Until around 150 years ago, the deep sea was regarded as a relatively uniform and stable habitat, and owing to the extreme abiotic conditions (lack of sunlight, high atmospheric pressure and low temperature), it was thought to contain no life. However, expeditions in the 1960s and 1970s revealed remarkably high biodiversity in the deep-sea realm; later, state-of-the-art technology (such as manned or autonomous submersibles) evidenced an unexpectedly high habitat heterogeneity and temporal variability. Although the deep sea (the pelagic and the benthic zone) constitutes the most extensive biome on Earth, it is still largely under-sampled and new habitats and species are still being discovered. There is a growing awareness of the global significance of this ecosystem since it hosts a large fraction of the Earth’s biodiversity, contains a large reservoir of mineral and biological resources, regulates the climate (by taking up carbon dioxide, which is a greenhouse gas) and is an important player in the recycling of nutrients. Human activities (e.g. waste disposal, extraction of fish, minerals and hydrocarbons, global warming) have been shown to alter deep-sea ecosystem properties and processes. Hence, it is of the utmost importance that we advance our knowledge on the functioning of the deep-sea ecosystem to underpin its sustainable management. International, collaborative research projects like HERMES (“Hotspot Ecosystem Research on the Margins of European Seas”, 2005-2009)/HERMIONE (“Hotspot Ecosystem Research and Man's Impact ON European Seas”, 2009-2012) and BIOFUN (“BIOdiversity and ecosystem FUNctioning in Southern European Deep-sea environments: from viruses to megafauna”, 2007-2011), which provided the frame for this doctoral research, were set up to gather more information on the structure, functioning and dynamics of deep-sea ecosystems.Nematodes, which constitute the predominant meiofaunal phylum, are the most abundant,speciose and ubiquitous metazoan organisms residing in deep-sea sediments. Consequently, they represent the ideal organisms to evaluate macro-ecological patterns and to examine the link between diversity and ecosystem functioning. Because of their high standing stock, high metabolic and reproductive rates, and their presumed intermediate trophic position (between detritus and/or bacteria, and predatory meiofauna and/or macro- or megafauna) these roundworms are thought to have an important role in the benthic carbon cycle in coastal habitats. Whether this also applies to nematodes living in the deep sea is unknown, since information on their life history strategies in this extreme environment is completely lacking. So far, we have not succeeded in characterizing the feeding behaviour and preferences of nematodes, and also the functional importance of nematode activities that are unrelated to foraging, remains a big unknown. An overview of the general characteristics of the deep-sea environment, the concept of biodiversity and the effect on ecosystem functioning, as well as the applicability to deep-sea nematodes are presented. |
