Water is essential to all forms of life on Earth. That said, the enormous increase in the human population over the past few decades has placed a greater strain on the world’s freshwater reserves through direct consumption, agriculture and manufacturing activities. Sadly water shortages are not uncommon in many parts of the world. These shortages can have devastating effects for both people and wildlife and can be exacerbated by climate change.
The UN recognises March 22nd as International World Water Day to encourage people to limit their use of water as well as to highlight the issue of water shortages. To mark the day, we thought we would highlight just a few of the many organisms that depend on freshwater for survival.
Water as a jealously guarded dive site
The striking yet elusive kingfisher (Alcedo atthis) is famous for diving from its perch into rivers to catch fish and invertebrates. As the kingfisher requires a relatively large amount of food to sustain itself it will aggressively defend its watery hunting ground from other kingfishers with threatening displays and even physical contest. As kingfishers require clear water to see their prey and vegetation on which to perch, their presence is a good indicator of a healthy river ecosystem.
Water as a spawning ground and nursery
Amphibians depend on freshwater in some form or another to lay their eggs, which develop into fully aquatic tadpoles. Predation on tadpoles is often high which is why most species lay a large number of eggs in a specific breeding season. This strategy is practiced by the green-thighed frog maximising the amount of offspring that survive to adulthood.
Water as a last refuge
The Cuban crocodile is found in only two freshwater swamps in Cuba. This extremely restricted range makes it highly vunerable to extinction and it depends on these specific habitats for its survival. Fortunately due to recent conservation efforts the Cuban crocodile’s numbers are recovering.
Water as a trap
A fierce predator in many ponds and lakes across Europe, the water boatman sits and waits near the surface of the water until it detects movement nearby… it then swoops in on its prey with a toxic bite!
Water as a place to grow
Freshwater ponds and lakes all around the world are home to a huge array of interesting and beautiful plant life. The white water-lily has many adaptations to a life in freshwater such as its large flat leaves that float on the surface of the water so as to receive more light. Aquatic plants also often have important roles in freshwater ecosystems, oxygenating the water, provide nesting sites and keeping algal blooms under control.
Water as a place to set up a fortress
The American beaver is famous for drastically altering its freshwater surroundings to make a suitable habitat. Using its tough incisors to fell trees for dams, the beaver creates an area of open, still water where it constructs its lodge. Entrance to the lodge is only possible from under the water and therefore the beaver and any offspring are protected from terrestrial predators. The beaver itself also has specific adaptations for a life in water with webbed feet and a large flat tail used for propulsion as well as a dense underfur that keeps it warm even in freezing water.
Water as a hunting ground
All ecosystems have a ‘top dog’ predator and in many rivers and creeks in Europe this will be the pike. A ferocious predator, the pike will remain perfectly still waiting for prey to come within a close distance and then move in for the kill with a lightening fast strike. Pike are likely to consider many of the animals in their watery environment as prey including fish, crayfish, frogs and newts and even ducklings and small mammals. Pike do need to be careful around members of their own species though as larger pike have been known to practice cannibalism!
Find out more about World Water Day 2012.
George Bradford, ARKive Media Researcher