They lurk in the water. They look harmless. But sometimes–not always, but sometimes–they can cause sickness: even death.
“They” are blue-green algae, and it’s a bit startling to think that algae, something we think of, when we think of them at all, as an unsightly but harmless scum, can be toxic–because most algae, most of the time, aren’t. But sometimes, some of them are.
Algae, says Grolier’s Encyclopedia, are “a diverse group of primarily aquatic, mostly plant-like organisms that occur in such dissimilar forms as microscopic single cells, loose, filmy conglomerations, matted or branched colonies, or giant seaweeds with root-like holdfasts and structures resembling stems and leaves.”
That’s an awfully broad definition, so algae are further categorized as yellow-green or golden-brown algae, dinoflagellates, euglenids, red algae, green algae, brown algae–or blue-green algae.
In some ways, blue-green algae seem more akin to bacteria than other algae, which is why they’re also called cyanobacteria. Like algae, they get their energy from the sun through photosynthesis–but unlike algae, they lack tiny chlorophyll-bearing structures called chloroplasts. Instead, chlorophyll is distributed throughout the cell. (In fact, like bacteria, they lack all specialized cell structures, such as nuclei; this makes them, with bacteria, the most primitive form of living cells.) Chlorophyll, of course, is what makes all plants green; the blue in “blue-green algae” comes from another photosynthetic pigment that they alone use, called phycocyanin.
Blue-green algae are abundant on tree bark, rocks (where they sometimes combine with fungi to form a lichen), in moist soil and in open water. They can grow at temperatures higher than those tolerated by any other form of life and endure both extreme dryness and bright light.
This resilience means blue-green algae are around us all the time, and most of the time, we don’t notice them. But every once in a while, particularly in hot weather, lakes, pools and puddles bloom with blue-green algae–and that’s when problems arise.
Warm water and bright sunshine provide blue-green algae with more energy for reproduction, and reproduce they do. Run-off from fertilized lawns and fields adds to the reproductive frenzy; the same nutrients that make crops and grass grow make algae grow. This would be no more than a nuisance if not for the fact that, for uncertain reasons, some species of blue-green algae produce toxins as their numbers swell.
Not all species of blue-green algae produce toxins and even within a species, there can be both toxic and non-toxic strains–which means you can never be sure that a particular bloom of blue-green algae is toxic without testing it. Not only that, the nature of the toxins can change from bloom to bloom, even within the same species.
Among the toxins identified as being produced by blue-green algae are neurotoxins (which affect the nervous system), hepatotoxins (which affect the liver) and contact irritants (which affect the skin). These toxins are sometimes been powerful enough to kill fish, dogs and livestock, and circumstantial evidence points to them causing skin reactions, inflammations of the eyes and nose, vomiting, diarrhea, mild hepatitis and even pneumonia in humans.
But having said all these bad things about blue-green algae, let me hasten to add that the world would definitely not be better off without them: if not for blue-green algae, we wouldn’t be here.
Remember I said blue-green algae are very primitive. That’s because they were among the earliest life forms to appear, 3.5 billion years ago, before humans were more than a twinkle in Earth’s eye. Blue-green algae probably played the largest role in pumping the Earth’s early atmosphere full of another toxin, one that undoubtedly killed hundreds of microscopic species that couldn’t adapt to it. Today, that toxin fills our atmosphere, and it’s a good thing it does: we call it oxygen.
Blue-green algae also play an important role in fixing nitrogen, taking it from the air and depositing it in the soil for use by plants…the plants which, either directly or through the animals that eat them, provide us with all of our food: which means blue-green algae are partly responsible for both the air we breathe and the food we eat.
That being the case, I think we can put up with the occasional toxic bloom. Just stay away from scummy water…good advice, one would think, any time, anywhere.
