Few traits are shared by all species of animals and plants. Movement is a noteworthy exception. Although many species seem permanently locked to a particular place, they inevitably move at some stage of their life cycles. The mobile phase can be adults, juveniles, or gametes. Species move for many reasons. Some move to seek food. Others move to avoid becoming food for someone else. Some move to seek favorable conditions. Others move to find a mate or an egg to fertilize. When these forms of movement occur over relatively short distances, they can play important roles in a wide range of ecological and evolutionary processes (Davidson et al., 2004). Much of marine ecology has focused on the dynamics and consequences of such local interactions.