Sea urchin barrens, how to rebuild an ecosystem without killing it

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In this blog I want to talk about sea urchin barrens and how to rebuild an ecosystem. These are the among the reasons I won’t personally be killing sea urchins in my local area. Sea urchin kills may not be a completely fruitless exercise on a local and targeted basis. It might buy us some time but it can be risky for the ecosystem. To create lasting improvement we need a new way of thinking, to address the underlying causes of decline. As humans we also have the choice to allow animals to recreate functioning 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 as a more wonderful and sustainable alternative. We can imagine and know how to rebuild a more vibrant bay ecosystem.

1. The bay and its nutrients

Port Phillip Bay was once an inland sea fringed by mangroves and surrounded by wetlands. It’s environment is still healing from the after-effects of European settlement. Today it faces modern threats. Sewage and the Western Treatment Plant leak pollution onto its coastline. Storms also channel farm nutrientsEnergy 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 into the north along the Yarra River.

Combined with summer sunlight, this extra nutrientA substance that contains the raw materials for life. At a chemical level, these are contained inside compounds that are absorbed into the body and essential energy-containing molecules are extracted, so that energy can be transformed into other chemical processes that use the energy for living. More grows algae. The unfettered growth of these microscopic plants is not always a good thing. Algal blooms can choke reef systems, poison fish and reduce sunlight to seagrass beds. A molecule of water entering northern Port Phillip Bay takes over 200 days to reach Bass Strait. To gain a level of balance with the surrounding environment, there has to be an animal-driven food chainA single thread in a food web illustrating the chain of animals that eat each other. At the base of the food chain are small high-energy (fast metabolism) animals and at the other end large low metabolism animals. An example would be whales eating krill that eat plankton that eat algae. Or lions that eat gazelles that eat grass. More to purify the water.

Sea urchins like to eat algae. The consequence is that they have the potential to remove the structural element that supports marine life. Bare rock doesn’t provide much of a foot hold for anything. By continually reloading the bay with nutrients, algae coats the rocks and makes ideal habitat for sea urchin infestations. Pressuring the Environment Protection Authority and Melbourne Water to control pollution should remain the greatest of priorities. Despite the upgrading of sewage facilities since 2004, there remains the legacy of nutrients trapped in settlement beds since 1897. But my feeling is that this is not the most significant problem though.

2. Sea urchins are protecting us from a more serious problem

Sea urchins are naturally occurring. These are not pests. They have become a problem because we have modified their environment. Our behaviour, if anything, has made us the pest while sea urchins are just doing their job.

Algae, like all plants, convert the sun’s energy into nutrients and unless they are eaten by something, they become waste. This is what we like to call ‘pollution’. Sea urchins are among the first line of defence against this. They simply became abundant after springing into action to reset an imbalance we caused.

The natural role of sea urchins

The excess nutrient we create, plus the waste generated by algae in the water column, settles on the seabed and feeds seaweed. Seaweeds are also a type of algae. A healthy reef has a structure comprising many types but this depends on sea urchins as they are one of the grazers. They create gaps so different species can gain foothold.[2]

Removing sea urchins from a healthy reef will create a monoculture where most seaweed species are pushed out and only a handful can dominate. This also causes pollution because the nutrient that was once absorbed by many animals becomes surplus to requirements. It drains into the surrounding environment.

Sea urchin barrens

Sea urchin barrens occur when the ecosystem favours only a few fast-growing seaweeds. Pollution is the trigger for this and it means sea urchins can thrive. The urchins nonetheless stop it from becoming a worse problem. Allowed to grow wild, the weed could potentially dominate further and choke adjacent reefs including marine parks.

What is the consequence, therefore, of mass removal of sea urchins from barrens?

On first thoughts it seems like a good idea to kill them. But all that does is remove a layer of animal biomass that is responsible for moderating a bigger problem. Inevitably something more serious will occur involving even greater numbers of other animals. Perhaps an infestation of sea lice, or more likely, a microbe. In 2014 there was evidence of this happening in Sydney Harbour.

