Florida’s Atlantic sea front, famed for its tropical waters and majestic

The dinoflagellate, Karenia brevis, colours the water red during a bloom. Source
The dinoflagellate, Karenia brevis, colours the water red during a bloom. Source

manatees, is every year invaded by a bloom of microscopic algae. Colouring the ocean a deep red, the algae, Karenia brevi, proliferates rapidly under the right conditions, forming what is known as the Red tide. However this is not an exception, harmful algal blooms (HABs) occur in every ocean, each capable of causing widespread damage to the natural environment through toxin production. With mounting evidence that these phenomena are on the rise worldwide, the jury is out as to what is the cause of their sudden increase. Having been a natural event for many centuries, there is much debate over whether their expanding geographical range and frequency over the last four decades is a direct correlation to increasing human activity, or alternatively they are a symptom of changing ocean temperatures and weather patterns.

Small but effective

Relied upon by many a marine organism; algae form an integral part of our oceans, ranging from giant 60 meter kelp to microscopic unicellular cyanobacteria. Karenia brevi is a form of algae known as a

The simple structure of the dinoflagellate, a form of algae. Source
The simple structure of the dinoflagellate, a form of algae. Source

dinoflagellate. This eukaryotic, single-celled form is simple but ancient, taking on a number of different roles within an ecosystem, including parasitic and benthic. Species such as K. brevi are free-living and therefore easily transported by ocean currents throughout the Gulf of Mexico and up the coast of Florida, and has been recorded as far north as Virginia. Due to its simplicity, the outside of the organism is unprotected, with no additional armour, leaving it very fragile and at risk of being broken up. When subjected to rough conditions, the exterior of the dinoflagellate is ruptured, allowing the release of toxins from within the organism, that if congregate at great enough densities, have harmful side effects. During such an event, the red tide carries these toxins within the water, with the harmful particles attaching themselves to the salt and being carried in aerosol spray and droplets. With this, the geographical potential of the red tide toxin is expansive, with inland areas even being known to have been effected.

Neurotoxic potential

The toxin released by Karenia brevi has powerful neurotoxic properties, with the capability of effecting a range of organisms, from small benthic shellfish to manatees and humans. Known as brevetoxins, these neuro effecting compounds are incredibly hard to detect, being tasteless and odourless, with their remarkable heat stability making them durable substances throughout a range of conditions in the oceans. By binding to voltage-gated sodium ions channels within the cell membranes of the brain, the toxin depolarises the channels, resulting in an uncontrolled and excess inward movement of sodium ions. Due to this influx, the composition of the cell membranes are altered which in turn can encourage further movement, resulting in an irreversible impact of the brain. Not only can the brain be effected, but also nerve cells throughout the body can be depolarised as well, leading to possible impact of the normal function of cardiac and respiratory systems essential for the animals survival. An organism that appears so small and simple can indeed have a dramatic effect on the entire body of an individual.

Diagram showing the normal function of a voltage-gated sodium ion channel. Brevetoxins effect the channels by allowing the continuous influx of sodium, rather than closing the gate. Source
Diagram showing the normal function of a voltage-gated sodium ion channel. Brevetoxins effect the channels by allowing the continuous influx of sodium, rather than closing the gate. Source

Mollusc to manatee

Occurring all over the world, poisoning events caused by the release of toxins from algae are known to have a range of effects. Possibly one the most well known cases, Neurotoxic shellfish poisoning (NSP), has been identified as a result of toxin production from Karenia brevi in the Gulf of Mexico, disrupting the cardiac and gastrointestinal systems of organisms, including humans. Caused by the consumption of shellfish contaminated with toxins, NSP effects muscle coordination and has been known to cause severe vomiting and stomach problems. Shellfish however are not the only organisms effect by the brevetoxins released from K. brevi, with fish, birds and mammals also highly susceptible. During peak tide times, an estimated 100 tonnes of finfish are killed per day, causing rapid paralysis and death through lack of respiratory and cardiac function. The majestic manatee has also been known to effected by these toxins when exposed to them in aerial form for a prolonged period of time, causing excess inhalation and subsequent damage to the manatees respiratory organs and brain.

An economic issue

Not only do the brevetoxins released by Karenia brevi have a disastrous effect on the biodiversity of the area, but also the local economies are severely impacted. During an active tide, fisheries in the area are almost non-existant, with the toxins infecting such a high proportion of fish, making it simply not safe to catch anything without the risk of NSP. Shellfish beds present all the way up the Florida coast are an economic goldmine for the inhabitants of the tropical shore, but every year they are plagued by the Red tide, forcing them to clear the beds where a huge abundance of molluscs once grew. However, the effects do not stop there, with public health and medical costs mounting up, estimated to have cost the US government $449,291,987 between 1987 and 1992.

The potential effect of the red tide. Tonnes of fish die on an annual basis due to infection by brevetoxins. Source
The potential effect of the red tide. Tonnes of fish die on an annual basis due to infection by brevetoxins. Source

With increased knowledge and invested interest in the monitoring of Red tides, many argue that the occurrence of these natural phenomena are on the rise, with speculation as to whether increased industrial activity is a major cause. There is no doubt that organic run-off from agricultural activity into the oceans leads to a higher concentration of minerals than are beneficial to the proliferation of dinoflagellates such as Karenia brevi, however whether this is actually leading to an increase in their occurrence is yet to be understood. Dynamic ocean processes and ever changing currents lead to the spreading of microorganisms and therefore could be responsible for new geographical range of certain species and increase in specific areas. Only through understanding the true effects of increased human activity on algal and whether it causes them to bloom, will this mystery finally be solved.

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