Interactions between microbial biofilms and marine fouling algae: a mini review

Ensuring carbon neutrality via algae-based wastewater treatment systems: Progress and future perspectives

The emergence of algal biorefineries has garnered considerable attention to researchers owing to their potential to ensure carbon neutrality via mitigation of atmospheric greenhouse gases. Algae-derived biofuels, characterized by their carbon-neutral nature, stand poised to play a pivotal role in advancing sustainable development initiatives aimed at enhancing environmental and societal well-being. In this context, algae-based wastewater treatment systems are greatly appreciated for their efficacy in nutrient removal and simultaneous bioenergy generation. These systems leverage the growth of algae species on wastewater nutrients-including carbon, nitrogen, and phosphorus-alongside carbon dioxide, thus facilitating a multifaceted approach to pollution remediation. This review seeks to delve into the realization of carbon neutrality through algae-mediated wastewater treatment approaches. Through a comprehensive analysis, this review scrutinizes the trajectory of algae-based wastewater treatment via bibliometric analysis. It subsequently examines the case studies and empirical insights pertaining to algae cultivation, treatment performance analysis, cost and life cycle analyses, and the implementation of optimization methodologies rooted in artificial intelligence and machine learning algorithms for algae-based wastewater treatment systems. By synthesizing these diverse perspectives, this study aims to offer valuable insights for the development of future engineering applications predicated on an in-depth understanding of carbon neutrality within the framework of circular economy paradigms.

Design, semi-synthesis of soft coral-derived Aspergillus sp. secondary metabolite geodin derivatives and their antibacterial activities

A series of novel ester derivatives 2 - 7, of natural product geodin 1, isolated from the soft coral-derived fungus Aspergillus sp., were designed and semi-synthesised through one step reaction with high yield. Compound 5 showed strong antifouling inhibitory activities with MIC of 4.80 μM while compound 4 showed selective inhibitory activities with MICs values 8.59 μM against Aeromonas salmonicida and Pseudomonas aeruginosa (Sea-Nine 211, MIC = 0.27 μM). Compounds 3, 4 and 6 showed potent anti-pathogenic inhibitory activities with MICs of 2.29 μM, 4.29 μM and 4.56 μM respectively against Staphylococcus aureus (Ciprofloxacin, MIC = 0.156 μM). Compound 2 showed weak inhibitory activity against A. salmonicida with MIC 18.75 μM (Sea-Nine 211, MIC = 0.27 μM) and with MICs 9.38 μM against S. aureus (ciprofloxacin, MIC = 0.156 μM). However, compound 7 showed very low antibacterial activities with MIC = >20 μM. The preliminary structure-activity relationships of compounds 2 - 7 further prove that the modification of 4-OH group of natural product geodin 1 improves the antibacterial activities such as antifouling and anti-pathogenic activities.

Response of biofilm-based systems for antibiotics removal from wastewater: Resource efficiency and process resiliency

Biofilm-based systems have efficient stability to cope-up influent shock loading with protective and abundant microbial assemblage, which are extensively exploited for biodegradation of recalcitrant antibiotics from wastewater. The system performance is subject to biofilm types, chemical composition, growth and thickness maintenance. The present study elaborates discussion on different type of biofilms and their formation mechanism involving extracellular polymeric substances secreted by microbes when exposed to antibiotics-laden wastewater. The biofilm models applied for estimation/prediction of biofilm-based systems performance are explored to classify the application feasibility. Further, the critical review of antibiotics removal efficiency, design and operation of different biofilm-based systems (e.g. rotating biological contactor, membrane biofilm bioreactor etc.) is performed. Extending the information on effect of various process parameters (e.g. hydraulic retention time, pH, biocarrier filling ratio etc.), the microbial community dynamics responsible of antibiotics biodegradation in biofilms, the technological problems, related prospective and key future research directions are demonstrated. The biofilm-based system with biocarriers filling ratio of ∼50-70% and predominantly enriched with bacterial species of phylum Proteobacteria protected under biofilm thickness of ∼1600 μm is effectively utilized for antibiotic biodegradation (>90%) when operated at DO concentration ≥3 mg/L. The C/N ratio ≥1 is best suitable condition to eliminate antibiotic pollution from biofilm-based systems. Considering the significance of biofilm-based systems, this review study could be beneficial for the researchers targeting to develop sustainable biofilm-based technologies with feasible regulatory strategies for treatment of mixed antibiotics-laden real wastewater.

Epilithic Bacterial Assemblages on Subtidal Rocky Reefs: Variation Among Alternative Habitats at Ambient and Enhanced Nutrient Levels

