Give Me More Salt! Trivia Quiz

Answer:

In broad terms, salinity is a measure of how salty something is and the label is usually applied to water-based systems (natural or otherwise). The property can, however, also be possessed by other forms of matter, such as soil. Salt doesn't necessarily refer to just sodium chloride (NaCl), it is used in a more general sense to cover ionic compounds such as potassium nitrate and magnesium sulphate.

In terms of aquatic habitats and ecosystems, salinity specifically relates to the concentration of salt in a body of water. The unit of measurement is typically grams per litre (g/L) but there is also a frequently used dimensionless unit - parts per mille (grams of salt per kilogram of water). Equipped with these units, a number of classifications have been developed to group different bodies of water based on their salinity.

An example of a part of the world where salinity can change quite drastically is the Makgadikgadi Pans of Botswana. During the dry season, the landscape is dominated by an expanse of crystalline salt (a crust) formed from the evaporation of salty water; the salinity is so high in the dry season that the ecosystem is classified as hypersaline (as salty as it gets). At this time of the year, only a small number of extremophile species - specifically halophiles (salt lovers) - have adapted to survive here.

One such extremophile that is able to thrive in the harshness of the dry season at the Makgadikgadi Pans is Moina belli, a crustacean that belongs to a group of animals informally called the "water fleas". According to studies, up to 600,000 of these tiny crustaceans can be found in a cubic metre of certain sections of the salt pans.

Moina belli is not the only species of crustacean able to survive in the hypersaline conditions of the dry season, there are quite a few others to keep it company. There is another tiny water flea called Daphnia barbata, a species that can also be found at Lake Chad as well as this incredible ecosystem in Botswana. If you are fed up of water fleas, well there are copepods ("oar feet") too, specifically Lovenula africana. Another extremophile species has a common name that specifically references salt, Branchinella spinosa or the halophilic fairy shrimp.

Adaptations that allow species such as Moina belli to colonise a salt pan include specialised osmoregulation processes (this allows for the excretion of excess salts and retention of water), rapid asexual reproduction to keep population counts high and eggs that have layers that protect against metal salts. Species such as Moina belli also have access in the pans to large quantities of food, be it plankton, algae, decaying organic matter or halophilic bacteria.

In the wet season - when the rivers in the area start to flow - the salinity is reduced due to the increased volume of water and the system fluctuates between hyposaline and mesosaline conditions (both of which refer to salt concentration greater than typically present in sea water). During such periods, the landscape is characterised by high saline lakes and wetlands that are somewhat more attractive to a greater variety of animal species.

Brine shrimp of the genus Artemia start to flourish in the more dilute conditions and, in turn, the brine shrimp become a source of food for both greater and lesser flamingos. Flamingos are joined by migratory birds including the great white pelican. In some of the grassy or shrubby verges, reptiles can be found such as Agama hispida, a spiny lizard that consists of two subspecies (both of which are endemic to the south of Africa).