Domoic Acid Poisoning
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.
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.