Temperate rocky reefs often support mosaics of alternative habitats such as macroalgal forests, algal turfs and sea urchin barrens. Although the composition of epilithic microbial biofilms (EMBs) is recognized as a major determinant of macroalgal recruitment, their role in regulating the stability of alternative habitats on temperate rocky reefs remains unexplored. On shallow rocky reefs of the Island of Capraia (NW Mediterranean), we compared EMB structure among canopy stands formed by the fucoid Ericaria brachycarpa, algal turfs, and urchin barrens under ambient versus experimentally enhanced nutrient levels. The three habitats shared a core microbial community consisting of 21.6 and 25.3% of total ASVs under ambient and enhanced nutrient conditions, respectively. Although Gammaproteobacteria, Alphaproteobacteria and Flavobacteriia were the most abundant classes across habitats, multivariate analyses at the ASV level showed marked differences in EMB composition among habitats. Enhancing nutrient level had no significant effect on EMBs, although it increased their similarity between macroalgal canopy and turf habitats. At both ambient and enriched nutrient levels, ASVs mostly belonging to Proteobacteria and Bacteroidetes were more abundant in EMBs from macroalgal canopies than barrens. In contrast, ASVs belonging to the phylum of Proteobacteria and, in particular, to the families of Rhodobacteraceae and Flavobacteriaceae at ambient nutrient levels and of Rhodobacteraceae and Bacteriovoracaceae at enhanced nutrient levels were more abundant in turf than canopy habitats. Our results show that primary surfaces from alternative habitats that form mosaics on shallow rocky reefs in oligotrophic areas host distinct microbial communities that are, to some extent, resistant to moderate nutrient enhancement. Understanding the role of EMBs in generating reinforcing feedback under different nutrient loading regimes appears crucial to advance our understanding of the mechanisms underpinning the stability of habitats alternative to macroalgal forests as well as their role in regulating reverse shifts.

Effect of Hydrogen Peroxide on Cyanobacterial Biofilms

Although a range of disinfecting formulations is commercially available, hydrogen peroxide is one of the safest chemical agents used for disinfection in aquatic environments. However, its effect on cyanobacterial biofilms is poorly investigated. In this work, biofilm formation by two filamentous cyanobacterial strains was evaluated over seven weeks on two surfaces commonly used in marine environments: glass and silicone-based paint (Sil-Ref) under controlled hydrodynamic conditions. After seven weeks, the biofilms were treated with a solution of hydrogen peroxide (H2O2) to assess if disinfection could affect long-term biofilm development. The cyanobacterial biofilms appeared to be tolerant to H2O2 treatment, and two weeks after treatment, the biofilms that developed on glass by one of the strains presented higher biomass amounts than the untreated biofilms. This result emphasizes the need to correctly evaluate the efficiency of disinfection in cyanobacterial biofilms, including assessing the possible consequences of inefficient disinfection on the regrowth of these biofilms.

Electric Potential Induced Prevention and Removal of an Algal Biofoulant from Planar SERS Substrates

Ulva zoospores are widespread marine macroalgae and a common organism found in biofouling communities due to their strong adhesive properties and quick settlement times. Using Ulva as a model organism, a strategy is presented where direct-current (DC) electric potentials are applied in conjunction with surface-enhanced Raman spectroscopy (SERS) to characterize, remove, and prevent Ulva from forming a biofilm on gold-capped nanopillar SERS substrates. Experiments were conducted within a poly(tetrafluoroethylene) (PTFE) flow channel device where the SERS substrates were used as an electrode. Ulva density, determined in situ by SERS and ex situ by electron and fluorescence microscopy, decreased under successively increasing low negative potentials up to -1.0 V. The presence of damaged Ulva suggests that the applied potential led to spore rupture. At the highest negative applied potential (-1.0 V), microparticles containing copper, which is known for its antimicrobial properties, were associated with Ulva on the SERS substrate and the lowest Ulva density was observed. These findings indicate that (1) SERS can be employed to study biofilm formation on nanostructured metal surfaces and (2) applying low-voltage electric potentials may be used to control Ulva biofouling on SERS marine sensors.

Biomimetic surfaces: Insights on the role of surface topography and wetting properties in bacterial attachment and biofilm formation

The study explores the impact of biomimetic surfaces on bacterial attachment and biofilm formation. Specifically, it investigates the effects of topographic scale and wetting behavior on the attachment and growth of Staphylococcus aureus and Escherichia coli on four different biomimetic surfaces: rose petals, Paragrass leaves, shark skin, and goose feathers. Using soft lithography, epoxy replicas with surface topographies similar to those of the natural surfaces were created. The static water contact angles of the replicas exceeded the hydrophobic threshold of 90°, while the hysteresis angles were found to be in the order of goose feathers, shark skin, Paragrass leaves, and rose petals. The results showed that bacterial attachment and biofilm formation were the lowest on rose petals and the highest on goose feathers, regardless of the bacterial strain. Additionally, the study revealed that surface topography had a significant impact on biofilm formation, with smaller feature sizes inhibiting biofilm formation. Hysteresis angle, rather than static water contact angle, was identified as a critical factor to consider when evaluating bacterial attachment behavior. These unique insights have the potential to lead to the development of more effective biomimetic surfaces for the prevention and eradication of biofilms, ultimately improving human health and safety.

