Parrotfish may look like your typical reef fish, but look past the bright colours and they are actually extremely interesting and ecologically important.
It is hard to choose which of the parrotfish’s many incredible characteristics and unique abilities is most remarkable. Is it their beautiful colours and patterns that gave them their name? Their ability to turn from male to female and back again at the drop of a hat? Is it that they sleep for over 10 hours at a time in cocoons of mucus? Or is it their ability to crunch through corals with their powerful beaks and poop out the sand? Regardless of which impresses you most, one thing becomes apparent when you learn more about these amazing animals, they are way more important than you ever imagined.
When you first come across parrotfish they appear to be very much like your average tropical reef fish. There are believed to be around 90 species belonging to the family Scaridae, commonly found living on coral reefs in the tropical regions of every major ocean. They have a fairly constrained size range only growing between one to four feet long across all species. With a lifespan of around seven years, which is pretty standard for fish of this size. They are omnivorous eating both plants and other small fish, however their diet is made up predominantly of the algae they scrape off corals. All in all there is nothing here to suggest that there is anything special about them, but when you look closer you find there is a lot more going on with these colourful coral crunchers than first meets the eye.
Almost all parrotfish start out their lives as female. Some are born male, known as primary males, but this is quite rare in most species. Instead juvenile females often form schools for the first few years of their lives until they are fully grown and sexually mature. At this point the largest female undergoes a sex change to become a secondary male. Parrotfish reproduce by spawning aggregations where males and females gather in groups to release their eggs and sperm into the water. Those eggs then become fertilized into tiny larvae that are carried to new reefs to start their lives. The reason most males are secondary compared to primary is that when a secondary male is created he becomes the one responsible for fertilizing the eggs of his old school, which has effectively become his personal harem. However the sex change is also reversible and those secondary males may later turn back into females.
These sex changes and defined gender roles are also what is responsible for the fantastic array of colours and patterns seen in parrotfish. Like most sexually dimorphic species, where the males and females look different to one another, it is the male parrotfish who have the more vibrant and brilliant colours. In fact in most species the females are usually very dark and monochromatic, but can develop the colourful patterns of the males when they undergo sex changes. The result is some truly stunning patterns, the most notable of which belong to species such as queen, stoplight, bicolour, marbled and green humphead parrotfish. However because the genders and juveniles of each species can all have different colours and patterns this can also make them a classification nightmare.
Another way parrotfish stand apart from most other fish species is in the way they sleep. They are unusually heavy sleepers for a fish, capable of going for 10 hours uninterrupted. That is a long time, especially if you are out in the open and unprotected from predators. However parrotfish are not unprotected when they nod off, because they cover themselves in a cocoon of mucus. This mucus is secreted by the parrotfish and in less than an hour they can create enough to completely cover their body in the stuff. It acts like an early warning system for the fish waking them up when something brushes past it or tries to take a bite. It also keeps them safe from tiny isopods that would try to nibble at their skins and can even provide a defence against the UV rays of the sun. When they wake up they simply swim on out until the next time they’re feeling tired.
Pooping out beaches
If you’ve ever taken a sunset stroll along a tropical white beach on your travels then chances are you’ve actually been walking through parrotfish poop. As we saw earlier their diet consists almost entirely on algae they extract from the corals they live in. However in reality the parrotfish tend to eat as much coral as they do algae. Their extremely powerful beaks are capable of easily breaking the calcium carbonate skeletons of corals creating a loud crunching sound that can be heard throughout tropical reefs. They then break down the coral with specialised teeth before digesting it and extracting the algal nutrients from it. Later they then expel the waste coral particles which in layman terms means pooping out sand. The average parrotfish will produce around 100kg of sand a year, but some species have been known to produce as much as a tonne annually.
Saving coral reefs
The sand parrotfish produce is great for making us luxury beaches, but the process also provides a much more important service for coral reefs. Algae directly compete with corals for space and sunlight on reefs. Unfortunately when algae win that battle it often means the death of corals and a majority of the life that lives among them. Herbivores like the parrotfish and anemones are therefore crucial in controlling algal growth on reefs. Especially when corals bleach because they quickly get overrun by algae before they can recover. However sharp decline in parrotfish, especially on Caribbean reefs, has led to more algal dominance and a loss in biodiversity.
Parrotfish are eaten for food in tropical regions although not as a main targeted species, apart from Polynesia where raw parrotfish was once considered a royal dish. The big problem though as been the bycatch of parrotfish from commercial overfishing and predation by invasive lionfish in the Caribbean and western Atlantic. A recent study from 2014 showed that maintaining healthy parrotfish populations is one of the most effective and easiest ways of protecting coral reefs. So therefore encouraging the recovery of these fascinating fish is of vital importance.
Not your ordinary fish
So as I am sure you are starting to realise, parrotfish are actually one of the most remarkable fish, or animal, you can find on a coral reef. Their incredible array of colours and patterns makes them as beautiful as they are ecologically important, and their unique abilities to change sex and protect themselves in mucus have made them incredibly successful. The only thing they are struggling with now is us and it is important we continue to protect these wonderful creatures and the coral reefs they live on.
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