The wonder of Japan’s star-shaped sand beaches

The Ryukyu Islands of Japan are home to beaches covered with starry sand, an extraordinary natural phenomenon due to the skeletons of Foraminifera and diatoms

Imagine walking on one of the beaches of the Ryukyu Islands in Japan, perhaps in Okinawa. You bend down, pick up a grain of sand, and, upon looking closely with a magnifying glass, you discover something extraordinary: that tiny grain is shaped like a star.

Japan is home to one of the highest concentrations of star-shaped sand beaches in the world. Unlike traditional sand, which is the result of rocks and corals being ground down over time, this sand was once alive. Kazuhiko Fujita, a professor at the University of the Ryukyus, explains the phenomenon:

“Star sand consists of the empty shells of single-celled microorganisms called Foraminifera. They look like living stars… with a round body and five or more spines, resembling a starfish.”

The beaches of islands like Taketomi, Hatoma, and Iriomote are covered with the skeletons of these microorganisms. They live under the sea, on coral reef crests or sandy seabeds sheltered from currents and waves. But do not be fooled by their apparent simplicity: these Foraminifera host another microorganism within their shell, a diatom.

The role of diatoms in the formation of star sand

Diatoms are microscopic algae that convert light into carbohydrates and oxygen through photosynthesis. The presence of diatoms within the Foraminifera is the secret to their star shape. The irregular points of the star allow light to penetrate the exoskeleton, reaching the diatoms that produce energy for themselves and their host.

When these microorganisms die, their skeletons are transported to the beaches, contributing to the creation of the enchanting star-shaped sand. According to Mark Wilson, an invertebrate paleontologist at the College of Wooster in Ohio:

“As the population of these Foraminifera grows, so does the number of these skeletons, contributing to the accumulation of sand. This could mean they might play a role in protecting small islands by adding material to the shores.”

Source: National Geographic