There is compelling evidence that urchin culls can actually be detrimental to coastal 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. I realise this is not the news people want to hear but it may be important to the integrity of our coastal ecosystem, especially the places we love the most. This raises several important questions we ought to be asking, before widespread culls of sea urchins start in Port Phillip Bay. Especially as the alternatives are far superior.
Recreating balance
Some context first. Important work on ecosystem modellingThe process, either mathematically or in the human brain, of creating an internal version of something that we can refer to, to better understand how it functions and our place within. Scientific modelling is where we take the best knowledge we have and build a version of what will happen, if we assume certain parameters. For example, we might model More, including by our own CSIRO, shows us that the shape and structure of an ecosystem enables balance. E.g. Blanchard et al (2017): Throughout the world, functioning ecosystems balance around a simple theory. All animals must be present at a proportional mass and abundance, to create stability.
Here is a conceptual model of our bay’s trophic system:
We have already lost the top two-thirds of this system.
Hence, we have two options:
- Risk removing a significant component of the next trophic levelDescribes the amount of energy contained within one step of the food chain. Animals in one trophic level utilise about 90% of the energy they absorb for living, emitting the rest as heat and waste. This means the next step up the trophic chain (e.g. the bigger animals that eat them) only have access to about 10% of the energy More (herbivores and urchins), pushing the system towards more nutrientEnergy 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 chaos(Of energy and ecosystems). Ecosystems are thermodynamically driven. Disorder occurs when energy dissipates and becomes more chaotic. For example, the release of hot air into the atmosphere results in that energy is freer to disperse (maximum entropy). The opposite is true when energy is locked into biological processes, when it is stored inside molecules (minimum entropy). Stability in ecosystems occurs More and eutrophication, and losing the important functional role of those herbivores; or
- Rebuild the trophic levels above, thus rebalancing the system and re-enabling the functioning of those herbivores as part of the whole.
The former risk may cause irreversible damage and undermine significant community values. The latter, however, does not. It rebuilds balance and enhances those values.
QUESTION #1: can careful urchin culling to some extent facilitate option #2, without creating irreversible damage? This is currently unknown.
What do urchin numbers have to do with their role and function?
Culling overlooks the movement, reproduction and consumptive dynamics of interrelated species. This was covered by Urmy et al (2022) that found ‘that none of the interactions could be accurately represented by a purely mean-field model.’ In other words, average density is not related to overgrazing.
There are a couple of important considerations in the case of urchins. Firstly, they move and aggregate naturally, in response to conditions we don’t understand. Occasional large aggregations may be important. Moreover, a proportion of individuals are the primary reef grazers and without them, the system collapses. We don’t know which urchins are the important ones.
Here is simply why culling randomly is risky. In the following hypothetical example, a series of culls results in the removal of 75% of the urchins that are required for reef 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. This results in collapse of the reef system, for reasons described above.
The next question we must ask, therefore, is:
QUESTION #2 Are willing to take the risk that this is the right thing to do, especially in a national park, without more disciplined scrutiny of the facts and methods being proposed?
What information do we have to know if this is risky or not?
There is nothing on the public record. Information about the baseline science, monitoring, results etc, are all experimental and yet to be proven to work. Why are these experiments happening inside parks and reserves?
- There is no comprehensive or publicly available ecological risk assessment that can be critiqued; and
- The justification appears overly simplified, omitting most of the related balancing parts of the system mentioned above (for example, it doesn’t consider rare coral reef, of which urchins form part of the biotope’s structure).
Question #3: Do we lose anything by taking a pause and asking to look more closely at the evidence, before ‘widespread culling’ is done?
- Coral reef biotope, for example, was not considered and depends on urchins.
- There are numerous other biotopes e.g. Caulerpa, which is the dominant algal cover and is poisonous to urchins, that could easily be overwhelmed and destroyed by removing the urchin herbivore function, resulting in a much worse flourish of turf algae, Ulva and Japanese kelp. We could tip the system into an algae state and make it almost impossible to rewild.
- Urchins are not uniform in terms of their ecology and behaviour. We do not know enough about the role and function of different age groups. A cull can easily remove a proportion of ecosystem-positive animals.
There are better, less risky and more sustainable ways to address this problem that are not being considered.
Question #4: What if these present a more viable alternative? Is there harm in doing more due diligence, before embarking on widespread culls?
