Danube an important industry. The Upper Danube ecoregion alone has about 60 fish species and the Lower Danube–Dniester ecoregion has about twice as many. Among these are an exceptionally high diversity of sturgeon, a total of six species (beluga, Russian sturgeon, bastard sturgeon, sterlet, starry sturgeon and European sea sturgeon), but these are all threatened and have largely–or entirely in the case of the European sea sturgeon–disappeared from the river. The huchen, one of the largest species of salmon, is endemic to the Danube basin, but has been introduced elsewhere by humans. Important tourist and natural spots along the Danube include
Atlantic horseshoe crab role in the local ecosystems, with their eggs providing an important food source for shorebirds, and the juveniles and adults being eaten by sea turtles. The other three extant (living) species in the family Limulidae are also called horseshoe crabs, but they are restricted to Asia. This group of animals is also known as horsefoot, or saucepan. Some people call the horseshoe crab a "helmet crab", but this common name is more frequently applied to a true crab, a malacostracan, of the species "Telmessus cheiragonus". The term "king crab" is sometimes used for horseshoe crabs, but it is more usually