The Sedimentary Milieu and its Consequences for Resident Organisms

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Abstract
While benthic ecologists have often studied the inter-relationships of benthic animals and sediment, only recently has the sediment been examined at a scale appropriate to the animals of interest. In studying sediment as food for benthic animals, it is commonplace for the nutritional value of the sediment to be characterized in terms of the size distribution of mineral grains and some measure of the organic matter content such as percent by weight of organic C and N. These measures have been shown to be nearly meaningless and have been replaced by measures of proteins and amino acids, bacterial and eucaryote biomass, and by a visual examination of the sediment using thin section techniques.The latter method also shows that marine muds are not very homogeneous over distances of hundreds of micrometers and that the relationship between mineral grains and organic matter in sediment is very complex. The interstitial pore waters of marine sediment have also come under increasing scrutiny, chiefly through the development and use of microelectrodes. Oxygen concentration is not well correlated with sediment color but is controlled by the rate of consumption within the sediment and diffusion, which is a function of distance and time from an oxygenated source, for example, the overlying water at the sediment-water interface or an actively ventilated burrow. The delivery of oxygen, the distribution of metabolizable organic matter, and the packing of sediment grains are all properties of sediment that vary on the scale of millimeters and may strongly affect the ability of resident organisms to live and reproduce.

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