The change of hydrometeorological and physicochemical factors
is the important reason of the occurrence of red tide.
The temperature of sea water is an important environmental factor
of red tide, and 20 degrees Celsius to 30 degrees Celsius is
the suitable temperature range of red tide. Scientists have found
that a sudden increase in water temperature of two degrees Celsius
in a week is a sign of red tides. Changes in the chemical factors
such as salinity change are also responsible for the mass reproduction
of "red tide" organisms.
If the salinity is in the range of 26 to 37, then red tide is likely
to occur. However, when the salinity is 15 to 21.6, it is easy to
form the thermocline and halocline. Their presence is a condition
for the aggregation of red tide organisms, which can easily induce red tide.
Because of the confluence of runoff, upwelling, water mass or current,
the nutrient salt of submarine layer rises to the upper layer of water,
resulting in the highly eutrophication of coastal waters.
The rapid increase of nutritive salt content causes the proliferation
of diatoms. These diatoms, especially the dense bones of diatoms,
often cause red tides.
These diatoms also provide rich diet for noctilucent algae,
which promotes the proliferation of noctilucent algae, thus creating
a pink glow of nocturnal algae.
According to the monitoring data, when red tides happen, the waters
are mostly dry and less rain, the weather is hot, the water temperature
is high, the wind is weak, or the tide is slow to wait for
the water environment.