Seasonal fluctuations in the nutritional value of particulate organic matter in a lagoon.

Water samples were collected on a fortnightly basis in the lagoon of S. Gilla (Sardinia, Mediterranean Sea) in order to study seasonal nutritional fluctuations of particulate organic matter. The lagoon is characterized by high quantities of suspended matter throughout the year. Thermohaline conditions had no effect on particulate matter quantity and composition, but the quantity as well as quality of suspended particles was drastically affected by the wind, the major effecter of sediment resuspension. As a result of sediment resuspension, seston was always richer in inorganic fraction. However, throughout the year of investigation, most particulate organic carbon was quite appealing for filter feeding communities, although the best POM quality was available during phytoplankton blooming. The phytoplankton pool of suspended matter was just a small fraction of the bulk, accounting for only 13% on average of particulate organic carbon. In terms of energy available in the seston, the highest amount was stored in organic matter heterotrophic fraction, whilst the smallest was to be found in living phytoplankton.