How hot can they handle? Deep-sea creatures and changing ocean temperatures

Greg Howard
7th November, 2025

How hot can they handle? Deep-sea creatures and changing ocean temperatures

Deep-sea copepods thrive in the extreme habitats of hydrothermal vents, inhabiting both the scorching, focused flows of Pompeii worm colonies (A) and the milder, diffuse flows among giant tubeworms and mussels (B).

Image adapted from: Messora et al. / CC BY (Source)

Key Findings

  • Deep-sea copepods from hydrothermal vents at the East Pacific Rise can tolerate high temperatures, but only for brief periods
  • Copepods living near rapidly flowing vent fluids (Pompeii worm habitats) withstand higher temperatures than those in slower flows (tubeworm & mussel habitats)
  • Lack of oxygen significantly reduces copepod survival more than temperature fluctuations, suggesting oxygen availability is a key limiting factor
Deep-sea hydrothermal vents are some of the most challenging environments on Earth, characterized by extreme pressure, darkness, and a chemical-rich fluid emanating from the ocean floor[2]. These vents support unique ecosystems, but the animals living there face constant stress from high temperatures, low oxygen levels, and toxic chemicals. Understanding how these animals survive, and what limits their distribution, is a major focus of marine biology. Researchers from NIOZ, Sorbonne Université-CNRS, University of Vienna, and Universidade de Aveiro recently investigated the thermal tolerance of small crustaceans called dirivultid copepods, which are common inhabitants of these vent systems[1]. The study focused on vents at the East Pacific Rise 9°50’N, specifically looking at copepod communities found in two main habitat types: ‘focused flow’ areas where vent fluid exits rapidly, and ‘diffuse flow’ areas where the fluid spreads out more gently. Previous research established that the foundations of these ecosystems are chemosynthetic bacteria and archaea, which derive energy from chemicals rather than sunlight[3]. These microbes support a food web that includes copepods and larger animals. The tolerance of these organisms to extreme conditions is often linked to physiological and behavioral adaptations, allowing them to exploit the resources available while avoiding the most harmful aspects of the vent environment. The researchers conducted experiments to determine the ‘thermal death time’ (TDT) – essentially, how long copepods can survive at different temperatures. They tested copepods collected from both focused and diffuse flow habitats, varying oxygen levels and pressure to see how these factors influenced their survival. The results showed that dirivultid copepods have a surprisingly high tolerance to heat, but only for very short periods. Importantly, the maximum temperatures they could withstand were strongly linked to the conditions of their native habitat; copepods from focused flow vents, which experience more extreme temperature fluctuations, were more tolerant than those from diffuse flow areas. Anoxia – the complete absence of oxygen – proved to be a significantly greater threat to copepod survival than temperature. Atmospheric pressure, however, had little to no effect on their tolerance. This is consistent with the general understanding of deep-sea animals being adapted to high pressure, making it less of a limiting factor than chemical or thermal stress[2]. Interestingly, the upper thermal tolerance of these copepods was similar to that observed in larger animals (macro- and megafauna) living in the same vent environments. However, tolerance to low or no oxygen increased with body size, suggesting that larger animals are better equipped to cope with oxygen deprivation. The research team also analyzed data on copepod abundance over the past two decades, combined with their new findings on temperature and oxygen tolerance. This revealed that physiological limits play a strong role in determining the composition of copepod communities in focused flow habitats, regardless of the stage of vent development. In contrast, the dynamics of copepod communities in diffuse flow habitats appear to be more complex, influenced by factors like competition between species and the availability of different food sources. A key point of comparison is the case of the Pompeii worm, Alvinella pompejana, which was once thought to thrive at temperatures exceeding 60°C[4]. However, more recent, controlled experiments showed that its upper thermal limit is actually below 55°C, and that it doesn't experience long-term exposure to temperatures above 50°C in its natural environment[4]. The findings from support this idea that animals may be able to tolerate brief exposures to extreme temperatures, but their long-term survival is limited by lower thresholds. The study highlights the importance of considering the duration of exposure when assessing the physiological limits of organisms in extreme environments.

EnvironmentEcologyMarine Biology

References

Main Study

1) Limits of life: Thermal tolerance of deep-sea hydrothermal vent copepods and implications for community succession

Published 5th November, 2025

https://doi.org/10.1371/journal.pone.0333996

Related Studies

2) Metazoans in extreme environments: adaptations of hydrothermal vent and hydrocarbon seep fauna.

Journal: Gravitational and space biology bulletin : publication of the American Society for Gravitational and Space Biology, Issue: Vol 13, Issue 2, Jun 2000

3) The microbiomes of deep-sea hydrothermal vents: distributed globally, shaped locally.

https://doi.org/10.1038/s41579-019-0160-2

4) Thermal limit for metazoan life in question: in vivo heat tolerance of the Pompeii worm.

https://doi.org/10.1371/journal.pone.0064074


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