Never in human history, have we degraded what surrounds us so much that in the last 50 years. The living world, which we are part of and which provides us with everything we need to survive, from air to water, food, medicine, livelihoods and so much more, is suffering because of us. Everywhere in the world, some species are disappearing, and most populations of animals and plants are declining at an unprecedented rate – so much that scientists are calling this global event the “6th global mass extinction”.
And although we are a terrestrial species, having colonized almost every bit of land where we could grow food, find water, extract fossil fuels and build houses, we have also in a way, colonized the ocean.
It is true that the ocean appears as this big blue thing out there, so difficult to reach, penetrate or discover as a whole. And yet, the impact of anthropogenic activities on marine biodiversity is astonishing. Only 3% of the ocean is described as free from human pressures and at least 66% of the ocean area is experiencing multiple, cumulative impacts from us.
But what are the real threats? What is causing populations of marine species to decline or disappear?
If we were to ask you to reply to the previous questions, what would be your guess? If we were to ask you to rank the top 5 threats to marine biodiversity, what would you put on top and so on?
It is not an easy task, because our representation of what is harming what surrounds us is conditioned by what we get to read online, what we see with our own eyes and what we get interested in. For that reason, people often mention plastic pollution as one of the main threats. It is true that plastic pollution is a real global issue, that we can see everywhere and on which it is relatively easy and crucial to act. However, it is not the only pressure causing harm to the living world, and we can go further in reducing our negative impact.
Let’s discover what the biggest threats to marine biodiversity are… and what we can do.
This ranking has been produced by the IPBES, (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services), which published in 2019 a highly comprehensive report on the question: the Global assessment report on biodiversity and ecosystem services.
The direct drivers of change in the ocean with the largest global impact are (in order of importance):
- Direct exploitation of organisms (fishing)
- Ecosystem loss
- Climate Change
- Pollution
- Invasive species
Those five threats are the result of multiple underlying causes, which are underpinned by cultural and societal values and behaviours – the way we, humans, live. But let’s dive deeper into each of these direct drivers of change.
- Overfishing
In the ocean, the over-exploitation of fish, shellfish and other organisms (targeted and non-targeted species) has the largest relative impact on biodiversity.Over the last 50 years, fishing has expanded at all scales: fishing boats are bigger, they go further, deeper, for a longer time, with increasing technical gear. As a result, the number of overexploited fish populations has been expanding too.However, we are not fishing more fish (in terms of tonnage) since 1996, when we’ve reached a peak of productivity. But to try to maintain this number we are continuing to exploit marine populations at a rate that is unsustainable – a rate at which, populations cannot regenerate fast enough to replenish and ensure the durability of the “stock”.The amount of bycaught species (accidentally caught) is also tremendous, with a global estimate of 40% of total marine catches being “unwanted” species, often released dead in the water or illegally sold.With all this, it seems obvious that the unsustainable exploitation of marine organisms is directly causing the biggest impact on life in the ocean.
- Loss of ecosystems
The second driver with the highest relative impact on the ocean is the “changes in the uses of the sea and coastal land” that are causing ecosystems to degrade or disappear.Urban development on the coastline, destructive fishing methods, construction of aquaculture facilities and pollution from rivers are physically and chemically impacting marine and coastal ecosystems.Mangrove forests, coral reefs, seagrass meadows, oyster reefs, macroalgae forests, and saltmarshes are the main coastal ecosystems found globally and hosting the majority of marine life. When anthropogenic pressures are causing the destruction and loss of these ecosystems, the entire living world found within them is lost alongside.
- Climate Change
Sometimes thought of as the main threat to our planet, climate change is actually the third driver with the largest relative impact on the ocean.The rises in atmospheric concentrations of greenhouse gases due to human activities are causing the whole planet to warm up, like never before. The ocean which acts as a buffer, absorbing the excess heat and gases from the atmosphere, is also suffering.As a consequence, water temperature is rising, the ocean is acidifying (the pH of the ocean is decreasing), the levels of oxygen are dropping, and marine heatwaves are increasing. These changes are contributing to widespread impacts on marine biodiversity, leading to alterations in species distribution, phenology (reproduction time), population dynamics, community structure and ecosystem function.To mention a relatively famous example, coral reefs are directly suffering from climate change. Corals are highly sensitive to water temperature: an increase in temperature makes the corals bleach (they expel a little alga that lives within them that provides them with nutrients), causing their death. As a result, the global coverage of living coral has declined by half since the 1950s and up to 90% of corals may be gone in the next few decades if we follow “business as usual”.The biggest danger of climate change is that, on top of directly impacting marine biodiversity through the changes previously stated, it is also exacerbating the impact of the other drivers of change…
- Pollution
Heavily represented in our society, through awareness-raising campaigns, marketing and documentaries, pollution is fairly well-known to most of us. But often, it is linked to one type of pollution: plastic pollution. However, here, when mentioning the fourth driver with the largest relative impact on marine biodiversity, plastic is not the guiltiest.Chemical pollution is the most widespread type of pollution having the most impact on the ocean and the life within it.The use of fertilizers and pesticides on land, for agricultural activities, is causing a lot of damage. These chemicals made of nitrogen and phosphate easily find their way to soils and rivers, and ultimately end up in the ocean where these two are found in limited quantity.Nitrogen and phosphate are both limiting factors for the growth of algae (and for crops, that’s exactly why we use them on land to increase agricultural yield). When large quantities of nitrogen and phosphate end up in the ocean, phytoplankton and algae get to live their best life and literally bloom.These massive blooms are disrupting the whole balance of the ecosystem: toxic small algae explode, a large amount of seaweed at the surface prohibits the sunlight to penetrate, depriving deeper species from this energy, and decaying algae are emptying the area from oxygen (because of the bacteria that use the surrounding oxygen to deteriorate the dead material).Chemical pollution is literally creating dead zones, like in the Gulf of Mexico or the Black Sea, where underwater life is almost inexistent.
