The Dead Sea is not really a sea, but an endorheic lake, into which all the rivers of its basin flow, and which has no contact with the sea. It is located at the bottom of a tectonic depression more than 400 meters below sea level and is characterized by its salinity with a concentration of dissolved salts of up to 28%, much higher than the average seawater, which is around 3.5 %. However, there are creatures capable of living in the Dead Sea.
Creatures that can live in the Dead Sea
This high salinity is what allows a person to float in its waters without difficulty. But in addition, its saline composition is different. Unlike seawater, whose salts are primarily composed of chlorine, sodium, sulfate, and magnesium ions, the Dead Sea is composed primarily of calcium, magnesium, potassium, and bromine salts.
This composition of salts, not only different, but extraordinarily concentrated, makes fish and amphibians unable to maintain osmotic balance, that is, the balance of salts between the inside of their body and the water that surrounds them. This total absence of fish and amphibians gives the lake its name..
In Hebrew it was known by two names, notably Yām ja-Melaj meaning “sea of salt” and in some writings Yām ja-Māvet or “sea of death”. However, the name “dead” or “dead” as we now call it, not only shows us that it is not a sea, but it is not dead either, considering that several creatures can be found here that can survive the environment.
If the history of evolution has taught us anything, it is that life cannot be contained, life is always making its way. And it did so in an environment as inhospitable as the Dead Sea, an environment where extremophile organisms that can live in extreme environments have found a niche to inhabit and formed a special microbial ecosystem.
Haloferax volcanii, the salt archaea
It is an archaea, a type of prokaryote, unicellular organisms without a nucleus, different from bacteria, which are actually closer to us than to them. It is a living thing that lives without difficulty in the hypersaline waters of the Dead Sea, but it also needs warmth, something easily obtained in an endorheic desert lake. For this reason, during the summer these archaea reproduce much more easily.
This archaea, moreover, can be cultivated relatively well in the laboratory. Adding to this the extremophile condition, this is a fantastic model organism for exobiology, meaning the study and understanding of what alien life might be like in inhospitable environments. However, its strength is also part of its weakness. Haloferax volcanii has a very narrow salinity range. Not only does it need high salinity, but if it is too high, it damages it. In recent decades, the extraction of water and silt from the Dead Sea makes its level lower and lower and its waters more and more salty, which endangers the conservation of this extremophile.
Haloferax volcanii is able to live in the extreme environment of the Dead Sea
Dunaliella parva, red green algae
We moved from prokaryote to eukaryote, a nucleated cell organism. Dunaliella parva is a small unicellular alga with a pair of cilia adapted to saline environments. It lacks a rigid cell wall. instead it has a starch coating. This gives it some flexibility, allowing it to expand and contract, absorbing or expelling water, depending on the salinity of the environment. In addition, its cytoplasm contains high concentrations of glycerol, which allow it to maintain fluidity despite having little water.
Although it belongs to the group of chlorophytes or green algae, its color is rather reddish, due to the high concentration of ß-carotene in its chloroplasts, the same pigments that give tomatoes or carrots their color. In fact, when large blooms of this algae occur in the Dead Sea, its waters turn pink. These pigments protect chlorophyll from extreme lighting. These algae are therefore extremophiles adapted to high salinity and strong sunlight.
They are also easy organisms to grow, although in this situation they turn green when in less stressful situations. These algae are cultivated for the extraction of ß-carotenoids used as a food or cosmetic colorant, or as a nutritional supplement. But its ease of cultivation also makes Dunaliella parva a good model organism for exobiology.
The elusive protozoa of the Dead Sea
During sampling in the 1940s, two protozoa were isolated and cultured from samples from the Dead Sea . One of them was a type of amoeba found in the mud, more than 300 meters deep. We are talking about a unicellular organism less than 80 microns in length. It was discovered that it had the peculiarity that, under certain conditions, it was capable of producing scourges.
On the other hand, they discovered a ciliate protozoan that was in close association with the earlier amoeba and algae of the genus Dunaliella. That single-celled organism was even smaller, no more than 24 microns, and had two hardened spines on its back. However, neither of the two cultures has survived to this day. Later studies tried to move these protozoa, but without success. So at this point, we can’t be sure if these creatures really exist in the Dead Sea or if it was some kind of contamination from the original samples from eight decades ago.