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Ulva spp. are among the most commonly encountered macroalgal species forming algal blooms and are responsible for many Green Tide events worldwide. Numerous adaptations have provided this genus with broad plasticity in carbon acquisition and metabolism, allowing rapid responses to nutrient inputs and sustained growth during the limiting conditions that arise during large bloom events. Because of this plasticity, the carbon isotopic composition of Ulva spp. may be highly variable. A compilation of 1,382 observations of Ulva δ¹³C signatures from literature sources and systematic surveys revealed an unusually wide range of values, much broader than what is typically reported for other marine macroalgae, with a bimodal distribution. This pattern suggests two distinct growth modes in Ulva spp.: one characteristic of non-limiting conditions, and another associated with bloom conditions where rapid growth and carbon limitation drive higher δ¹³C signatures. Analysis of environmental drivers in New England sites further showed that enriched Ulva δ¹³C values arise under the limiting conditions that develop within dense macroalgal canopies in eutrophic estuaries. Excess nutrient inputs stimulate large macroalgal accumulations, which then alter the surrounding physicochemical environment and shift isotopic signatures. These results confirm that Ulva δ¹³C is a valuable tool for assessing the trophic status of coastal environments.

To assess effects of N loads, season, and down-estuary transit on estuarine concentrations of nitrate (NO₃), ammonium (NH₄), dissolved organic nitrogen (DON), and total dissolved nitrogen (TDN), we sampled three estuaries within Waquoit Bay, MA (USA), subject to different N loads, from spring to fall, at nine stations spanning the salinity range. Conventional statistical analysis on the basis of entire data for the three estuaries suggested significant effects of N loads on concentrations, but comparisons with effect size measures suggested that the effects were minor, largely an artifactual result from the large number of samples. Constraining variation by binning data into weekly means, and partitioning data by season (summer vs. spring-fall) and down-estuary transit (based on salinity) improved interpretations, allowing emergence of detectable increases in NO₃ concentrations in estuaries subject to larger N loads, confirmed interactions between N load and season (seasonal increases in NO₃ larger in estuaries subject to higher N loads), and down-estuary gradients (highest NO₃ concentrations in fresher reaches and significant down-estuary decreases in NO₃). NH₄ and DON were less responsive to N loads, with rapid uptake of NH₄ and seasonal trajectories of DON subject to within-estuary features. TDN concentrations decreased down-estuary, with 13–36% of loss attributable to within-estuary interception, a considerable effect in spite of short water residence times. Management implications include the need to sample seasonally and cover the salinity gradient, checking conventional statistical analyses of pooled data from large databases, using effect size measures to ensure meaningful biological and management results, and attention to the limited lability of DON often included in considering estuarine TDN and N loads.

Bacterial surface components, especially exopolysaccharides, in combination with bacterial Quorum Sensing signals are crucial for the formation of biofilms in most species studied so far. Biofilm formation allows soil bacteria to colonize their surrounding habitat and survive common environmental stresses such as desiccation and nutrient limitation. This mode of life is often essential for survival in bacteria of the genera Mesorhizobium, Sinorhizobium, Bradyrhizobium, and Rhizobium. The role of biofilm formation in symbiosis has been investigated in detail for Sinorhizobium meliloti and Bradyrhizobium japonicum. However, for S. fredii this process has not been studied. In this work we have demonstrated that biofilm formation is crucial for an optimal root colonization and symbiosis between S. fredii SMH12 and Glycine max cv Osumi. In this bacterium, nod-gene inducing flavonoids and the NodD1 protein are required for the transition of the biofilm structure from monolayer to microcolony. Quorum Sensing systems are also required for the full development of both types of biofilms. In fact, both the nodD1 mutant and the lactonase strain (the lactonase enzyme prevents AHL accumulation) are defective in soybean root colonization. The impairment of the lactonase strain in its colonization ability leads to a decrease in the symbiotic parameters. Interestingly, NodD1 together with flavonoids activates certain quorum sensing systems implicit in the development of the symbiotic biofilm. Thus, S. fredii SMH12 by means of a unique key molecule, the flavonoid, efficiently forms biofilm, colonizes the legume roots and activates the synthesis of Nod factors, required for successfully symbiosis.

