Microbial transformations of toxic monomethylmercury (MMHg) and dissolved gaseous mercury (DGM) at the lower levels of the marine food web are not well understood,especially in ohgotrophic and phosphorus-limited seas.To examine the effects of probable phosphorus limitation (PP-limitation) on relations between mercury (Hg) fractions and microorganisms,we determined the total mercury (THg),total methylated mercury (MeHg),DGM,and microbio-logical and chemical parameters in the Central Adriatic Sea.Using statistical analysis,we assessed the potential microbial effects on Hg transformations and bioaccumulation.Only in the absence of PP-limitation conditions (NO-PP-limitation) is MeHg significantly related to most chemical and microbial parameters,indicating metabolism-dependent Hg transformations.The heterotrophic activity of low nucleic acid bacteria (abundant in oligotrophic regions) seems responsible for most of Hg methylation under NO-PP-limitation.Under these conditions,DGM is strongly related to microbial fractions and chlorophyll a,indicating biological DGM production,which is probably not metabolically induced,as most of these relations are also observed under PP-limitation.MMHg biomagnification was observed through an increased bioaccumulation factor from microseston to mesozooplankton.Our results indicate that Hg transformations and uptake might be enhanced under NO-PP-limitation conditions,emphasizing their impact on the transfer of Hg to higher trophic levels.