Much of the white sand on tropical beaches is actually parrotfish poop.

Parrotfish are essential bioeroders in coral reef ecosystems. They use their beak-like teeth to scrape algae and polyps off coral colonies. During this process, they ingest significant amounts of the coral's calcium carbonate skeleton. Their specialized pharyngeal teeth then grind the rock into a fine powder before it passes through their digestive tract.According to a study published in the journal 'Geology' by researchers from the University of Exeter, parrotfish are responsible for more than 80% of the sand production on certain reefs in the Maldives. In these tropical environments, a single Chlorurus gibbus (steephead parrotfish) can excrete approximately 450 kilograms (nearly 1,000 pounds) of sand annually. This process is vital for the maintenance of island landmasses and beach replenishment.The sand produced by parrotfish is distinct from silica-based sand found on temperate beaches. This biogenic sand is composed of high-purity calcium carbonate, which gives tropical beaches their signature brilliant white appearance and soft texture. Without these fish, many tropical islands would face accelerated erosion due to rising sea levels and the lack of new sediment production. Their role highlights a complex ecological cycle where the destruction of coral structures directly leads to the creation of coastal habitats.