Significance We report a novel linear mixed-linkage (1→3)(1→4)-β-glucan produced by the bacterium Sinorhizobium meliloti upon raising cyclic diguanylate (c-di-GMP) intracellular levels. This unique bacterial polysaccharide resembles (1→3)(1→4)-β-glucans found in cereals and certain lichens but has a distinctive primary structure. Genes, proteins, and regulatory pathways for producing this new polymer are described. Our findings open the possibility of using bacteria to produce (1→3)(1→4)-β-glucans, which are receiving increasing interest as bioactive compounds, and provide new elements to disclose molecular mechanisms of c-di-GMP regulation as well as for investigating the evolution, activity, and specificity of glycosyl transferases. An artificial increase of cyclic diguanylate (c-di-GMP) levels in Sinorhizobium meliloti 8530, a bacterium that does not carry known cellulose synthesis genes, leads to overproduction of a substance that binds the dyes Congo red and calcofluor. Sugar composition and methylation analyses and NMR studies identified this compound as a linear mixed-linkage (1→3)(1→4)-β- d -glucan (ML β-glucan), not previously described in bacteria but resembling ML β-glucans found in plants and lichens. This unique polymer is hydrolyzed by the specific endoglucanase lichenase, but, unlike lichenan and barley glucan, it generates a disaccharidic →4)-β- d -Glc p -(1→3)-β- d -Glc p -(1→ repeating unit. A two-gene operon bgsBA required for production of this ML β-glucan is conserved among several genera within the order Rhizobiales, where bgsA encodes a glycosyl transferase with domain resemblance and phylogenetic relationship to curdlan synthases and to bacterial cellulose synthases. ML β-glucan synthesis is subjected to both transcriptional and posttranslational regulation. bgsBA transcription is dependent on the exopolysaccharide/quorum sensing ExpR/SinI regulatory system, and posttranslational regulation seems to involve allosteric activation of the ML β-glucan synthase BgsA by c-di-GMP binding to its C-terminal domain. To our knowledge, this is the first report on a linear mixed-linkage (1→3)(1→4)-β-glucan produced by a bacterium. The S . meliloti ML β-glucan participates in bacterial aggregation and biofilm formation and is required for efficient attachment to the roots of a host plant, resembling the biological role of cellulose in other bacteria.

As one of the main forms of reactive nitrogen delivered by anthropogenic sources, atmospheric emissions of nitrogen oxides and their subsequent deposition has significantly perturbed the natural nitrogen cycle in sensitive receiving ecosystems worldwide. In North America, despite of decades of increasingly stringent regulations of emissions, decreases in the deposition of nitrogen oxides were not observed until the turn of the century. Analysis of available deposition data and trends at various spatial scales revealed that the decrease took place at a continental scale, but is particularly evident in the eastern side of the continent, where there was an unprecedented 50 % decrease in deposition. The magnitude, timing and geographical extension of the observed changes in deposition resulted from a combination of successfully and relatively coordinated application of emission controls in major contributing regions and increasingly lower amounts of nitrogen oxides being transported from source to receptor areas, thereby extending the effects of emission controls over large geographical scales.

Concern over the ecological damage of excess nitrogen has brought increased attention to the role of research institutions and universities in contributing to this problem. Institutions often utilize the concept of the ecological ‘footprint’ to quantify and track nitrogen emissions resulting from their activities and guide plans and commitments to reduce emissions. Often, large-scale changes and commitments to reduce nitrogen footprints are not feasible at small institutions due to monetary and manpower constraints. We partnered with managers in the dining and facilities departments at the Marine Biological Laboratory (MBL), a small research institution in Woods Hole, Massachusetts, to develop five low-effort strategies to address nitrogen emissions at the institution using only resources currently available within those departments. Each proposed strategy achieved emissions reductions in their sector and in the overall nitrogen footprint of the MBL. If all modelled strategies are applied simultaneously, the MBL can achieve a 7.7% decrease in its nitrogen footprint. Managers at MBL considered strategies that required no monetary input most feasible. The intersection of carbon and nitrogen emissions also means the modelled strategies had the co-benefit of reducing the MBL’s carbon footprint, strengthening the argument for applying these strategies. This paper may serve as a model for similar institutions looking to reduce the ecological impact of their activities.

