Description: We identified defense compounds that are present on the surface of Zostera marina and inhibit settlement of microfoulers at natural concentration. Moderately polar eelgrass surface extract prepared with propan-2-ol inhibited the settlement of seven marine bacteria that originated from nonliving substrata and of one yeast, while five other bacterial strains that had been directly isolated from eelgrass surfaces were all insensitive (see https://doi.pangaea.de/10.1594/PANGAEA.877254). In contrast, microbial growth was not inhibited by these extracts (see https://doi.pangaea.de/10.1594/PANGAEA.877255 and https://doi.pangaea.de/10.1594/PANGAEA.877379). Avter solvent evaporation propan-2-ol extract could be redissolved in methanol without activiy loss (see https://doi.pangaea.de/10.1594/PANGAEA.877380). Of six fractions prepared from propan-2-ol crude extract by HPLC three inhibited certain microorganisms (see https://doi.pangaea.de/10.1594/PANGAEA.877384). Rosmarinic acid, luteolin-7-sulfate and diosmetin-7-sulfate or its isomer chrysoeriol-7-sulfate were identified as main components in these fractions and all three compounds prevented bacterial settlement in a dose-dependent manner (see https://doi.pangaea.de/10.1594/PANGAEA.877732 and https://doi.pangaea.de/10.1594/PANGAEA.877734).

Description: Dose-response experiments for yeast growth or settlement were conducted in 96-well plates impregnated with eelgrass extracts Concentrations of leaf surface extracts were related to naturally occurring concentrations on Z. marina surfaces assuming a leaf area / fresh-weight ratio of 78.99 cm2*g-1. Correspondingly, a 1-fold natural concentration of surface extract was tested when extract obtained from 0.955 cm² leaf surface was impregnated onto 0.955 cm² well surface. Concentrations of tissue extracts were dosed based on the assumption of a dry-weight / fresh-weight proportion of 10%. Correspondingly, a 1-fold natural concentration of tissue extract was tested when extract obtained from 10 mg dry weight was present in the final volume of 100 µl. The yeasts were maintained at 25°C on a shaker in liquid medium containing: 3 g of yeast extract, 3 g of malt extract, 5 g of peptone, 10 g of glucose, and sea salt 3%. For settlement assays aliquots of yeast liquid cultures were pipetted into the wells. After 2 h, the wells were emptied and cells attached to the walls were stained with Calcofluor white for 10 min. The unattached cells and the excess dye were removed by rinsing with sterile seawater, and the fluorescence of stained cells attached to the wells was measured at 350 nm excitation and 430 nm emission. For growth bioassays, 100 µl medium containing yeast cells at 0.07-0.17 initial OD610 were pipetted into the wells. Plates were incubated at 25°C on a shaker in darkness and OD610 was repeatedly measured over 20 h. Exponential growth curves were fitted with the GraphPad Prism 5.0 software package to OD data time series obtained for each well allowing determination of division rates. Division rates obtained for single wells with addition of compounds were then related to mean division rates obtained for six control wells without such addition.

Description: 13 response variable have been measured for Fucus vesiculosus and Zostera marina. Year: 2015 Where: Kiel Outdoor Benthocosm Treatments: - Co (0HW) = ambient treatment with no heatwaves - 1HW = one summer heatwave - 3HWs = three heatwaves, 2 spring/early summer heatwaves After 3HW means end of the experiment.

Description: Climate change will not only shift environmental means but will also increase the intensity of extreme events, exerting additional stress on ecosystems. While field observations on the ecological consequences of heat waves are emerging, experimental evidence is rare, and lacking at the community level. Using a novel “near‐natural” outdoor mesocosms approach, this study tested whether marine summer heat waves have detrimental consequences for macrofauna of a temperate coastal community, and whether sequential heat waves provoke an increase or decrease of sensitivity to thermal stress. Three treatments were applied, defined and characterized through a statistical analysis of 15 years of temperature records from the experimental site: (1) no heat wave, (2) two heat waves in June and July followed by a summer heat wave in August and (3) the summer heat wave only. Overall, 50% of the species showed positive, negative or positive/negative responses in either abundance and/or biomass. We highlight four possible ways in which single species responded to either three subsequent heat waves or one summer heat wave: (1) absence of a response (tolerance, 50% of species), (2) negative accumulative effects by three subsequent heat waves (tellinid bivalve), (3) buffering by proceeding heat waves due to acclimation and/or shifts in phenology (spionid polychaete) and (4) an accumulative positive effect by subsequent heat waves (amphipod). The differential responses to single or sequential heat waves at the species level entailed shifts at the community level. Community‐level differences between single and triple heat waves were more pronounced than those between regimes with vs. without heat waves. Detritivory was reduced by the single heat wave while suspension feeding was less common in the triple heat wave regime. Critical extreme events occur already today and will occur more frequently in a changing climate, thus, leading to detrimental impacts on coastal marine systems.

Description: The goals of this study were (1) to investigate whether Fucus vesiculosus regulates the production of its antifouling defence chemicals against microfoulers in response to light limitation and temperature shifts and (2) to investigate if different surface concentrations of defence compounds shape epibacterial communities. F. vesiculosus was incubated in indoor mesocosms at five different temperature conditions (5 to 25°C) and in outdoor mesocosms under six differently reduced sunlight conditions (0 to 100%), respectively. Algal surface concentrations of previously identified antifouling compounds - dimethylsulphopropionate (DMSP), fucoxanthin and proline – were determined and the bacterial community composition was characterized by in-depth sequencing of the 16S-rRNA gene. Altogether, the effect of different treatment levels upon defence compound concentrations was limited. Under all conditions DMSP alone appeared to be sufficiently concentrated to warrant for at least a partial inhibitory action against epibiotic bacteria of F. vesiculosus. In contrast, proline and fucoxanthin rarely reached the necessary concentration ranges for self-contained inhibition. Nonetheless, in both experiments along with the direct influence of temperature and light, all three compounds apparently affected (and thereby shaped) the overall bacterial community composition associated with F. vesiculosus since tendencies for insensitivity towards all three compounds were observed among bacterial taxa that typically dominate those communities. Given that the concentrations of at least one of the compounds (in most cases DMSP) were always high enough to inhibit bacterial settlement, we conclude that the capacity of F. vesiculosus for such defence will hardly be compromised by shading or warming to temperatures up to 25°C.