11.3. Enhydra lutris: Sea Otter http://www.ck12.org
mostly at sea. Able to give birth and raise their young in water, they can also go without fresh water for as long as
they live. Sea otters can live in the water without ever coming out of the water. They can come on land if they want
to, but they rarely do because of predators.
Biology
Cell Biology
Sea otters have eukaryotic cells, which have a nucleus and many organelles. Organelles are like miniature organs
in a cell. Organelles include the nucleus, which contains the genetic material, the mitochondria, which provides
the energy, vesicles, which transport materials, vacuoles, which are the storage centers, and lysosomes, which have
digestive enzymes. Ribosomes are where the proteins are made.
Sea otters have red blood cells and white blood cells. The red blood cell is shaped with a pocket that traps oxygen
and brings it to the rest of the body. Interestingly enough, mature red blood cells do not have nuclei. White blood
cells are used for fighting off bacteria, disease, and infection. The sea otter also has nerve cells and skin cells. Nerve
cells are long and stringy. They create a line of communication between other nerves and can quickly send signals
throughout the body. Skins cells are flat and fit tightly together to protect the body.
Sea otter cells divide in two ways, mitosis and meiosis. Mitosis is when one cell replicates its chromosomes, then
divides them equally in two replicated cells. Meiosis produces cells necessary for sexual reproduction. Meiosis
creates gametes, or sperm and egg cells.
Evolution
No one knows exactly where sea otters came from, but they believe they arose from a fish-eating, otter-like mammal
about 5 to 7 million years ago near the Pliocene and Miocene periods. Their ancestors were originally land mammals
that went into water to hide from predators and look for food. Once their ancestors entered the water, they began
developing permanent characteristics to adapt to the water like their waterproof coat, flippers, and webbed feet.
Ecology
The sea otter’s main predators are the great white shark and humans. People still skin them and eat their meat, but
it’s not as popular as it used to be. Their prey includes sea urchins, clams, abalone, mollusks, and snails. There is a
cat parasite that is currently infecting sea otters. This parasite is a protozoan and is named Toxoplasma gondii.
Amazingly sea otters can help save the world from climate change. While eating lots of sea urchins, the sea otters
help the kelp beds and create less carbon dioxide. Sea urchins feed on kelp beds, which are like our trees, keeping
the water clean and removing the carbon dioxide. When sea otters eat the urchins, they save the kelp beds and keep
them alive.
Birth takes place around May and June in northern regions and January and February in southern regions. They
usually give birth once a year, to only one pup. If there are twin pups, one will be abandoned and left to fend for
itself, while the other stays with its mother and hopefully lives a full and happy life.
Physiology
The sea otter is a mammal and is also a vertebrate. Mammals can adapt quicker to an environment than any other
class of animals. They are able to keep their body temperatures warmer or cooler than the environment they are
currently in. Their fur is thick and keeps them warm in colder temperatures. The sea otter’s lower jaw is connected