While traipsing around the tide pools in Asilomar State Park in Pacific Grove, California on a gloomy May day, marine science communicator and conservationist Molly Fishman spotted a curious color. Something purple was sitting there amid the brown rocks and green algae. Fishman took a closer look and realized she was looking at a complete sea otter skeleton, but this wasn’t any old skeleton. Each and every bone on the skeleton was a bright and iridescent purple.
“The wave of emotions [I] felt included elation, gratitude, sorrow, peace,” Fishman tells Popular Science. “It can be a common occurrence to find marine mammal bones along the intertidal [zone]. I have friends who have found a random purple otter bone here or there, but to find the entire skeleton still very much intact is extraordinary.”
Some sea otter bones are purple because many of the furry marine mammals specialize in eating purple sea urchins. Over time, a purple pigment from the sea urchins called echinochrome builds up in their teeth and bones and stains them. This phenomenon is called echinochrome staining, and it can range from a few purple teeth to a whole purple skeleton.
“This otter was full grown, hopefully lived a long life, and can confirm it definitely munched on a wild amount of purple sea urchins,” Fishman explains.
Otters are not the only organisms whose bodies can be changed by what they eat. Humans who eat too many carrots can develop a similar condition called carotenemia, when pigments called carotenoids build up and color the skin, hair, or nails shades of yellow or orange. Some tree frog bones can turn green, while flamingoes get their signature pink hue from eating shrimp.
“Although many animals can change colors based on their diets like flamingos, it doesn’t necessarily mean those pigments will penetrate their bone structures,” says Fishman.
As exciting as finding a purple sea otter skeleton is, it’s important to leave bustling ecosystems like tide pools alone, for the animals’ sake—and our own.
“I do want to reiterate that it’s illegal to collect these bones under the Marine Mammal Protection Act,” Fishman says.
