Commentary/What causes abrupt changes in ecosystems?
Large and abrupt changes in forests, coral reefs, and Arctic sea ice are generally driven by climate change, food production, and urbanisation. Managing their causes can reduce the occurrence of these shifts around the world and ensure the well-being of local communities.
One morning in 2016, fishers in Nueva Venecia on the Colombian Caribbean coast woke up to find a thick carpet of dead fish floating in the water. The mass fish death had been caused by an overload of nutrients in the adjacent Ciénaga Grande de Santa Marta, the largest coastal lagoon and wetland system in the country.
It was the rainy season, and when the rain finally arrived in 2016, the Magdalena river that feeds the wetland system brought with it an unusually high concentration of nutrients and sediments.
That year was also an El Niño year, and unusually high temperatures had made the water in the lagoon, rivers, and on the coast warmer than normal. The warm conditions and high levels of nutrients created conditions perfect for algal blooms. During blooms, algae grow in great numbers and consume oxygen to the point where few other organisms can survive in the water. The fish had suffocated.
For fishers this is more than an ecological tragedy. “This affects us in all respects – our economic situation, because in Nueva Venecia our livelihood is fishing, without fish there is nothing,” says Edgardo Camargo from the Association of Fish Producers in Nueva Venecia.
Ciénaga Grande de Santa Marta, a 4,280-sq-km lagoon complex, is home to many fishing and agricultural communities. “81% of our city’s inhabitants live off fishing,” says Francisco Gutierrez, who, as mayor of the town Pueblo Viejo in the Ciénaga, was concerned about how the fish death would impact the livelihoods of the fishing communities – which are made up of 64,000 fishers in Pueblo Viejo alone.
In the last 50 years the Ciénaga went from producing around 30,000 tonnes of fish per year to only 5,000 tonnes, according to fishers in the area. An estimated 18 tonnes of fish perished in the mass fish death of 2016. And the dead fish was not only a wasted resource; it was also a source of disease and foul odours when it was left to rot.
The drastic changes the fishers experienced in Nueva Venecia were not an isolated event. Sudden and unexpected disruptions to ecosystems occur all over the world, often with dire consequences for the people who depend on them. Insights into what causes these changes can improve management strategies to avoid shifts recurring.
Dead fish float to the surface after suffocating when oxygen levels in the water dropped. Photo: R. Saldaña/flickr
Abrupt and persistent regime shifts
Large, abrupt, and persistent changes in the function and structure of ecosystems are known as regime shifts. They are very hard to predict; costly and difficult or impossible to reverse; and they often affect people’s well-being.
The type of regime shift that occurred in Ciénaga, where normal levels of oxygen dropped to oxygen-starved levels, has been documented in over 300 case studies around the world. Some cases have been temporary events where the ecosystems could recover, others have been permanent shifts where the water became acidic and only bacteria could survive.11. R. J. Díaz, R. Rosenberg, Spreading Dead Zones and Consequences for Marine Ecosystems. Science. 321, 926–929 (2008).See all references
This is one of over 30 different types of so-called regime shifts that have been identified in the world’s ecosystems – in water, on land, and in polar environments.
In 2009, a group of researchers started developing the Regime Shifts Database at the Stockholm Resilience Centre. Today it is the world’s largest database on regime shifts that identifies the main drivers, impacts, and causal mechanisms that underlie regime shifts. To date, the database has gathered information from more than 1,000 scientific papers and provides a knowledge base for researchers and practitioners dealing with regime shifts.
The Regime Shifts Database gathers information about regime shifts around the world. Each dot in this map represents a literature review of a generic regime shift (orange) or case study (blue). Click this link to go to the interactive version of the map where you can find links to the literature review in the database and learn more about these phenomena.
From reef to algae, rainforest to savanna
Fishers in Colombia are not the only ones affected by regime shifts, which are not always limited to small communities. In 2016, 21 million people in São Paulo were in the midst of one of the worst droughts on record and politicians and decision makers were worried about the risk of riots. Researchers suggested that the lack of rain was triggered by increasing deforestation in the Amazon rainforest. This connection was also emphasised by the state-owned water company serving most of São Paulo.
“The Amazon creates a movement of water. If you could follow a molecule of water you would see that most of the clouds that are over São Paulo have passed across the Amazon. If the forest is cut, we’ll be in trouble,” Jerson Kelman, president of the water company Sabesp, said in an interview with the Guardian.
