Natural variability in hard bottom communities and possible drivers assessed by a time-series study in the SW Baltic Sea: know the noise to detect the change

In order to detect shifts in community structure and function associated with global change, the natural background fluctuation in these traits must be known. In a 6-yr study we quantified year to year variability of taxonomic and functional composition of benthic hard bottom communities in the Western Baltic. While taxonomic fluctuations were substantial, functionality of the communities seems preserved in most cases. Environmental conditions potentially driving these fluctuations are winter temperatures and current regimes. We tentatively define a confidence range of natural variability in productivity, composition and diversity a departure from which might help identifying an ongoing regime shift driven by global change. In addition, we propose a statistical procedure distinguishing directional shifts ("signal") from natural fluctuations ("noise").