How Bumphead Battlers Build Ecosystems

My daily food consumption, according to National Geographic is about a tonne a year. 

The Green Bumphead Parrotfish consumes something in the order of five tonnes, much of which, passes through its gut to be expelled as sand, the foundation of tropical islands.

“Thank heavens for the Bumphead Parrotfish” we hear sunbathers say, as they lie bronzing on beaches of the southern Pacific. 

Well they don’t ... but they should. 

Not only do these remarkable fish - and their smaller cousins - eek out a living processing algae from coral they undoubtedly contribute greatly to the building blocks of an ecosystem. 

When we talk about ‘biodiversity’ in the context of species conservation we’re not talking about protecting the number of animals but the processes they are part of. Keystone wildlife are plants or animals that play a crucial role in ecosystem function. 

So why wouldn’t you want to lose a keystone species like Bumphead Parrotfish? 

Consider a sports league with players that specialise in different positions. Take away the team’s striker and you generate a goal deficit. The number of players on the field hasn’t changed and it may take a season or so for the team to get relegated (lag effects are also rife in ecology) but to anyone who understands the sport, the consequences are predictable. Take away all the strikers and only ever recruit defenders to forward positions and the whole game takes on a different and rather less attractive form. Sponsors and fans start to pull out and it’s not long before the game’s whole value is permanently reduced.    

We encountered Bumphead Parrotfish in the Coral Sea, on a trip with Pindito this year. They aren’t particularly uncommon but they are declining across their range and have disappeared altogether from some reefs. 

Why I started thinking about them in these terms was because it was obvious from a single encounter, how extraordinary they are.   

It’s fascinating to come across megafauna living in near-pristine environments that are significant on face value yet barely studied. Bumphead Parrotfish are big. It takes them 10-20 years to reach their maximum size, which is over a metre and they are thought to live to at least forty. Parading around in mixed social groups, there is a structure to their society and many facets of their behaviour will forever be unknown. 

They are considered ‘non-selective’ foragers. In other words, they’ll eat different types of coral. However, they browse on particular spots, which they crop with enormous rock-crushing beaks. So they feed in a manner similar to land-based ruminants like deer, giraffes and sheep, that select the lushest of leaves and young shoots. 

It’s suggested Bumpheads help build reef resilience because ‘bioerosion’ makes it harder for one species of coral or algae, to dominate - much in the same way traditional mammal stocks can help improve the richness of ancient grassland by creating a patchwork mosaic of grass types and structure.

It maybe coincidence but fun to know that Bumphead Parrotfish, like deer and goats, also aggressively bump heads in territorial disputes. Perhaps male Bumpheads and their land-dwelling counterparts both benefit from such robust displays of territorial dominance - either way, it would be a sight to behold, as researchers did in Wake Atoll (Solomon Islands) in 2012.

“We heard loud jarring sounds and confirmed they arose from violent impacts between males engaged in repeated, ritualized headbutting behavior. During headbutting bouts, males utilized their caudal fins to rapidly collide with their cephalic humps, immediately followed by fast swimming in a semicircle where each fish tried to bite the back and flank of its opponent. Following circling, fish swam apart in opposite directions and then turned again face to face to initiate additional collisions”. It seems as though this particular behaviour is unique among fish.

It wasn’t until quite recently that scientists began to consider the role of animal behavioural research in conservation. 

In 1998, William Sutherland wrote “in view of the exciting research developments in animal behaviour, it is surprising that this subject has made a negligible contribution to conservation biology”. Yet it makes perfect sense, that to understand how animals interact with ecosystem processes, means observing their behaviour. This is what allows experts to predict consequences of change. Merely knowing how many doesn’t help once the environment is changing.

For instance, the larvae of Bumphead Parrotfish disperse on currents, possibly settling in shallow lagoon areas, mangroves or sheltered corals. Maybe they are pelagic (open-ocean), we don’t really know. There are almost no recorded juveniles in the Great Barrier Reef, meaning they may mature elsewhere and move back into these areas. Even this behavioural information tells us that population management may need to be a multi-national effort. The Coral Triangle could be the epicentre of their distribution - a population source.    