Trees contribute to increased humidity, and when they disappear rainfall volumes in the region decrease as the humidity drops. Fewer trees also means less water vapour flowing higher up to the atmosphere, which in turn means less rainfall somewhere else, further away. Ecosystems are connected across great distances, through things like flows of water and water vapour, migrations of animals, and dispersal of seeds. And in the same way that São Paulo is feeling the consequences of deforestation, couldn’t it be possible that other regions are suffering the consequences of changes in the Amazon forest as well? Researchers believe that changes in moisture recycling from the Amazon can have impacts in the mountain forests and agricultural landscapes in the Andes.22. N. Morueta-Holme et al., Strong upslope shifts in Chimborazo’s vegetation over two centuries since Humboldt. P Natl Acad Sci Usa (2015).See all references
Continued deforestation together with climate change could eventually cause the Amazon to shift from rainforest to savanna. Such a shift would mean that all the benefits from the forests would be lost, including carbon storage and oxygen production.
Another worrying ongoing regime shift is the coral die-off around the world. In Australia, a nine-month marine heatwave in 2016 caused 30% of the corals on the Great Barrier Reef to die. Coral reefs provide important ecosystem services such as storm and wave erosion protection in coastal areas. They are home to many species of fish and other animals that fishers depend on, and a hotspot of biodiversity that fuels an important tourism industry. A combination of climate change, fishing pressure, pollution, and nutrient run-off from land is gradually eroding the reefs’ capacity to deal with shocks and disturbances, such as storms or heatwaves – in other words reducing their resilience, and putting these ecosystems at risk of a regime shift.
Regime shifts in coral reefs typically involve a change in species dominance from hard corals to algal dominance. They also include shifts from hard corals to urchin barrens , pictured here. These regime shifts result in loss of diversity and structural complexity, and are typically triggered by a combination overfishing, pollution, diseases and climate change. Images have been cropped to fit. Left: NOAA/flickr. Right: Travis/flickr
Resilience turns out to be key to understanding regime shifts. In fact, all the examples of regime shifts from across the globe show that ecosystems tip from one state into another when they lose their resilience. Shifts often happen because of a shock, such as a heatwave, hurricane, or heavy pollution, or a slow change that makes it less likely that the ecosystem can recover – for example deforestation – or a combination of both. Research has shown, over and over again, that ecosystems have thresholds – critical points – where they can flip and turn into something different, changing their structure, function, and ability to provide services that are important for society.
In Ciénaga Grande de Santa Marta it was the low level of oxygen that caused huge numbers of fish to die in 2016. In the Amazon, deforestation reduces the evaporation and moisture to feed the rain that is supposed to fall in São Paulo and leads to drought. And in Australia the increase in heatwaves and the number of days with higher-than-normal temperatures is causing corals to die. The level of oxygen that would be tolerable, the minimum humidity that would still create rain, or the number of days that a coral can stand heat – these tipping points are moving targets.
The exact value of the tipping point is different from place to place, from species to species, and might even differ dramatically within the same place, from one situation to another depending on a number of other conditions. This can be compared to knowledge that smoking can cause lung cancer. While research has shown this clearly, the exact number of cigarettes that will trigger the effect varies from person to person, and the risk of getting cancer can be influenced by other factors such as air pollution, exposure to asbestos, and a person’s genes. Knowledge about potential causes can shed light on what actions are necessary to avoid the tipping point where cancer forms. This is also true for regime shifts in the environment.
Ball-and-cup model: As conditions change, a system (the orange ball) changes, represented by motion. As the barriers to jump into a new state shift, a system might jump to another configuration (one of the three cups here). Animation/illustration: E. Wikander/Azote.
Data to derail drastic changes
So what are the main causes of regime shifts globally? Researchers have used the regime shifts database to identify what the main causes, or drivers, of regime shifts are, and to study patterns of how different drivers occur together. Understanding the drivers behind regime shifts can generate insights around how to prevent ecosystems from tipping into undesired states, or how to reverse changes. They found that climate change, food production, and urbanisation are the three main groups of drivers of regime shifts.33. Rocha JC, Peterson GD, Biggs R (2015) Regime Shifts in the Anthropocene: Drivers, Risks, and Resilience. PLoS ONE 10(8): e0134639. https://doi.org/10.1371/journal.pone.0134639Link to articleSee all references
Managing these will be crucial for avoiding regime shifts; however, they cannot be managed at the same scale.
