CORDIS - EU research results

Migration pathways into deep-sea chemosynthetic environments

Final Activity Report Summary - MIGPAT (Migration pathways into deep-sea chemosynthetic environments)

The origin and possible antiquity of faunas at deep-sea hydrothermal vents and seeps have been debated since their discovery. The fossil record of seep mollusks was used to show that the living seep genera have significantly longer geologic ranges than the marine mollusks in general, but have ranges similar to deep-sea taxa, suggesting that seep faunas may be shaped by those factors that drive the evolution of life in the deep-sea in general. These data indicate that deep-sea anoxic/dysoxic events did not affect seep faunas, casting doubt on the suggested anoxic nature and/or global extent of these events.

The evolutionary history of invertebrate communities utilising whale carcasses and sunken wood in the deep-sea was explored using fossil evidence. Compared to modern whale-fall communities, the Eo-Oligocene examples lack those vent-type taxa that most heavily rely on sulphide produced by anaerobic breakdown of bone lipids, but are very similar in their trophic structure to contemporaneous wood-falls. This sheds doubt on the hypothesis that whale-falls were evolutionary stepping stones for taxa that now inhabit hydrothermal vents and seeps. It is suggested that early Cenozoic whale-fall communities represent a new ecologic stage among whale-falls, coined 'chemosymbiotic opportunist stage', and that the 'sulphophilic stage' of modern whale-falls developed during the early Miocene, resulting from a significant increase in both body size and/or oil content of bones among cetaceans during this time.

Field work on Hokkaido, northern Japan, lead to the discovery of Late Cretaceous examples of wood-fall communities from deep-water sediments of the Yezo Group on Hokkaido, Japan. Many of the recovered species belong to modern groups and are similar or identical to those found on plesiosaur bones and hydrocarbon seeps in the same sediments, showing that many members of the modern chemotrophic deep-sea fauna colonised this range of habitats at least since Late Cretaceous time.

The main underlying task to achieve the objectives of this project was a better identification and classification of the mollusks that inhabited chemosynthetic ecosystems in the geologic past. During the course of the fellowship, the Researcher has visited various new and known fossil hydrocarbon-seep sites, and also screened museum collections for relevant material, and carried out systematic work on the newly collected material. This work provided and provides reliable data for the evolutionary analyses carried out and for future work on the evolutionary history of these fascinating ecosystems.