The effect of surface colour on the formation of marine micro and macrofouling communities

<div><p>The effect of substratum colour on the formation of micro- and macro fouling communities was investigated. Acrylic tiles, painted either black or white were covered with transparent sheets in order to ensure similar surface properties. All substrata were exposed to biofouling at 1 m depth for 40 d in the Marina Bandar al Rowdha (Muscat, Sea of Oman). Studies were conducted in 2010 over a time course of 5, 10 and 20 d, and in 2012 samples were collected at 7, 14 and 21 d. The densities of bacteria on the black and white substrata were similar with the exception of day 10, when the black substrata had a higher abundance than white ones. Pyrosequencing <i>via</i> 454 of 16S rRNA genes of bacteria from white and black substrata revealed that Alphaproteobacteria and Firmicutes were the dominant groups. SIMPER analysis demonstrated that bacterial phylotypes (uncultured Gammaproteobacteria, <i>Actibacter</i>, <i>Gaetbulicola, Thalassobius</i> and <i>Silicibacter</i>) and the diatoms (<i>Navicula directa</i>, <i>Navicula</i> sp. and <i>Nitzschia</i> sp.) contributed to the dissimilarities between communities developed on white and black substrata. At day 20, the highest amount of chlorophyll <i>a</i> was recorded in biofilms developed on black substrata. SIMPER analysis showed that <i>Folliculina</i> sp., <i>Ulva</i> sp. and <i>Balanus amphitrite</i> were the major macro fouling species that contributed to the dissimilarities between the communities formed on white and black substrata. Higher densities of these species were observed on black tiles. The results emphasise the effect of substratum colour on the formation of micro and macro fouling communities; substratum colour should to be taken into account in future studies.</p> </div

Antifouling properties of zinc oxide nanorod coatings

<div><p>In laboratory experiments, the antifouling (AF) properties of zinc oxide (ZnO) nanorod coatings were investigated using the marine bacterium <i>Acinetobacter</i> sp. AZ4C, larvae of the bryozoan <i>Bugula neritina</i> and the microalga <i>Tetraselmis</i> sp. ZnO nanorod coatings were fabricated on microscope glass substrata by a simple hydrothermal technique using two different molar concentrations (5 and 10 mM) of zinc precursors. These coatings were tested for 5 h under artificial sunlight (1060 W m⁻² or 530 W m⁻²) and in the dark (no irradiation). In the presence of light, both the ZnO nanorod coatings significantly reduced the density of <i>Acinetobacter</i> sp. AZ4C and <i>Tetraselmis</i> sp. in comparison to the control (microscope glass substratum without a ZnO coating). High mortality and low settlement of <i>B. neritina</i> larvae was observed on ZnO nanorod coatings subjected to light irradiation. In darkness, neither mortality nor enhanced settlement of larvae was observed. Larvae of <i>B. neritina</i> were not affected by Zn²⁺ ions. The AF effect of the ZnO nanorod coatings was thus attributed to the reactive oxygen species (ROS) produced by photocatalysis. It was concluded that ZnO nanorod coatings effectively prevented marine micro and macrofouling in static conditions.</p></div

Algal phlorotannin content.

<p>Tissue phlorotannin content (means + SD; n = 3) in <i>Sargassum</i> spp. from Japan (white bars; <i>S</i>. <i>muticum</i> (<i>SM</i> (nat), <i>S</i>. <i>fusiforme</i> (<i>SF</i>), <i>S</i>. <i>horneri</i> (<i>SH</i>)) and <i>S</i>. <i>muticum</i> (<i>SM</i> (inv.) and <i>F</i>. <i>vesiculosus</i> (<i>FV</i>) from the North Sea (black bars). Different letters above the bars indicate significant differences between tissue concentrations (ANOVA, Tukey post hoc test, p < 0.05).</p

Self-decontaminating photocatalytic zinc oxide nanorod coatings for prevention of marine microfouling: a mesocosm study

