Seep environments have now been recognised for two decades. During this period many new seep locations have been discovered and thorough descriptions of seep communities have emerged. However, mechanistic understanding of their function and dynamics is in its infancy, particularly with respect to higher organisms residing within seep sediments. Research has revealed a strong control on faunal evolution, adaptation and distribution by the availability of reduced compounds. Further investigations that integrate the geophysical, geochemical and microbial processes controlling this availability, with animal functional and numerical responses, should yield valuable insight. Many ecological processes, such as animal migrations, reproduction, larval settlement, behaviour, nutrition, biotic interactions, and community succession at seeps all are likely to be tightly linked to aspects of fluid flow and microbial processes. These interactions will be complex, with significant spatial and temporal variation in the players and processes on multiple scales. A melding of geochemistry with genomics and ecology will further elucidate the dynamics of seep environments, as it has begun to do for hydrothermal ecosystems (Reysenbach & Shock 2002). Future investigation of organic inputs from and exports to the non-seep marine system will benefit from advances in fatty acid, isotope and micro technologies. Such studies will clarify the role of seeps in global processes such as biogeochemical cycling and biodiversity maintenance. The difficult problems of larval dispersal and population connectivity among seeps may soon be addressed by novel applications of microchemistry (elemental fingerprinting) and molecular identifications of larvae.
Because there have been only a few detailed investigations of seep macro- and meiofauna, very little is known about the biogeography of these organisms on a global basis. The extent to which species are shared with background communities or with hydrothermal vent, whale fall or other reducing ecosystems has been examined only for bivalves and tubeworms. Typically there are shared genera (Vesicomya, Calyptogena, Bathymodiolus, Lamellibrachia) but not species (Baco & Smith 2003). At least some overlap is expected among infauna, but comparison of seep and whale fall dorvilleids from the Pacific show few species in common (G. Mendoza et al. personal communication). Sahling et al. (2002) reported four shared species between Hydrate Ridge seeps and Guaymas hydrothermal mounds.
Numerous seep specialist taxa have evolved to tolerate high sulphide concentrations (mainly annelids and bivalves), but the magnitude of tolerances and the underlying mechanisms are unknown for most taxa except for selected vestimentiferan tubeworms, mussels and bivalves. Certain seep assemblages have yet to be studied in detail. These include most infaunal assemblages and the macrofauna associated with carbonate concretions (but see Jensen et al. 1992).
Many new seep sites and settings will be discovered in the coming decades, including some in parts of the world where seeps have yet to be identified. Especially novel environments are likely to be found where seeps interact with other unusual geological or oceanographic constructs (e.g., with oxygen minimum zones, in trenches, or at subducting spreading ridges). From these discoveries will spring an endless fount of interdisciplinary research challenges for biologists, microbiologists and oceanographers.
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