In the western Mediterranean, an iconic group of sea fans known as gorgonians has suffered severe losses over the past decade and a half as ocean temperatures climb. Researchers note that at certain depths these olive-green, tree-like organisms show surprising resistance to warming, a finding attributed to temperature gradients and the natural buffering provided by depth. This insight comes from a team led by Lorenzo Bramanti at the French National Centre for Scientific Research, commonly known as CNRS, whose work highlights how depth can influence vulnerability to heat waves. [CNRS]
Gorgonians are eschewing the rigid, calcium-rich skeleton of reef-building corals. Instead, their structure relies on a flexible, protein-based framework. Their distinctive form has earned them the nickname of underwater forests. When densely packed, these sea fans resemble terrestrial woodlands, providing a sheltering complex that supports a diverse array of marine life. This metaphor—an underwater forest—helps scientists and ocean stewards visualize a habitat where many species find refuge and vitality. [CNRS]
From an ecological standpoint, the notion of animal forests illuminates how a healthy, dense stand can foster biodiversity. The concept emphasizes shelter, feeding grounds, and nursery spaces that empower numerous organisms to thrive in a relatively stable microcosm beneath the waves. Such imagery also underscores the potential for these habitats to function much like Noah’s Ark, safeguarding biodiversity as climate pressures intensify. [CNRS]
Beyond shelter, gorgonians contribute to the biogeochemical cycling of matter. They transform organic material and participate in nutrient pathways that sustain broader reef ecosystems. Within the red gorgon Paramuricea clavata, which is among the most common and vulnerable species, researchers have documented a depth range spanning roughly 20 to 200 meters, and even deeper in some locales. This species is distributed across the northwest Mediterranean, including Spain, France, Italy, Greece, and Turkey. [CNRS, ONE Ocean Foundation]
The ongoing project enjoys support from the ONE Ocean Foundation and UNESCO, which has welcomed Bramanti to discuss findings at its Paris headquarters. The collaboration brings together CNRS and the LECOB Oceanological Research Unit, with Banyuls-sur-Mer Observatory in France coordinating field efforts over a two-year period. [ONE Ocean Foundation, UNESCO]
Mortality rate of gorgons by temperature
Researchers report a clear pattern: during the last fifteen years, heat-driven mortality in gorgonian populations has surged. Summer heat waves have caused dramatic losses, with some populations showing declines of 70 to 80 percent in extreme years. The task now is to understand the mechanisms behind this mortality, particularly at depths where most divers typically explore, around 20 to 40 meters. [CNRS]
Observations indicate that gorgon populations living at depths beyond 40 to 60 meters exhibit much lower signs of distress, a trend confirmed by field data collected from depths between 50 and 150 meters during coordinated work with ONE Ocean experts. The prevailing hypothesis suggests that deeper waters do not experience the same heat waves, creating potential refuges where gorgonians can endure while surface and shallow-water populations struggle. [ONE Ocean Foundation]
In these cooler refuges, jagged pockets or vaults of cooler water are thought to provide protection from rising temperatures. While this is encouraging news for remaining gorgon populations, researchers caution that the duration of this reprieve is uncertain as heat waves intensify in frequency and intensity. The team stresses that this is not a permanent shield and ongoing monitoring is essential to understand long-term dynamics. [CNRS]
The project is organized in three phases: collecting samples, performing analyses, and conducting genetic studies. Initial efforts incorporate data from other scientific investigations to build a comprehensive picture of resilience and decline.
Larvae for reproduction
In the second phase, researchers focus on recruitment and dispersion. Gorgonian populations serve as refuges because they can survive without relying on surface populations. The demography strengthens as these fixed organisms release larvae annually, which drift and settle in new locations, gradually expanding the forest-like cover beneath the sea. This reproductive pattern forms a practical model for understanding how reserves could safeguard these habitats. [CNRS]
Genetic analyses help determine the longevity of gorgon forests, clarifying whether deep-sea populations are self-sustaining. If new individuals fail to arrive, refuges may shrink or disappear, highlighting the need to protect connectivity across depths and regions. A third phase investigates gorgon forests that form around submerged shipwrecks, with the sinking date helping to estimate the age and persistence of these assemblages. [UNESCO, CNRS]
Promote marine protected areas
Temperature data collected from 0 to 40 meters by the Barcelona Institute of Marine Sciences, part of the Mediterranean division of the Higher Council for Scientific Research, proves valuable. While this dataset emphasizes shallow zones, it is noted that practical protection should extend to depths of 80 to 90 meters to capture the full range of refuges. The collaborative nature of the study means the dataset fills crucial gaps in the overall puzzle. [ICM-CSIC]
The researchers advocate establishing and expanding marine protected areas to safeguard gorgonians and the species that rely on them. They emphasize a broader commitment to cutting greenhouse gas emissions across sectors, including tourism, noting that deep-sea refuges could support climate resilience for marine forests. [CNRS, ONE Ocean Foundation]
Additional remarks stress that protection requires coordinated policy action and sustained, evidence-based management across jurisdictions. The work continues to unfold as more data are gathered and analyzed, offering a clearer view of how underwater forests might endure in a warming world. [CNRS, UNESCO]
Note: contact details and publication identifiers have been removed to align with current requirements and to focus on the scientific content itself. The project remains a collaborative effort among CNRS, the ONE Ocean Foundation, UNESCO, and regional oceanographic partners. [CNRS, ONE Ocean Foundation, UNESCO]