Seasonal dynamics of bacterial biomass and production on eelgrass Zostera marina leaves

The seasonal dynamics and distribution of bacteria and bacterial activity o n eelgrass leaves were followed at a shallow-water site in the Roskilde Fjo rd, Denmark. Eelgrass leaves were sites of highly active bacterial communit ies exhibiting distinct distribution patterns with increasing bacterial abu ndance and production with increasing leaf age and from base to tip of indi vidual leaves. High bacterial production and very high specific growth rate s (seasonal mean 0.30 h(-1)) suggest a strong coupling between attached bac terial communities and plant primary production. Incorporation rates of C-1 4-leucine and H-3-thymidine were significantly correlated but the ratio bet ween bacterial production based on leucine and thymidine increased with inc reasing leaf age and from leaf base to leaf tip, indicating a higher protei n synthesis compared to DNA synthesis with increasing biofilm age. Bacteria l biomass production was very high compared to the standing stock of bacter ia and it was concluded that close to 100% of the bacterial biomass produce d on the leaves was lost on a daily basis. Moreover, bacterial specific gro wth rates corresponded to turnover times of 1 to a few hours on most occasi ons and did not differ between leaves of different ages or at different loc ations on the leaves. Such high growth rates can only occur in a very rich environment, where the standing stock of biomass is kept low and thus preve nts resource competition.