<p>The antifouling (AF) properties of zinc oxide (ZnO) nanorod coated glass substrata were investigated in an out-door mesocosm experiment under natural sunlight (14:10 light: dark photoperiod) over a period of five days. The total bacterial density (a six-fold reduction) and viability (a three-fold reduction) was significantly reduced by nanocoatings in the presence of sunlight. In the absence of sunlight, coated and control substrata were colonized equally by bacteria. MiSeq Illumina sequencing of 16S rRNA genes revealed distinct bacterial communities on the nanocoated and control substrata in the presence and absence of light. Diatom communities also varied on nanocoated substrata in the presence and the absence of light. The observed AF activity of the ZnO nanocoatings is attributed to the formation of reactive oxygen species (ROS) through photocatalysis in the presence of sunlight. These nanocoatings are a significant step towards the production of an environmentally friendly AF coating that utilizes a sustainable supply of sunlight.</p

Bacterial growth inhibition.

<p>Log response ratios (LogRR) of bacterial growth of strains 1–6 (a-f) in response to different concentrations of crude and surface extracts of <i>Sargassum fusiforme</i> (<i>S</i>.<i>f</i>.), <i>Sargassum horneri</i> (<i>S</i>.<i>h</i>.), native (nat.) and invasive (inv.) <i>Sargassum muticum</i> (<i>S</i>.<i>m</i>.), <i>Fucus vesiculosus</i> (<i>F</i>.<i>v</i>.) and the antibiotic positive control (AB; gentamicin or penicilin; 100 μg/ml). Circle–natural concentrations, square– 2-times natural concentrated extracts. Asterisks indicate significant differences between treatments and solvent control (ANOVA, Tukey post-hoc test p < 0.05).</p

Antidiatom activity of algal extracts.

<p>Effect of crude (black) and surface (grey) extracts of <i>S</i>. <i>fusiforme</i> (<i>S</i>.<i>f</i>.), <i>S</i>. <i>horneri</i> (<i>S</i>.<i>h</i>.), native and invasive <i>S</i>. <i>muticum</i> (<i>S</i>.<i>m</i>. (nat.) and (inv.)), and <i>F</i>. <i>vesiculosus</i> (<i>F</i>.<i>v</i>.) on cell densities (mean ± SD, n = 6) of the diatom <i>C</i>. <i>closterium</i> after 7 days. Extracts were tested at the natural concentrations. Methanol was used as the control (C). Significant differences (p < 0.05) are indicated by different letters (upper- and lower case letters for crude and surface extracts, respectively) above the bars (according to Kruskal–Wallis test with the Dunn′s multiple post-hoc comparison test).</p

Summary of the results of the experiments comparing the chemical defence of the invasive and native <i>S</i>. <i>muticum</i>, <i>Sargassum</i> spp. from Japan, and the brown alga <i>F</i>. <i>vesiculosus</i> from the North Sea.

<p>The antibacterial activity is presented as the percent of inhibited bacterial strains and MIC-values are provided for inhibition of QS (X-times natural concentration, ‘-’ = no inhibition). The settlement inhibitory activity is presented as both, the MIC inhibiting diatom (<i>C</i>. <i>closterium</i>) growth and bryozoan (<i>B</i>. <i>neritina</i>) larval settlement (‘+’ = settlement inhibition after 24h; ‘-’ = no settlement inhibition; n.c. = not conducted). Algal zygote settlement inhibition is presented as the MIC inhibiting <i>F</i>. <i>vesiculosus</i> zygote settlement (as X-times natural concentration [x N]). The amount of phlorotannins in algal tissues is represented as the proportion of total phenolic content (TPC) per algal dry weight (dw).</p

Biomass of tested brown algae and their specific extract yield.

<p>Biomass of tested brown algae and their specific extract yield.</p

Blast identification and percentage similarity of bacterial 16S rDNA sequences.

<p>Blast identification and percentage similarity of bacterial 16S rDNA sequences.</p

Anti-QS and growth inhibitiory activity of <i>Chromobacterium violaceum</i> by algal extracts.

<p>Anti-QS and growth inhibitiory activity of <i>Chromobacterium violaceum</i> by algal extracts.</p