Unlike seals, whales, and other such marine mammals, sea otters do not have blubber (a thick layer of subcutaneous fat) to keep themselves warm in cold ocean waters. Instead, sea otters are insulated by a remarkable coat of fur. At 150,000 strands of hair for each square centimeter of skin, the sea otter’s fur is the densest of any animal in the world, and keeps cold water from even touching the animal’s skin. The fur must be kept scrupulously clean in order to retain its insulating properties, and so sea otters spend a great deal of their time grooming and washing. Their skin is so loose that the otter can easily reach and groom every square inch of its body. The fur will also trap air bubbles between the outer “guard” layer and the undercoat, which not only helps keep the otter warm but will aid in buoyancy. In fact, a newborn sea otter’s fur will retain so much air that, after careful grooming by its mother, the baby literally cannot sink; it bobs in the water like a cork.
The grass is always greener! March marks Seagrass Awareness Month, a time to recognize the importance of healthy seagrass beds in maintaining our ocean’s health.
In places like Monterey Bay National Marine Sanctuary, eelgrass – a type of seagrass – provides a primary food source for a variety of marine animals, and protection for others. In addition, seagrasses can help filter pollutants out of the water and prevent erosion, keeping the water column healthy and clear.
Here, otters raft together in Elkhorn Slough, a tidal salt marsh in Monterey Bay, where they provide a critical service to eelgrass beds. Otters help protect these precious grasses by munching on predators like crabs that would otherwise threaten eelgrass beds.
What will you do to make like an otter and protect seagrasses?
Sea otters are extraordinarily devoted mothers. Female sea otters will carry their pups on their chests, constantly grooming their fur to make sure the pup stays warm and buoyant. She will leave her baby only to find food, and will wrap the pup in kelp to make sure it stays safe and in one place. Her milk, rich in fat like that of whales or seals, sustains her baby for up to six months in southern populations, or up to a year in northern areas. If the pup dies, the mother will continue to carry the little corpse for days following its death. Female sea otters have also been recorded adopting orphaned pups.
On the other extreme, however, if conditions become particularly harsh a mother sea otter may abandon her pup. In particular, on the rare occasion that a sea otter gives birth to twins, the weaker pup may be abandoned to ensure the survival of its sibling.
Sea otters spend much of their time alone, but when resting they form all-female or all-male groups called “rafts”. These rafts can be as small as ten animals or as large as a hundred, but the largest raft ever recorded contained over two thousand otters! While sleeping, otters in a raft or alone may wrap their bodies in kelp to keep themselves from floating out to sea.
Sea otters only became strictly marine/aquatic animals around two million years ago, in contrast to the pinnipeds (seals/sea lions), which entered the water around 20 million years ago. In some ways, however, the sea otter has adapted even better to their ocean home than their distant cousins. Seals and sea lions must give birth and nurse their young on land, usually ice floes or beaches. Sea otters, in contrast, give birth to their young and nurse them in the water.
Sea otters are what is known as a keystone species; a species whose presence has an extreme effect on their ecosystem. For example, one of the favourite prey animals of the sea otter is the sea urchin, an echinoderm that feeds on the lower stems of kelp and other seaweed. Sea otters keep the urchin numbers low, allowing the growth and continued health of kelp forests, one of the richest and most productive marine ecosystems in the world.
Areas where sea otters have been extirpated, on the other hand, have degenerated into “urchin barrens”; barren rocky areas of seafloor where only urchins and other invertebrates can flourish. Even worse is that these urchin barrens can spread; once a population of urchins has eliminated all of the kelp in an area, they will move on to destroy another kelp forest. The reintroduction of sea otters to areas such as coastal British Columbia has dramatically improved the health and productivity of the coastal ecosystems.