The Twin Threats of Species Extinction and Emergence in Warming Oceans

The world’s oceans are in the middle of a biological reckoning. As global temperatures rise, two contradictory processes are unfolding simultaneously beneath the waves: species that have inhabited ocean ecosystems for millions of years are being pushed toward extinction, while other species – often invasive and ecologically disruptive – are expanding into territories they have never occupied before. This isn’t a distant future scenario. It is happening now, and the evidence from both the fossil record and current ecological monitoring is hard to ignore.

Historical extinction events linked to climate change
Emergence of new species in warming and polar regions
The lionfish invasion
Jellyfish and other range-expanding species
Biodiversity loss and ecosystem services
Strategies for mitigating extinctions
Marine protected areas and network design
Assisted evolution and coral restoration
Invasive species management
Integrating community and policy action

Historical extinction events linked to climate change

To understand where ocean ecosystems are headed, it helps to look back at where they’ve been. Earth has experienced five major mass extinction events, and climate-driven changes in ocean chemistry have played a central role in several of them. The most instructive parallel is the end-Permian extinction, approximately 252 million years ago, which wiped out an estimated 90% of all marine species – the deadliest extinction event in Earth’s history.

Research from the University of Washington and Princeton University has traced the primary cause of this catastrophe to massive volcanic activity in Siberia that flooded the atmosphere with greenhouse gases. Oceans warmed dramatically, losing roughly 80% of their dissolved oxygen. Marine animals’ metabolic rates increased as water temperatures rose, meaning they demanded more oxygen at precisely the moment the supply collapsed. The result was a cascading failure across marine food webs. Species at higher latitudes – the polar regions – suffered the most, because they had no cooler refugia to retreat to. Tropical species fared slightly better, as their physiology was already adapted to warmer, lower-oxygen conditions.

This pattern – polar species facing extinction while tropical species shift poleward – is not ancient history. It is the exact trajectory that current climate models project for this century under business-as-usual emissions scenarios. A 2022 study published in Science found that unchecked greenhouse gas emissions could drive marine extinctions comparable in scale to the end-Permian event, driven by the same dual mechanism: warming and oxygen loss.

Emergence of new species in warming and polar regions

While some species face extinction, others are capitalizing on the changing conditions. Warming oceans are effectively opening new geographic territory to species that were previously confined to warmer latitudes. This isn’t species adaptation in the evolutionary sense – it is range expansion, and it is happening fast enough to destabilize the ecosystems these newcomers enter.

The lionfish invasion

Few examples illustrate this dynamic more clearly than the lionfish. Lionfish (Pterois volitans) are native to the tropical waters of the South Pacific and Indian Oceans. They were first recorded off the Florida coast in 1985, likely introduced through aquarium releases. For years, sightings were sporadic. Then ocean temperatures began rising steadily, and the situation changed dramatically.

Today, lionfish have spread across the Atlantic, the Gulf of Mexico, and throughout the Caribbean, and their populations show no signs of peaking. A NOAA and University of North Carolina-Wilmington study found that warming Atlantic temperatures are enabling lionfish to expand into areas previously too cold for them to survive year-round. The only factor that had previously limited their northern expansion – cold winter bottom temperatures – is progressively being removed as a barrier.

The ecological consequences are severe. Lionfish are voracious predators with no natural enemies in Atlantic waters. They consume herbivores that keep algae in check on coral reefs. Without those herbivores, unchecked algal growth smothers coral – a reef ecosystem already stressed by bleaching, acidification, and overfishing. The lionfish is not just a new resident; it is actively degrading the habitat it moves into.

Jellyfish and other range-expanding species

Lionfish are not the only species expanding their ranges. Jellyfish populations, including some of the world’s most venomous species, are thriving in warmer waters. Research cited by National Geographic found that jellyfish reproduction increases in warmer water, and the majority of jellyfish species studied show abundance increases as temperatures rise. Deadly box jellyfish, previously confined to tropical Australian waters, have been recorded moving southward into more populated coastal zones. Crown-of-thorns starfish – which feed on coral – are similarly expanding their range into the Great Barrier Reef from their traditional Indo-Pacific distribution.

The common thread across these cases is that climate change is expanding hospitable warm waters into higher latitudes, and species with few natural predators in their new environments are moving in fast. The result is ecosystems flooded with newcomers that native species have no evolutionary history of dealing with.

Biodiversity loss and ecosystem services

The combined pressure of extinction on one end and invasive species disruption on the other is eroding marine biodiversity at a pace that carries real-world consequences for hundreds of millions of people.

Coral reefs are the clearest example. Coral reefs cover less than 1% of the ocean floor but support at least 25% of all marine species, according to the UN Environment Programme. The ecosystem services they provide – coastal protection, fisheries, tourism, and pharmaceutical resources – are valued at an estimated $2.7 trillion per year globally. Six million fishers across nearly 100 countries rely on coral reef ecosystems for their livelihoods.