A decision support framework for the management of lagoon ecosystems was tested using four European Lagoons: Ria de Aveiro (Portugal), Mar Menor (Spain), Tyligulskyi Liman (Ukraine) and Vistula Lagoon (Poland/Russia). Our aim was to formulate integrated management recommendations for European lagoons. To achieve this we followed a DPSIR ( Drivers-Pressures-State Change-Impacts-Responses ) approach, with focus on integrating aspects of human wellbeing, welfare and ecosystem sustainability. The most important drivers in each lagoon were identified, based on information gathered from the lagoons’ stakeholders, complemented by scientific knowledge on each lagoon as seen from a land-sea perspective. The DPSIR cycles for each driver were combined into a mosaic-DPSIR conceptual model to examine the interdependency between the multiple and interacting uses of the lagoon. This framework emphasizes the common links, but also the specificities of responses to drivers and the ecosystem services provided. The information collected was used to formulate recommendations for the sustainable management of lagoons within a Pan-European context. Several common management recommendations were proposed, but specificities were also identified. The study synthesizes the present conditions for the management of lagoons, thus analysing and examining the activities that might be developed in different scenarios, scenarios which facilitate ecosystem protection without compromising future generations.

Recent findings have shown that photosynthesis in the skin of the seed of Posidonia oceanica enhances seedling growth. The seagrass genus Posidonia is found only in two distant parts of the world, the Mediterranean Sea and southern Australia. This fact led us to question whether the acquisition of this novel mechanism in the evolution of this seagrass was a pre-adaptation prior to geological isolation of the Mediterranean from Tethys Sea in the Eocene. Photosynthetic activity in seeds of Australian species of Posidonia is still unknown. This study shows oxygen production and respiration rates, and maximum PSII photochemical efficiency (Fv : Fm) in seeds of two Australian Posidonia species (P. australis and P. sinuosa), and compares these with previous results for P. oceanica. Results showed relatively high oxygen production and respiratory rates in all three species but with significant differences among them, suggesting the existence of an adaptive mechanism to compensate for the relatively high oxygen demands of the seeds. In all cases maximal photochemical efficiency of photosystem II rates reached similar values. The existence of photosynthetic activity in the seeds of all three species implicates that it was an ability probably acquired from a common ancestor during the Late Eocene, when this adaptive strategy could have helped Posidonia species to survive in nutrient-poor temperate seas. This study sheds new light on some aspects of the evolution of marine plants and represents an important contribution to global knowledge of the paleogeographic patterns of seagrass distribution.

In addition to their important effects on nitrogen (N) cycling via excretion and assimilation (by macrofauna and macroflora, respectively), many macrobiota also host or facilitate microbial taxa responsible for N transformations. Interest in this topic is expanding, especially as it applies to coastal marine systems where N is a limiting nutrient. Our understanding of the diversity of microbes associated with coastal marine macrofauna (invertebrate and vertebrate animals) and macrophytes (seaweeds and marine plants) is improving, and recent studies indicate that the collection of microbes living in direct association with macrobiota (the microbiome) may directly contribute to N cycling. Here, we review the roles that macrobiota play in coastal N cycling, review current knowledge of macrobial–microbial associations in terms of N processing, and suggest implications for coastal ecosystem function as animals are harvested and as foundational habitat is lost or degraded. Given the biodiversity of microbial associates of macrobiota, we advocate for more research into the functional consequences of these associations for the coastal N cycle.