Sediment underneath charophyte meadows is enriched in viable ephippia and enhances the benthic periphytic biofilm

We contribute to the knowledge of charophyte meadows as key components of aquatic systems by analysing how they affect wetland sediments. We performed a factorial-design experiment with limnocorrals (outdoor mesocosms) in a Mediterranean protected wetland with presence or absence of charophytes [Chara vulgaris (CV) and Chara hispida (CH), planted from cultures or recruited in situ from germination of their fructifications]. The first 1 cm-surficial and 2 cm-bottom sediment layers were analysed for cladoceran ephippia, ostracods valves, benthic community of bacteria and periphytic biofilm, and charophyte fructifications. In the surficial sediment, the ephippia density was fourfold higher in the conditions with charophytes than in sites with no-charophytes and higher apparent viability was found. The surficial sediment periphyton biofilm was composed mainly of diatoms, with tenfold higher biomass underneath charophytes, and a much diverse community. The specific microhabitat generated by each charophyte species was reflected in the different abundances and relationships between the analysed components, firstly establishing a divergence with the sediment without meadows and, secondly, a distinction between the meadows of CH and CV that exhibit particular morphology-architecture, might exudate different metabolites and might have different allelopathic capacities over microalgae and microinvertebrates. Thus, the charophyte–sediment tandem is relevant for biodiversity and habitat conservation.

Periphytic Biofilm Formation on Natural and Artificial Substrates: Comparison of Microbial Compositions, Interactions, and Functions

Periphytic biofilms have been widely used in wastewater purification and water ecological restoration, and artificial substrates have been progressively used for periphyton immobilisation to substitute natural substrates. However, there is insufficient knowledge regarding the interaction network structure and microbial functions in biofilm communities on artificial substrates, which are essential attribute affecting their applications in biofilm immobilisation. This study compared the community structure, co-occurrence network, and metabolic functions of bacterial and microeukaryotic periphytic biofilms during a 35-day indoor cultivation on artificial substrates, such as artificial carbon fibre (ACF) and polyvinyl chloride (PVC), and natural substrates, such as pebble and wood. Results demonstrated that different types of artificial substrates could affect the community composition and functional diversity of bacterial and microeukaryotic biofilms. The bacterial and microeukaryotic community on ACF and PVC showed significantly higher Simpson index compared to those on wood. Bacterial networks on artificial substrates were more complex than those on natural substrates, while the keystone species on natural substrates were more abundant, indicating that the bacterial communities on artificial substrates had stronger stability and resistance to external interference. Furthermore, the functional metabolic profiles predicted showed the abilities of bacterial communities to metabolise nitrogen and carbon sources colonised on artificial substrates were stronger than those on natural substrates. These findings demonstrated that artificial substrates could be special niches for microbial colonisation, possibly altering microbial compositions, interactions, and functions. Therefore, this study provides a powerful theoretical basis for choosing suitable artificial substrates for microbial aggregation and immobilisation technology.

Macrophyte meadows mediate the response of the sediment microbial community to ultraviolet radiation

The decrease of the water level in Mediterranean wetlands due to global warming allows UVR to reach the sediment microbial community. Macrophyte meadows, through their structure and compounds contribution, exert influence on this community. Our goal was to establish how the sediment microbial community of a wetland is harmed by UVR, and how the macrophytes mitigate such effects. We performed a field factorial experiment (UVR and macrophytes as factors) in a Mediterranean wetland. The abundance and composition of the sediment microbial community (bacteria, Archaea, microalgae and cyanobacteria) and sediment stoichiometry in superficial and sub-superficial layers were analysed. The microbial community was altered even by the small doses of UVR of the Mediterranean coastal wetlands by decreasing the periphyton abundance, including bacteria involved in C and N metabolism. Submerged macrophytes favoured the periphytic biofilm and increased sub-superficial carbon and nitrogen amounts, by promoting bacteria involved in their cycles. The shade exerted by the meadows minimized the UVR effects, driving to a community similar to that of the UVR-filtered environment. Therefore, macrophytes, through different mechanisms, can mitigate the harmful effects of UVR in sediment communities. Thus, the conservation of macrophyte meadows in highly vulnerable wetlands becomes crucial in a global change context.

Periphyton use on microbial dynamics, water quality, and Nile tilapia growth in rearing tanks

The objective of this work was to evaluate the effect of the use of an artificial substrate for periphytic biofilm growth on the microbiological composition of the biofilm, water quality, and zootechnical performance of Nile tilapia (Oreochromis niloticus) in rearing tanks. The experiment consisted of two treatments: presence and absence of artificial substrate for the growth of periphyton, with five replicates. Water quality parameters were evaluated throughout the entire experimental period. Every two weeks, samples of the periphyton were collected for the analysis of its microbiological composition and biometric measurements of the fish were performed. The number of heterotrophic bacteria in the biofilm increased during the experimental period, but that of Aeromonas decreased with the use of the artificial substrate. The total ammonia nitrogen in the tanks with periphyton reduced in 30% compared with that of the control. Tilapia reared with the biofilm showed a final weight 2.4 times greater than that of those subjected to the control, as well as an increase of 59.19% in their productivity. The use of an artificial substrate for periphytic biofilm in Nile tilapia rearing tanks favors the maintenance of the quality of the culture water, the protection of the fish against pathogens, and the improvement of the zootechnical performance of the fish.