Effect of Particle Size on Organic Content and Microbial Abundance Within Four Marine Sediments

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Abstract
Sieved size fractions of 4 marine sediments were examined for 4 quantities presumably related to nutritional value-organic C, bacteria, chlorophyll a and C:N ratio of organic matter to determine whether they showed a consistent relation with particle size. There was no predictable relationship between these quantities and particle size either within or among the 4 sediments. Despite wide variations in organic C, bacterial abundance and chlorophyll a content C:N ratios were similar (near 7) for most of the size fractions from all 4 areas; apparently there was a large, and as yet unidentified, pool of organic C in these sediments other than living bacteria or microalgae with a C:N ratio near 7. Variation of microbial abundance between winter and summer was inconsistent, but bacteria always accounted for less than 2% of the organic C in the sediment. The difficulty in attempting to predict nutritional value of sediments from bulk samples is emphasized.