Waterbird aggregations and droughts affect nutrient and microbial dynamics in wetlands. We analysed the effects of high densities of flamingos on nutrients and microbial dynamics in a saline lake during a wet and a dry hydrological year, and explored the effects of guano on prokaryotic growth. Concentrations of dissolved organic carbon, total phosphorus and total nitrogen in the surface waters were 2–3 fold higher during the drought and were correlated with salinity. Flamingos stimulated prokaryotic heterotrophic production and triggered cascading effects on prokaryotic abundance, viruses and dissolved nitrogen. This stimulus of heterotrophic prokaryotes was associated with soluble phosphorus inputs from guano, and also from sediments. In the experiments, the specific growth rate and the carrying capacity were almost twice as high after guano addition than in the control treatments, and were coupled with soluble phosphorus assimilation. Flamingo guano was also rich in nitrogen. Dissolved N in lake water lagged behind the abundance of flamingos, but the causes of this lag are unclear. This study demonstrates that intense droughts could lead to increases in total nutrients in wetlands; however, microbial activity is likely constrained by the availability of soluble phosphorus, which appears to be more dependent on the abundance of waterbirds.

Traditional aquaculture produces wastewater with high nutrient and organic matter concentrations. Poly-culture can improve this problem including "extractive species" such as sea cucumbers along with the primary species. The influence of sea cucumbers on transparent exopolymer particles (TEP) (i.e. biofilm precursors) has not been previously explored. Here, we monitored during 1 year the concentration of nutrients, total organic carbon (TOC), particulate organic matter (POM), TEP, chlorophylla and bacteria in two tanks of 50,000 L. One tank only contained Anemonia sulcata, whereas the other tank also included holothurians. To complement these time-series, we performed three short-term experiments in smaller (300 L) tanks. Three tanks contained A. sulcata plus Holothuria tubulosa (+H treatment) and other four tanks contained only A. sulcata (−H treatment). In the time-series, we found that the concentration of ammonium, nitrate, TOC, POM, TEP and bacteria in the effluent of the tank with holothurians was lower than in the effluent of the tank without holothurians. The three experiments confirmed that the holothurians reduced significantly nitrates, bacterial abundance and TEP concentration. Therefore, these invertebrates can control bacterial proliferation and prevent biofilm formation minimizing likely the risk of outbreak of pathogenic bacteria and improving the hygiene of the tanks.

Coastal wetlands are valuable aquatic ecosystems with high biological productivity, which provide services such as a reduction in nitrogen loading into coastal waters and storage of organic carbon acting as carbon dioxide sinks. The predicted rise of sea level or freshwater extractions, particularly in the arid Mediterranean biome, will salinize many coastal wetlands. However, there is considerable uncertainty about how salinization will affect microbial communities and biogeochemical processes. We determined the abundance of total prokaryotes, cyanobacteria, and viruses and quantified the heterotrophic production of prokaryotes sensitive- (predominantly Bacteria) and resistant- (predominantly Archaea) to erythromycin in 112 ponds from nine coastal wetlands. We explored the main drivers of prokaryotic abundance and heterotrophic production using generalized linear models (GLMs). The best GLM, including all the wetlands, indicated that the concentration of total dissolved nitrogen (TDN) positively affected the total abundance of prokaryotes and the heterotrophic erythromycin-resistant (ery-R) production. In contrast, heterotrophic erythromycin-sensitive (ery-S) production was negatively related to TDN. This negative relationship appeared to be mediated by salinity and virus abundance. Heterotrophic ery-S production declined as salinity and virus abundance increased. Consequently, we observed a switch from heterotrophic ery-S production towards ery-R production as salinity and virus abundance increased. Our results imply that microbial activity will change from heterotrophic bacterial-dominated processes to archaeal-dominated processes with anthropogenic nitrogen and salinization increases. However, more studies are required to link the mineralization rates of dissolved nitrogen and organic carbon with specific archaeal taxa to enable more accurate predictions on future scenarios in coastal wetlands.

Abstract. Coastal wetlands are valuable ecosystems with high biological productivity and diversity, which provide ecosystem services such as a reduction in the inputs of nitrogen into coastal waters, and storage of organic carbon, thus, acting as net carbon sinks. The rise of sea level as a consequence of climatic warming will salinize many coastal wetlands, but there is considerable uncertainty about how salinization will affect microbial communities and biogeochemical processes. We analyzed prokaryotic abundance and heterotrophic bacterial and archaeal production in 112 ponds within nine coastal wetlands from the western Mediterranean coast. We determined the main drivers of prokaryotic abundance and production in these wetlands using generalized linear models (GLMs). The best GLM, including all the coastal wetlands, indicated that the concentration of total dissolved nitrogen (TDN) positively affected the abundance of heterotrophic prokaryotes and heterotrophic archaeal production. In contrast, heterotrophic bacterial production was negatively related to TDN. This negative relationship appeared to be mediated by salinity and virus abundance. Heterotrophic bacterial production declined as salinity, and virus abundance, increased. We observed a switch from heterotrophic bacterial production towards heterotrophic archaeal production as salinity and virus abundance increased. Our results imply that microbial activity will change from bacterial-dominated processes to archaeal-dominated processes along with increases of nitrogen inputs and salinity. However, more studies are required to link the mineralization rates of dissolved nitrogen and organic carbon with specific archaeal taxa, to enable more accurate predictions on future scenarios of wetlands salinization and anthropogenic nitrogen inputs.

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