- Invasive species
The fifth driver of global change in biodiversity is the spread and invasion of alien species.Alien species? That’s just the name given to species that are finding their way to places where they are not usually found, where they establish and colonize everything, at the expense of the other species previously there. The introduction of new species by humans deliberately or accidentally is causing new forms of ecosystems to form, often not really diverse nor resilient.Transported by floating debris across oceans, or by attaching to cargo hulls or in the ballast waters of ships, many organisms find their way from one part of the world to another. The globalization of the world, accompanied by the development of global marine transport is responsible for it. But when new species arrive in a new place, they are usually found without their usual predators or parasites that normally regulate them. They often become better competitors and predators than the locally found species and end up dominating everything.One of the most common examples is the invasion of the lionfish. Originally found in the Indo-Pacific, this species has been able to colonize all oceans. Released from aquariums in Florida as well as moving through the Suez Canal, this species has been able to reach the Caribbean and the Mediterranean Sea respectively. In these regions of the ocean where it is not native, this species has established itself as a fierce predator: being able to eat almost every other species, the lionfish has been spreading at the expense of other fish populations.
What can we do?
As much as it looks like a terrific and overwhelming situation to face, all is not lost yet. The living world can be conserved, restored and used sustainably whilst meeting human needs. But this requires urgent and concerted efforts. Individual and collective actions are required to create a transformative change.
Each of these different threats (overfishing, ecosystem loss, climate change, pollution and invasive species) has its specificities that require targeted and precise actions such as changes in consumption, changes in practices on land and at sea, and new policies implemented etc. We do feel the need to dive deeper into each of these threats and what needs to be put in place specifically for each of them – which we will do in future articles.
But we have to remember that the ultimate driver causing this “top 5” is linked to the way we, humans, live on this planet. So, ultimately, if we want to slow down the global collapse of biodiversity, we have to think about the way we chose to live our lives.
When stating the different solutions and what needs to be put in place, the scientists of the IPBES report mention that we need to change our vision of what living a “good life” is.
A good life is considered as “the achievement of a fulfilled human life (…) comprising access to food, water, energy and livelihood security, and also health, good social relationships and equity, security, cultural identity, and freedom of choice and action. (…) It is multidimensional, having material as well as immaterial and spiritual components. (…) The concept of human well-being used in many western societies and its variants, together with those of living in harmony with nature and living well in balance and harmony with Mother Earth, are examples of different perspectives on a good quality of life”.
So, what do we want our lives to be like? Knowing that we are part of a whole living world, and not extracted from it and that we depend on it more than anything else, what life do we want to conduct in order to respect what sustains us?
Sustainable changes need to be external as much as internal. “External” actions such as putting in place marine protected areas, slowing down coastal development, reducing fishing effort, and restoring actively marine ecosystems are crucial… So is our way of considering and watching the world that surrounds us, in order to find a more harmonious and balanced way to live on this planet.
These few paragraphs you’ve just read are an introduction to the situation we are facing, or should we say a foundation to understand it. Before diving deeper into each of these specific threats, it was important for us to draw the big picture so that we can always keep it in mind and remind ourselves that the problem is large, underlined by many cumulative drivers and that as a result, solutions need to be intelligent and holistic.
Keep your eyes open as we will be sharing more on each of these threats as well as concrete, individual and collective solutions to tackle them.
References
Albins MA, Hixon MA (2008) Invasive Indo-Pacific lionfish Pterois volitans reduce recruitment of Atlantic coral-reef fishes. Mar Ecol Prog Ser 367:233–238. https://doi.org/10.3354/meps07620
Halpern BS, Walbridge S, Selkoe KA et al. (2008) A global map of human impact on marine ecosystems. Science 319:948-952 DOI: 10.1126/science.1149345
Molnar JL, Gamboa RL, Revenga C, Spalding MD (2008) Assessing the global threat of invasive species to marine biodiversity. Front Ecol Environ 6:485–492. https://doi.org/10.1890/070064
Davies RWD, Cripps SJ, Nickson A, Porter G (2009) Defining and estimating global marine fisheries bycatch. Mar Policy 33:661–672. https://doi.org/10.1016/j.marpol.2009.01.003
Pauly D, Zeller D (2016) Catch reconstructions reveal that global marine fisheries catches are higher than reported and declining. Nat Commun 7:. https://doi.org/10.1038/ncomms10244
IPBES (2019): Global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. E. S. Brondizio, J. Settele, S. Díaz, and H. T. Ngo (editors). IPBES secretariat, Bonn, Germany. 1148 pages. https://doi.org/10.5281/zenodo.3831673
Hughes TP, Kerry JT, Baird AH, et al (2019) Global warming impairs stock–recruitment dynamics of corals. Nature 568:387–390. https://doi.org/10.1038/s41586-019-1081-y
Eddy TD, Lam VWY, Reygondeau G, et al (2021) Global decline in capacity of coral reefs to provide ecosystem services. One Earth 4:1278–1285. https://doi.org/10.1016/j.oneear.2021.08.016