Abstract
Marine hydrothermal systems are a special kind of extreme environments associated with submarine volcanic activity and characterized by harsh chemo-physical conditions, in terms of hot temperature, high concentrations of CO2 and H2S, and low pH. Such conditions strongly impact the living organisms, which have to develop adaptation strategies to survive. Hydrothermal systems have attracted the interest of researchers due to their enormous ecological and biotechnological relevance. From ecological perspective, these acidified habitats are useful natural laboratories to predict the effects of global environmental changes, such as ocean acidification at ecosystem level, through the observation of the marine organism responses to environmental extremes. In addition, hydrothermal vents are known as optimal sources for isolation of thermophilic and hyperthermophilic microbes, with biotechnological potential. This double aspect is the focus of this review, which aims at providing a picture of the ecological features of the main Mediterranean hydrothermal vents. The physiological responses, abundance, and distribution of biotic components are elucidated, by focusing on the necto-benthic fauna and prokaryotic communities recognized to possess pivotal role in the marine ecosystem dynamics and as indicator species. The scientific interest in hydrothermal vents will be also reviewed by pointing out their relevance as source of bioactive molecules.
Highlights
The extreme conditions have characterized our planet since primordial eras and have been maintained over time in some specific sites with unique features, ranging from extremely cold and hot regions, anoxic basins, deep sea, hydrothermal vents, and areas with harsh conditions of pressure, salinity, nutrient concentration, and oxygen availability
This review aims at focusing on the biodiversity of marine hydrothermal vents of the Mediterranean area, with a special hotspot on necto-benthic and microbial communities
Salinity does not show a significant differences compared to the ambient seawater values [27,40]; oxygen concentration along with redox potential is usually lower at vents and reflect oxygen consumption due to the oxidation of metals, such as iron, and reduced gases, such as H2 and H2S [40,41]; high total organic carbon (TOC) concentration as well as Biopolymeric Organic Carbon (BPC) increase in the sediment at vent sites [42,43], with protein dominating the carbon pool, followed by lipids and carbohydrates
Summary
The extreme conditions have characterized our planet since primordial eras and have been maintained over time in some specific sites with unique features, ranging from extremely cold and hot regions, anoxic basins, deep sea, hydrothermal vents, and areas with harsh conditions of pressure, salinity, nutrient concentration, and oxygen availability. Hydrothermal conditions have a low impact on microorganisms, which tolerate strong physical and chemical gradients, thanks to nutritional requirements and overall metabolic pathways ideally suited to such ecosystems [3] In both types of environments (DHVs and SHVs), microbial communities play a crucial ecological supporting role, by transforming into biomass the inorganic compounds released from vent emissions. Unlike DHVs, where the ecosystem functioning is mainly based on chemosynthesis, the primary production at SHVs is based both on photosynthesis and chemosynthesis processes, granted by sunlight and oxidation of reduced compounds as energy sources [5,6,7] These microbial processes are at the base of the hydrothermal trophic food chain and involve several forms, i.e., free-living microorganisms associated with the dismissed vent fluids, free-living microorganisms on the surface of flowing vent waters, or symbiotic forms associated with invertebrates [8].
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