Keep It Simple: Improving the Ex Situ Culture of Cystoseira s.l. to Restore Macroalgal Forests

Brown algae from genus Cystoseira s.l. form dense underwater forests that represent the most productive areas in the Mediterranean Sea. Due to the combined effects of global and local stressors such as climate change, urbanization, and herbivore outbreaks, there has been a severe decline in brown algal forests in the Mediterranean Sea. Natural recovery of depleted sites is unlikely due to the low dispersal capacity of these species, and efficient techniques to restore such habitats are needed. In this context, the aims of our study were (1) to improve and simplify the current ex situ laboratory protocol for the cultivation of Gongolaria barbata by testing the feasibility of some cost-effective and time-efficient techniques on two donor sites of G. barbata and (2) to evaluate the survival and growth of young thalli during the laboratory phase and during the most critical five months after out-planting. Specifically, the following ex situ cultivation methods were tested: (A) cultivation on clay tiles in mesocosms with culture water prepared by three different procedures (a) filtered seawater with a 0.22 μm filter membrane, (b) filtered seawater with a 0.7 μm filter membrane (GF), and (c) UV-sterilized water, and (B) cultivation on clay tiles in open laboratory systems. After two weeks, all thalli were fixed to plastic lantern net baskets suspended at a depth of 2 m in the coastal sea (hybrid method), and the algal success was monitored in relation to the different donor sites and cultivation protocol. The satisfactory results of this study indicate that UV-sterilized water is suitable for the cultivation of G. barbata in mesocosm, which significantly reduces the cost of the laboratory phase. This opens the possibility of numerous and frequent algal cultures during the reproductive period of the species. Additionally, if the young thalli remain in the lantern net baskets for an extended period of several months, they can grow significantly in the marine environment without being exposed to pressure from herbivorous fish.

Bacteria and microalgae associations in periphyton-mechanisms and biotechnological opportunities

Phototrophic and heterotrophic microorganisms coexist in complex and dynamic structures called periphyton. These structures shape the biogeochemistry and biodiversity of aquatic ecosystems. In particular, microalgae-bacteria interactions are a prominent focus of study by microbial ecologists and can provide biotechnological opportunities for numerous applications (i.e. microalgal bloom control, aquaculture, biorefinery, and wastewater bioremediation). In this review, we analyze the species dynamics (i.e. periphyton formation and factors determining the prevalence of one species over another), coexisting communities, exchange of resources, and communication mechanisms of periphytic microalgae and bacteria. We extend periphyton mathematical modelling as a tool to comprehend complex interactions. This review is expected to boost the applicability of microalgae-bacteria consortia, by drawing out knowledge from natural periphyton.

Variations in epilithic microbial biofilm composition and recruitment of a canopy-forming alga between pristine and urban rocky shores

Brown algae of the genus Ericaria are habitat formers on Mediterranean rocky shores supporting marine biodiversity and ecosystem functioning. Their population decline has prompted attempts for restoration of threatened populations. Although epilithic microbial biofilms (EMBs) are determinant for macroalgal settlement, their role in regulating the recovery of populations through the recruitment of new thalli is yet to be explored. In this study, we assessed variations in microbial biofilms composition on the settlement of Ericaria amentacea at sites exposed to different human pressures. Artificial fouling surfaces were deployed in two areas at each of three study sites in the Ligurian Sea (Capraia Island, Secche della Meloria and the mainland coast of Livorno), to allow bacterial biofilm colonization. In the laboratory, zygotes of E. amentacea were released on these surfaces to evaluate the survival of germlings. The EMB's composition was assessed through DNA metabarcoding analysis, which revealed a difference between the EMB of Capraia Island and that of Livorno. Fouling surfaces from Capraia Island had higher rates of zygote settlement than the other two sites. This suggests that different environmental conditions can influence the EMB composition on substrata, possibly influencing algal settlement rate. Assessing the suitability of rocky substrata for E. amentacea settlement is crucial for successful restoration.

Biofouling potential of surface-enhanced Raman scattering-based seawater quality sensors by Ulva spp

This study investigated the biofouling potential of surface-enhanced Raman scattering (SERS)-based sensor materials in the context of marine environments. Uncoated and monolithic commercial gold (Au) silicon nanopillar array SERS substrates, Au-coated carbon black nanoparticle (AuCB NP) substrates, uncoated and Au sputter-coated in-house SERS, and uncoated and Au sputter-coated glass controls were tested for biofouling potential using Ulva spp. as model biofouling organisms. The mean percentages of Ulva spp. zoospores that adhered per mm2 (×103) on the uncoated and coated Au silicon nanopillar array, AuCB NP, uncoated and Au sputter-coated in-house, and uncoated and Au sputter-coated glass substrates were 10.28%, 5.45%, 10.49%, 3.25%, 24.84%, 12.86% and 7.78%, respectively. Results indicated that surface properties such as hydrophobicity, roughness, Au sputter-coating and the presence of micro-refuges on nano- and microstructured substrates were critical to the biofouling formation.

A versatile “3M” methodology to obtain superhydrophobic PDMS-based materials for antifouling applications

Fouling, including inorganic, organic, bio-, and composite fouling seriously affects our daily life. To reduce these effects, antifouling strategies including fouling resistance, release, and degrading, have been proposed. Superhydrophobicity, the most widely used characteristic for antifouling that relies on surface wettability, can provide surfaces with antifouling abilities owing to its fouling resistance and/or release effects. PDMS shows valuable and wide applications in many fields, and due to the inherent hydrophobicity, superhydrophobicity can be achieved simply by roughening the surface of pure PDMS or its composites. In this review, we propose a versatile “3M” methodology (materials, methods, and morphologies) to guide the fabrication of superhydrophobic PDMS-based materials for antifouling applications. Regarding materials, pure PDMS, PDMS with nanoparticles, and PDMS with other materials were introduced. The available methods are discussed based on the different materials. Materials based on PDMS with nanoparticles (zero-, one-, two-, and three-dimensional nanoparticles) are discussed systematically as typical examples with different morphologies. Carefully selected materials, methods, and morphologies were reviewed in this paper, which is expected to be a helpful reference for future research on superhydrophobic PDMS-based materials for antifouling applications.

