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“Algae” is a term of very imprecise meaning. It is used to refer to the microscopic, unicellular protists like the many species of diatoms and dinoflagellates that make up the producing trophic foundation of most aquatic (especially marine) ecosystems. It is also the term, though, applied to the large, multicellular, plant-like, seaweeds like kelp (which can grow over 50 m long!) or nori which is used to wrap types of sushi. “Algae” has also been used a bit inappropriately but very regularly to describe some bacterial cells like the cyanobacteria (“the blue-green algae”). The one thing that all of these very different “algae” organisms can do, though, is carry out green plant photosynthesis. They utilize a wide array of complex pigments to capture energy from sunlight and then use that energy to make sugars out of carbon dioxide and water. And, as a consequence of this energy capture and transfer, all of these “algae” generate oxygen as a waste product, a fact that is much appreciated by all of us who carry out respiration!
The blue-green algae are the most ancient of these “algal” organisms. Some 2.5 billion years ago blue-green algae formed thick, floating mats on the surface of the Earth’s primordial oceans. They photosynthesized furiously and produced so much oxygen that they transformed the Earth’s atmosphere from a poisonous, reducing cloud of volcanic gases into the present day’s sustaining, oxygenated system. All of this added oxygen then selected for certain types of energy metabolisms and changed the course of biotic evolution.
Blue-green algae are nowhere as abundant today as they were 2.5 billion years ago, but they still show up in a variety of mostly freshwater ecosystems. I have written about some of these modern day blue-green algae before (see Signs of Summer 1 (June 12, 2014), and Signs of Fall 13 (November 30, 2017)). They are also abundantly represented in the news today from southern Florida where they are clogging up the warm, phosphate and nitrogen rich waters of Lake Okeechobee doing great damage to the fish population of the lake and the human population surrounding it.
When an algae population of any type grows out of control it is referred to as a Harmful Algae Bloom (“HAB”). HAB’s frequently involve blue-green algae or the unicellular protist algae but not, as far as I know, the edible sushi seaweeds or kelp (although I do have something to say about a large, macro-seaweed algae HAB later on!). HABs are caused by a complex interplay of environmental factors. Excessive levels of nutrients (especially phosphorus and nitrogen), warm temperatures, changes in salinity, changes in wind or current direction, and alterations in deep ocean upwellings may all contribute to a HAB event. There is also evidence that iron rich dust blown across the Atlantic Ocean all the way from the Sahara Desert may be a factor in stimulating dinoflagellate populations on both the east and west coasts of the United States! Some of these factors are natural and have been causing HABs throughout recorded history. Other of these factors are human generated and may be the reason that the frequency and duration of HABs have been greatly increasing in recent decades.
“Red tide” is a term that is frequently applied to a HAB that occurs along an ocean shoreline or in an estuarine ecosystem. Red tides are caused by the out of control boom and bust of some of the species of dinoflagellate protists. When these dinoflagellate populations race out of equilibrium they make the waters in which they live cloudy with their massive numbers. Most species of dinoflagellates contain in their intracellular plastids large concentrations of carotinoid pigments which they use as secondary light capturing and transferring pigments in photosynthesis. Carotinoids are the same secondary pigments found in many green plant leaves. They are the pigments that are “revealed” (and, possibly, preferentially synthesized), for example, when a maple tree stops making chlorophyll in the fall and its leaves turn a brilliant red. Shoreline waters with abundant dinoflagellates, then, often turn red with the abundant intra- and extracellular concentrations of carotinoids (hence the term “red tide”). The big problem in a red tide, though, are all of the other chemicals that are concentrated in and released from the dinoflagellate cells. Many of these chemicals are directly toxic to fish, sea mammals, birds and humans and embody the devastating biological threat of the red tide.
On the Atlantic and Gulf Coasts of the United States that most common dinoflagellate that generates red tide events is Karenia brevis. Around the world, though, many other dinoflagellate species and even species from other protist groups can become over-stimulated and generate HABS (which may or not be red, and which may or may not generate significant levels of biological toxins).
Florida is currently experiencing a severe and very prolonged red tide that was possibly triggered by the release of a large amount of fertilizer and septic system enriched water from Lake Okeechobee in November 2017. This was two months after Hurricane Irma pounded the Florida peninsula with rain, and the lake water was released to prevent more flooding across the southern part of the state. The high levels of nitrogen and phosphates in the released lake water when combined with the very warm waters of the Gulf triggered a HAB and a red tide that spread up the Gulf Coast and even spilled out to the Atlantic Coast. Most red tides are self-limiting and fade out as cooler weather and seasonal ocean currents and winds disperse the algal masses. This red tide, though, persisted through the year and is intensifying as the normal, red tide season begins again. Back in 1990’s a red tide in Florida lasted for a record two and half years! Experts say that this current red tide may exceed this thirty month time interval.
As of early October the Florida red tide has killed over one hundred manatees, dozens of dolphins, three hundred seas turtles and thousands of fish (including a twenty-six foot whale shark (the world’s largest fish)). The Florida Fish and Wildlife Conservation Commission estimates that 145 miles of the Florida coast are affected by the red tide. Shellfish harvesting and fishing have been severely curtailed. Some people are not even able to go near the seashore during a red tide outbreak because air and sea spray-borne transport of algal generated toxins. One beach visitor reported that the experience of breathing in these toxins was like being sprayed with tear gas! Allergic and asthmatic reactions to these toxins are also being reported.
So Florida is experiencing two types of HAB’s all at once! The blue green algae explosion in Lake Okeechobee and the Karina brevis explosion on their ocean coastlines. The consensus from the experts is we can only sit and wait for the populations of each of these types of algae to return to some degree of normal equilibrium. We may be waiting for many months or years for that to happen!
There is another type of algae exploding in abundance, too. This is a large, macro-algae that floats on the ocean surface and accumulates on unfortunately located beaches throughout the Gulf of Mexico and Caribbean. Next week we’ll talk about sargassum!