May 7, 2026
Deep-sea ecosystems as climate refugia: a hidden lifeline for marine species
BY: Helena Alvarez
Topics: Habitat Protection
Climate change is having profound and unprecedented impacts on the ocean, causing ocean warming, acidification, and deoxygenation, among other changes. These impacts modify the environmental conditions where many marine species live, to the point where they face unprecedented stress. However, some studies highlight that deeper areas may be relatively more insulated from climate-driven changes, and so may provide suitable conditions for species to persist and adapt to increasing environmental stress.
The key role of deep-sea habitats
Little is still known about the deep sea, where sunlight fades away, starting from around 200 metres below the surface. What we do know is that the habitats there provide a host of essential ecosystem functions, including these three key ones:
- Home to diverse marine life: Deep-sea ecosystems such as cold-water coral reefs, sponge grounds, and seamount communities play an important role in forming marine habitats. Their complex three-dimensional structures create a wide variety of microhabitats that provide shelter, feeding grounds, and nursery areas for numerous species. These habitats are typically considered as ‘vulnerable marine ecosystems’ (VMEs), which are extremely sensitive to external impacts due to their slow metabolism, long lifespans, and fragility to external impacts.
- Climate refugia for marine species: Deep areas typically experience lower temperature variations and more uniform conditions than the surface, where daily sunlight, seasonal cycles, and heatwaves cause large fluctuations. This relative environmental stability makes some deeper habitats potential climate refugia for species.
- Help regulate our climate: Deep-sea communities play an important role in the ocean’s capacity to store carbon. They do so by locking carbon away in sediments and skeletal structures for long periods, thereby helping to mitigate climate change.
The Mediterranean context
The Mediterranean Sea is recognised as a climate change hotspot. In this sea, which is warming at a rate two to three times faster than the global average, fish, crustaceans, and other benthic organisms (those living on or near the seafloor) have been observed to be moving into deeper waters as the surface warms. Although not all species can tolerate the darkness and high pressure of the deep sea, some with temperate or cold-water affinities are already predicted to migrate into deeper and cooler waters.
Recent studies combining information about habitat occurrence with climate projections suggest that certain deep-sea sessile (immobile) species, including cold-water corals, bamboo corals, and sea pens, could face substantial habitat loss by the end of the century. By 2100, around 60% of the areas where these habitats occur may disappear. Much of this decline is linked to a projected increase of 1-2 °C in bottom-water temperatures along continental margins. In the Mediterranean, climate impacts are expected to result in greater habitat loss in the eastern and central basins, particularly in the deep sea between 600 and 1000 m depth.
Mediterranean deep-sea ecosystems are globally unique and irreplaceable. For example, bamboo coral (Isidella elongata) plays a crucial ecological role by providing feeding, spawning, and nursery grounds for many other organisms, including commercially important ones like blackmouth catshark (Galeus melastomus), deep-sea shrimps (Aristeus antennatus, Aristaeomorpha foliacea, Parapenaeus longirostris), and European hake (Merluccius merluccius). However, Isidella elongata is highly sensitive to even small temperature changes, which can affect its survival. It is also classified as Critically Endangered by the International Union for the Conservation of Nature, due to drastic population declines that have primarily been caused by bottom trawling.
Threats to deep-sea refugia
Given their vital role in the marine environment, keeping deep-sea habitats healthy is of the utmost importance. Yet not all refugia can survive under changing conditions, and only ecosystems in healthy condition are likely to withstand climate stress. Many VMEs are highly sensitive to external stressors, including the impacts of destructive fishing gears like bottom trawls, bottom longlines, and traps, which are increasingly moving into deeper waters in the Mediterranean. Bottom trawling has already caused the near-collapse of Isidella elongata colonies and long-lasting damage to coral and sponge communities. For VMEs such as these, recovery from this damage can take centuries. Further, once physically damaged, the ability of these habitats to serve as refugia is greatly reduced. So is their capacity to mitigate climate change because as they lose their structure, their capacity to store carbon is also diminished.
Protecting Mediterranean deep-sea ecosystems: a precautionary approach
Active restoration in the deep sea remains extremely challenging, but some studies indicate that safeguarding undisturbed deep-sea environments, alongside supporting recovery in physically degraded areas, may help strengthen ecosystem resilience as climate pressures intensify. A straightforward option is creating strictly protected areas – areas where no human activity is allowed – as the most effective way of preserving these deep-sea biodiversity hotspots.
One simple way to reduce human impacts in the Mediterranean Sea would be to prohibit bottom trawling at depths greater than 800 m. Such a ban currently exists below 1000 m depth, which was established in 2005 under the General Fisheries Commission for the Mediterranean (GFCM). Extending this ban to include waters between 800-1000 m depth would protect an additional 100 000 km2 of deep sea, and encompass a large number of VMEs, according to Oceana data. Doing so would reduce cumulative fishing impacts, preserve climate refugia, maintain carbon storage, and support the sustainability of fisheries by protecting key habitats of importance for commercial species. It would align not only with the practices of Regional Fisheries Management Organisations and contribute to the GFCM 2030 Strategy, but a GFCM expert group on VMEs also recently endorsed such a ban.
Protecting deep-sea habitats in this way is the most effective approach to preserving biodiversity, and enhancing ecosystem resilience in the face of accelerating climate change and destructive human impacts. It is not just a matter of preserving still unexplored ecosystems, but a strategic investment in the planetary resilience.
Watch this video of scientists supporting extending the Mediterranean deep-sea trawl ban
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