Abstract

In this study, we discuss results from a Russian sea floor survey over the Mid-Atlantic Ridge north of the North Equatorial Recirculation Region where large quantities of pelagic Sargassum were found both at the surface, and along the bottom in different stages of decomposition. Model backtracks from the survey location trace this Sargassum to the Gulf of Guinea along an extensive, indirect path where significant growth and mortality must have occurred. Growth and mortality of pelagic Sargassum are key parameters necessary for quantifying model based forecasts of Sargassum events when long transport times and distances are involved. It is also necessary for understanding important issues such as global carbon sequestration and potential increases in fishery biomasses. But it is poorly known. Previous work on mortality has focused on (1) beaching and (2) sinking to bladder failure depths in Langmuir cells. Predation is not considered a major mortality factor. Beaching, although impressive locally, in the long term can only account for a small percentage of mortality needed to balance the growth rate. We discuss breaking of Sargassum plants by wave action, Langmuir Cells, Langmuir Mixing and the need for relatively simple but standardized measure-ments of mortality by sinking.

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