Impairment of a cyanobacterial glycosyltransferase that modifies a pilin results in biofilm development

A biofilm inhibiting mechanism operates in the cyanobacterium Synechococcus elongatus. Here, we demonstrate that the glycosyltransferase homologue, Ogt, participates in the inhibitory process - inactivation of ogt results in robust biofilm formation. Furthermore, a mutational approach shows requirement of the glycosyltransferase activity for biofilm inhibition. This enzyme is necessary for glycosylation of the pilus subunit and for adequate pilus formation. In contrast to wild-type culture in which most cells exhibit several pili, only 25% of the mutant cells are piliated, half of which possess a single pilus. In spite of this poor piliation, natural DNA competence was similar to that of wild-type; therefore, we propose that the unglycosylated pili facilitate DNA transformation. Additionally, conditioned medium from wild-type culture, which contains a biofilm inhibiting substance(s), only partially blocks biofilm development by the ogt-mutant. Thus, we suggest that inactivation of ogt affects multiple processes including production or secretion of the inhibitor as well as the ability to sense or respond to it.

A metallic anti-biofouling surface with a hierarchical topography containing nanostructures on curved micro-riblets

Metallic surface finishes have been used in the anti-biofouling, but it is very difficult to produce surfaces with hierarchically ordered structures. In the present study, anti-biofouling metallic surfaces with nanostructures superimposed on curved micro-riblets were produced via top-down fabrication. According to the attachment theory, these surfaces feature few attachment points for organisms, the nanostructures prevent the attachment of bacteria and algal zoospores, while the micro-riblets prohibit the settlement of macrofoulers. Anodic oxidation was performed to induce superhydrophilicity. It forms a hydration layer on the surface, which physically blocks foulant adsorption along with the anti-biofouling topography. We characterized the surfaces via scanning electron and atomic force microscopy, contact-angle measurement, and wear-resistance testing. The contact angle of the hierarchical structures was less than 1°. Laboratory settlement assays verified that bacterial attachment was dramatically reduced by the nanostructures and/or the hydration layer, attributable to superhydrophilicity. The micro-riblets prohibited the settlement of macrofoulers. Over 77 days of static immersion in the sea during summer, the metallic surface showed significantly less biofouling compared to a surface painted with an anticorrosive coating.

Anti-Biofouling Polymers with Special Surface Wettability for Biomedical Applications

The use of anti-biofouling polymers has widespread potential for counteracting marine, medical, and industrial biofouling. The anti-biofouling action is usually related to the degree of surface wettability. This review is focusing on anti-biofouling polymers with special surface wettability, and it will provide a new perspective to promote the development of anti-biofouling polymers for biomedical applications. Firstly, current anti-biofouling strategies are discussed followed by a comprehensive review of anti-biofouling polymers with specific types of surface wettability, including superhydrophilicity, hydrophilicity, and hydrophobicity. We then summarize the applications of anti-biofouling polymers with specific surface wettability in typical biomedical fields both in vivo and in vitro, such as cardiology, ophthalmology, and nephrology. Finally, the challenges and directions of the development of anti-biofouling polymers with special surface wettability are discussed. It is helpful for future researchers to choose suitable anti-biofouling polymers with special surface wettability for specific biomedical applications.

Enzymatic Functionalization of Wood as an Antifouling Strategy against the Marine Bacterium Cobetia marina

The protection of wood in marine environments is a major challenge due to the high sensitivity of wood to both water and marine microorganisms. Besides, the environmental regulations are pushing the industry to develop novel effective and environmentally friendly treatments to protect wood in marine environments. The present study focused on the development of a new green methodology based on the laccase-assisted grafting of lauryl gallate (LG) onto wood to improve its marine antifouling properties. Initially, the enzymatic treatment conditions (laccase dose, time of reaction, LG concentration) and the effect of the wood specie (beech, pine, and eucalyptus) were assessed by water contact angle (WCA) measurements. The surface properties of the enzymatically modified wood veneers were assessed by X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FTIR). Antifouling properties of the functionalized wood veneers against marine bacterium Cobetia marina were studied by scanning electron microscopy (SEM) and protein measurements. XPS and FTIR analysis suggested the stable grafting of LG onto the surface of wood veneers after laccase-assisted treatment. WCA measurements showed that the hydrophobicity of the wood veneers significantly increased after the enzymatic treatment. Protein measurements and SEM pictures showed that enzymatically-hydrophobized wood veneers modified the pattern of bacterial attachment and remarkably reduced the bacterium colonization. Thus, the results observed in the present study confirmed the potential efficiency of laccase-assisted treatments to improve the marine antifouling properties of wood.

