Ecology of Cold Seep Habitats

Cold seep ecosystems are fuelled by subsurface methane, hydrogen sulfide, and bicarbonate emission, which is exploited by diverse and endemic faunal communities. Although considered unconventional, at cold seep sites, chemosynthesis is the mechanism by which the bacterial community fixes carbon by utilizing hydrocarbon emissions. With discoveries of seep sites globally, including a new seep site in the Indian Ocean in 2018, it is imperative to understand its highly specialized faunal communities and their evolved functional attributes. Cold seeps have evolved unique metazoan lineages such as giant clams and long-living gutless polychaetes, which retain vital chemosymbiotic bacteria. With a very diverse invertebrate community, cold seeps share these endemics only with other such sites or hydrothermal vents and whale fall sites. Despite such sites being globally scattered thousands of kilometers apart, the communities therein display remarkable genetic affinity and connectivity. We discuss their survival, dispersal, and ecophysiology that has evolved to extract nutrition from hydrocarbons, resist toxic seepages, and regulate bacterial harvest. Seep communities have global implications in terms of climate change as they metabolize greenhouse gases at source; thus, their conservation is essential, with the potential of such sites as a commercial energy source. The seep organisms possess great scientific value as they can potentially synthesize biomedically important compounds. For the past four decades, workers have extensively studied cold seep ecosystems, their faunal attributes, and the mechanisms that govern these endemics: this review appraises the current research on seep ecosystems.