Scientists estimate that up to 70% of the sand on white sandy beaches in the Caribbean and Hawai‘i has been excreted by parrotfish. A large adult parrotfish can excrete over a ton of sand per year. Areas that have parrotfish produce more sand than similar areas with few or no parrotfish. This sediment production rate is especially important in areas like Hawai‘i, where there is little terrestrial input, and almost all of the sand is of biogenic origin.

https://manoa.hawaii.edu/exploringourfluidearth/physical/coastal-interactions/beaches-and-sand/weird-science-parrotfish-and-sand