‘Ian Bedwell, who has been swimming and snorkelling in the bay for more than 40 years, believed the crushing of sea urchins was contributing to the proliferation of black, “clumpy” algae, causing the degradation of the bay’s sea floor. He believed swimmers and snorkellers were crushing sea urchins to feed fish, oblivious to the consequences of the bay’s 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 being adversely affected’.

The Daily Telegraph, 2014

Ecosystem science is never a straightforward case of 1+1 = 2, it’s about hundreds of things adding together to create an outcome infinitely more valuable and variable. Care for the ecosystem and this complexity provides the 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 to avoid problems like sea urchin barrens.

Killing sea urchins is not a solution

Sea urchins are not the problem, they are in actual fact, a key part of any solution. The more important thing to do is to restore the structure and 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 of the food chain that they are part of.

Unfortunately the main problem is annihilation of the sea urchin’s natural predators – large fish. This is going to be hard to resolve, as it pits a powerful fishing lobby against the future of Port Phillip Bay. It hardly needs mentioning that one can’t exist without the other, which makes it a strange conflict.

I don’t believe enough is being done to explain this to anyone on either side of the debate.

3. Increasing predator biomass makes ecosystems healthier

By the turn of the century, recreational fishing was already equivalent to commercial catches.[1] Back then, hobby fishers were already taking 500 tonnes from the Bay each year. Today Fisheries Victoria undertakes no stock assessment on the majority of fish caught. There is little to no effective control or regulation despite the enormous volumes extracted.

Unlike commercial fishing, many recreational fishers focus on reef fish, which live in tiny fragmented areas of habitat. This is increasingly around marine parks and other zones and contributes to the rapid decline of our remaining marine ecosystems.

Natural predators of sea urchins

Natural predators of sea urchins are benthic-feeding sharks like Port Jacksons, harmless Gummy Sharks and large reef fish such as Blue Gropers and Rock Lobsters (crayfish). Early settlers reported catching up to 500 in a single evening on the Mornington Peninsula. They are now virtually extinct inside the bay.

Blue Gropers are a type of fish that live in social groups and can grow to 1m and 18kg. This species is now rare and only small individuals are left in the bay. Spearfishing and sport fishing, especially unregulated and unenforced, targets the largest fish first. Spearfishing, even within regulations, is a particularly invasive and damaging past-time, wherever it occurs.[5],[8]

‘In the 1950s … 30% of all fish taken in spearfishing competitions in the Sydney region were Eastern Blue Groper’

Gillanders, 1999[6]

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Gummy Sharks, according to friends, are regularly fished illegally from shore around their breeding grounds at Point Cook. Illegal fishing and harvesting of shellfish is so widespread that it’s common to see it happening on almost every snorkel trip to a marine park. The police and Fisheries Victoria simply have no capacity to respond.

‘In the absence of high abundances of large predators such as rock lobsters, urchins have established in large numbers and are destructively overgrazing kelp beds’

Dr Scott Ling

A cynic might say there is little incentive for control when Fisheries Victoria are intent on doubling the number of fishers to a million. The absence of any reasonable enforcement of offences certainly indicates that priorities lie beyond looking after the health of the bay’s ecosystems.

The impact of individual fish on sea urchins. Example: Blue Groper

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 scientists regularly underestimate the impact of small numbers of animals on ecosystems.

• First, you can’t measure what doesn’t exist any more.
• Second, the outcomes are always greater than any simple scientific modelThe 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 can predict.
• Third, most studies are peppered with too many caveats to be used as evidence for ecosystem restoration. The evidence for this isn’t presented in research studies, mostly for the first two reasons.

For many of us it is hard to imagine, for example, that a few Blue Groper could potentially inhibit the growth of entire sea urchin barrens. However, it makes sense.

