The Ultimate Survivors
Tadpoles shrimps live in seasonal brackish (slightly salty) or freshwater pools, which dry out in the summer. When the pools dry out all predators and competitors are killed off however the Tadpole shrimps have adapted to survive. Their pools may only last a few weeks before drying out, and then it may be years or even decades before the water returns. As a result of their short lived habitats Tadpole shrimps have a very rapid development, maturing from an egg to adulthood in just two to three weeks. Utilising such an inhospitable and difficult habitat is believed to be one of the reasons why this group of animals has been able to survive for so many millions of years.
Tadpole shrimp (Triops cancriformis) (c) Geoffrey Fryer
Tadpole shrimps are able to survive in temporary pools due to the unique properties of their eggs. When they are laid a proportion of the eggs hatch, and the rest go into 'diapause' - this means the eggs dry out and their development is stopped. In diapause Tadpole shrimp eggs are very durable and can survive up to an amazing 27 years. The eggs can also endure extreme temperatures, as well as transportation by winds, and can be eaten and excreted by an animal without harm! Once these eggs are rehydrated and the environmental conditions are right the diapause will end and the eggs will hatch forming a new generation of Tadpole shrimps.
These animals are prehistoric and look it, with a shield shaped carapace; they look like a cross between a horseshoe and an extinct trilobite. Lacking modern gills, they breathe with primitive leaf-like extensions on their legs. In the wild our native Tadpole shrimp (Triops cancriformis) can grow up to 11cm (4.5") in length (not including the tail). Tadpole shrimps are omnivorous feeders - they will eat small aquatic invertebrates, aquatic plants and sediment. They are also furious eaters, this is necessary to sustain their fast development; daily they have to eat about 40% of their body mass to sustain their rapid growth rate.
Britain has only one species of native Tadpole shrimp (Triops cancriformis) and it is currently found in only two locations, one is in the New Forest (Hampshire) and the other is in Scotland near the Solway Firth. The only other record this century is from the Kirkcudbrightshire coast, however it was lost to coastal erosion in the 1960s. Our native species of tadpole shrimp is also found across the globe including countries such as: EuropeRussia and the Middle East. However, the Tadpole shrimp taxonomy needs updating, and it is possible that the British population may be found to be of international significance.
With a limited distribution there a number of issues are threatening the existence of our small native population. These include the introduction of predators, pollution and invasive aquatic plants. Tadpole shrimps are especially vulnerable when they are young as they lack mobility, size, as well defense against predators. Consequently if a predator is introduced to habitat containing young Tadpole shrimps they can easily wipe out a whole generation. Due to their rarity in Great Britain our native species (Triops cancriformis) is classified as Endangered and is protected under Schedule 5 of the Wildlife and Countryside Act 1981.