Have you ever wondered where the sand comes from when enjoying a day at a white sandy beach? A major part of it is fish poop!
So during your last amazing beach holiday you were lying around on poop while praising its beauty.
The sand particles on tropical and subtropical beaches are pieces of coral, rock, shell and eroded limestone. Coral reefs are a significant source of sand particles. Scientists estimate that around 70% of the beaches are produces through parrotfish and other sand producing marine animals. The other parts come from through waves eroded rocks and pieces of shell.
Bumpheads or humpheads are the biggest members of the family of the parrotfish with a size of up to 1.5 m and a weight of 75 kg. They can live for 40 years. Each bumphead parrotfish ingests an estimated amount of 5 to 6 tonnes of structural reef carbonates per year, almost half being living corals.
Can you imagine the amount of sand that is in one lifetime?
Bumphead parrotfish are mostly found in schools of up to 100 individuals cruising along reefs producing clouds of sand around them. They are born as females and only become males if the dominant male leaves the group or dies.
Most parrotfish are nibbling off algae from coral and rocks with their beak-like teeth (hence the name). Doing this they break off pieces of coral together with the algae. The particles which cannot be digested are discarded into the ocean as sand grains.
This works differently for the bumpheads as they actually eat coral. With their heads they bump into coral, bite smaller pieces off and finally grind these using their pharyngeal teeth in the throat. The small pieces go directly to the digestive tract as there is no stomach. The nutrients are absorbed and everything else is released as sand.
Importance to the reef health
Coral reefs are extremely complex ecosystems which are affected by overfishing, physical damage, water temperature and pollution. It has been shown in the Caribbean that parrotfish are the number one factor to keep coral reefs healthy. The healthiest coral in the area are in the regions where parrotfish are protected from overfishing by practices like fish traps and spear fishing. While most other reefs have been dominated by algea in the last two decades. Coral covered in algae get less sunlight and nutients causing a stop of growth or even the death of the coral. The report also shows that protecting parrotfish and sea urchins (another creature feeding on the algae) could reverse the effect and allow coral reefs to restore.
Importance for island building
Reef islands like in the Maledives are unique landscapes made out of sediment from the surrounding coral reef. A study has found that all the different species of parrot fish produce at least 85% of the new sand-grade sediment which makes up these islands. Another 10% is produced by macroalgae (Halimeda). These numbers make it very clear that a healthy parrotfish population is essential for the preservation of sandy islands.
Unfortunately parrotfish are delicacies in many places and are catched as food. People who like to look at beautiful coral reefs and white sandy beaches (so kind of everyone) might wanna rethink eating parrotfish.
Bolbometopon muricatum in IUCN Red List of Threatened Species. Retrieved August 16, 2016 from http://www.iucnredlist.org/details/63571/0
Bolbometopon muricatum, Green Humphead Parrotfish in Encyclopedia of Life. Retrieved August 16, 2016 from http://www.eol.org/pages/339152/details
From despair to repair: Dramatic decline of Caribbean corals can be reversed in IUCN. Retrieved August 16, 2016 from http://www.iucn.org/content/despair-repair-dramatic-decline-caribbean-corals-can-be-reversed
C. T. Perry, P. S. Kench, M. J. O’Leary, K. M. Morgan, F. Januchowski-Hartley. Linking reef ecology to island building: Parrotfish identified as major producers of island-building sediment in the Maldives.Geology, 2015; DOI: 10.1130/G36623.1
Parrotfish key to reef survival in International Coral Reef Initiative. Retrieved August 16, 2016 from http://www.icriforum.org/caribbeanreport