Toxic algae blooms: What you should know about the mysterious phenomena

In August1961, a bizarre scene unfolded in the skies above the coastal town of Capitola, Calif.,on the northern end ofMonterey Bay.

Residents watched in terror as seabirdsdive-bombed into the ground at kamikaze speed andviolentlyvomitedfish. The carcasses of hundreds of birds were strewnin the streets.

The strangeincidentpartly inspired Alfred Hitchcock's1963 horror flickThe Birds, but exactly what happenedremained a mysteryfor five decades.

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In 2011, a research group revealed that the birds were victims of poisoning by domoic acid, a potent toxin produced by algae that targets the nervous system, inducing severe seizures and killing wildlife.

A bloom thought to be the largest ever observedon the West Coast of North America is currently menacing Monterey Bay with unprecedented levels of domoic acid. Wild and farmed shellfish operations from California to B.C.have been forced to stop harvesting until the bloom clears.

While toxic algae are common in waters across the planet,there is mounting evidence that thefrequency and severity of these events are on the rise and that global climate change may exacerbatethe problem.

Here's some important background on toxic algal blooms and how they could affect you.

What are toxic algal blooms?

The massive growth ofalgaeon the West Coast falls under a category of natural phenomena that scientists call harmful algal blooms, orHABs. They are oftencalled red tides because they sometimes render the water a rusty-crimson colour. This is a misnomer, however,asalgal blooms can be many colours and aren't necessarily connected to tides.

Under the right conditions, a bloom can blanket surface waters for weeks on end, sometimes becoming a floatingtoxic glob that stretches thousands of kilometres in length and tens of metres deep.Some get so large they can be seen clearly from space.

While there are many kinds of harmful bloomsthat have varying effects on aquatic ecosystems, only a small percentage of algae species actually produce biological toxins.Those that do, however, cancreate some of the most harmful natural toxins known to science.

These toxins make their way up the food chain and can accumulate in dangerously high concentrations in aquatic animals that people eat, especiallyshellfish like oysters and mussels. Some shellfish can store toxins for weeks after a bloom passes.

How can toxic algaeaffect humans?

There are generally four widely recognized conditions associated with toxins produced by algae, as well as several lesser-known illnesses.

Perhaps the most well-known in Canada is Paralytic Shellfish Poisoning (PSP), which leads to symptoms from slight numbness in the extremities to full-on paralysis and even death in humans.

PSP is caused by saxitoxins, which generally do not break down under high heat conditions. In other words, cooking your mussels won't save you. The U.S. National Oceanic and Atmospheric Administration has recorded algal blooms that produced so much of the toxin that one or two small contaminated mussels could kill a healthy adult human.

Saxitoxins were among the first shellfish-derived poisons to be isolated and studied, including by the U.S. military, who tried to develop chemical weapons intended to disrupt the neurological function of enemy soldiers on the battlefield. During the Cold War, someAmerican spy plane pilots carried a doseof pure saxitoxinto take their own lives if faced with the prospect of capture.

Domoic acidis responsible for amnesic shellfish poisoning andcan cause severe short and long-term memory lossin humans. Similarly, the potent neurotoxinhas been implicated in whale deaths and has been proposed as an explanation for mysterious behaviour occasionally observed in manatees in Florida.

Algae are similarlyresponsible for diarrhetic shellfish poisoningyou can probably guess the primary symptomand neurotoxicshellfish poisoning, which tends to be less severe than other algal toxin-related conditions.

There is also an unusualgroup of blue-green algae (which are actually bacteria) called cyanobacteria, which live in both oceans and lakes. These speciescan produce potent toxins that cause liver and respiratory failure in humans and animals.

What causes toxic algal blooms?

The short answer is thatno one reallyknows.

The thousands of species of phytoplankton are in a constant, complex dance with numerous factors such as sunlight, water temperature, currents and the presence of essential nutrients like nitrogen, phosphorous and carbon.

What combination of these factors causes a bloom to explode is not entirely clear.In some instances, a sudden increase in nutrient levels seems to be theprimary cause. For example, in the western basin of Lake Erie, farm run-off high in phosphoroushas been blamed for an increasingly persistent bloom that forms each summer and fouls drinking water for hundredsof thousands of people.

Interestingly, some algae species capable of producing toxinsare not always toxic. Consider the enigmatic fish-killing speciesHeterosigmaakashiwo, which decimated farmed salmon populations in B.C. in the 1980s.Heterosigmais always present in some concentration, but only becomes toxic under certain conditions.

It's as if some combination of environmental factors simply flips a switch, but just what those conditions are remains elusive (it's not even known what type oftoxinHeterosigmaproduces).

Or in 2011, when an algae species that has likely persisted in B.C.'s waters for millennia without producing a toxin made 62 peopleacross Canada sick with diarrhetic shellfish poisoning after eating contaminated oysters harvested in the Gulf Islands. Once again, what induced toxicity in that particular year remains a mystery.