Monday, September 3, 2018

The Red Tide in Florida 8 months and counting

A Red Tide, a harmful algal bloom that at high concentrations discolors the water , is currently affecting about 145 miles of the southwest coast of Florida. Karenia brevis the algae that causes red tides produces nuerotoxins that can cause fish kills, respiratory irritation, and mortality of sea turtles, manatees, and dolphins. This has been a particularly long Red Tide. It started in October 2017 and continued through spring of 2018, and by early summer had re-surged and was detected in five southwest Florida counties.

Red Tides form in the Gulf Coast mostly in Florida and Texas. They are caused by the rapid growth of the microscopic algae called Karenia brevi and generally form more than 40 miles from the Florida coast. When large amounts of this algae are present, it can cause a harmful algal bloom that has be seen from space. Karenia brevi at high concentrations discolors water often red, but also light or dark green or even brown. No single factor causes a Red Tide. The algae bloom needs the organism, Karenia brevi, natural or man-made nutrients for growth, the right concentration rain and sunlight and transport from the wind and waves. No single factor causes it.

The Florida Department of Health reports that tests are being conducted to see if coastal nutrients enhance or prolong blooms. However, it seems logical that man-made nutrients do encourage and feed growth. We know that man-made nutrients feed algal blooms elsewhere. Not all algal blooms are harmful. Many ocean algae blooms are beneficial because the algae provide food for ocean animals and essential part of the ocean food web.

A small percentage of algae, however, produce powerful toxins that can kill fish, shellfish, mammals, and birds, and may directly or indirectly cause illness in people. Algae blooms of non-toxic species can have harmful effects on marine ecosystems. For example, the “Dead Zone” in the Chesapeake Bay when masses of algae die and decompose, the decaying process can deplete oxygen in the water, causing the water to become so low in oxygen that animals either leave the area or die.

The Florida Red Tide organism, Karenia brevis, produces potent neurotoxins, called brevetoxins, that can affect the central nervous systems of many animals, causing them to die. That is why Red Tides are often associated with fish kills and the death of other species, including manatees, dolphins, sea turtles, and birds. In the 16th century a Spanish explorer recorded stories by Florida Indians of toxic "red water" and the resulting death of birds and fish.

Wave action near beaches can break open Karenia brevi cells and release the toxins into the air, leading to respiratory irritation. For people with severe or chronic respiratory conditions, such as emphysema or asthma, the Red Tide can cause serious illness. People with respiratory problems should always avoid affected beaches during Red Tides.

The Red Tide toxins can also accumulate in filter-feeder mollusks such as oysters and clams, which can lead to neurotoxic shellfish poisoning in people who consume the contaminated shellfish. Neurotoxic shellfish poisoning is not fatal, but hospitalizations occur. According to the National Institute of Health neurotoxic shellfish poisoning involves a cluster of gastrointestinal and neurological symptoms: nausea and vomiting, paresthesias of the mouth, lips and tongue as well as distal paresthesias, ataxia, slurred speech and dizziness. Neurological symptoms can progress to partial paralysis; respiratory distress has been recorded. In most cases only diarrhea is reported.

Rigorous state monitoring of water and shellfish assures that commercial shellfish is safe, often by closing harvest beds. Commercially available shellfish in restaurants and grocery stores is safe because it comes from water free of Red Tide and is monitored. Recreational harvesters have the greatest risk of neurotoxic shellfish poisoning, often due to a lack of awareness of the problem.

Red Tides are a natural phenomenon that require the right conditions to expand and linger. This Red Tide is unusual but not unprecedented in its duration. In 2005, a Red Tide started off the coast of St. Petersburg, Florida, in January and then spread to Pensacola and Naples by October, persisting for the majority of the year. In the 1994 there was a Red Tide that lasted 2 years. Since the late 1990's Red Tides have occurred each year. The last protracted period of red tides occurred in the 1870's.The duration of a bloom in nearshore Florida waters depends on physical and biological conditions that influence its growth and persistence, including sunlight, nutrients, and salinity, as well as the speed and direction of wind and water currents.

There are currently no means of controlling the occurrence of red tide, research continues in hopes of finding ways to better address the causes and effects of Red Tides and other harmful algal blooms.

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