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Nodules of filamentous algae have been discovered in a tidal channel crossing an oolite shoal west of Frazers Hog Cay, Bahamas. The nodules range in size from about 1.5 to 3 cm. They have a subspherical form, and are typically concave outward on one side and depressed on the other. At the sampled locality, the nodules completely cover the sea floor, except where marine grasses or stalked algae break the cover. The water depth at the sampled locality is about 7 ft. Average surface current velocities as high as 0.6 knots have been measured in the vicinity.
Mucilaginous algal filaments in the nodules entrap skeletal and nonskeletal sedimentary particles. However, examination of the sediment remaining after digestion of several nodules in sodium hypochlorite revealed that the nodule sediment was enriched in Foraminiferida by an order of magnitude relative to nearby sediments. The foraminiferal fauna is dominated by one or more species of highly irregular milioline forams with very thin porcelaneous walls. These forams are beautifully preserved in the nodules whereas, in other Bahamian sediment samples, similar forms tend to be broken and eroded. In all probability, therefore, the algal nodules are a preferred microhabitat for the milioline forams. Similar presumed algal-foraminiferal consortia (e.g., Osagia) are well known in late Paleozo c carbonate rocks.
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