Size and morphology of the benthic foraminifer Melonis barleeanum; relationships with marine organic matter

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Abstract
A high percentage of Melonis barleeanum in deepsea benthic foraminiferal assemblages is related to the availability of food in the form of abundant, little-altered, marine organic matter. A suitable condition exists in upwelling areas. In a core taken from 2,552 m depth, west of Mauritania, the lower part (last glacial maximum and deglaciation) was deposited during upwelling that resulted in abundant fallout of little-altered organic matter on the bottom. In contrast, the upper part (Holocene) represents slower sedimentation of considerably altered organic matter, the upwelling having shifted eastward on the continental shelf. A biometric analysis of Melonis barleeanum populations in the two stratigraphic intervals of this core shows that Melonis barleeanum: 1) has a higher average size, 2) may attain twice the mean size in some individuals, 3) shows a lower percentage of juvenile forms, and 4) includes a higher percentage of abnormal individuals in the lower part of the core, which is influenced by marine organic matter, than in the upper part.