Abstract The Kiel Canal is one of the world’s most frequently used inland waterways and connects the SW Baltic Sea with the Wadden Sea. At the same time, the canal is a highly eutrophicated environment that is characterized by salinities that range from 3 to 16. This brackish character could make the Kiel Canal an important stepping stone for the introductions of species into the inner Baltic Sea. It could also hinder the identification of native and introduced species, given the fact that salinity sometimes severely affects algal morphology. Here we report on a survey of introduced and native seaweed species in the canal, focusing on the dominant groups, which are Fucales and Ulvales. Of the Fucales, the introduced species Fucus evanescens was detected nearly exclusively inside the canal, while Fucus vesiculosus dominated rockweed communities directly outside the sluice gates. Morphological analysis and genetic barcoding distinguished three species of Ulvales, Ulva linza, Ulva intestinalis and an unknown and possibly introduced species of the genus Blidingia . Species distributions and – in the case of U. intestinalis – branching patterns were clearly affected by salinity, while thallus sizes appeared to be affected by the specific eutrophication status of sites within the canal.
Hydrogels based on the polysaccharide ulvan from the green macroalgae Ulva fenestrata were synthesized and evaluated as an adsorbent for heavy metals ions and methylene blue. Ulvan was extracted from Ulva fenestrata using diluted hydrochloric acid and recovered by precipitation with EtOH. The extracted ulvan was converted into ulvan dialdehyde via periodate-oxidation and subsequently combined with gelatin yielding hydrogels. The hydrogels showed good water-uptake capacity with a maximum swelling degree of 2400 % in water and 900 % in PBS buffer. Adsorption tests of methylene blue showed a maximum adsorption capacity of 465 mg/g. The adsorption data of methylene blue followed the pseudo-second order kinetics and agreed with the Langmuir adsorption isotherm. The maximum adsorption capacity of heavy metal ions was 14 mg/g for Cu2+, 7 mg/g for Co2+and 6 mg/g for Ni2+and Zn2+ indicating that the hydrogels have a stronger affinity for Cu2+ than for Co2+, Ni2+, and Zn2+.
The genus Ulva is has broadly negative connotations because of its ability to form harmful “green tides” and the problems it causes with precise species identification, due to its morphological plasticity. During recent years, tides of unattached Ulva compressa U. Linneus 1753 with an atypical sheet-like morphology were for the first time observed in the German Baltic. Here we report that this nuisance alga is conspecific with the type strain of U. mutabilis Foyn 1958 from Faro in Portugal, an important model organism to study morphogenesis, morphogenetics and mutualistic interactions. Different approaches were used to examine conspecificity: (1) Comparisons on vegetative and reproductive features of cultured material of Ulva mutabilis and German Ulva compressa resulted in congruent results proving that a certain morphogenetic mutation pattern is shared. Spontaneous mutations of “slender-like” thalli are appearing whilst the common form exhibits a “leaf-like” wildtype morphology. (2) Interbreeding experiments of gametes of Ulva compressa and Ulva mutabilis were successful and showed a fertile first-generation offspring exhibiting the typical wildtype morphology similar to the phenotype of the parental generation. (3) Phylogenetic and species delimitation analyses were carried out on 128 tufA sequences of Ulva compressa specimens sampled in 2014–2016 in Germany and on tufA sequences of two clones of the strains Ulva mutabilis (sl-G[mt+]) and Ulva mutabilis (wt-[mt-]) to identify Molecular Operational Taxonomic Units (MOTUs).
The Generalized Mixed Yule-Coalescent (GMYC)
method comprises one major MOTU containing all included sequences of Ulva compressa and Ulva mutabilis, while reference sequences included in the analysis clustered outside this MOTU. This highly supports the monophyly of Ulva compressa and Ulva mutabilis, which can be treated as the same species. As a consequence, U. mutabilis is also a suitable model for future studies of green tides and their molecular and morphogenetic basis in the Baltic Sea.
Macroalgal biomass has the potential to become an important source of chemicals and commodities in a future biorefinery. Currently, production of macroalgal biomass is expensive and the content of high-value compounds is often low. Therefore, in this study the biochemical composition of Ulva intestinalis along the Swedish west coast and the east coast up to Stockholm was assessed with the aim of determining how the content of potentially valuable compounds, such as rhamnose, iduronic acid and PUFAs, could be maximized by utilizing natural variation in the choice of marine cultivation site. Along the investigated coastline, the salinity dropped from 19.4‰ at high latitudes along the west coast to 5.4‰ at Stockholm. Nitrogen and phosphorus availability varied, while temperature was similar at all locations. The two major components of biomass, carbohydrates and ash, varied inversely with the highest content of ash in the west and carbohydrates in the east. In addition, total fatty acids were significantly higher in west coast samples at 3.2 g 100 g–1 dw, with a higher proportion of mono- and polyunsaturated fatty acids. Some health-beneficial fatty acids were found, including EPA and DPA, at 10–50 mg 100 g–1 dw, respectively. The metal content and elemental composition varied widely, probably due to the influence of specific local conditions. The P content was correlated with the phosphorus concentration in waters at the locations. In PCA analysis, the monosaccharides constituting the cell wall polysaccharide ulvan were found to vary by geographical location, with higher levels possibly associated with lower salinities. However, only glucuronic acid differed significantly between sites. These results show the considerable geographical variability in the composition of Swedish U. intestinalis and suggest that different salinities could be used to create a lipid- or carbohydrate-rich biomass.
