Shark diaries: Red tide

Dear Ultimate Animal Friend,

At the moment there is a lot of red tide in False Bay. This has prevented us from going to sea, (because the visibility of the water is so poor), forcing us to cancel many trips.

Please note that the red tide in False Bay is non toxic, at present, but red tide is known to be very dangerous and we urge you not to eat the local shell fish.

What is red tide?

Red tide is a common name for one type of manifestation of a phenomenon known as an algal bloom, an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column, or "bloom". These algae, more correctly termed phytoplankton, are microscopic, plant-like organisms that can form dense, visible patches near the water's surface.

Red tides usually occur along the Cape west or south coasts in late summer and autumn

Certain species of phytoplankton contain photosynthetic pigments that vary in color from green to brown to red, and when the algae are present in high concentrations, the water appears to be discolored or murky, varying in color from white to almost black, normally being red or brown. Not all algal blooms are dense enough to cause water discoloration, and not all discolored waters associated with algal blooms are red. Additionally, red tides are not typically associated with tidal movement of water, hence the preference among scientists to use the term algal bloom.

The most conspicuous effects of red tides are the associated wildlife mortalities among marine and coastal species of fish, birds, marine mammals and other organisms. In the case of Florida red tides, these mortalities are caused by exposure to a potent neurotoxin called brevetoxin.

Initial signs of shellfish poisoning from red tide toxins such as domoic acid 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 treatment consists of keeping the patient alive until the toxin has passed from the system.

Additional information on red tide and shellfish poisoning:

http://en.wikipedia.org/wiki/Red_tide
http://en.wikipedia.org/wiki/Shellfish_Poisoning
http://www.botany.uwc.ac.za/Envfacts/redtides/index.htm

Rob and Karen Lawrence
African Shark Eco-Charters