Dynamics of marine bacterial biofouling communities after initial Alteromonas genovensis biofilm attachment to anti-fouling paint substrates

To determine how bacterial communities succeed after the initial attachment of the bacterial biofilm adhesion using 16S rDNA meta-barcoding in plates coated with copper-based anti-fouling (AF) and non-AF (control) coatings as well as ambient seawater, coated plates were submerged in a marine environment in situ. Alteromonas genovensis (Gammaproteobacteria) in AF coating and Pacificibacter sp. (Alphaproteobacteria) in the control plate were initially abundant. In the AF coating, the abundance of A. genovensis decreased rapidly, whereas that of genus Phaeobacter (Alphaproteobacteria), Serratia (Gammaproteobacteria) and Cupriavidus (Betaproteobacteria) increased. Bacterial community in the control plate had a strong connection to pathogenic Vibrio spp. associated with the growth of invertebrates. Therefore, in the in situ AF coating experiment, A. genovensis accumulation was initially and intensively increased, and the bacteria responded to chemical antagonism, induced the proliferation of specific biofilm bacteria and influenced the interactions and recruitment of additional bacterial communities.

Quantitative proteomic analysis of marine biofilms formed by filamentous cyanobacterium

Cyanobacterial molecular biology can identify pathways that affect the adhesion and settlement of biofouling organisms and, consequently, obtain novel antifouling strategies for marine applications. Proteomic analyses can provide an essential understanding of how cyanobacteria adapt to different environmental settings. However, only a few qualitative studies have been performed in some cyanobacterial strains. Considering the limited knowledge about protein expression in cyanobacteria in different growing conditions, a quantitative proteomic analysis by LC-MS/MS of biofilm cells from a filamentous strain was performed. Biofilms were also analysed through standard methodologies for following cyanobacterial biofilm development. Biofilms were formed on glass and perspex at two relevant hydrodynamic conditions for marine environments (average shear rates of 4 s^-1 and 40 s^-1). Biofilm development was higher at 4 s^-1 and no significant differences were found between surfaces. Proteomic analysis identified 546 proteins and 41 were differentially expressed. Differences in protein expression were more noticeable between biofilms formed on glass and perspex at 4 s^-1. When comparing biofilms formed on different surfaces, results suggest that biofilm development may be related to the expression of several proteins like a beta-propeller domain-containing protein, chaperone DnaK, SLH domain-containing proteins, an OMF family outer membrane protein, and/or additional uncharacterized proteins. Regarding the hydrodynamic effect, biofilm development can be related to SOD enzyme expression, to proteins related to photosynthetic processes and to a set of uncharacterized proteins with calcium binding domains, disordered proteins, and others involved in electron transfer activity. Studies that combine distinct approaches are essential for finding new targets for antibiofilm agents. The characterisation performed in this work provides new insights into how shear rate and surface affect cyanobacterial biofilm development and how cyanobacteria adapt to these different environmental settings from a macroscopic standpoint to a proteomics context.

Engineered topographies and hydrodynamics in relation to biofouling control-a review

Biofouling, the unwanted growth of microorganisms on submerged surfaces, has appeared as a significant impediment for underwater structures, water vessels, and medical devices. For fixing the biofouling issue, modification of the submerged surface is being experimented as a non-toxic approach worldwide. This technique necessitated altering the surface topography and roughness and developing a surface with a nano- to micro-structured pattern. The main objective of this study is to review the recent advancements in surface modification and hydrodynamic analysis concerning biofouling control. This study described the occurrence of the biofouling process, techniques suitable for biofouling control, and current state of research advancements comprehensively. Different biofilms under various hydrodynamic conditions have also been outlined in this study. Scenarios of biomimetic surfaces and underwater super-hydrophobicity, locomotion of microorganisms, nano- and micro-hydrodynamics on various surfaces around microorganisms, and material stiffness were explained thoroughly. The review also documented the approaches to inhibit the initial settlement of microorganisms and prolong the subsequent biofilm formation process for patterned surfaces. Though it is well documented that biofouling can be controlled to various degrees with different nano- and micro-structured patterned surfaces, the understanding of the underlying mechanism is still imprecise. Therefore, this review strived to present the possibilities of implementing the patterned surfaces as a physical deterrent against the settlement of fouling organisms and developing an active microfluidic environment to inhibit the initial bacterial settlement process. In general, microtopography equivalent to that of bacterial cells influences attachment via hydrodynamics, topography-induced cell placement, and air-entrapment, whereas nanotopography influences physicochemical forces through macromolecular conditioning.

Environmental factors shape the epiphytic bacterial communities of Gracilariopsis lemaneiformis

Macroalgae host various symbionts on their surface, which play a critical role in their growth and development processes. However, there is still incomplete understanding of this epiphytic bacteria-host algae interactions. This study comprehensively analysed variation of the epiphytic bacterial communities (EBC) composition of red macroalga Gracilariopsis lemaneiformis at different geographic locations and environmental factors (i.e., nitrogen and phosphorus), which shape the EBC composition of G. lemaneiformis. The composition and structure of EBC were characterized using high throughput sequencing of the V3-V4 hypervariable region of the 16S rRNA gene. The results revealed that epiphytic bacteria varied significantly among three different geographic locations in China, i.e., Nan'ao Island (NA), Lianjiang County (LJ), and Nanri Island (NR). Redundancy analysis (RDA) showed that the relative abundance of Bacteroidetes, Firmicutes, Verrucomicrobia, and Epsilonbacteraeota at NR were strongly positively correlated with total nitrogen (TN), total phosphorus (TP), nitrate nitrogen (NO₃-N), and dissolved inorganic nitrogen (DIN), but negatively correlated with nitrite nitrogen (NO₂-N). The relative abundance of Cyanobacteria at NA and LJ were strongly positively correlated with NO₂-N, but negatively correlated with TN, TP, NO₃-N, and DIN. Besides, the Mantel test results indicated that the EBC composition was significantly correlated with these environmental factors, which was also confirmed by Spearman correlation analysis. Thus, environmental factors such as NO₃-N and DIN play a key role in the community composition of epiphytic bacteria on G. lemaneiformis. This study provides important baseline knowledge on the community composition of epiphytic bacteria on G. lemaneiformis and shows correlation between different epiphytic bacteria and their surrounding environmental factors.

