Role of the bacterial community in the annual benthic metabolism of two contrasted temperate intertidal sites (Roscoff Aber Bay, France)

The role of the bacterial community in the annual benthic metabolism of Roscoff Aber Bay, France, was estimated during low tide at 2 sampling sites of different trophic status, located at either end of a strong environmental gradient. The benthic gross primary production (GPP) and community respiration (BCR) were assessed in situ over 1 yr with a benthic chamber; simultaneously, bacterial production (BP) was estimated by radiotracer incorporation in slurries. BP appeared to be significantly controlled by temperature during low tide. On an annual scale, microphytobenthos gross primary production (GPP.), bacterial production (BPa), meiofauna production (MePa), macrofauna production (MaP(a)) and benthic community respiration (BCRa were estimated. While the estimated annual processes were generally higher at the muddy station, our results indicated that (1) the contribution of BPa to the annual benthic community production (CPa = BPa + MePa + MaP(a) increased with increasing grain size, and (2) the bacterial community can modulate its growth efficiency (BGE(a)) when exposed to an environmental gradient: in intertidal sediments, the production of new cells is enhanced when the organic matter concentration is lower, sustaining the development of the community on the annual scale. This behaviour was inferred to be the predominant factor affecting the trophic state of the system.