.
We may not be able to predict the harmful algae blooms that cause domoic acid poisoning, but we
can certainly learn from the animals under the care of marine mammal rescue and rehab programs such as
those at the Marine Mammal Center in Sausalito, CA and the Pacific Marine Mammal Center located in
Laguna Beach, CA. The efforts of these dedicated staff members help to successfully release animals into
the wild and help us learn not only about the effects of the domoic acid toxicity in marine mammals, but
also the impacts it can have on humans.
Marine mammals are ambassadors for their species offering us great educational value. Through
animal tagging and tracking, research, and environmental impact studies, we are able to catalogue our
findings to gain a better understanding of the world we live in and the interconnections of ecosystems.
Scientists are able to extrapolate our findings and compare what we learn from animals to better
understand people. These efforts are all completed in hope of building environmental stewardship and a
great appreciation for animals and the environment.