No abstract

The EU Marine Strategy Framework Directive 2008/56/EC (MSFD) defines a framework for Community actions in the field of marine environmental policy in order to achieve and/or maintain the Good Environmental Status (GES) of the European seas by 2020. Microbial assemblages (from viruses to microbial-sized metazoa) provide a major contribution to global biodiversity and play a crucial role in the functioning of marine ecosystems, but are largely ignored by the MSFD. Prokaryotes are only seen as "microbial pathogens," without defining their role in GES indicators. However, structural or functional prokaryotic variables (abundance, biodiversity and metabolism) can be easily incorporated into several MSFD descriptors (i.e. D1. biodiversity, D4. food webs, D5. eutrophication, D8. contaminants and D9. contaminants in seafood) with beneficial effects. This review provides a critical analysis of the current MSFD descriptors and illustrates the reliability and advantages of the potential incorporation of some prokaryotic variables within the set of indicators of marine environmental quality. Following a cost/benefit analysis against scientific and economic criteria, we conclude that marine microbial components, and particularly prokaryotes, are highly effective for detecting the effects of anthropogenic pressures on marine environments and for assessing changes in the environmental health status. Thus, we recommend the inclusion of these components in future implementations of the MSFD.

The distribution of extracellular enzymatic activities (EEA) [leucine aminopeptidase (LAP), ß-glucosidase (GLU), alkaline phosphatase (AP)], as well as that of prokaryotic abundance (PA) and biomass (PB), dissolved organic carbon (DOC), particulate organic carbon and particulate total nitrogen (POC, PTN), was determined in the epi-, meso-, and bathypelagic waters of the Mediterranean Sea along a West-East transect and at one Atlantic station located outside the Strait of Gibraltar. This study represents a synoptical evaluation of the microbial metabolism during early summer. Decreasing trends with depth were observed for most of the parameters (PA, PB, AP, DOC, POC, PTN). Significant differences between the western and eastern basins of the Mediterranean Sea were found, displaying higher rates of LAP and GLU and lower C/N ratios more in the eastern than in the western areas. Conversely, in the epipelagic layer, PA and PB were found to be higher in the western than in the eastern basins. PB was significantly related to DOC concentration (all data, n = 145, r = 0.53, P < 0.01), while significant correlations of EEA with POC and PTN were found in the epipelagic layer, indicating an active response of microbial metabolism to organic substrates. Specific enzyme activities normalized to cell abundance pointed out high values of LAP and GLU in the bathypelagic layer, especially in the eastern basin, while cell-specific AP was high in the epi- and bathypelagic zone of the eastern basin indicating a rapid regeneration of inorganic P for both prokaryotes and phytoplankton needs. Low activity and abundance characterized the Atlantic station, while opposite trends of these parameters were observed along the Mediterranean transect, showing the uncoupling between abundance and activity data. In the east Mediterranean Sea, decomposition processes increased probably in response to mesoscale structures which lead to organic matter downwelling.

[1] Dissolved and particulate organic carbon, bacterial biomass, microbial enzymatic activities (EEA: leucine aminopeptidase, b-glucosidase, and alkaline phosphatase), bacterial production, respiration rates, and bacterial growth efficiency were determined in 10 stations of the Ionian Sea (winter 1998-1999) with the aim of characterizing the recycling of biogenic carbon and phosphorus in the different water masses, previously identified on the basis of their hydrographical properties. All microbial activities decreased markedly with depth, with a sharp increase in the benthic boundary layer, where potential remineralization rates of phosphorus up to 1.03 mg PÁdm À3 d À1 and bacterial carbon production of 0.078 mg CÁdm À3 d À1 were recorded. Those rates were close to the surface ones; the bacterial growth efficiency was also around 20%, similar to the surface value, sustaining the microbial food chain at the bottom. The daily hydrolysis of the organic carbon pool estimated by EEA varied from 0.67% (Ionian Surface Water) to 0.02% (Deep Water). Alkaline phosphatase activity was generally low in the intermediate and deep layers, in relation to the higher inorganic P content. The last facts support the hypothesis that deep waters of Ionian Sea, and in general of the entire Mediterranean basin, because of their young age, carry a larger amount of labile dissolved organic carbon, which reduces the need for a high recycling activity by bacterial community. As a matter of fact, a relatively higher activity per cell in carbon production rates was found in the deep layer where a large volume of the very recently formed Cretan Sea Outflow Water was present.