Filmmaker Nitya Navelkar loves to live near Miramar Beach in Goa, India. To get away from the chaos of the world, she often goes for walks along the beach. During one of these walks, she came across small balls of sand, which she first thought were crab eggs. There was also an interesting pattern around them, which made Nitya curious. As she was taking pictures of the sand balls, she started to notice tiny crabs, busy making the little spheres.

“It was fascinating, and I immediately did research and found out that they are sand bubbler crabs”, she says. Nitya’s curiosity led her to make a documentary short film on these crabs called Sand Laddoo. The documentary was screened at Italy’s Duemila30 Festival in 2024 and also received an honorable mention at the Neum Underwater Film Festival.

Sand bubbler crabs belong to the family Dotillidae of the genus Scopimera and Dotillia. They are found throughout the Indo-Pacific region on tropical and sub-tropical sandy beaches. During high tide, these small, round-bodied crustaceans are found in burrows that contain a trapped pocket of air. This helps the crabs breathe. At low tide, they feed on surface detritus, non-living organic matter, such as dead plants, and stranded plankton.

These crabs have large membranous disks (called “tympana” or gas windows) on the meral segments of their legs and in some species, like Dotilla, on the thoracic sternum for exchanging gases, specifically, oxygen and carbon dioxide.  

The balls of sand that Nitya came across are part of the sand bubbler crabs’ feeding process. When the sand is wet, these crabs use their mouthparts to sieve the sand for detritus and microscopic organisms. They discard the nutrient-deficient sand by moulding it into tiny balls. With remarkable speed to scour for food, the crabs leave behind patterns on the sand, which gave them their nickname ‘sand artists’.

Image credit: Nitya Navelkar photographing the sand bubbler crabs at the Caranzalem Beach, Panaji, Goa. Photo by Nitya Navelkar.

Nitya points out that their feeding process is important to the coastal ecosystem. “While they are eating their food, they are also taking care of the environment. If they stop doing what they are doing, then the organic matter will remain trapped in the sand and slowly start to stink. So, the beach will smell”, she explains. “In living their own life, they are also contributing to the health of the ecosystem.”

However, today, beaches across the world are littered with plastic waste and microplastics. A 2023 study that analysed seven most famous and crowded beaches found around 80 microplastics per cubic metre of sand or water. Worse, about 30% of commercial fish from these areas contained microplastics. This extensive presence of microplastics on beaches is a constant threat to marine life such as the sand bubbler crabs.

“A lot of microplastics are trapped in sand particles, and these crabs are unknowingly ingesting them”, says Nitya sadly before adding, “There’s [also] a lot of barge movement in the sea. So, when there are oil spills, oil can get trapped in the sand.” She concludes, “The crabs, while feeding, tend to unknowingly consume it, which is harmful for them.”