Extreme environments are defined by their persistent or fluctuating exposure to one or more environmental stressors, including high or low temperatures, elevated salinity, variable osmolarity, intense ultraviolet (UV) radiation, absence of light, increased hydrostatic pressure, extreme pH levels or low oxygen concentrations.

In marine ecosystems, extreme habitats such as hydrothermal vents, hypersaline lagoons, polar seas, and deep-sea trenches host a huge biodiversity. However, such conditions challenge the survival and proliferation of most organisms, meanwhile fostering the development of unique ecosystems characterized by specialized biological communities. More precisely, these environments harbor a remarkable array of both microbial and multicellular lifeforms, including coevolutive symbiotic interactions, many of which are uniquely adapted to withstand stressors that define their habitats. Studying these habitats not only enhances our understanding of biodiversity in extreme marine environments but also uncovers novel biochemical pathways and evolutionary mechanisms, holding profound implications for defining the limits of life on Earth.

Studying extreme environments involves logistical challenges, specialized methodologies, advanced equipment, and costly infrastructure. Access to these harsh habitats has historically hampered accurate experimental research. However, technological advancements and omics approaches have dramatically facilitated investigative capability and data elaboration. Scientific innovations significantly instigated research expansion on extreme environments. New insights are being gained on the physiological, ecological and evolutionary adaptations that enable organisms to survive and flourish under challenging conditions. These may involve molecular, organelle and cellular adjustments, as well as multi-organismal cooperation and behavioral processes. Despite current progress in the field, the biodiversity of these environments remains largely uncharted, as well as the ecological roles and evolutionary histories of these extreme inhabitants.

Ongoing efforts to study the life forms in these ecosystems are essential, not only for understanding the resilience and adaptability to extreme conditions, but also to formulate hypothesis on future communities under global change.

The aim of this Research Topic is to collect studies on the biosphere of marine extreme habitats, increasing our knowledge on the (i) biodiversity, (ii) ecological functioning, (iii) biochemical adaptation, and (iv) evolutionary history of the organismal forms living in these particular habitats and their extremozymes and other associated biomolecules.

We warmly invite scientists working in this field to present their valuable contributions to the scientific community through reviews, original research articles, or short communications focusing on life in marine extreme and hostile environments. These contributions may encompass studies from a variety of extreme marine environments, such as cold and deep-sea ecosystems, hydrothermal vents, high-pressure zones, high-salinity habitats hypoxic and anoxic environments, and other challenging systems. Through this collection, we aim to advance our understanding of the exceptional biochemical and ecological adaptations in these extraordinary settings.

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Adaptation and Evolution in Marine Extreme Environments