In the heat of summer, nothing is more pleasant than a good swim, and if the sea is far away, the pool is a good option.
A swimming pool requires good maintenance of its infrastructure and water. Generally, the optimal treatment is done with chemical products, based on chlorine or compounds derived from chlorine that have highly oxidizing properties, which, in recommended doses, is lethal to bacteria, fungi, algae, protozoa and small animals. Pool filters remove the remains of organic and inorganic matter deposited in the water, either blown by the wind, or by users who have not taken a convenient shower before entering the pool.
But another of the properties of chlorine is that it evaporates relatively easily, and if pool maintenance is abandoned, if the water filtering pumps are stopped, a mass of stagnant water is formed that can be easily colonized by multiple beings. alive.
life makes its way
Most of these organisms arrive blown by the wind, in the form of spores or other resistance structures, although they can also be introduced by people or by other bodies that fall into the water, such as dry leaves. The most rapidly proliferating organisms are cyanobacteria, filamentous green algae, and protozoa. Some of these organisms include free-living amoebae, such as those belonging to the genus Acanthomoeba or Balamuthia mandillaris , which can cause health problems in people and animals. Specifically, these amoebas are the cause of a serious disease called amoebic granulomatous encephalitis .
The pond-like ecosystem that can form in a pool with stagnant water also includes animals of many kinds.
Invertebrates in my pool
Most of the animals that proliferate in an abandoned pool, as well as the algae, are practically invertebrates.
Some of the organisms that most easily colonize this type of environment are rotifers, microscopic invertebrates that have the ability to become encysted if the environment in which they live dries up. These cysts function as a form of resistance, they can remain dormant for years, and are dragged by the wind along with the dust, until the temperature and water conditions are right, at which time they hatch again.
Rotifers are also euthelic , that is, they always have the same number of cells in their body in their adult life, determined by the species. These cells do not reproduce or age, the growth of the animal is due exclusively to the growth of the size of its cells.
Other invertebrates that can enter these environments are the staves , worms from the group of flatworms . The complex life cycle of these animals involves several intermediate hosts, the most important in this case being the freshwater snail. It can leave a pond and colonize another nearby, and does not differentiate natural ponds from abandoned pools. If an infected snail enters the pool, the fluke larvae, called cercariae , enter the water and live as zooplankton, waiting to infect a mammal, such as a human.
Although flukes are not common in Europe, in tropical settings they can be a significant health risk.
Crustaceans, the great colonizers
But of all the diversity that can be found in an abandoned pool, it is the crustaceans that dominate the scene by far: many species can colonize this environment.
Among them, the cladocerans , such as the species of the genus Daphnia or water fleas. They are very small animals, between 0.5 and 4 millimeters, that are part of the zooplankton. They feed on protozoa and bacteria in suspension, filtering the water. They have a translucent exoskeleton and a practically transparent body, but, in spite of everything, if you pay attention, they can be seen with the naked eye, swimming as if in fits and starts.
Other conspicuous crustaceans are the copepods , similar in size to the cladocerans, although more tapering, and with only one eye. This group of crustaceans are considered the most abundant arthropods, and there are species adapted to practically all types of aquatic environments. Copepods can also be intermediates for parasites that can affect humans, such as the cestode Diphyllobothrium latum , which causes diphryllobothrosis, or the bacterium Vibrio cholerae , which produces the cholera toxin.
Insects, colonizers by their own means
Most of the living beings described so far are organisms that would reach an abandoned pool dragged by the wind, dry leaves or the entry of other animals. However, there are many other animals that can find their habitat in a pool by deliberately entering, among them, insects are probably the most striking.
Apart from visiting insects that only come to the pools to drink water or look for food, such as wasps, many insects lay their eggs in the water, and their larvae reside at the bottom or on the surface. Dragonflies, stone flies… however, most prefer clean and well-oxygenated water, conditions that do not usually occur in an unattended pool.
In this type of stagnant water, the most common insect larvae are mosquitoes. Some, like the tiger mosquito , have found an ideal place for breeding in these environments and today they are an invasive species in Spain.
But the insects most likely to inhabit a pool—sometimes even well-maintained, treated pools—are beetles . There are almost 500 different species of aquatic beetles in mainland Spain, belonging to 12 different families, and most of them can colonize swimming pools.
Finally, and if the pool is left long enough, frogs, newts, snakes and other vertebrates can colonize it.
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