To tackle climate change, international efforts and a global approach are required – countries need to cooperate with one another and reduce their emissions to fulfil the Paris agreement, for example. But food production and urbanisation are different – they can be managed at the national level, in an individual country’s agricultural policies or fishing rules, and sometimes even at the community level, such as in a city’s growth planning.
Doing something about the drivers on a local level can build resilience, increasing the probability that an ecosystem will withstand disturbances, and buy some time to tackle the much trickier challenge of dealing with global drivers. For example, researchers have found that by managing local-scale drivers, such as pollution or fishing pressure, the impacts of climate change on coral reefs can be delayed, buying up to a decade of time to tackle climate change.44. E. V. Kennedy et al., Avoiding Coral Reef Functional Collapse Requires Local and Global Action. Current Biology (2013), doi:10.1016/j.cub.2013.04.020.Link to articleSee all references
However, to ensure that ecosystems can continue to provide the critical services that people depend on, the global challenges cannot be neglected.
Lack of information and insufficient data make it harder to study regime shifts in developing countries. Traditional methods to study these shifts are not always applicable; typically data that have been collected in a consistent way and over long time periods are needed. Understanding true drivers, finding tipping points, or anticipating potential shifts is harder when data are scarce.
In the absence of solid science, what could managers or policymakers do to avoid undesirable regime shifts, or to create changes that might lead to more desirable regime shifts? Researchers working with the Regime Shifts Database have compared case studies to better understand different types of regime shifts, and documented ways to manage the causes – lessons learned can be useful in places that are vulnerable to the same types of regime shifts.55. Rocha, J., J. Yletyinen, R. Biggs, T. Blenckner, G. Peterson. 2014. Marine regime shifts: drivers and impacts on ecosystems services. Philosophical transactions B. DOI: 10.1098/rstb.2013.0273Link to articleSee all references
For example, managing drivers related to coastal development, fishing, and pollution can prevent regime shifts in coastal ecosystems. Research shows that the drivers of change on coral reefs are in many ways the same across the world – including overfishing, pollution, and climate change. Successful management in one place on the globe can offer insights that are useful somewhere else.
Preparing for the unexpected
Not all regime shifts are negative for all of society. Although the database focuses on regime shifts that negatively affect people, some regime shifts are considered more desirable. In the Arctic, for example, climate change could lead to some beneficial changes for ocean-living algae. This could be good for organisms that feed on algae and could benefit fisheries and people who depend on fish for protein, as fish populations may grow when more food becomes available for them. Another example is the boreal forest expanding north in North America, Scandinavia, and Russia. As the forest expands, new timber industries could develop.
However, while fishers may benefit from increased fish stocks in the Arctic, other groups might feel the negative consequences of climate change – Indigenous groups that depend on cold conditions for accessing hunting grounds will be affected by new warmer conditions of the Arctic. And while forest expansion might be a positive development for people interested in timber, it will disrupt the migration routes of reindeer and caribou that many Indigenous groups depend on in the Arctic circle. Both of these scenarios are uncertain, and the effects of the shifts are hypothetical. It is important to keep in mind that when regime shifts occur there are always winners and losers.
Resilience thinking offers a new way of approaching these challenges, and stresses the need to understand how different parts of a system are connected to and affect each other. It is about acknowledging that society and nature impact and are dependent on each other, and that they can change in abrupt and non-linear ways. Implementing this non-linear thinking in the ways policies are planned and decisions are made collectively about how to manage ecosystems will make it possible for nature and people to benefit – and to avoid undesirable states, such as the changes the fishers experienced in Ciénaga.
Show references (5)
1. R. J. Díaz, R. Rosenberg, Spreading Dead Zones and Consequences for Marine Ecosystems. Science. 321, 926–929 (2008).
2. N. Morueta-Holme et al., Strong upslope shifts in Chimborazo’s vegetation over two centuries since Humboldt. P Natl Acad Sci Usa (2015).
3. Rocha JC, Peterson GD, Biggs R (2015) Regime Shifts in the Anthropocene: Drivers, Risks, and Resilience. PLoS ONE 10(8): e0134639. https://doi.org/10.1371/journal.pone.0134639Link to article
4. E. V. Kennedy et al., Avoiding Coral Reef Functional Collapse Requires Local and Global Action. Current Biology (2013), doi:10.1016/j.cub.2013.04.020.Link to article
5. Rocha, J., J. Yletyinen, R. Biggs, T. Blenckner, G. Peterson. 2014. Marine regime shifts: drivers and impacts on ecosystems services. Philosophical transactions B. DOI: 10.1098/rstb.2013.0273Link to article