The underwater world holds many challenges. The most basic of these is movement. The density of water makes it difficult for animals to move. Forward movement is a complex interaction of underwater forces. Among these is thrust, the force in the direction of movement. Another important force is drag, which slows forward movement by opposing thrust. When thrust exceeds drag, there is movement forward (Source: Buchheim).
Additionally, water itself has movement. Strong currents carry incredible power that can easily sweep creatures away. As we will see, the challenges to aquatic movement result in a variety of swimming methods, used by a wide range of animals. The result is a dazzling underwater ballet.
Fish rely on their skeleton, fins, and muscles to move. Their skeleton enables the basic physics of swimming. Their skull acts as a fulcrum and their vertebrae act as levers. Fins control pitch, yaw, and roll. Muscles are arranged to allow the complex movement necessary to produce thrust. Smooth, streamlined bodies help to reduce friction and drag (Source: Buchheim).
Invertebrates have evolved numerous solutions to movement in the aquatic world. Shrimp crawl and swim with short bursts of their tail. Jellyfish, without backbones or fins, swim using a form of jet propulsion. By squeezing their bowl-shaped bodies, they send out small bursts of water, forcing their delicate bodies forward.
Many mammals have adapted well to movement underwater: whales, dolphins, manatees, seals, sea lions. Among the most animated of sea mammals is the North Pacific sea otter. Streamlined, flexible bodies and powerful hind legs make it an expert swimmer (Source: 'Movement').
From the smallest of fishes to the largest of marine mammals, the challenges of underwater movement have inspired countless solutions.