You’ve just caught a glimpse of something stunning, and yet it’s already disappeared beyond your sight. What was it? A parrot-fish? A wrasse? Or something rarer? It can be very tempting to throw a tasty morsel into the water so it’ll stay around long enough to snap an Instagram-worthy photograph. We’re all guilty of it. After all, you don’t see these tropical beauties every day.

What you don’t know is the damage you may be unknowingly causing for five seconds of your own thrills. So why is it so bad?

Despite regular controversy over whether artificial feeding of tropical fish is actually harmful, very little research has been conducted and therefore, potential effects can only be speculated. The implications this can have on the delicate and unique ecosystem of a coral reef, and the individuals that live in it as a whole, may be devastating.

Disruption of a Balanced Ecosystem

Food is enough to drive any one individual’s behavior, and when species need spend less time hunting or foraging for food that is now so easily accessible, they are able to spend more time being social, and more time finding a mate. Species that benefit more from this supplementary feeding tend to be of the aggressive variety, such as moray eels and snappers.

A diver hand-feeding a sting ray. Taken by Jacob Jose, 2011. Sourced.

This can lead to aggression domination within an ecosystem due to increased population densities, whereby enhanced natural selection allows these species to dominate habitats. This can drastically alter the physiological and genetic structures of coral reef communities. One of two effects may come of this. More predators could mean an increase in direct competition for food, resulting in a decrease in prey species.  Greater numbers of predators in turn produce a larger amount of faeces, which may lead to a modification in habitat features. This can increase the sediment deposits on the reef, in turn leading to hypoxic, and sometimes anoxic, conditions. This is due to a layer of sediment forming over the reef, preventing oxygen exchange, and suffocating the reef.

On the other hand, the opposite effect can happen whereby predators are deterred from feeding on prey species due to fast-feeding elsewhere, and may lead to an increase in prey density. This in turn can negatively impact the reef ecosystem in that species that feed on the reef itself, such as damsels, surgeons and rabbit-fish will devour the habitat.  Either way, this negatively impacts the dynamics of a coral reef ecosystem.


All organisms play an important role in the food chain. The majority of reef fish graze on algae that grow mainly on coral reefs, exhibiting a top-down control on the growth rates of the algae. This prevents reefs from being suffocated, and maintains a perfect balance so the reef can function at an optimum level. By feeding these primary algae-eaters, a process called microbialization destroys this delicate link that is essential in maintaining the coral reef ecosystem (see photo below).

Algae-dominated coral reef, photographed by Bernado Vargas-Angel at Jarvis Island. Sourced.

Fish that are too full from gorging on human food all day will not go about their janitor duties maintaining the reef, resulting in an explosion of fleshy algae that grows over the corals. Copious amounts of dissolved organic carbon are released by the algae, which are in turn feasted upon by microbes, threatening the health of coral reefs by either using and removing oxygen from the environment, or introducing disease. Once these microbes begin to take over, corals die and free up even more space for microbes to dominate, leading to a cascading mortality of the coral reef.


Healthy coral reef, taken in 2010 of the Great Barrier Reef by Kyle Taylor. Sourced.


The vast majority of wild animals are incredibly wary of humans, and while they sometimes allow people to approach them, and even sometimes approach people themselves, they generally maintain a safe distance. This is a natural instinctive behavioural adaptation that allows the animals to escape quickly from any potential danger when necessary. However when food is made readily available to marine life by humans, it enhances a behaviour known as “conditioning,” whereby the animal learns to associate human presence with food. Therefore marine fish will frequent areas of regular human activity. The sound of a boat passing overhead may trigger an animal to swim to the surface expecting a tasty treat, but instead will be met by a mighty propeller and a nasty end.

It is easy to forget that tropical fish are wild animals, and unnatural meal times can cause aggression in species, especially when they’ve learned that humans mean food. Fish will actively pursue divers and even attack when their desire for food in high. Divers feeding larger tropical species such as barracudas, moray eels, gropers and even sharks have experienced face mauling, chunks taken out of their arms, and even their fingers, earlobes and lips bitten off. This results from behavioural conditioning, where fish may attack a human by mistaking body parts for food. The video below demonstrates how a moray eel exhibits aggression when a diver tries to feed it.

As seen in this video, attacks can not just cause bodily harm, but in this case the diver is seen to panic and ascend quickly and uncontrollably towards the surface. Although divers all receive training regarding decompression sickness, when in a state of panic not everyone can remain calm and collected, especially when they are attacked!

As you can see, there are many consequences to your actions. Your five minutes of enjoyment just to take that perfect photo may be affecting the future of our coral reefs. Is it really worth it?


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