NOAA confirmed a fourth global coral bleaching event between February 2023 and April 2024, driven by prolonged marine heatwaves. Under the IPCC’s high-emissions scenario, up to 90% of coral reefs could disappear by 2100 if global temperatures rise more than 2°C above pre-industrial levels. When coral reefs collapse, the services they provide don’t simply shift elsewhere – they disappear. Coastal communities lose their natural storm barriers. Fisheries decline. Carbon sequestration capacity drops, since reef-adjacent seagrass meadows also depend on the structural protection reefs provide.

Polar ecosystems face a parallel crisis. Polar species are at the highest risk of global extinction because they have nowhere colder to go. As Arctic and Antarctic waters warm, cold-adapted species like certain krill, fish, and marine mammals lose habitat from both ends – warming from below their range and invasive warm-water species encroaching from above. The North Atlantic right whale, one of the world’s most endangered large whale species, has already shifted its distribution patterns in response to changes in prey location caused by warming waters – placing it in new conflict zones with fishing gear and ship traffic.

The IPBES 2019 Global Assessment estimated that one million species are currently threatened with extinction, including more than a third of reef-building corals and more than a third of marine mammals. Climate change currently affects 45% of marine species at risk, and under unchecked emissions, it could rival all other human pressures combined by the end of this century.

Strategies for mitigating extinctions

The science is sobering, but it consistently points to one finding that matters enormously for policy: the scale of marine extinction is directly tied to the scale of emissions reductions. A study published in Science found that reversing greenhouse gas emissions trends could reduce marine extinction risks by more than 70%, preserving biodiversity accumulated over approximately 50 million years of evolutionary history. That single statistic reframes the entire conversation – the primary mitigation strategy is decarbonization.

Beyond emissions reductions, conservation practitioners have developed a toolkit of complementary approaches.

Marine protected areas and network design

Marine Protected Areas (MPAs) are widely recognized as a critical tool. MPA networks – coordinated groups of protected zones rather than isolated reserves – are more effective than individual MPAs because they spread extinction risk and protect both short- and long-distance dispersing species. The Kunming-Montreal Global Biodiversity Framework set a target of protecting 30% of ocean areas by 2030. Currently, effective protection falls far short of that goal. MPAs work best when paired with fisheries regulations, pollution control, and broader coastal management frameworks – they are not effective in isolation.

Assisted evolution and coral restoration

For coral reefs specifically, researchers are exploring human-assisted evolution – selectively breeding or genetically modifying stress-tolerant coral colonies and transplanting them onto degraded reefs. This approach aims to increase thermal resistance so that corals can survive bleaching events that would otherwise kill them. Organizations are also using micro-fragmentation technology to accelerate coral growth, compressing recovery timescales from decades to years. While promising, scientists caution that over-reliance on a small number of resistant strains could itself reduce overall reef biodiversity.

Invasive species management

Managing range-expanding invasive species requires active intervention. For lionfish, NOAA and its partners have promoted lionfish as a commercially viable food fish, creating market incentives for targeted removal. Culling programs in marine reserves have demonstrated that active removal can reduce lionfish populations enough to allow native reef fish communities to partially recover. However, complete eradication from open-ocean environments is not considered feasible – ongoing management is the realistic goal.

Integrating community and policy action

Effective conservation cannot operate only at the scientific level. Coastal communities that depend directly on marine ecosystems have become increasingly central to conservation efforts, pairing ecosystem restoration with sustainable livelihoods such as dive training, reef monitoring, and ecotourism. At the policy level, the Convention on Biological Diversity and national biodiversity strategies are beginning to incorporate binding targets for reef protection, though implementation remains inconsistent across countries.

The twin threats of extinction and invasive species emergence are not separate problems – they are two symptoms of the same underlying cause: ocean systems absorbing the thermal and chemical consequences of atmospheric carbon emissions. Addressing one without the other, or addressing both without confronting emissions at their source, leaves the core problem intact.

What do you think? If climate-driven extinctions and invasive species expansions are ultimately two sides of the same emissions problem, should marine conservation funding be primarily directed at habitat protection and restoration – or at the upstream effort to reduce greenhouse gas emissions that drive both threats? And as polar species face extinction from warming with nowhere colder to migrate, what ethical responsibilities do we have to actively intervene in their survival, versus allowing natural processes to unfold?

References

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Table of Contents

Historical extinction events linked to climate change 🔗

Emergence of new species in warming and polar regions 🔗

The lionfish invasion 🔗

Jellyfish and other range-expanding species 🔗

Biodiversity loss and ecosystem services 🔗

Strategies for mitigating extinctions 🔗

Marine protected areas and network design 🔗

Assisted evolution and coral restoration 🔗

Invasive species management 🔗

Integrating community and policy action 🔗