Five of the last seven years have seen blooms of Pseudo-nitchia, a species of phytoplankton that produces domoic acid (DA), a deadly neuro-toxin, in the waters off California. Harmful algal blooms (HAB’s) occur when conditions – namely sunlight and nutrients – are favorable for the growth of phytoplankton. The only recorded human case of DA poisoning was in 1987, when shellfish from Prince Edward Island were consumed and three elderly people died, and over a hundred developed various toxic symptoms, the most serious being permanent loss of short term memory. Since then continual testing of mussels and other shellfish has been instated, preventing harvesting during HAB’s. No further cases of human DA poisoning are known.
DA gets passed to marine mammals and Birds from small fish such as anchovies, herring and sardines, as well as shellfish like mussels and clams, that feed on Pseudo-nitchia, building concentrated amounts of DA in their systems. Michele Hunter, Director of the Pacific Marine Mammal Center in Laguna Canyon, has seen the effects mainly in pregnant sea lions that are eating higher than normal amounts of fish. A recent study by the Center for Coastal Environmental Health and Biomolecular Research linked epileptic seizures and behavioral abnormalities in sea lions to exposure to DA as a fetus. Hunter’s center has taken in 16 sea lions with DA poisoning since April 19. One has been released, two are still under care, and the other 13 have died.
There are economic impacts as well – fishermen are barred from harvesting mussels, clams, and various fish during HAB’s.
HAB’s often happen in spring due to increasing daylight and upwelling of water rich in nutrients like phosphate, nitrate, carbon dioxide, carbonate and ammonium that are the building blocks of all life. When these conditions combine in sufficient amounts, Pseudo-nitchia and other phytoplankton in the water can grow wildly. There was a bloom in 2003 followed by massive blooms in 2006 and 2007, a smaller bloom in 2008 and a significant one again this year. Although this is an alarming pattern – five blooms in seven years – there is little or no data before 2003 which could put this pattern in a larger context. In 2002 the Pacific marine Mammal Center had 123 sea lion deaths due to DA, over three times the amount during the massive 2007 bloom.
HAB’s are not fully understood and causal hypotheses abound, one of which targets human generated runoff. In his 2006 Pulitzer Prize winning series for the LA Times entitled “Altered Oceans,” Kenneth Weiss asserts, “Industrial society is overdosing the oceans with basic nutrients — the nitrogen, carbon, iron and phosphorous compounds that curl out of smokestacks and tailpipes, wash into the sea from fertilized lawns and cropland, seep out of septic tanks and gush from sewer pipes.”
Scientists are working feverishly to both prove and disprove this. A 2005 Stanford study showed phytoplankton blooms in the Sea of Cortez, Mexico, directly following fertilization and irrigation of fields, in the Yaqui Valley, over five years.
Dave Caron, a professor of microbial ecology at USC and phytoplankton expert, notes that this hypothesis does not explain DA outbreaks in areas not affected by agricultural runoff, like parts of the Northern California and Oregon coast. HAB’s, and the various conditions that cause them, are too complex for a “silver bullet explanation,” as he puts it. There are thousands of species of phytoplankton that thrive in various conditions.
Caron points out that 2005, a year with very high runoff from the Los Angeles, Santa Ana and San Gabriel Rivers, there was a massive bloom of Lingulodinium, a phytoplankton that colors the water red, but is not toxic. DA levels were undetectable. In 2007, however, a year with much less river runoff, there was a massive bloom of Pseudo-nitchia, which is very toxic but does not discolor the water. Public awareness seems pulled toward “red tide,” a misnomer of an event that is not linked to tides or Pseudo-nitchia, and is caused by blooms of various species that can discolor the water, some toxic, some not. The relative importance of natural sources of nutrients for HAB’s relative to human-caused sources is little known. This leads Caron to refrain from labeling human pollutants in runoff as the primary culprit.
“Certainly our human activities may have some role in the stimulus of this, but we don’t have any smoking guns yet,” says Caron.
DA mimics glutamate, a neuro-chemical transmitter in the brain, and causes nerve connections to continually fire until they literally burn out and die. Most damage is done in the hippocampus, the part of the brain largely responsible for memory and spatial navigation. Initially DA poisoning causes nausea, headache, abdominal pain, vomiting, seizures, disorientation, vision disturbances, and motor weakness.
A bizarre event in 1961 in Capitola, CA, in which hundreds of sooty shearwater birds attacked people and crashed through windows is attributed to DA poisoning. The birds, a non-aggressive species that feeds on the fish that eat Pseudo-nitchia showed behavior consistent with more recent cases of DA poisoned birds. Alfred Hitchcock was staying in nearby Santa Cruz at the time, and supposedly used this instance as part of his inspiration for his film, “The Birds.”