Red Tides: When Tiny, Toxic, Single-Celled Animals Attack!


Red tides kill huge schools of fish, poison oyster and shellfish beds, and leave swimmers’ skin itchy, irritated and inflamed. Is this fearful phenomenon a case of nature running amok, or is human activity at least partly to blame?

Roll Tide!

(images via: Water Babies, Alan Guisewite and Underwater Times)

Crimson tides are cool when you’re sitting in a stadium cheering on your team. In the ocean or the odd freshwater lake, not so much. Though they may appear exotic and beautiful – especially at night in some cases – red tides often mean bad news for sea creatures and those who consume them… like us.

(images via: Island Nature, Life In Freshwater and CNRS)

Let’s clear up a few misconceptions. Red tides aren’t tides per se, and their appearance bears no relation to the sea’s natural tidal cycle. The term “red tide” originated at a time when observers didn’t have the technology to look closer – MUCH closer – at what was tinting the water red.

(images via: Expateek and Worth1000)

Though it’s probable that red tides have been appearing for many thousands of years, if not longer. The toxic red tides that continue to plague Florida’s coasts in modern times were first documented in the ship’s logs of 16th century Spanish explorers. Speaking of plagues, the phenomenon may have been noted even earlier, in the Bible’s Old Testament. The first of the Ten Plagues inflicted upon the Egyptians was described in the Book of Exodus thusly: “… and all the waters that were in the river turned to blood. And the fish that were in the river died, and the water stank.”

Whip It, Whip It Good

(images via: Marine Science, Underwater Times and Pixdaus)

With the invention of the microscope, biologists were for the first time able to determine the nature of red tides and the type of tiny creatures that produce them. Turns out the culprits are dinoflagellates, a type of protist or single-celled creature that has characteristics of both plants and animals. The term “dinoflagellate” is derived from the Greek word dinos, meaning “whirling”, and the Latin word flagellum which translates to “whip.”

(images via: Coastal Care, Sir Francis Drake Highschool, Rashid’s Blog and Green Prophet/M.Godfrey)

Basically, these tiny creatures propel themselves through the water by whirling and whipping a threadlike extension of their bodies. Though some dinoflagellates are semi-transparent and colorless, others are tinted various shades including red. When the populations of dinoflagellates boom; or “bloom”, as is often stated, their abundance can change the hue of large expanses of ocean to red, pink, purple, orange, gold – and every hue in between. The spectacular red tide bloom just above was caused by dinoflagellates of the species Noctiluca Scintillans, and occurred just off the coast of New Zealand.

(image via: NASA Earth Observatory)

Red tides are often reddish but their color depends on both the concentration and the type of the responsible protists. Photosynthetic algae can burst into huge greenish blooms that can be seen from orbit. Red tides and other harmful algae blooms (HABs, for short) have also been spied by satellites, as the image above shows: check out Florida’s southwest coast.

(images via: Microbial Life, Growing Algae and NASA Earth Observatory)

Being the color of blood alone was enough to worry ancient mariners but the effects of red tides sealed their reputation as harbingers of death and destruction – to sea life, at least. Some (but not all) of the dinoflagellates responsible for red tides produce a potent neurotoxin that is released when they’re ingested. A single dinoflagellate pumps out a tiny amount of toxin, but multiply that by multi-billions and you’ve got poison in the poisson… pardon my French.

Selfish Shellfish

(images via: Slate, Smithsonian NMNH and FEIS)

Massive fish kills – at times numbering in the millions – are often associated with red tide events but it’s what lies beneath that concerns health-conscious seafood consumers. Commercial shellfish such as clams, scallops and oysters can survive red tides but in doing so, they concentrate the neurotoxins in their tissues.

(images via: Lonelee Planet and Serious Eats)

Eating contaminated shellfish (which aren’t red, by the way) can induce symptoms of paralytic shellfish poisoning (PSP), the effects of which are similar to those induced by toxins ingested in poorly prepared Fugu (Puffer fish) at sushi restaurants.

