Updated: Aug 12
In the Caribbean, we are fortunate to have sandy white beaches that don't burn your feet, even on the hottest days, and amazing turquoise water nearly all year round. The world-renowned Playa Norte in Isla Mujeres is a testament to this. So what do we owe all this? Well, it would seem that parrotfish have much to do with it. They are incredibly important reef-grazing fish with a fascinating life story.
So, is our beaches parrot fish poop as it is rumoured? Well, let's start with what is sand.
Sand is defined by its size, not composition; it is any mineral coarser than silt but finer than gravel.
Rachel Carson wrote, "In every curving beach, in every grain of sand, there is a story of the Earth", and she is not wrong.
Some beaches, like those in Florida, are the erosion of minerals over thousands of years. Tan beaches result from iron oxide, and black beaches from eroded volcanic material such as lava. Bermuda even has pink beaches due to the erosion of a single-cell, shelled organism called foraminifera.
If a beach is a coastal beach where coral reefs dominate, then the chances are that a high concentration of what you are walking on has passed through a parrot fish. One study showed that 85% of the sand on a Maldivian island was thanks to parrotfish.
So how much sand does a parrotfish poop? In one year, a parrotfish can produce 1000 pounds/450kg of sand (although reports on this vary). That is equivalent to the weight of a baby grand piano.
A parrotfish is a grazer and will spend up to 90% of its day chewing on coral. They eat the hard calcium skeleton -the soft-bodied polyps, and the zooxanthellae -the algae that symbiotically live within the coral. When the fish eat the coral, the soft tissues are absorbed, and the rest form white sand inside the parrotfish. This white sand not only fills our beaches but also acts as a filler for the physical structure of the reef, supporting the coral's skeletons.
That beautiful white sand is also the reason for the colour of our waters. "The water is this beautiful turquoise because the bottom is either white sand or white rocks," Gene Feldman explains.
"What happens is the light comes down, and blue light gets down, hits the bottom, and then reflects back up so you make this beautiful light blue color in the water."
Why doesn't the sand burn my feet? Well, that is thanks to the parrot fish and algae called Halimeda. As the algae die, small segments turn white, fragment, and become powder dispersed between the grains of sand. Up to 30% of the sand composition is the fine white powder of Halimeda.
Parrotfish (from the Scaridae family) can graze all day because of their powerful "beaks", from which they get their name. These beaks comprise roughly 1000 teeth, lined up in 15 rows and cemented together to form the beak-like structure. These teeth constantly wear out and fall to the ocean floor, which is ok, because there is always another set waiting behind them.
These teeth are stronger than copper, silver, and gold. They are made of fluorapatite, which contains calcium and helps make the tip of the parrotfish teeth harder than any other biomineral in the world. They can also withstand a LOT of pressure. Around 530 tons per square inch. Put another way, according to a study by Dr Pupa Gilbert, the equivalent of the weight of 88 elephants.
You can hear the distinctive sound of the parrotfish eating coral throughout your dives.
So how does all this eating and pooping benefit the reef? We owe them gratitude for our sandy white beaches, but is all this eating good for the reef? The answer is yes, so much so that studies have found that reefs have declined by nearly 50% since the 1970s. Not because of climate change or pollution, as widely believed, but mainly due to the loss of natural reef grazers such as parrotfish and sea urchins. Unidentified diseases and overfishing have been the main culprits, and it has been found that the healthiest reefs have restricted or banned fishing practices that harm parrotfish.
The service that these fish provide to the reef is of incredible importance. Algae compete with coral for sunlight on the reefs. When the algae win, the coral and the life that lives among them often die. Therefore, herbivores are crucial to controlling the algal growth on the reef. When corals bleach, algal growth can rapidly take over before the coral can recover. The constant grazing of the herbivores controls excessive algal growth and opens the substrate for more coral growth or formation. The decline of parrotfish and other reef grazers is directly responsible for the algal dominance and loss of biodiversity.
Parrotfish are a keystone species that provide critical functions in a coral reef ecosystem.
What else about them? What else makes them so interesting (besides their bowel movements)? Well, they build sleeping bags out of mucus, for a start. WHAT???
Parrotfish are heavy sleepers. And I mean heavy. They are capable of sleeping for up to 10 hours at a time. I guess all that non-stop eating can tire you out. This is a long time for a marine animal to remain unprotected.
Parrotfish have glands behind their gills that secrete mucus that slowly emerges from the mouth of the parrotfish over the space of about an hour. This transparent cocoon encases the fish completely. It is speculated that this covers the scent of the fish, protecting it from predation and that it might also protect it from parasitic isopods. It can also serve as an early warning system if a predator brushes against it and can even protect the fish from the sun's UV rays. When the fish wakes, it just swims out and creates one next time it is tired.
How do they breed? Most parrotfish are born females, although a few rare males are sometimes born. These males are called primary males. Juvenile females usually form schools until maturity, and then a dominant female will change sex. When a female changes sex, she becomes a secondary male and is responsible for fertilising the harem. This secondary male may, however, revert back to female.
Generally, a single male will defend its harem of smaller, duller-coloured females (sexual dimorphism) and supply all the sperm needed for egg fertilisation. As the females grow, more dominant females will often change sex and challenge other males to lead the group. This gender change is called "protogynous hermaphroditism"; when they change sex, their colour changes too.
9% of the world's coral reefs are found in The Caribbean, one of the most diverse ecosystems on the planet. These reefs span 38 countries and are vital to the regional economy, generating more than $3 billion annually. Also, the protection offered by the reef to coastal communities, in the form of storm and hurricane protection, is beyond value.
"Parrotfish populations, which are crucial to the very survival of coral reefs, are being destroyed despite their enormous economic and ecological value," says Jerker Tamelander, head of the UNEP coral reef unit. "We urge the Caribbean nations to work together to protect them and jointly respond to the Caribbean coral reef crisis."
As local fishing increasingly targets parrot fish, their essential function as consumers of algae decreases. The major problem for parrot fish comes from commercial fishing bycatch (like always) and predation by lionfish. Be conscious of your consumption of fish. Choose wisely what you put on your plate.
A recent study from 2014 showed that maintaining healthy populations of parrotfish was the most effective and easy way to protect the coral reef. More importantly, it showed that all is not out of control and that some vital steps can be made to help our reefs recover. The conservation of this keystone species may be the only way to restore and maintain the structure and integrity of coral communities in the Caribbean.
It has been proven that strong, healthy populations of grazers are a common attribute of healthy Caribbean reefs. This is due to strong local protection (such as the national parks in Quintana Roo with the help of Semarnat and Conamp). Because of this, coral coverage in these areas is double or triple the average seen elsewhere throughout the Caribbean, where these strong measures are not enforced.
Not your average fish
So it is becoming increasingly apparent that the parrotfish is one of the reef's most essential and remarkable fish. Not only are their colours and patterns beautiful to behold, but they are also incredibly ecologically important. Their success as a species is due to their unique abilities to change sex, build protective cocoons and have teeth powerful enough to graze continuously on coral.
We are only starting to realise their importance as a keystone species. If strong protective measures are taken now, then much of the damage done by the existence and ignorance of humans can be undone. We are their biggest threat, and due to their decline, reefs are suffering.
If we act now and change our consumption choices, put in protective measures against overfishing and bycatch, and do everything we can to protect this species, our reefs not only have a chance to survive but also recover.
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