Why are soils in the Marshall Islands sandy and low in fertility?

The Marshall Islands are composed of low-lying coral atolls rather than volcanic landmasses. These atolls consist of small islands formed atop coral reefs that have accumulated around submerged volcanoes.12

Because these islands are essentially coral caps, their soil composition is derived from the breakdown of coral and marine materials, which results in a sandy texture that is inherently low in fertility compared to the richer soils found on volcanic islands.12