Seaweeds are a group of essential photosynthetic organisms that harbor a rich diversity of associated microbial communities with substantial functions related to host health and defense. Environmental and anthropogenic stressors may disrupt the microbial communities and their metabolic activity, leading to host physiological alterations that negatively affect seaweeds’ performance and survival. Here, the bacterial communities associated with one of the most common seaweed, Ulva laetevirens Areshough, were sampled over a year at three sites of the lagoon of Venice affected by different environmental and anthropogenic stressors. Bacterial communities were characterized through Illumina sequencing of the V4 hypervariable region of 16S rRNA genes. The study demonstrated that the seaweed associated bacterial communities at sites impacted by environmental stressors were host-specific and differed significantly from the less affected site. Furthermore, these communities were significantly distinct from those of the surrounding seawater. The bacterial communities’ composition was significantly correlated with environmental parameters (nutrient concentrations, dissolved oxygen saturation, and pH) across sites. This study showed that several more abundant bacteria on U. laetevirens at stressed sites belonged to taxa related to the host response to the stressors. Overall, environmental parameters and anthropogenic stressors were shown to substantially affect seaweed associated bacterial communities, which reflect the host response to environmental variations.

The determination of the trophic status of transitional ecosystems from the physico-chemical and biological point of view is one of the requirements of the European Water Framework Directive (WFD 2000/60/EC). In Italy, its determination is implemented by the Regional Agencies for Environmental Protection (ARPAs) that have activated multi-annual monitoring programs. However, as the availability of funds is increasingly scarce, the number of environmental parameters to detect environmental changes should be conveniently managed. The high number of environmental parameters, nutrient and macrophyte datasets available for the LTER-Italia site “Venice lagoon” can be an useful tool to analyze the trophic changes over recent years and to foresee environmental evolutions. Nutrient data on a spatial basis have been available since 1948, whereas macroalgal maps date back to 1980. The aim of this paper is to highlight the changes of the trophic status of the lagoon since the middle of the 20^th century by considering the concentrations of nutrients in the surface sediments and in the water column, the variation of some physico-chemical parameters and the biomass of macroalgae and also to foresee the way it will possibly evolve. In fact, after many anthropogenic impacts that in the second half of the 20^th century affected the lagoon, starting from the year 2010, the ecological status is progressively improving. Nutrients show a significant reduction both in the water column and in surface sediments, and the macrophytes are represented by species of higher ecological value while the opportunistic species such as the Ulvaceae are in strong regression.

The paper reports the results obtained after 4 years of aquatic angiosperm transplants in areas of the Venice Lagoon (North Adriatic Sea, Mediterranean) where meadows almost disappeared due to eutrophication, pollution and overexploitation of clam resources. The project LIFE12 NAT/IT/000331-SeResto, funded by the European Union, allowed to recolonize the Habitat 1150* (coastal lagoons) in the northernmost part of the lagoon, by extensive manual transplants of small sods or single rhizomes of Zostera marina, Zostera noltei, Ruppia cirrhosa and, in some stations also of Cymodocea nodosa. Over the 4 years of the project more than 75,000 rhizomes were transplanted in 35 stations with the support of local stakeholders (fishermen, hunters and sport clubs). Plants took root in 32 stations forming extensive meadows on a surface of approx. 10 km² even if some failures were recorded in areas affected by outflows of freshwater rich in nutrients and suspended particulate matter. The rapid recovery of the ecological status of the involved areas was the result of this meadow restoration, which was in compliance with Water Framework Directive (WFD 2000/60/EC) objectives. Moreover, the monitoring of environmental parameters in the water column and in surface sediments allowed to identify the best conditions for successful transplants. Small, widespread interventions and the participation of local stakeholders in the environmental recovery, make this action economically cheap and easily transposable in other similar environments.

Since the 1960s, the Venice Lagoon has suffered a sharp aquatic plant constriction due to eutrophication, pollution, and clam fishing. Those anthropogenic impacts began to decline during the 2010s, and since then the ecological status of the lagoon has improved, but in many choked areas no plant recolonization has been recorded due to the lack of seeds. The project funded by the European Union (LIFE12 NAT/IT/000331-SeResto) allowed to recolonize one of these areas, which is situated in the northern lagoon, by widespread transplantation of small sods and individual rhizomes. In-field activities were supported by fishermen, hunters, and sport associations; the interested surface measured approximately 36.6 km². In the 35 stations of the chosen area, 24,261 rhizomes were transplanted during the first year, accounting for 693 rhizomes per station. About 37% of them took root in 31 stations forming several patches that joined together to form extensive meadows. Plant rooting was successful where the waters were clear and the trophic status low. But, near the outflows of freshwater rich in nutrients and suspended particulate matter, the action failed. Results demonstrate the effectiveness of small, widespread interventions and the importance of engaging the population in the recovery of the environment, which makes the action economically cheap and replicable in other similar environments.