Red tide

A "red tide" off the coast of La Jolla, California.

Red tide is estuarine or marine algal bloom. Red tide is caused by species of dinoflagellates, often present in sufficient numbers (thousands or millions of cells per milliliter) to turn the water red or brown. The species responsible for red tides on the gulf coast of Florida is a dinoflagellate called Karenia brevis (formerly Gymnodinium breve.) It produces brevetoxins which produce respiratory irritation in humans.

Coastal water pollution produced by humans and systematic increase in sea water temperature appear to be causal factors in red tides. On the Pacific Coast of the U.S. there have been apparent increases in the occurrence of red tides since about 1991. These increases are correlated with a marine temperature rise of about one degree Celsius, and also with increased nutrient loading into ocean waters. Additionally, red tide can assume its dormant form if the water cools to a sufficient degree. When it does this it forms cysts which drop to the ocean floor and rebloom if the right conditions occur. As another example, non- red tide algal blooms in lakes and rivers may be caused by greatly increased amounts of phosphorus or nitrogen entering an aquatic ecosystem from either sewage systems or surface runoff of agricultural fertilizers. Some red tides on the Pacific coast have also been linked to occurrences of El Nino events. Red tides also occur in places where there are no obvious associated human activities.

Some red tides produce large quantities of toxins, such as saxitoxin, which disrupt the proper function of ion channels in neurons. Domoic acid, causative of neurological damage in certain marine mammals, is one toxin associated with red tides. The red tide toxins can induce neurological damage and death in marine mammals which feed on affected filter feeders, these include whales, seals, and otters. Red tide can also increase fish mortality; they are also accumulated in the digestive tracts of filter feeders. This bioaccumulation of toxins causes bivalves – like oysters and clams – collected in areas affected by algal blooms to be potentially dangerous for human consumption. Initial signs of poisoning from this toxin is tingling in the lips followed by a reduction of motor abilities and difficulty breathing and can be fatal if consumed in sufficient amounts. If these symptoms occur after eating shellfish, seek immediate medical treatment. Standard medical treatment is to give victims oxygen, or to hook them up to a breather. There exists no antidote, and the idea is to keep the person alive until the toxin has passed from the system.

There is more than one type of red tide, something that frequently goes unnoticed. For example, the red tide that effects the Gulf Region produces, in addition to the toxins that accumulate within filter feeders, an airborne vector that can cause difficulty breathing, especially for those with preexisting conditions whereas that which occurs in the Northeast US doesn't have an airborne vector. It should also be noted that red tide is far from being entirely understood.

Gymnocin A is a cytotoxic polyether and a typical representative of toxins associated with red tide .

Gymnocin A

External links

• Harmful Algae and Red Tide Information from the Coastal Ocean Institute, Woods Hole Oceanographic Institution
• Toxic Blooms: Understanding Red Tides, a seminar by the Woods Hole Oceanographic Institution
• Gulf of Mexico Dead Zone and Red Tides
• Red Tide updates for the Gulf Coast of Florida provided by Mote Marine Laboratory in Sarasota, FL