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Deep-sea bioturbation and the role of the sea urchin Echinocrepis rostrata


The following dissertation research studied bioturbation activity in the benthic community at a site in the eastern North Pacific (Station M; 34⁰50'N, 123⁰00'W; 4100 m depth). Time-lapse photography, animal collections and sediment core samples were used to examine whether bioturbation rates of Echinocrepis rostrata echinoids at Station M changed significantly over an 18-year period between 1989 and 2007, if these possible changes are correlated to food supply and surface conditions/climate, and how E. rostrata bioturbation affects deep-sea sediment chemistry. First, animal aggregation behavior was addressed as a potential bias in the time-lapse camera data used to conduct the long-term observations at Station M. Genetic tests were conducted to determine the phylogenetic relationships among the three commonly observed color morphs of E. rostrata (designated tan, purple and white). The reproductive behavior of E rostrata, which has never been described, was also examined. Abundance, size and speed data from the photographic record were used to track long-term changes in bioturbation by E. rostrata, and how those changes were correlated to variations in climate and particulate organic carbon (POC) flux rates. Radioactive isotope activity, carbon content and chlorophyll concentrations were measured in the top four cm of thirty-two paired push core samples collected at Station M from sediment trails recently created by E. rostrata and local undisturbed sediment. The results showed that the rate of bioturbation of E. rostrata echinoids at Station M was correlated to food supply and climate indices. Aggregation behavior and possible multiple species of Echinocrepis were ruled out as confounding factors which might have affected the data used to conduct the bioturbation study, while examination of the reproductive anatomy of E. rostrata showed that this species is unlikely to broadcast spawn or reproduce seasonally. Finally, there was no conclusive evidence of the effect of E. rostrata bioturbation on sediment chemistry; however, further research is required

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