Influence of the Intrinsic Characteristics of Cementitious Materials on Biofouling in the Marine Environment

Coastal marine ecosystems provide essential benefits and services to humanity, but many are rapidly degrading. Human activities are leading to significant land take along coastlines and to major changes in ecosystems. Ecological engineering tools capable of promoting large-scale restoration of coastal ecosystems are needed today in the face of intensifying climatic stress and human activities. Concrete is one of the materials most commonly used in the construction of coastal and marine infrastructure. Immersed in seawater, concretes are rapidly colonized by microorganisms and macroorganisms. Surface colonization and subsequent biofilm and biofouling formation provide numerous advantages to these organisms and support critical ecological and biogeochemical functions in the changing marine environment. The new challenge of the 21st century is to develop innovative concretes that, in addition to their usual properties, provide improved bioreceptivity in order to enhance marine biodiversity. The aim of this study is to master and clarify the intrinsic parameters that influence the bioreceptivity (biocolonization) of cementitious materials in the marine environment. By coupling biofilm (culture-based methods) and biofouling (image-analysis-based method and wet-/dry-weight biomass measurement) quantification techniques, this study showed that the application of a curing compound to the concrete surface reduced the biocolonization of cementitious materials in seawater, whereas green formwork oil had the opposite effect. This study also found that certain surface conditions (faceted and patterned surface, rough surface) promote the bacterial and macroorganism colonization of cementitious materials. Among the parameters examined, surface roughness proved to be the factor that promotes biocolonization most effectively. These results could be taken up in future recommendations to enable engineers to eco-design more eco-friendly marine infrastructure and develop green-engineering projects.

Substrate properties as controlling parameters in attached algal cultivation

There is growing interest in attached algae cultivation systems because they could provide a more cost- and energy-efficient alternative to planktonic (suspended algae) cultivation systems for many applications. However, attached growth systems have been far less studied than planktonic systems and have largely emphasized algae strains of most interest for biofuels. New algal biorefinery pathways have assessed the commercial potentials of algal biomass beyond biofuel production and placed more emphasis on value-added products from that biomass. Therefore, algal strain selection criteria and biomass cultivation methods need to be updated to include additional strains for improved efficiency. One possible way of improving attached cultivation systems is through engineering substrate surface characteristics to boost algal adhesion and enable strain selective algal colonization and growth. This review explores the effect of substrate chemical and topographical characteristics on the cultivation of attached algae. It also highlights the importance of considering algal community structure and attachment mechanisms in investigating attached algae systems using the example of filamentous algae found in algal turf scrubber (ATS™) systems. KEY POINTS : • Attached algal cultivation is a promising alternative to planktonic cultivation. • Performance increase results from tuning surface qualities of attachment substrates. • Attachment adaptation of periphytic algae has innate potential for cultivation.

Ecological and Industrial Implications of Dynamic Seaweed-Associated Microbiota Interactions

Seaweeds are broadly distributed and represent an important source of secondary metabolites (e.g., halogenated compounds, polyphenols) eliciting various pharmacological activities and playing a relevant ecological role in the anti-epibiosis. Importantly, host (as known as basibiont such as algae)–microbe (as known as epibiont such as bacteria) interaction (as known as halobiont) is a driving force for coevolution in the marine environment. Nevertheless, halobionts may be fundamental (harmless) or detrimental (harmful) to the functioning of the host. In addition to biotic factors, abiotic factors (e.g., pH, salinity, temperature, nutrients) regulate halobionts. Spatiotemporal and functional exploration of such dynamic interactions appear crucial. Indeed, environmental stress in a constantly changing ocean may disturb complex mutualistic relations, through mechanisms involving host chemical defense strategies (e.g., secretion of secondary metabolites and antifouling chemicals by quorum sensing). It is worth mentioning that many of bioactive compounds, such as terpenoids, previously attributed to macroalgae are in fact produced or metabolized by their associated microorganisms (e.g., bacteria, fungi, viruses, parasites). Eventually, recent metagenomics analyses suggest that microbes may have acquired seaweed associated genes because of increased seaweed in diets. This article retrospectively reviews pertinent studies on the spatiotemporal and functional seaweed-associated microbiota interactions which can lead to the production of bioactive compounds with high antifouling, theranostic, and biotechnological potential.

Characterization of planktonic and biofilm cells from two filamentous cyanobacteria using a shotgun proteomic approach

Cyanobacteria promote marine biofouling with significant impacts. A qualitative proteomic analysis, by LC-MS/MS, of planktonic and biofilm cells from two cyanobacteria was performed. Biofilms were formed on glass and perspex at two relevant hydrodynamic conditions for marine environments (average shear rates of 4 s^-1 and 40 s^-1). For both strains and surfaces, biofilm development was higher at 4 s^-1. Biofilm development of Nodosilinea sp. LEGE 06145 was substantially higher than Nodosilinea sp. LEGE 06119, but no significant differences were found between surfaces. Overall, 377 and 301 different proteins were identified for Nodosilinea sp. LEGE 06145 and Nodosilinea sp. LEGE 06119. Differences in protein composition were more noticeable in biofilms formed under different hydrodynamic conditions than in those formed on different surfaces. Ribosomal and photosynthetic proteins were identified in most conditions. The characterization performed gives new insights into how shear rate and surface affect the planktonic to biofilm transition, from a structural and proteomics perspective.

