SIZE STRUCTURE AND POTENTIAL FOOD VALUE OF THE PLANKTON COMMUNITY TO OSTREA-EDULIS L IN A TRADITIONAL NORWEGIAN OSTERSPOLL

The phytoplankton of a Norwegian oyster pond ("poll") was examined in terms of particle size spectrum and qualitative composition. Bacteria-sized particles were generally among the largest biomass fractions. During summer, the veliger larvae of the oyster made a particularly heavy demand upon the 2-8-μm ESD (Equivalent Spherical Diameter) fractions. The algae were dominated by species of low food value. The low plankton biomass of the pond cannot carry the grazing pressure of the large number of filter-feeding adult oysters and their planktonic larvae. The variable yield of spat may therefore be due to starvation as long as a pond like this is stocked artificially and run under near "natural" conditions. The particular hydrography of Norwegian oyster ponds may permit careful experimentation to increase productivity of planktonic algae. © 1990.