Seasonally fluctuating fouling control of Fucus vesiculosus and Fucus serratus from the Baltic Sea: Is fouling control linked to abiotic and biotic variables?

In this doctoral project, I investigated the putative seasonal fluctuating chemical fouling control of the perennial macroalgae Fucus vesiculosus and Fucus serratus from the Baltic Sea under in situ conditions as well as potential links between the chemical fouling control and different abiotic and biotic factors. My thesis highlights the seasonal dynamics of the chemical micro- and macrofouling control of F. vesiculosus and F. serratus from the Baltic Sea tested under in situ conditions as well as the impact of environmental variables on the fouling control strength. Further, this work demonstrates that both Fucus species exhibit pro- and antifouling properties during summer when fouling pressure is highest indicating a complex regulation of biofouling control. The study thus provides new insides into the complex algae-environment-fouler interactions and their seasonal dynamics

Seasonally fluctuating fouling control of Fucus vesiculosus and Fucus serratus from the Baltic Sea : is fouling control linked to abiotic and biotic variables?

In this doctoral project, I investigated the putative seasonal fluctuating chemical fouling control of the perennial macroalgae Fucus vesiculosus and Fucus serratus from the Baltic Sea under in situ conditions as well as potential links between the chemical fouling control and different abiotic and biotic factors. My thesis highlights the seasonal dynamics of the chemical micro- and macrofouling control of F. vesiculosus and F. serratus from the Baltic Sea tested under in situ conditions as well as the impact of environmental variables on the fouling control strength. Further, this work demonstrates that both Fucus species exhibit pro- and antifouling properties during summer when fouling pressure is highest indicating a complex regulation of biofouling control. The study thus provides new insides into the complex algae-environment-fouler interactions and their seasonal dynamics.In dieser Doktorarbeit wurde die vermeintlich saisonal fluktuierende chemische Fouling-Kontrolle der mehrjährigen Makroalgen Fucus vesiculosus und Fucus serratus aus der Ostsee unter in situ Bedingungen sowie mögliche Zusammenhänge zwischen der chemischen Foulingkontrolle und verschiedenen abiotischen und biotischen Faktoren untersucht. Meine Doktorarbeit verdeutlicht die jahreszeitliche Dynamik der chemischen Mikro- und Makrofouling-Kontrolle von F. vesiculosus und F. serratus aus der Ostsee unter in situ Bedingungen sowie den Einfluss von Umweltvariablen auf die Fouling Kontrollstärke. Zusätzlich zeigt diese Arbeit, dass beide Fucus Arten pro- und antifouling Eigenschaften im Sommer aufweisen, wenn der Fouling-Druck am höchsten ist, was eine komplexe Regulierung der Biofouling-Kontrolle andeutet. Diese Studie liefert somit neue Einsichten in die komplexe Algen-Umwelt-Fouler Interaktion und ihre jahreszeitliche Dynamik

Seasonal Variations in Surface Metabolite Composition of Fucus vesiculosus and Fucus serratus from the Baltic Sea

Perennial macroalgae within the genus Fucus are known to exude metabolites through their outer thallus surface. Some of these metabolites have pro- and/or antifouling properties. Seasonal fluctuations of natural fouling pressure and chemical fouling control strength against micro- and macrofoulers have previously been observed in Fucus, suggesting that control strength varies with threat. To date, a study on the seasonal composition of surface associated metabolites, responsible for much of the fouling control, has not been done. We sampled individuals of the two co-occurring species F. vesiculosus and F. serratus at monthly intervals (six per species and month) during a one-year field study. We analysed the chemical composition of surface associated metabolites of both Fucus species by means of gas chromatography-mass spectrometry (GC-MS) to describe temporal patterns in chemical surface composition. Additionally, we correlated abiotic and biotic parameters recorded monthly within the sampled habitat with the variation in the chemical surface landscape of Fucus. Our study revealed that the chemical surface composition of both Fucus species exhibits substantial seasonal differences between spring/summer and autumn/winter months. Light and temperature explained most of the seasonal variability in surface metabolite composition of both Fucus species. A strong summerly up-regulation of eighteen saccharides and two hydroxy acids in F. vesiculosus as well as of four fatty acids and two saccharides in F. serratus was observed. We discuss how these up-regulated molecules may have a complex effect on associated microfoulers, both promoting or decreasing fouling depending on metabolite and bacterial identity. These seasonal shifts in the surface metabolome seem to exert a compound control of density and composition of the Fucus associated biofilm