Method for the mass production of seedlings of the tropical brown seaweed Sargassum (Phaeophyceae, Ochrophyta)

Farming of Sargassum to produce harvestable crop can be a challenging task to seaweed farmers.•

Sexually-produced Sargassum seedlings can be propagated in a hatchery using 140-liter plastic tanks connected with PVC pipes and seawater supply directly pumped from the sea, passing through a filter system.

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First step of this method is to collect large amount of fertilized eggs from special branches called receptacles, found at the ends of lateral branches of Sargassum, excised from fertile thalli during its spawning season and collecting their eggs for recruitment into artificial substrate tanks.

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Egg collection involves force-releasing the fertilized eggs by vigorous shaking of a small vessel where 100-200 egg-bearing receptacles excised from fertile plants are contained. Each tank can produce up to 2000–3000 seedlings that can supply at least a hectare of farm. Scaling up the production to several hectares of farm is done by simply increasing the number of recruitment tanks and the number of recruitment panels in the hatchery system.

Love at First Taste: Induction of Larval Settlement by Marine Microbes

Marine biofilms are composed of many species of bacteria, unicellular algae, and protozoa. Biofilms can induce, inhibit, or have no effect on settlement of larvae and spores of algae. In this review, we focus on induction of larval settlement by marine bacteria and unicellular eukaryotes and review publications from 2010 to September 2019. This review provides insights from meta-analysis on what is known about the effect of marine biofilms on larval settlement. Of great interest is the impact of different components of marine biofilms, such as bacteria and diatoms, extracellular polymeric substances, quorum sensing signals, unique inductive compounds, exoenzymes, and structural protein degradation products on larval settlement and metamorphosis. Molecular aspects of larval settlement and impact of climate change are reviewed and, finally, potential areas of future investigations are provided.

Development of Marine Antifouling Epoxy Coating Enhanced with Clay Nanotubes

An antifouling epoxy resin doped with natural clay nanotubes that are loaded with biocide or silver allowed extended protection against the proliferation of marine microorganisms. Compared to the 2–3 months of protection with antifoulant dichlorooctylisothiazolone (DCOIT) directly admixed into epoxy resin, the DCOIT release time of the halloysite formulations was extended to 12 months by incorporating biocide-loaded nanoclay in the polymer matrix. The protective properties of the epoxy-halloysite nanocomposites showed much less adhesion and proliferation of marine bacteria Vibrio natriegens on the resin surface after a two-month exposure to seawater than the coating formulations directly doped with non-encapsulated DCOIT. The coating formulation protection efficiency was further confirmed by twelve-month shallow field tests in the South China Sea. Replacing 2 wt.% biocide in the traditional formula with DCOIT-loaded natural environmentally friendly halloysite clay drastically improved the antifouling properties of the epoxy coating, promising scalable applications in protective marine coating. The antifouling property of epoxy resin was enhanced with silver particles synthesized on halloysite nanotubes. A natural mixture of MnO particles and halloysite could also be used as a nonbiocide additive to marine coating. The short-term White Sea water test of epoxy coating with 5% of Ag-halloysite composite of MnO-halloysite natural mixture showed no visible fouling.

Marine biofilms: diversity of communities and of chemical cues

Surfaces immersed in seawater are rapidly colonized by various microorganisms, resulting in the formation of heterogenic marine biofilms. These communities are known to influence the settlement of algae spores and invertebrate larvae, triggering a succession of fouling events, with significant environmental and economic impacts. This review covers recent research regarding the differences in composition of biofilms isolated from different artificial surface types and the influence of environmental factors on their formation. One particular phenomenon - bacterial quorum sensing (QS) - allows bacteria to coordinate swarming, biofilm formation among other phenomena. Some other marine biofilm chemical cues are believed to modulate the settlement and the succession of macrofouling organisms, and they are also reviewed here. Finally, since the formation of a marine biofilm is considered to be an initial, QS-dependent step in the development of marine fouling events, QS inhibition is discussed on its potential as a tool for antibiofouling control in marine settings.

Short-term succession of marine microbial fouling communities and the identification of primary and secondary colonizers

Microbial succession during the initial stages of marine biofouling has been rarely studied, especially in the Arabian Gulf. This study was undertaken to follow temporal shifts in biofouling communities in order to identify primary and secondary colonizers. Quantitative analysis revealed a significant increase in total biomass, coverage of macrofoulers, chlorophyll a concentrations, and bacterial counts with time. The relative abundance of the adnate diatoms increased with time, whereas it decreased in the case of the plocon diatoms. Non-metric multidimensional scaling (NMDS) ordination based on MiSeq data placed the bacterial communities in three distinct clusters, depending on the time of sampling. While the relative abundance of Alphaproteobacteria and Flavobacteriia decreased with time, suggesting their role as primary colonizers, the relative abundance of Actinobacteria and Planctomycetia increased with time, suggesting their role as secondary colonizers. Biofouling is a dynamic process that involves temporal quantitative and qualitative shifts in the micro- and macrofouling communities.