Modelling by scientists at NOAA in the US has very roughly estimated Bumpheads to number about 1.5 million fish (6.2-16.7 million) across their complete geographic range. This average would mean a total sediment processed by Bumpheads each year in the order of 75 million cubic metres. 

The Melbourne Channel Deepening Project, a 3-year program to deepen channels for larger ships, created 22.9 million cubic metres of material. 

To return to the sports analogy ... Bumphead Parrotfish could fill the MCG stadium about 45 times a year!   So let’s put those two processes, dredging and an ecosystem service provided by Bumphead Parrotfish, into an economic perspective. 

In ecological terms, the Channel Deepening Project cost $500 million and created 22.9 million cubic metres of material impact on a marine ecosystem, while in the same three years, Bumphead Parrotfish generated 225 million cubic metres per year, contributing to healthy functioning of an environment and cost us absolutely nothing. 

This has to be one of the most compelling comparisons I’ve found recently, that describes our innate inability as humans, to value natural systems over our own engineered systems. 

$500 million dollars is the amount just pledged by Australia to help manage the Great Barrier Reef ... the same amount spent on a single domestic dredging project ... but none is spent directly on conserving Bumphead Parrotfish.  

The role of Bumphead Parrotfish in reef ecology looks and feels staggeringly valuable, so it probably is. If no-one’s quantified that yet, the right questions haven’t been asked.

In 2009 a paper in Ecology and Society said:

“Plans to solve complex environmental problems should always consider the role of surprise. Nevertheless, there is a tendency to emphasize known computable aspects of a problem while neglecting aspects that are unknown and failing to ask questions about them”.

In other words, the longer we put off accepting the obvious, the greater the risk of catastrophe.

Ecology is one of those disciplines that is at once quite simple to grasp and at the same time, complex, so can feels as much like philosophy as science - twenty years would lead me to believe the most valuable ecological studies contribute either to the ‘philosophy’ or help us meaningfully understand how to manage habitat through behavioural studies. 

Good environmental managers and decision-makers know this. Sadly, the complexity and uncertainty of ecological science also makes it prone to manipulation by people who know ultimate proof is a panacea. 

The difficulties of studying ecology are:

  • it’s simple to identify ecological change but very hard to identify what causes it; 
  • it’s hard to quantify intrinsic importance because there are no single consistent measures of value (and ecosystems are incredibly complex); and 
  • it’s almost impossible to reverse damage once its done - though ironically, that’s often the first sign something is worth looking at.

Since it’s easier to identify things that have changed, most studies focus on comparing damage once its done, which makes it very hard to reconcile. You’re almost always up against the effects that created the problem and the decision-makers who allowed it in the first place. 

For instance, this week in Australia, news broke of a 2,000 ha deforestation in the Normanby catchment of Cape York peninsula. This from the same government that just pledged $500 million to tackle the Great Barrier Reef’s declining health. 

In “How to Build a Universe” by Brian Cox and Robin Ince (from the hilarious and brilliant podcast series Infinite Monkey Cage), Cox writes “how many equations are required to summarise the behaviour of a gnat compared to a pulsar? What processes are required to crawl and catch a fly compared to those that cause a sun to shine?” 

Fact is, we know less about the function of simple biological organisms and ecosystems than we do the first few minutes after the big bang. So any hope we have in conserving Bumphead Parrotfish means slowing down their disappearance, accepting their importance on face value today and using them to help us understand how to manage our priceless coral reef ecosystems.   

That I find myself reconciling cosmology with ecology, brings to mind lying back staring at the solar system from the deck of Pindito earlier this year, having spent that afternoon swimming with Bumphead Parrotfish.  

So you see, my seemingly indiscriminate digression isn’t so random after all! 

