Red tides
From
time to time especially near the coast, the sea becomes bright red literally
over-night. This phenomenon is called a red tide. Red tides occur world-wide in
warm seas. They are massive blooms of phytoplanktons. At the peak of a red tide
there may be hundreds of thousands of cells in a single drop. Red tides aren’t
always red. They can be orange, brown or green in colour. Only around 6% of all
phytoplankton species are known to cause red tides. In red tide discoloration
of sea water usually caused by dinoflagellates. But many other organisms like
cyanobacteria, diatoms and chrysophyta can also cause red tides.
There
are many factors that influence red tide event. Warm ocean surface
temperatures, low salinity, high nutrient content, calm seas and rain followed
by sunny days during the summer months are some of them. Algae related to red
tide can spread or be carried long distances by winds, currents storms or
ships.
Because
of this phenomena there can be happen harmful algal blooms. About the third of
red tide organisms produce poisons. Among them there are most powerful toxins
too. These toxic substances may be lethal to fish and other marine life. It may
be a threat to human health, fisheries, coastal aesthetics and the economy.
Mussels, clams, crabs and other shellfish often tolerate the toxin by storing
them away in the digestive gland, kidney, liver or other tissues.
People
who eat the shellfish can suffer nausea, diarrhea, vomiting, numbness and
tingling, loss of balance and memory, slurred speech, shooting pains,
paralysis, and even death. And these organisms release toxic air born irritants
which can cause sore throats, eye irritation and skin complaints.
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