Blue Groper have very small home ranges, in the order of 4.5 hectares. For Port Phillip Bay users’ reference, Ricketts Point Marine Sanctuary, covers an area of about 115 hectares. The very small home range of fish like this makes them highly vulnerable to fishing but also viable candidates for ecosystem restoration. They are among the largest bony fish in south east Australia and live for decades. Larger fish eat more sea urchins and as few as 25 individuals could influence the whole park ecosystem [3]. These are the elephants of the reef, creating dynamics that open up space for other animals and plants.

Let’s assume 25 fish eat 9% of their body weight per day, each fish weighs 15kg and sea urchins are 30% of diet, providing about 20g of nutrition per urchin.

Those 25 fish could consume over 200,000 sea urchins per year. When sea urchins are at normal abundance this becomes very significant. The 18 million urchins estimated to be destroying Tasmania’s east coast, could be consumed by as few as 2,500 Gropers, except they have been almost wiped out by fishing. Similar effects are observed on the Great Barrier Reef.[9]

‘We found a very strong relationship between the abundance of crown-of-thorns starfish on the Great Barrier Reef and the removal of predatory fish through fisheries.’

Frederieke Kroon, Australia Institute of Marine Science

Restoring ecosystems is about more than one type of animal

Fisheries sets catch limits based partly on minimum size but some reef fish can live for many decades. Small fish reappear fast and this presents the illusion that fish stocks are doing okay. That’s the basis for most fisheries management.

But what is the ecosystem consequence of removing only the larger individuals? No-one knows why size limits were chosen. The likelihood is that they were made up and have never been questioned since. For instance, has anyone considered that killing the biggest reef fish creates sea urchin barrens?

The reality is, all the smaller fish are now gone too, due to spearfishing and no doubt, much illegal activity over time. The science becomes rather moot when most of your reef systems are functionally dead. It only leaves you one option: restoration.

It’s important to note that you don’t just introduce one species of fish. Blue Gropers are one of many species that would benefit from an ecosystem approach to restoration. They are likely to be the most important due to their size and absence (other remnant species can begin to flourish in their wake). Time and time again, it’s been shown that ‘rewilding’ landscapes results in significant and unexpected benefits that cannot be predicted by researchers.

‘There is evidence that the ecological shift from macroalgal habitat to urchin barrens habitat in Tasmania has been exacerbated by low numbers of large predators’.

Casper et al, 2010 [4]

4. Make recreational activity about restoration, not destruction

Connecting people to nature is one of the most important objectives for global conservation today. Unless we can create a change in human values we are not going to succeed.

Snorkelling and diving, for example, is a passive and highly emotional activity that is largely harmless. Watching animals is a healthy past time that our ancestors have been doing for many thousands of years. Much of our culture and ability to feed our populations for thousands of years was based on an understanding of wildlife comings and goings.

It’s only recently that we’ve begun to think we can control natural outcomes by ‘managing’ wildlife. In truth, we create far more problems than we solve. Our First Nations people understand this better. They worked with the land and its wildlife, not against it. We cannot restore Port Phillip Bay’s ecosystems by simply killing sea urchins but we can learn to take care of the bay by learning about what caused the problem.

Also, killing wild animals isn’t something anyone should feel they need to do. It makes me uncomfortable for all the reasons discussed here. Killing animals got us into this problem in the first place, so why would we think it will make things any better?

Removing a layer of animal 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 like pouring fertiliser. It will create a monoculture, kill everything else and pollute the surrounding environment. I may not be popular for saying this but I think this work needs to be stopped before further damage is done.

It worries me that public money and good intention will be wasted. It’s not a good way to engage in conservation.

Making people part of a wonderful solution instead

Being part of decisions about how to protect the bay’s broader ecosystem, however, should be something everyone is given the chance to be part of.

What if local people became custodians of their own resident populations of Blue Groper? Reintroducing and protecting them would be a marvellous thing for everyone to help with, wouldn’t it?

What will it take for Parks Victoria to relinquish control and empower local people to make a difference? This kind of marine stewardship is practised successfully in New Zealand, where locals, policy-makers and scientists work together.

