Fish control starfish on the Great Barrier Reef

The Australian Institute of Marine Sciences claimed to be the first to demonstrate the role of fisheries in crown-of-thorns outbreaks. The fact that fish control starfish on the Great Barrier Reef should be no surprise, as @seasaver pointed out. If we embraced the underlying reasons for animal impactWhat is Animal Impact? Without wildlife, Earth would not be habitable for humans, because it's animals that stabilise ecosystems. It’s a fundamental law of nature that animals (and humans) exist because we are the most likely lifeforms to minimise environmental chaos. Animal impact, therefore, is a measure of how much all wildlife is collectively responsible for creating a habitable Earth. The More, we should have worked this out a long time ago. The only thing that balances ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More is wildlife. Period.

Eradicating starfish does not make things better

Every time I raise this it’s controversial. Why? Because we stigmatise ‘pests’ when there is, in actual fact, no such thing. Pests are simply animals rebuilding broken ecosystem structures.

Further, the majority of scientists do not understand how ecosystems work. Instead we regard animals as the icing on the cake and think we can control outcomes by killing more animals. That is the narrative we feed the public. Because doing something is better than sitting around and allowing nature to rebuild itself.

But none of this makes any sense, at least not to someone who understands ecosystem structure, function(Of an ecosystem). A subset of ecosystem processes and structures, where the ecosystem does something that provides an ecosystem service of value to people. More and process (biodiversityWhat is the definition of biodiversity? When we ask, what is the definition of biodiversity? It depends on what we want to do with it. The term is widely and commonly misused, leading to significant misinterpretation of the importance of how animals function on Earth and why they matter a great deal, to human survival. Here I will try to More). The fact is, ecologists are not taught about ecosystem science. A holistic understanding is almost absent from the intellectual library of even the most established experts.

‘I sort of bumbled my way through, and I came to think that understanding ecosystems and what threatens their equilibrium is going to be the next big thing in biological science. To save the environment, we have to find out how to save the ecosystems.’

Edward O. Wilson (1929 – 2021), 2019. Quanta Magazine.

Killing starfish makes things worse, not better

I’m cynical when I see Tweets like the one below from CSIRO claiming to be able to ‘manage’ crown-of-thorns starfish. And while we’re at it, there is no such thing as Artificial Intelligence, it’s machine learning. And that’s only as good as the human mind that uses it, or the human data it’s fed. If we think we can kill starfish to save the reef then that is what our machines will tell us.

In an ecosystem there are several layers of energyEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More consumption (trophic layers) which make up a stable structure. For example, after the fur trade killed sea otters it went from a three, to a two-level system. Subsequently there were huge impacts on fisheries. This was described in a paper in 2011 [1] as evidence of ‘trophic downgrading’.

Trophically downgraded ecosystems are becoming more common worldwide, which is leading to conservationWhy is animal conservation important? Animal conservation is important, because animals are the only mechanism to create biodiversity, which is the mechanism that creates a habitable planet for humans. Without animals, the energy from today’s plants (algae, trees, flowers etc) will eventually reach the atmosphere and ocean, much of it as carbon. The quantity of this plant-based waste is so More concerns due to the associated losses of biodiversity, productivityThe power of an ecosystem to process energy. The most productive ecosystems have reached a steady stable-state with maximum entropy production. That’s to say, the number of species has reached an optimum and the functions they fulfil, have translated free surplus energy into nutrients that is either stored inside plants and animals, or is entrained within the biological cycles that More, and community resilienceReferring to an ecosystem’s ability to maintain a steady stable-state. The need to build resilience is entirely anthropocentric and symptomatic of ecosystems that are damaged or declining, leading to loss of ecosystem services on which humans depend. More. Downgrading often results in the formation of alternate stable states.

