Reference no: EM132797282

Harmful Algal Blooms and Domoic Acid

Read the overview and complete the activities that follow. 

In this case, you wil learn about the dangerous toxins that are produced by algal blooms and how they affect marine life and humans. In 2005, a ban on clamming was instituted along much of the Oregon coast due to an algal bloom of the phytoplankton Pseudo-nitzschia that produces domoic acid, a potent toxin that can be deadly to marine life and humans. Filter feeders accumulate high levels of this toxin and ingestion of the toxin can produce headache, dizziness, nausea, confusion, and potentially permanent loss of short-term memory. A different kind of shellfish illness, paralytic shellfish poisoning, results from ingesting saxitoxins, which are, like domoic acid, produced by certain species of algae. In this case, algae in the genus Alexandrium produce the toxin, which then accumulates in mussels, clams, scallops, oysters, crabs, and lobsters during periods of greater than usual algal growth. Ingestion of saxitoxin by humans can lead to numbness, paralysis, disorientation, and death due to respiratory failure. Neither domoic acid nor saxitoxin is affected by temperature, so cooking or freezing has no effect on the toxin. Shortly after the 2005 shellfish harvesting closure, the Oregon Harmful Algal Bloom Monitoring Project was initiated. The project monitors water at five locations along the Oregon coast, retrieving samples every week or two (depending on the site) and examining each sample for the presence of algal species that produce domoic acid or saxitoxin. When sudden blooms lead to high levels of harmful algae, specific harvesting controls can be instituted. In Oregon, beaches are closed to clamming when domoic acid levels reach 20 parts per million (ppm) in randomly selected clams. Projects like this operate throughout the United States to ensure the safety of harvested seafood. Officials try to keep harvest control measures as geographically limited and short-lived as possible. On June 21, 2006, due in part to ongoing water sampling by the Oregon Harmful Bloom Monitoring Project, the entire Oregon coast was opened to razor clamming for the first time in 4 years (although short stretches of beach were temporarily closed later in the summer). Continued monitoring of the filter feeders along the Oregon coast has eventually allowed clamming to reopen in certain areas. Algal blooms have been traced to runoff from farms that includes high levels of nitrogen and phosphorus.

1. Domoic acid is produced by Pseudo-nitzschia, a ______

• marine mammal
• fungus
• aquatic snail
• phytoplankton
• filter feeder

2. Domoic acid and a similar toxin, saxitoxin, are both heat-labile.

True

False

3. When levels of domoic acid reach 20 ppm in certain clams, Oregon officials

• stop people from harvesting clams from affected sites.
• tell people to snap freeze their clams before cooking them.
• tell people to cook their clams very well before eating them.
• stop people from swimming at the affected sites.
• stop people from drinking water from the affected area.

4. Algal blooms are frequently caused by high levels of ______ and ______ in runoff from nearby farms.

• phosphorous; sulfur
• nitrite; phosphorous
• nitrogen; phosphorous
• nitrogen; carbon
• sulfur; nitrogen