‘Fishing pressure is not the only factor that influences fish stocks. We also consider things like changes to the marine ecosystem that may affect sustainability, such as habitat degradation or pollution’

Sunlive.co.nz

What if we gave people the knowledge to understand the bay’s ecology and then asked them to present their own ideas about what to do? What if everyone – fishers, conservationists, school kids, snorkelers – were asked to draw a picture of the ecosystem they wanted to see in ten years? Would that provide a suitable blueprint for such work?

I might be able to find merit in harvesting sea urchins for conservation once predator control and fish biomass is restored. Some careful experimentation and harvesting of sea urchins could create a new and useful dynamic – humans are still part of ecosystems. But only when there are other animals and fish present to maintain the system alongside us – otherwise it’s a waste of time.

5. Animals should never be killed except as a last resort.

While this might sound controversial at first, recreational killing of animals – including fish – is ill-advised.

You starve to death if you overfish an area and are reliant on it for food. Killing animals is the last resort. Sport and recreation, however, has no natural control mechanism when it comes to killing animals. It’s just for fun.

Animals play the most vital role of all in making ecosystems habitable for humans. Fish are no different, nor are sea urchins. If you haven’t considered this before, then it may be unwise to propose lethal intervention before thinking very carefully about the consequence.

The irony is that fishing literally depends on having fish-filled ecosystems. So it is bizarre in the least to have an absence of fish over sea urchin barrens and expect that killing sea urchins will miraculously solve the problem. The fish aren’t going to come back until the ecosystem returns and that won’t happen without the fish.

To address the problem that is sea urchin over-abundance, means reintroducing the fish and removing threats to their survival. That means no killing of any fish that are integral to reef ecology.

Bay users need to take a step back and look at the bigger picture and try to imagine how a healthy ecosystem would function, then altering our behaviour to make this a reality. The results would be rapid.

The urgency of the problem

The bay’s ecology is collapsing under the pressures of nutrient input and overfishing. Is it any surprise that we resort to killing sea urchins as a solution to a greater problem? Who is telling the other part of the story? Why isn’t this what we are hearing from ecologists? Why is no-one discussing the impact of recreational fishing in particular? It’s the elephant in the room. Ironically, restoring fish populations is the quickest, easiest and most cost-effective method of fixing our broken bay ecosystems.

Marine parks support the few fish left and even once-abundant species like flathead have become uncommon. These are drastic times and warrant measures that are effective and can rapidly rebuild lost opportunity and bay health. Unless we make these decisions soon, it’s obvious that even recreational fishing cannot survive. How can fishing survive the death of most fish?

Towards a better solution

The fact is, killing sea urchins doesn’t even work at the scale needed, so it’s pointless, if it’s the first and only strategy. There simply aren’t enough willing divers and snorkelers to regularly kill them all – realistically, this is only going to be done in tiny locations, which are commercially important e.g. for the abalone industry. In one study it took 54 days of diving at a cost of $35,000 to cull urchins from eight point locations and this would have to be repeated at least once a year.[10] The bay covers 2,000 km². This is why we need predators to do the job for us.

Despite culling thousands of urchins, divers culled urchins only from within a small proportion of the total barrens patches on particular reefs. Thus, urchin density, size-frequency of barrens patches, and benthic community structure showed no detectable change relative to ‘no-cull’ control reefs.

Sanderson et al, 2015 [7]

Farming sea urchins doesn’t work either, it just monetises an existing problem, adding another reason to do nothing to address ecosystem decline. Also, it can’t prosper if we fix the bay’s ecology as sea urchin numbers will decline. If we have mass sea urchin farms, we say goodbye to fishing. Why would we create something that depends on a broken ecosystem and destroys other ways of life? Sustainable harvesting is still a possibility. That’s to say, there could be a lucrative industry around small-scale harvesting of urchins from pristine environments. But for that, we have to rebuild ecosystem function and structure, as the roe quality declines when the area becomes barren.