In all seriousness though, cosmologists are allowed to think philosophically. Perhaps it’s because they can quantify many things mathematically and that no matter how it’s interpreted, the political fall out is relatively benign.   

Ecological findings and suggestions have a myriad of consequences for people living on Earth, right now, often in close proximity to researchers whose suggestion that a change in our way of life may be necessary, don’t always go down too well. 

Managing a species is a multi-faceted task, requiring acknowledgment and input from so many, as to be an almost impossible task for any individual. 

In a paper on the importance of Conservation Biology in 1993, David Given wrote:    

“important characteristics of conservation biology are that it is a crisis discipline and it is holistic. It needs integration of research and management, and a range of relevant skills”.  

You’ll find common criticism of conservation biologists being too focused on their subject to ‘see the bigger picture’. Tell a song-writer to run a music venue and see how long they can stay a song-writer - without songs, the music industry collapses. We expect too much from conservation biologists and should instead be supporting them. 

What conservation biologists are experts at, is understanding animal behaviour and connectivity to ecosystem processes.  

Add interpretation by expert theoretical ecologists and a habitat management framework and you’ve the basis for an adaptive and continual-improvement plan. Informed trial and error, lean management ... however you want to frame it, creating outcomes requires we value the instinct and expertise of researchers and ecologists who can get on and do a job, while building evidence - too much forward planning fails: see Tom Wujec’s marshmallow challenge to find out how kindergarten kids beat CEOs when faced with a simple engineering task and only experts give the CEOs the edge to win!  

Conservation biology is vastly under-represented and under-funded because we are terrible at putting real monetary value on ecosystem services. Wildlife management is the ‘elephant in the room’, so to speak.  

So when we get all philosophical about ecosystem protection and wildlife conservation, we can quote one of the world’s most famous cosmologists. Carl Sagan said in 1995, “science is part and parcel humility”. 

And that’s what all at once fascinates about the world. It’s the inexplicable that makes things extraordinary. The most important answer in science is ‘I don’t know’ and because we know so little about Bumphead Parrotfish, humility is the essential ingredient. 

Not knowing shouldn’t be the same as not caring.  

Each time I have the benefit to stare on anything in the natural world, I am reminded of Gavin Maxwell’s Ring of Bright Water (1960) and the infamous quote which I have always lived by:

“I am convinced that man has suffered in his separation from the soil and from the other living creatures of the world; the evolution of his intellect has outrun his needs as an animal, and as yet he must still, for security, look long at some portion of the earth as it was before he tampered with it.” 

Perhaps that’s why, for people who don’t look at wildlife, staring at stars can be their security. 

Staring at a portion of the Earth, or its animals, doesn’t seem to be the most rigorous of scientific aims for an ecologist but if we and our leaders took more notice of animals like the Bumphead Parrotfish, perhaps there would less question about their value ... a landscape without its megafauna would, after all, never be the landscape it was. 


WRITTEN by Simon Mustoe



Muñoz RC, Zgliczynski BJ, Laughlin JL, Teer BZ (2012) Extraordinary Aggressive Behavior from the Giant Coral Reef Fish, Bolbometopon muricatum, in a Remote Marine Reserve. PLoS ONE 7(6): e38120.

David R. Given (1993) What is conservation biology and why is it so important?, Journal of the Royal Society of New Zealand, 23:2, 55-60

Sutherland et al (2009) One Hundred Questions of Importance to the Conservation of Global Biological Diversity. Conservation Biology, Volume 23, No. 3, 557–567

Sutherland (1998) The importance of behavioural studies in conservation biology. Animal Behaviour, 1998, 56, 801–809

Kobayashi, D. R., A. Friedlander, C. Grimes, R. Nichols, and B. Zgliczynski. 2011. Bumphead Parrotfish (Bolbometopon muricatum) Status Review. U.S. Dep. Commer., NOAA Tech. Memo., NOAA-TM-NMFS-PIFSC-26, 102 p. + Appendix.