Invasion success of the seaweed Gracilaria vermiculophylla correlates with low palatability

Differences with respect to anti-herbivore defense were investigated in invasive and native populations of the seaweed Gracilaria vermiculophylla. Specimens from 6 native populations in East Asia and from 8 populations invasive in Europe and the Mexican Pacific coast were maintained under identical conditions and offered to herbivorous snails from both the native range (Littorina brevicula) and Europe (L. littorea) in no-choice feeding assays. L. brevicula consumed in total significantly larger amounts of G. vermiculophylla tissue than did L. littorea. Further, both snail species least consumed the seaweed specimens originating from either non-native populations or from populations native to the Korean East Sea/Sea of Japan. The Korean East Sea/Sea of Japan had previously been identified as putative donor region of all the invasive populations of G. vermiculophylla. Thus, populations in the donor region as well as non-native populations in different invaded realms feature an increased capacity to resist feeding pressure. Differences in nutrient content did not account for the observed patterns of consumption, as palatability and carbon to nitrogen (C:N) ratio were not significantly correlated. Thus, mechanical or chemical defenses or the content of feeding cues influenced the behavior of the snails. We suggest that low palatability contributed to the invasion success of the species

Can targeted defense elicitation improve seaweed aquaculture?

Diseases increasingly threaten aquaculture of kelps and other seaweeds. At the same time, protection concepts that are based upon application of biocides are usually not applicable, as such compounds would be rapidly diluted in the sea, causing ecological damage. An alternative concept could be the application of immune stimulants to prevent and control diseases in farmed seaweeds. We here present a pilot study that investigated the effects of oligoalginate elicitation on juvenile and adult sporophytes of Saccharina japonica cultivated in China and on adult sporophytes of Saccharina latissima cultivated in Germany. In two consecutive years, treatment with oligoalginate clearly reduced the detachment of S. japonica juveniles from their substrate curtains during the nursery stage in greenhouse ponds. Oligoalginate elicitation also decreased the density of endobionts and the number of bacterial cells on sporophytes of S. latissima that were cultivated on sea-based rafts. However, the treatment increased the susceptibility of kelp adults to settlement of epibionts (barnacles in Germany and filamentous algal epiphytes in China). In addition, oligoalginate elicitation accelerated the aging of S. japonica adults. Based upon these findings, oligoalginate elicitation could be a feasible way to provide “environmentally friendly” protection of kelp juveniles in nurseries. The same treatment causes not only beneficial, but also unwanted effects in adult kelp sporophytes. Therefore, it is not recommended as a treatment after the juvenile stage is completed. Future tests with other elicitors and other cultivated seaweed species may allow for the development of more feasible applications of targeted defense elicitation in seaweed aquaculture

Geographic variation in fitness-related traits of the bladderwrack Fucus vesiculosus along the Baltic Sea-North Sea salinity gradient

In the course of the ongoing global intensification and diversification of human pressures, the study of variation patterns of biological traits along environmental gradients can provide relevant information on the performance of species under shifting conditions. The pronounced salinity gradient, co-occurrence of multiple stressors, and accelerated rates of change make the Baltic Sea and its transition to North Sea a suitable region for this type of study. Focusing on the bladderwrack Fucus vesiculosus, one of the main foundation species on hard-bottoms of the Baltic Sea, we analyzed the phenotypic variation among populations occurring along 2,000 km of coasts subjected to salinities from 4 to >30 and a variety of other stressors. Morphological and biochemical traits, including palatability for grazers, were recorded at 20 stations along the Baltic Sea and four stations in the North Sea. We evaluated in a common modeling framework the relative contribution of multiple environmental drivers to the observed trait patterns. Salinity was the main and, in some cases, the only environmental driver of the geographic trait variation in F. vesiculosus. The decrease in salinity from North Sea to Baltic Sea stations was accompanied by a decline in thallus size, photosynthetic pigments, and energy storage compounds, and affected the interaction of the alga with herbivores and epibiota. For some traits, drivers that vary locally such as wave exposure, light availability or nutrient enrichment were also important. The strong genetic population structure in this macroalgae might play a role in the generation and maintenance of phenotypic patterns across geographic scales. In light of our results, the desalination process projected for the Baltic Sea could have detrimental impacts on F. vesiculosus in areas close to its tolerance limit, affecting ecosystem functions such as habitat formation, primary production, and food supply.Peer reviewe