Edwards & Kona, (2020) Nature [2]

Why would we think we could fix an ecosystem by removing another trophic layer? What do we imagine the starfish are there for? It’s simply really. The starfish are consuming an abundance of free energyThe energy of a system that is emitted as waste and is not part of ecosystem processes. There is always some free surplus energy as this creates the basis for evolution where new species exploit gaps in the ecosystem where free energy becomes available. Surplus energy can occur as a result of disruption or disturbance. When free surplus energy reaches More created by the loss of other animals. Remove the starfish and the free energy is released once more – most likely to cause an infestation of bacteria or viruses. Killing more animals doesn’t solve the problem until the underlying structural problems are addressed. In actual fact, it makes things worse.

Fish are the ecosystem

Fish, and other marine creatures, have always built marine ecosystems. Therefore, the only way to address their collapse is by allowing or encouraging their populations to restore. This is why the paper published in Nature goes on to say that:

‘Designing targeted fisheries management with consideration of [starfish] population dynamics may offer a tangible and promising contribution to effectively reduce the detrimental impacts of [starfish] outbreaks across the Indo-Pacific’.

The word ‘may’ is important here. Naturally, publishers of scientific studies do not often make explicit recommendations. But I would say that fisheries management is the only way to address the problem. Though as I said earlier, this is a controversial topic, and it can take funding away from powerful establishments. Which is another reason why there is disagreement.

It irks me somewhat that the same mentality that makes fishers think they are in competition with seals and seabirds, leads conservationists to think we’re in competition with starfish.

For instance, another of the institute’s recent papers recommends:

‘Manual control as the most direct, and only effective, means of reducing [starfish] densities and improving hard coral cover currently available at a site’.

What next for fish and starfish?

There is substantial evidence for the relationship between fish predators and ecosystem function. Furthermore, the absolute, exclusive and integral role that wildlife plays in ecosystem stability should, by the 21st century, have already been accepted outright. However, scientists (including me) were not taught this.

Overall, scientific researchers working in ecology, do not unequivocally acknowledge the over-riding role of animals in maintaining ecosystem stability. This relationship is as fundamental to Earth function and our survival as Einstein’s theory of relativity is to physics. Yet, there is little or no discussion or consideration of this in conservation ecology.

Once you understand the structure and function of animal-driven systems, the idea that fish will control crown-of-thorns-starfish (COTS) outbreaks, is obvious. Which leads me to a point of contention. The same scientists propose manual removal of starfish as the only effective means of reducing COTS density. However, when you apply principles of animal impact to removing COTS, it reveals this to be problematic. In the absence of appropriate fish populations, removing another layer of biomassThe weight of living organisms. Biomass can be measured in relation to the amount of carbon, the dry weight (with all moisture removed) or living weight. In general it can be used to describe the volume of energy that is contained inside systems, as the size of animals relates to their metabolism and therefore, how much energy they contain and More is a very high-risk strategy. In a nutshell, if we’re not yet fully aware of the implications of removing fish biomass, why would we risk removing more biomass?

As a footnote, it is interesting that the aforementioned papers are happy to say ‘findings support manual control’ but only that fisheries management ‘may’ help. It’s more common to see caveats added where they affect a commercial entity than in relation to controlled killing of animals.

References

1. Estes, James & Terborgh, John & Brashares, Justin & Power, Mary & Berger, Joel & Bond, William & Carpenter, Stephen & Essington, Timothy & Holt, Robert & Jackson, Jeremy & Marquis, Robert & Oksanen, Lauri & Oksanen, Tarja & Paine, Robert & Pikitch, Ellen & Ripple, William & Sandin, Stuart & Scheffer, Marten & Schoener, Thomas & Wardle, David. (2011). Trophic Downgrading of Planet Earth. Science (New York, N.Y.). 333. 301-6. 10.1126/science.1205106.
2. Edwards, M.S., Konar, B. Trophic downgrading reduces spatial variability on rocky reefs. Sci Rep 10, 18079 (2020). https://doi.org/10.1038/s41598-020-75117-2