Salinity and time can alter epibacterial communities of an invasive seaweed

The establishment of epibacterial communities is fundamental to seaweed health, and fitness, in modulating ecological interactions and may also facilitate adaptation to new environments. Few recent studies have investigated the influence of abiotic factors like light, temperature as drivers of epibacterial community composition on seaweeds. Although salinity can determine bacterial abundance, growth and community composition, influence of salinity as a driver of epibacterial community composition (until species level) has not been investigated for seaweeds and especially under long time scales. We also do not know how abiotic stressors may influence the ‘core’ bacterial species of seaweeds. Following an initial (immediately after field collection, T0) sampling of epibacterial community of an invasive red seaweed Agarophyton vermicullophylum, we conducted a long term mesocosm experiment for 5 months, to examine the influence of three different salinities (low, medium and high) at two different time points (T1, T2) on the epibacterial community richness and composition of Agarophyton. Metagenomic sequencing showed that epibacterial communities changed significantly according to salinity and time points sampled. Epibacterial richness was significantly different between low and high salinities at both time points. Epibacterial richness also varied significantly among T1 and T2 within low, medium and high salinity level. Irrespective of salinity levels and time points sampled 727 taxa consistently appeared in all Agarophyton samples hinting at the presence of core bacterial species on the surface of the alga. Our results indicate that both salinity and time can be major driving forces in structuring epibacterial communities of seaweeds with respect to richness and β diversity. We highlight the necessity of conducting long term experiments allowing us to detect and understand epibacterial succession over time on seaweeds

Aquaculture of Fucus species in the Baltic Sea by means of vegetative reproduction

Species of the brown algal genus Fucus are important ecosystem engineers of northern hemisphere coasts. Their biomass is harvested commercially for the production of cosmetic extracts and food supplements, e.g., at the coasts of France, Ireland and Iceland. However, environmental change (e.g., warming, eutrophication) poses increasing risk on wild Fucus stocks and has already caused some population declines, for instance in the Baltic Sea, where harvesting of wild stocks is prohibited as consequence. Commercial cultivation of Fucus would therefore be a useful alternative to the harvesting of wild stocks especially in the light of an increasing interest in algal products. But so far, no cultivation method for the commercial production of Fucus species has been developed. Therefore, a theoretical vegetative cultivation approach has been described which includes the following steps: thallus pieces with apical meristems (“seedlings”) are cut from wild plants and reared unattached in baskets/ net cages deployed in the sea; after a season of growth, the biomass is harvested and new seedlings are cut from the harvest which are used as initial biomass for the next growth season. This process is then repeated after each growth season. The aim of this doctoral thesis was to test various aspects of this cultivation approach in culture experiments. The experiments were performed in an experimental farm located in the Kiel fjord, western Baltic Sea. Two local Fucus species (F. vesiculosus, F. serratus) were used. First, it was tested if Fucus thalli survive long-term culture with the described cultivation method and which role the formation of sexual organs (receptacles) plays in the cultivation process. It could be shown that principally thalli survive and grow continually in culture with the described method. However, the formation of receptacles and their natural degradation after gamete shedding reduced the growth potential significantly. Therefore, the question was raised how culture biomass with low fertility (i.e., a low percentage of thallus apices with receptacles) can be obtained. In order to answer this question, two approaches were adopted: first, it was tested if thalli from attached wild populations with naturally high fertility acclimatize towards lower fertility if they are cultivated unattached. Second, it was tested if thalli from an unattached wild population in Glücksburg (Flensburg fjord), which morphologically resembles F. vesiculosus and exhibits low fertility in the wild, retain their low fertility in culture. Thalli from attached high-fertility populations retained their high fertility in culture and did not acclimatize towards lower fertilities by unattached cultivation. On the other hand, thalli from the unattached population in Glücksburg retained their low fertility over one year of cultivation. Consequently, only thalli from unattached low-fertility populations are potentially useful for the envisaged vegetative cultivation method. Second, the question was raised if epizoan fouling, which was frequently encountered on the culture biomass, can be reduced by regular desiccation during the cultivation process. In order to answer this question, the effect of different desiccation regimes (different frequencies and intensities of desiccation) on weight and abundance of the most common epizoans (Electra pilosa (Bryozoa), Amphibalanus improvisus (Crustacea, Cirripedia), Mytilus sp. (Mollusca, Bivalvia)) as well as on the growth rate of the cultivated Fucus species was tested. Desiccation regimes affected weight and abundance of epizoans as well as Fucus growth rates at varying degrees. Frequent mild desiccations (F. vesiculosus: 3x week -1 to 80% of wet weight, F. serratus: 3x week -1 to 90% of wet weight) proved most effective as they reduced epizoan fouling significantly but had no effect on Fucus growth. By applying these regimes, the epizoan share of the final harvest could be reduced from 13.0 ± 4.8% in undesiccated controls to 1.8 ± 0.2% for F. vesiculosus and from 19.1 ± 2.7 to 1.0 ± 0.1% for F. serratus. In conclusion, Fucus aquaculture with the described vegetative cultivation approach is possible if the cultivated biomass can be kept at low fertility (which seems to be possible by using seedling material from unattached low-fertility populations) and if epizoan fouling is reduced by regular desiccation. Future studies should investigate the genetic control of fertility in Fucus and the influence of environmental factors on fertility since low fertility is a crucial factor for long-term cultivation success. Alternative cultivation techniques (e.g., in land-based tanks) might enable a cultivation without epizoan fouling and should also be subject of future research

Reallabor Eckernförder Bucht 2030 – the first living lab covering sea, coast and land

1. The living lab method (German: “Reallabor”) is a proven tool from sustainability research. Although it offers a lot of potential for application to complex challenges in marine conservation, it has scarcely been used in this context so far. 2. This article presents the project "Reallabor Eckernförder Bucht 2030", which is the first living lab addressing the areas of sea, coast and land together. 3. The project was developed in co-design between science, ministries and other stakeholders. 4. It was possible to show that the Living lab method is suitable for a multi-stakeholder dialogue with many interlinked challenges, e.g. agriculture, fisheries, nature protection and tourism. 5. Synthesis and applications: The living lab method is suitable for addressing complex challenges addressing the areas of sea, coast and land together in a geographically limited space. A cooperation between science, society and administration helps to tackle environmental problems by identifying solutions that a) have a high societal acceptance, b) are based on interdisciplinary scientific knowledge, and c) fulfil administrative rules and conditions. The "Reallabor Eckernförder Bucht 2030" serves as a blueprint for projects also on international level