school energy&environment

The shark: a perfect machine

Incredible examples of adaptation can be found, in particular, among the sea organisms, that must live in a context such as water. You surely must have looked underwater with a mask, and surely you must have noticed how difficult it is to see far away. In fact visibility in the sea depends on a number of factors such as: the temperature of the water, the sea bottom, the plankton organisms and the suspension of various elements. Now imagine you live in this strange ecosystem and you are a large predator that must find food. In the depths of the sea very little light penetrates and often the suspension of a number of organisms makes it difficult to see clearly, but you are a famished shark that is looking for a succulent prey. Everything is very dark, yet you notice that the prey you want is there, and with a rapid stroke you capture it between your teeth! Good eyes surely are not enough to be an efficient predator and therefore nature has had to “invent” really particular adapting strategies in order to survive. In fact sharks have two senses more than us humans: the lateral line sensory organ and the Ampullae of Lorenzini. The lateral line sensory organ consists of a series of small channels along the shark’s sides, under the skin surface, that contain tiny sensory hair like structures that are sensitive to the water movements around the body provoked by waves, prey or predators. Therefore this organ allows the sharks to identify objects that are moving (even without seeing them!) and to pinpoint their position remarkably precisely. In fact, every moving body in the water produces vibrations that are transmitted in the environment, spreading out like concentric rings that form on the surface of a lake after a stone has been thrown into it. These vibrations differ, depending on the size of the animal and its state of health. And this is the reason why sharks almost magically appear in a few seconds when a fish is captured or wounded! However, the sharks’ adaptation to life underwater does not finish here, in fact they have another important sensory organ, the Ampullae of Lorenzini. This organ consists of small pores in the area of the shark’s head, with ampoules that are filled with a conductor gel, connected with nerve fibres. The sensory cells can distinguish very weak electrical fields generated by other animals at a close distance (20-30 cm, maximum a few metres). In fact all living organisms have an electric potential (in fact, electrocardiograms and encephalograms are based on this phenomenon). So thanks to this very particular organ sharks become like metal detectors, and can locate magnetic fields generated by their prey, that may be perfectly hidden or mimetically invisible, but will certainly not be able to inhibit the electricity of their body. For this reason not even a sole, that remains perfectly hidden under the sand is safe! The Ampoules of Lorenzini are an organ that is so sensitive that it can capture magnetic fields ranging from 0.01 to 0.0005 microvolt per centimetre, which means that a battery that we consider completely dead, could be an enormous source of energy for a shark.