eddies mix the layers of water which would otherwise become stagnant and less conducive to life. Nutrients are thus circulated and re-used. The large ocean currents transport warm water from the tropics to the poles and cold water the other way. They help to stabilise the planet's temperature and to minimise its extremes. For instance, because of warm ocean currents arriving from the north, the temperature of New Zealand is 3-4 degrees higher than it would be without them. For the creatures in the sea, ocean currents allow their larvae to be dispersed and to be carried great distances. Many creatures spawn only during storms when large waves can mix their gametes effectively. Coastal creatures living in shallow water experience the brunt of the waves directly. In order to survive there, they need to be robust and adaptable. Thus waves maintain a gradient of biodiversity all the way from the surface, down to depths of 30m or more. Without waves, there would not be as many species living in the sea. Waves pound rocks and make them erode faster, but sea organisms covering these rocks, delay this process. Waves make beaches by transporting sand from deeper down towards the shore and by washing the sand and removing fine particles. Waves stir and suspend the sand so that currents or gravity can transport it. Wave motion Anyone having watched water waves rippling outward from the point where a stone was thrown in, should have noticed how effortlessly waves can propagate along