What we could do now

There is nothing more wonderful that I can imagine than restoring the bay’s wildlife populations. Not only is it something the community would get behind, it is the quickest, cheapest and most sustainable way forward. The results would be nothing short of miraculous. It would secure the future of sustainable fishing and allow bay users to marvel in the power of nature to heal. It will make us more resilient to climate change, moderate pollution and allow all of Melbourne’s residents to see the beauty and real diversity of our marine environment.

In a perfect world, this is what I would do as a start:

1. The immediate removal of all bag limits for anything other than migratory pelagic fish (e.g. Australian Salmon) throughout the bay. Recreational fishers must be required to put back any fish that are associated with reefs. The argument for eating fish is fine, once the ecosystem is restored. In its current condition, it’s declining fast.
2. Ban spearfishing from within 2km of the bay’s coast.
3. For extra certainty, place a 2 km wide exclusion zone around the national parks. This is to avoid inevitable illegal activity. Fisheries Victoria cannot currently control this and there is no indication that will change soon.
4. Involve the community in reintroducing top predators into those marine parks. Blue Groper and Rock Lobster are candidates.
5. Monitor the populations and protect them. Follow how the system adapts and perform some careful and trivial management. Where at all possible, do not intervene*.
6. Use evidence of success from these processes to expand into other parts of the bay.

*This component won’t be easy and there will be some failings. But to rebuild a healthy bay, there is no option but to find a way to make it work. This is where scientific research is best applied. It has to be experimental which means a commitment to learning from mistakes and adaptation is essential.

References

1. Knuckey et al (2017) The social drivers and implications of an ecological risk as sessment of both recreational and commercial fishing – A case study from Port Phillip Bay. FRDC Project No 2014/207
2. Duggins, David O., (1981), Sea urchins and kelp: The effects of short term changes in urchin diet, Limnology and OceanographyThe study of the physical, chemical and biological properties of the ocean. More, 26, doi: 10.4319/lo.1981.26.2.0391.
3. 1 Shepherd, S. A. & Brook, J. B. (2003) FORAGING ECOLOGY OF THE WESTERN BLUE GROPER,
   ACHOERODUS GOULDII, AT THE ALTHORPE ISLANDS, SOUTH AUSTRALIA Transactions of the Royal Society of S. Aust. (2005), 129(2), 202-208.
4. RM Casper, NS Barrett, N Bax, AJ Hobday (2010) Pre-adapting a Tasmanian coastal ecosystem to ongoing climate change through re-introduction of a locally extinct species Principal Investigator: Nic Bax For milestone due 30 September 2011: Review of the Eastern Blue Groper. Institute of Marine and Antarctic Studies, University of Tasmania. CSIRO Climate Adaptation Flagship
5. Nevill, J., Submission to inquiry into recreational fishing (including The impacts of spearfishing: notes on the effects of recreational diving on shallow marine reefs in Australia). 2010: Only One Planet Consulting. 22 March 2010.
6. Gillanders B (1999) Blue groper. In: Andrew N (ed) Under Southern Seas: the ecology of Australia’s rocky reefs. UNSW Press, Sydney, pp 188-193
7. Sanderson, J. & Ling, Scott & Dominguez, J & Johnson, Craig. (2015). Limited effectiveness of divers to mitigate ‘barrens’ formation by culling sea urchins while fishing for abalone. Marine and Freshwater Research. 67. 10.1071/MF14255.
8. Nevill, J (2006) The impacts of spearfishing: notes on the effects of recreational diving on shallow marine reefs in Australia. First published in 19842, revised July 30, 2006
9. Kroon, F.J., Barneche, D.R. & Emslie, M.J. Fish predators control outbreaks of Crown-of-Thorns Starfish. Nat Commun 12, 6986 (2021). https://doi.org/10.1038/s41467-021-26786-8
10. Harry Gorfine, Justin Bell, Kade Mills & Zac Lewis (2012) Removing sea urchins (Centrostephanus rodgersii) to recover abalone (Haliotis rubra) habitat. Fisheries Victoria Internal Report Series. No. 46.