The primary cause is the rapid proliferation of algae, which leads to a decrease in oxygen levels in the water.
Biologist Philipp Sapozhnikov, in his scientific article for the journal "Science and Life," explained that when colonies of microalgae reach the shoreline, they begin to interact with organic substances that enter the water from land.
Under such conditions, the reproduction of algae accelerates dramatically, and there can be millions of cells in a single liter of seawater.
He noted that the high density of these microorganisms prevents sunlight from penetrating deeply, which in turn slows down the process of photosynthesis and creates an oxygen deficit.
This has a devastating effect on the underwater world: some creatures manage to escape, but a significant number perish. The decomposing remains are processed by bacteria, which also consume oxygen, further reducing its concentration.
If the bloom affects extensive areas, the consequences for the ecosystem can be severe.
According to the National Oceanic and Atmospheric Administration of the United States, certain species of microalgae can synthesize toxic substances.
In large clusters, they begin to produce toxins, such as Karenia brevis, which affect sodium channels in the cell membranes of the nervous system. This poses a danger to vertebrate animals.
For example, between October 2017 and September 2018, a massive die-off of marine fauna was recorded along the Florida coast due to a "red tide."
The recent reddening of the water in the Caspian Sea has already raised concerns among residents, but scientists believe there is no need for alarm.
Experts explain that the algae bloom affects only a small portion of the sea, and its overall volume is too large for it to significantly impact the ecosystem.
Additionally, most mobile organisms simply migrate to other areas. After the bloom ends, the dead algae settle and become organic sediment—detritus.
This enriches the water in the sea with mineral compounds and nourishes fish larvae, filter-feeding organisms, and crustaceans.
According to the Ecology Department of the Mangistau Region, such phenomena occur annually.
As Erjan Zhumashev explained, this is a natural process that mainly affects shallow areas where large marine animals do not reside.
Currently, there are no signs of toxic compounds being released by the algae.