DNA barcoding analysis, using tufA, revealed considerable differences between the expected and observed species inventory of Ulva sensu lato in the Baltic and North Sea areas of the German state of Schleswig-Holstein. Of 20 observed genetic entities, at least four (U. australis, U. californica, U. gigantea and Umbraulva dangeardii) had been introduced recently, whereas three others (one Ulva sp. and two Blidingia spp.) could not be identified at the species level and could also represent recently introduced species. In addition, the observed distributions of Kornmannia leptoderma and U. rigida were much more extensive than indicated by historical records, whereas Blidingia minima and Gayralia oxysperma were absent or much less common than expected. Barcoding analysis also revealed that both U. tenera (type material) and U. pseudocurvata (historical vouchers) from Helgoland, an off-shore island in the North Sea, actually belong to U. lactuca, a species that appears to be restricted to this island. Furthermore, past morphological descriptions of U. intestinalis and U. compressa have apparently been too restrictive and have been responsible for numerous misidentifications. The same is true for U. linza, which, in northern Germany, clusters into two genetically closely related but morphologically indistinguishable entities. One of these entities is present on Helgoland, while the second is present on North Sea and Baltic Sea mainland coasts.
The green seaweed Ulva relies on associated bacteria for morphogenesis and is an important model to study algal-bacterial interactions. Ulva -associated bacteria exhibit high turnover across environmental gradients, leading to the hypothesis that bacteria contribute to the acclimation potential of the host. However, the functional variation of these bacteria in relation to environmental changes remains unclear. We analyzed 91 Ulva samples across a 2000-kilometer Atlantic–Baltic Sea salinity gradient using metagenomic sequencing. Metabolic reconstruction of 639 metagenome-assembled genomes revealed widespread potential for carbon, nitrogen, sulfur, and vitamin metabolism. Although the R 2 value for salinity explained 70% of taxonomic variation, it accounted only for 17% of functional variation. The limited variation was attributed to typical high-salinity bacteria exhibiting enrichment in genes for thiamine, pyridoxal, and betaine biosynthesis, which likely contribute to stress mitigation and osmotic homeostasis in response to salinity variations. Our results emphasize the importance of functional profiling to understand the seaweed holobiont and its collective response to environmental change.
Abstract The ubiquitous and species rich genus Ulva comprises entities of green macroalgae with variable morphologies. Ulva species are important from ecological and economic perspectives, but their identification is often problematic. Current knowledge on Ulva diversity has focused mainly on foliose individuals of temperate regions, but genetic and morphological data on tubular species are often insufficient and the species richness is ambiguous due to the lack of molecularly identified type vouchers. Together with a previous study, our study demonstrates that due to the crypticity of tubular entities of the genus Ulva present in the Atlantic-Baltic Sea transect, certain species remained undetected until recently whereas molecular evidence of other historically identified species is missing. An entity which appears to be a relatively frequent species in the Atlantic-Baltic Sea transect and which was probably mis-identified with other species in the past is here described as Ulva capillata sp. nov.. The description is based on molecular identification using tuf A and rbcL sequences, and by comparing the species´ phylogenetic relationships, distribution and range margins in the Atlantic-Baltic Sea transect, as well as on morpho-anatomical characters, and early ontogenetic development. By comparisons with closely related and potentially morphologically overlapping species concepts we were able to identify the uniqueness of U. capillata . Therefore, the description of U. capillata as a new species within the genus Ulva is supported by a combination of molecular, morphological, and ontogentic evidence which confirm their uniqueness in comparison to other species concepts. Furthermore, our results strongly emphasize the importance and necessity to molecularly investigate especially tubular historic type vouchers within the genus Ulva to facilitate a clear species identification to omit continuing with taxonomic confusion and ongoing misapplication of names of e.g. cryptic species concepts within this important green algal genus.
Abstract The genus Ulva is globally distributed and has been thoroughly studied because of its functional biochemical composition, rapid growth rates and opportunistic features, and interest in Ulva cultivation is growing worldwide. In Europe, mostly near- and on-shore flow-through cultivation systems are used and land-based recirculating aquaculture systems (RAS) using fresh water or artificial seawater have not been developed for Ulva . While RAS provides quality control and can be located inland, maintenance costs are high. Using selected strains adapted to low-salinity could reduce seawater production costs and improve the economic feasibility. Therefore, our study assessed how salinity can be used as a tool for strain selection and optimization of functional traits. Growth rates and antioxidant activity of three species (four strains) of tubular and foliose Ulva from the NE-Atlantic and Mediterranean (foliose: Ulva lacinulata – two geographical strains, tubular: Ulva linza and Ulva flexuosa ) were followed for three weeks at salinities ranging from 10 to 30 PSU. The tubular strains achieved optimal growth at a lower salinity than U. lacinulata . However, growth rates of both foliose strains were higher than of tubular strains, even at sub-optimal salinity. Therefore, U. lacinulata is a good candidate for RAS with artificial seawater, and the cost of salt can be reduced by up to 33.3% (20 PSU) without significantly reducing the growth rate of U. lacinulata . Higher antioxidant activity was achieved by reducing the salinity to 10 PSU for 10 days, suggesting that the functional traits of cultivated Ulva lacinulata can be optimized prior to harvest.
