# Sandy Scaridae (DD-591)

> Parrotfish are the family Scaridae, about 90 species of reef fish named for their fused, beak-like teeth. They bite and scrape the surfaces of dead coral and rock, mainly for the algae and other microscopic organisms growing on and in them, and swallow chunks of the calcium-carbonate reef along the way. A second set of tooth plates in the throat, the pharyngeal mill, grinds that material down, the digestible part is absorbed, and the rest comes out as fine white sand. NOAA says parrotfish can produce hundreds of pounds of sand a year, and a large bumphead parrotfish may produce several hundred pounds. The University of Hawaii's Exploring Our Fluid Earth estimates that up to 70% of the sand on white beaches in the Caribbean and Hawaii was excreted by parrotfish. A 2021 study on a Maldivian reef put individual production anywhere from under 3 to over 5,000 kilograms a year, depending on species and size. Grazing also keeps algae from overgrowing reefs, which is why parrotfish are seen as important to reef health. The footage shows a blue-and-purple parrotfish grazing over rocky reef.

- Department: Nature
- First published: 2025-06-07
- Last updated: 2025-06-07
- Permalink: https://detailenjoyer.com/case/sandy-scaridae/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-591-F01**: Parrotfish grind swallowed reef material with a pharyngeal mill in the throat. _(Write-up · Exhibit B (A mill in the throat))_
- **DD-591-F02**: Parrotfish can produce hundreds of pounds of sand a year. _(Write-up · Exhibit D (Hundreds of pounds))_

## Write-up

Some white beaches are fish poop. Up to 70% of the sand on some Hawaiian and Caribbean beaches came out of parrotfish.

1. **A fused beak**: Parrotfish teeth are fused into a beak used to scrape dead coral and rock.
2. **A mill in the throat**: Tooth plates in the throat, the pharyngeal mill, grind the swallowed reef material.
3. **Out comes sand**: The ground-up carbonate passes through the gut and comes out as fine white sand.
4. **Hundreds of pounds**: NOAA says parrotfish can produce hundreds of pounds of sand a year.
5. **Beach builders**: Up to 70% of the sand on some Hawaiian and Caribbean white beaches came from parrotfish.

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## Reel vs. record

- **Note**: 'These teeth are fused into strong dental plates that allows them to grind coral': I'd split that in two. The fused beak scrapes the coral, and a separate set of tooth plates in the throat, the pharyngeal mill, does the grinding.
- **Note**: 'Extracting nutrients': the food is mostly the algae and microscopic organisms growing on and in the coral. The coral rock itself passes through as sand.
- **Note**: 'Hundreds of pounds of sand each year': matches NOAA. I'd add that it varies a lot by species and size; one study puts it between under 3 and over 5,000 kilograms a year.

## Video: Sandy Scaridae: Some White Beaches Are Fish Poop

- Duration: 22.8 s · Published: 2025-06-07
- File: https://detailenjoyer.com/assets/videos/DKmRD6CRuGV.mp4

### Transcript

DID YOU KNOW? Parrotfish are brightly colored reef dwellers known for their beak-like teeth, which they use to scrape algae off coral and rocks. These teeth are fused into strong dental plates that allows them to grind coral, extracting nutrients and inadvertently producing fine white sand. A single parrotfish can create hundreds of pounds of sand each year. They play a crucial ecological role by controlling algae growth and helping maintain healthy coral reefs. NOW YOU KNOW!

## Questions & answers

**Q: What are parrotfish teeth fused into?**  
A: It gives them their name. _(Source: Write-up · Exhibit A (A fused beak) · University of Hawaii, Exploring Our Fluid Earth: Weird Science: Parrotfish and Sand; Wikipedia: Parrotfish)_

**Q: What grinds the reef material a parrotfish swallows?**  
A: A second set of tooth plates. _(Source: Write-up · Exhibit B (A mill in the throat) · University of Hawaii, Exploring Our Fluid Earth: Weird Science: Parrotfish and Sand; Yarlett et al., Quantifying production rates and size fractions of parrotfish-derived sediment, Ecology and Evolution (2021))_

**Q: What does the ground-up coral become?**  
A: It passes through the gut. _(Source: Write-up · Exhibit C (Out comes sand) · NOAA National Ocean Service: How does sand form?; University of Hawaii, Exploring Our Fluid Earth: Weird Science: Parrotfish and Sand)_

**Q: How much sand can a parrotfish make in a year, according to NOAA?**  
A: Big species produce the most. _(Source: Write-up · Exhibit D (Hundreds of pounds) · NOAA National Ocean Service: How does sand form?; Yarlett et al., Quantifying production rates and size fractions of parrotfish-derived sediment, Ecology and Evolution (2021))_

**Q: Up to what share of the sand on some white beaches came from parrotfish?**  
A: In Hawaii and the Caribbean. _(Source: Write-up · Exhibit E (Beach builders) · University of Hawaii, Exploring Our Fluid Earth: Weird Science: Parrotfish and Sand)_

## Sources

- [NOAA National Ocean Service: How does sand form?](https://oceanservice.noaa.gov/facts/sand.html)
- [University of Hawaii, Exploring Our Fluid Earth: Weird Science: Parrotfish and Sand](https://manoa.hawaii.edu/exploringourfluidearth/physical/coastal-interactions/beaches-and-sand/weird-science-parrotfish-and-sand)
- [Yarlett et al., Quantifying production rates and size fractions of parrotfish-derived sediment, Ecology and Evolution (2021)](https://doi.org/10.1002/ece3.8306)
- [Wikipedia: Parrotfish](https://en.wikipedia.org/wiki/Parrotfish)

## Cite this case file

Easterling, Marcus. "Sandy Scaridae." The Detail Department (DetailEnjoyer), case file DD-591, last updated Jun 7, 2025. https://detailenjoyer.com/case/sandy-scaridae/