South Pole Sea Urchins

In the icy waters of Antarctica, many sea urchin species have evolved a surprising parenting practice.

Most marine invertebrates wouldn't win the award for parent of the year. Their parental investment typically ends when they release eggs and sperm into the sea, where some might manage to meet for fertilization before drifting too far apart. In most parts of the world, sea urchins tend to follow the same strategy, but in Antarctica, many species harbor their developing young in special pouches or indentations among their spines. This behavior, called brooding, has evolved at least three separate times in Antarctic sea urchins.

In March, Academy scientist Rich Mooi and his student, Suzanne Lockhart, traveled to Antarctica to participate in an Antarctic Marine Living Resources (AMLR) survey. Aboard a trawler for a month, Mooi and Lockhart were responsible for collecting and identifying marine invertebrates. During the trip, they collected a number of brooding sea urchins, some of which may represent new species. One of these, a "regular" sea urchin that belongs to the cidaroid group, stores its developing young in depressions around its mouth. The other, part of the "irregular" group, actually broods its young in a pouch inside its body. When the young are fully developed, the adult urchin appears to "give birth," as the plates around an opening at the top of the body fold down to allow the small urchins to emerge. As part of a larger effort to understand evolution at Earth's extremes, Academy scientists are working to discover when and why these behaviors evolved.

Typical shoreline at the foot of a glacier near Admiralty Bay on King George Island.
This urchin, Rynchocidaris triplopora, is arguably the most common cidaroid in Antarctica's South Shetland region, which is fortunate for Mooi's studies, since it also happens to be infected by a bizarre parasite that turns the reproductive system of the unfortunate host upside down.
After dredging up a mass of wriggling organisms, Mooi and Lockhart spent most of their time sorting the invertebrates by type, always keeping an eye out for special sea urchins.
The young of most Antarctic cidaroids, such as this Notocidaris gaussensis, are protected by the mother in a deepened area around her mouth.
Map by Colleen Sudekum