(images via: Kleepet, The National Academies and LIFE)

Paralytic shellfish poisoning (PSP) has been noted on both the east and west coasts of the United States and a range of dinoflagellate species have been implicated as the original source of the toxins – the species of dinoflagellate known as Alexandrium Fundyense is blamed for red tides in the American northeast coast and the Gulf of Maine.

(images via: Texas Parks and Wildlife, BC/CDC and Alaska Tsunami Papers)

It’s not even necessary to EAT contaminated seafood in order to be adversely affected by red tide toxins. The red tide organism Karenia Brevis, which blooms on a near-annual basis in the Gulf of Mexico, exudes a neurotoxin known as Brevitoxin. Winds blowing inshore can pick up the toxin as an airborne aerosol, causing people living up to several miles inland to suffer respiratory irritation, coughing, sneezing, and tearing. The aerosol can affect marine mammals such as seals, manatees and whales as well. The Humpback whale shown above right washed up on a Massachusetts beach after feeding in a red tide.

(images via: Coastal Care)

In response to the perceived dangers red tides can cause, both the Florida Fish and Wildlife Conservation Commission and the Texas Parks and Wildlife Department regularly issue and update online status reports on red tides along their respective coastlines.

Don’t You Make My Red Tide Blue

(image via: The Jetpacker)

“Red tides at night, red tides at night, oh OH…” Can you see a red tide at night? Yes and no… the customary red hue is invisible by night but a different color is often easily and spectacularly evident: blue! many red tide organisms are also bioluminescent – that is, they produce and emit ghostly blue light through through a chemical reaction that occurs within their bodies.

(images via: The Olsons, Comcast Forums and Photoshelter)

Wave action, stormy weather and other sorts of disturbance will provoke these tiny creatures to pump out blue light, but swimmers should keep in mind light isn’t the only thing dinoflagellates can produce.

(image via: Panoramio/Joeyrigatoni)

Waves washing onto beaches can also bring dinoflagellates onto dry land. The tiny creatures can remain alive for some time on or in wave-soaked beach sand, and tales have been told of beachcombers leaving eerie blue footprints as they stroll along the seashore.

Red Tides, Dead Zones… Red Zones?

(image via: Harmful Algae)

Red tides and other algae blooms are prompted by a sudden influx of nutrients into lakes or oceans – yes, even lakes can experience red tides, as seen in the photo of an Italian alpine lake above.

(images via: WIRED and Mongabay)

Nitrate- and phosphate-rich agricultural runoff is one such nutrient source. Not only can runoff spark red tides, over a period of time the result can be a marine “dead zone” like the one in the northern Gulf of Mexico.

(images via: Esquire and Shorecrest)

Excess fertilizer, untreated sewage, farm waste and other organic material washed down the Mississippi river pour into the Gulf, cause massive algae blooms, and deoxygenate the water as billions of protists die and sink to the ocean floor. Similar scenes occur with regularity on the coasts of dense urban conglomerations such as Hong Kong (above).

(images via: Daily KOS, National Geographic and WN.com)

Nutrients aren’t always organic or farm-related, however. Scientists have established a distinct correlation between windblown dust from the Sahara Desert and algae blooms in coastal Florida waters: the iron oxide in the dust acts as a nutrient to certain types of algae.

(image via: National Geographic)

El Niño events and natural upwelling of nutrients caused by ocean currents also play a role in the formation of red tides but it can be stated that without human activity, there would be a corresponding reduction in the frequency and severity of many red tides and algae blooms.

I Sea Red

(images via: Coastsider, Harmful Algae and Daily Telegraph)

If red tides have one saving grace, it’s their redness: it acts as a giant, liquid STOP sign for those who would normally enjoy seafood and shellfish oblivious to any consequences. To that we can probably add their often quite astonishing beauty, as illustrated in the many striking images that accompany this article.

(images via: MSauder and North County Times)

Better red than dead? Absolutely – not a single human fatality has occurred over the long history of Florida’s frequent red tides so look, admire and enjoy nature’s colorful show… and don’t plan any clambakes.

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