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Introduction:
Red tide is a phenomenon caused by algal blooms (www.Wikipedia.com definition) during which algae become so numerous that they discolor coastal waters (hence the name “red tide”). The algal bloom may also deplete oxygen in the waters and/or release toxins that may cause illness in humans and other animals. Species in the United States that release these harmful toxins include:

1) Alexandrium fundyense – found along the Atlantic coast from the Canadian Maritimes to southern New England.
2) Alexandrium catenella – found along the Pacific coast from California to Alaska.
3) Karenia brevis – found in the Gulf of Mexico along the west coast of Florida.

WHAT CAUSE RED TIDE ?
Major factors influencing red tide events include warm ocean surface temperatures, low salinity, high nutrient content, calm seas, and rain followed by sunny days during the summer months. In addition, algae related to red tide can spread or be carried long distances by winds, currents, storms, or ships.

WHERE ARE RED TIDES FOUND?
Red tide is a global phenomenon. However, since the 1980s harmful red tide events have become more frequent and widespread. Detection of a spread is thought to be influenced by higher awareness of red tide, better equipment for detecting and analyzing red tide, and nutrient loading from farming and industrial runoff. Countries affected by red tide events include: Argentina, Australia, Brazil, Canada, Chile, Denmark, England, France, Guatemala, Hong Kong, India, Ireland, Italy, Japan, the Netherlands, New Zealand, Norway, New Guinea, Peru, the Philippines, Romania, Russia, Scotland, Spain, Sweden, Thailand, the United States, and Venezuela.

Why there are harmful ?
Red tide algae make potent natural toxins. It is unknown why these toxins are created, but some can be hazardous to larger organisms through the processes of biomagnification and bioaccumulation. Grazers such as fish and krill are unaffected by the toxins, so as they eat the algae the toxins are concentrated and accumulate to a level that is poisonous eat to organisms that feed on them. Large fish kills and several mammalian diseases and deaths have been attributed to consumption of shellfish during red tide algal blooms. Diseases that may affect humans include:
1) Paralytic Shellfish Poisoning (PSP) – This disease is caused by the production of saxitoxin by the Alexandrium species. It is common along the Atlantic and Pacific coasts in the US and Canada. Poisoning occurs when one ingests shellfish contaminated with PSP toxins causing disruption of nerve function and paralysis. Extreme cases may result in death by asphyxiation by respiratory paralysis.

2) Diarrhetic Shellfish Poisoning (DSP) – This disease is caused by the Dinophysisspecies. It generally occurs in Japan and Europe, but it has also been found in other countries such as Canada, the US, Chile, New Zealand, and Thailand. Symptoms of DSP include diarrhea, nausea, vomiting, abdominal pain, and cramps. DSP is generally not lethal.

History of red tide in Hong Kong:
The Agriculture, Fisheries and Conservation Department (AFCD) started to record the occurrences of red tide since 1975. From 1975 to 2013, a total of 875 red tide incidents were recorded in Hong Kong waters. Amongst these incidents, only 27 were associated with fish kills.
A total of 77 algal species have been recorded to form red tides in Hong Kong, but majority of them are harmless. 19 of these algal species are considered as harmful or toxic. Amongst these harmful/toxic algal species, 5 of them resulting in fish kills and the other two causing contamination of shellfish by toxin in Hong Kong. The red tide associated fish kill events were mostly recorded in the 80’s and early 90’s.

Red tide in United Arab Emirates:

Dubai: The Ministry of Environment and Water has monitored the presence of algal bloom or overgrowth of microscopic marine plants in the country’s territorial waters overlooking the Arabian Gulf, off Ras Al Khaimah’s territorial coasts.
The marine phenomenon, which scientists refer to as “harmful algal bloom”, happens when tiny algae or marine plants rapidly multiply that can often deplete oxygen in the water or produce natural toxins. These toxins could kill fish and make shellfish dangerous to eat in what is commonly known as “red tide” because the overgrowth of algae usually turns the seawater red.
The ministry is currently working in cooperation with the Regional Organisation for Protecting Marine Environment on controlling the phenomenon and minimising its impact on marine life. Images were taken to show the biological activity off the country’s coastline in the Arabian Gulf, which indicates the potential occurrence of the red tide.
The move comes as part of the National Work Plan to Monitor the Red Tide Phenomenon, to ensure a swift response to tackle potential red tide whenever it happens or in case of the presence of algae bloom, also known as Cochlodinium Polykrikoides, or the death of fish and other marine species.

More photos about Red Tide in UAE:

References:

(1) : http://serc.carleton.edu/microbelife/topics/redtide/index.html
(2) : http://serc.carleton.edu/microbelife/topics/redtide/index.html
(3) : http://serc.carleton.edu/microbelife/topics/redtide/index.html
(4) : http://serc.carleton.edu/microbelife/topics/redtide/index.html
(5) : http://gulfnews.com/news/gulf/uae/environment/ministry-of-environment-monitors-algal-bloom-in-uae-s-waters-1.1271712

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