Natural vs. mariculture induced variability in nutrients and plankton in the eastern Mediterranean

The water column in three Mediterranean fish farms was investigated in terms of physical, chemical and biological characteristics. A significant increase in concentrations of phosphate and ammonium was detected within the cages over the control site in one of the farms but without any significant effect on chlorophyll concentration. Analysis of variation within the data set identified location and season as the major factors of variability in most of the variables examined except phosphate and ammonium for which variability induced by fish farming seemed to be of major importance. Plankton abundance for the major taxonomic groups (diatoms, flagellates, dinoflagellates and ciliates), microplankton species diversity and community structure were also determined by the effects of season and location rather than by fish farming.