Towards eco-friendly biocides: preparation, antibiofilm activity of hemibastadin analogues

The antibiofilm activity of three hemibastadins analogues was evaluated against different marine bacterial strains through mono-species biofilms and through a multi-species model of biofilm. Results showed that compound 3 exhibited interesting antibiofilm efficiencies effective concentrations (EC₅₀ ) in the range of 30-100 μmol l^-1 without acute toxicity against bacteria. Toxicity against nontargeted organisms was also considered showing that the compound did not affect the global bacterial community at a concentration of 75-100 μmol l^-1 . These results provided baseline data concerning the toxicity of antibiofilm biocides against marine organisms. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reports relevant information about antibiofilm activity of original derivatives of hemibastadin alkaloids. The most active compound was shown to act as a specific anti-biofilm inhibitor without affecting viability of the targeted bacteria no more than those of the global bacterial community of a seawater sample. Taken together, these findings indicate the potentiality of such compounds to be used as original nonbiocidal molecules for designing eco-friendly antifouling solutions.

Microalgal biofilms: A further step over current microalgal cultivation techniques

The scientific community has turned its interest to microalgae lately, because of their countless applications such as wastewater treatment and pharmaceutical industry. Nevertheless, so far applied cultivation methods are still prohibitive. Ordinary cultivation techniques in which microalgae are suspended in liquid medium suffer from many bottlenecks, such as low biomass productivities, difficulty in biomass harvesting and recovery, high installation and operating cost, high water requirements etc. Although, microalgal biofilms are known to be a nuisance because of surfaces fouling, they have emerged as an innovative technology with which microalgae are developed attached to a solid surface. This technique seems to be advantageous as compared to conventional cultivation systems. Microalgal biofilm systems could resolve the problematic aspects of ordinary cultivation techniques such as low biomass productivities, water management and biomass recovery. A detailed description of this technique with respect to the parameters affecting them is reviewed in this work.

A Multi-Bioassay Integrated Approach to Assess the Antifouling Potential of the Cyanobacterial Metabolites Portoamides

The cyclic peptides portoamides produced by the cyanobacterium Phormidium sp. LEGE 05292 were previously isolated and their ability to condition microcommunities by allelopathic effect was described. These interesting bioactive properties are, however, still underexplored as their biotechnological applications may be vast. This study aims to investigate the antifouling potential of portoamides, given that a challenge in the search for new environmentally friendly antifouling products is to find non-toxic natural alternatives with the ability to prevent colonization of different biofouling species, from bacteria to macroinvertebrates. A multi-bioassay approach was applied to assess portoamides antifouling properties, marine ecotoxicity and molecular mode of action. Results showed high effectiveness in the prevention of mussel larvae settlement (EC50 = 3.16 µM), and also bioactivity towards growth and biofilm disruption of marine biofouling bacterial strains, while not showing toxicity towards both target and non-target species. Antifouling molecular targets in mussel larvae include energy metabolism modifications (failure in proton-transporting ATPases activity), structural alterations of the gills and protein and gene regulatory mechanisms. Overall, portoamides reveal a broad-spectrum bioactivity towards diverse biofouling species, including a non-toxic and reversible effect towards mussel larvae, showing potential to be incorporated as an active ingredient in antifouling coatings.

A multi-step approach for testing non-toxic amphiphilic antifouling coatings against marine microfouling at different levels of biological complexity

Marine biofouling on artificial surfaces such as ship hulls or fish farming nets causes enormous economic damage. The time for the developmental process of antifouling coatings can be shortened by reliable laboratory assays. For designing such test systems, it is important that toxic effects can be excluded, that multiple parameters can be addressed simultaneously and that mechanistic aspects can be included. In this study, a multi-step approach for testing antifouling coatings was established employing photoautotrophic biofilm formation of marine microorganisms in micro- and mesoscoms. Degree and pattern of biofilm formation was determined by quantification of chlorophyll fluorescence. For the microcosms, co-cultures of diatoms and a heterotrophic bacterium were exposed to fouling-release coatings. For the mesocosms, a novel device was developed that permits parallel quantification of a multitude of coatings under defined conditions with varying degrees of shear stress. Additionally, the antifouling coatings were tested for leaching of potential compounds and finally tested in sea trials. This multistep-approach revealed that the individual steps led to consistent results regarding antifouling activity of the coatings. Furthermore, the novel mesocosm system can be employed for advanced antifouling analysis including metagenomic approaches for determination of microbial diversity attaching to different coatings under changing shear forces.

Biofilm community structure and the associated drag penalties of a groomed fouling release ship hull coating

Grooming is a proactive method to keep a ship's hull free of fouling. This approach uses a frequent and gentle wiping of the hull surface to prevent the recruitment of fouling organisms. A study was designed to compare the community composition and the drag associated with biofilms formed on a groomed and ungroomed fouling release coating. The groomed biofilms were dominated by members of the Gammaproteobacteria and Alphaproteobacteria as well the diatoms Navicula, Gomphonemopsis, Cocconeis, and Amphora. Ungroomed biofilms were characterized by Phyllobacteriaceae, Xenococcaceae, Rhodobacteraceae, and the pennate diatoms Cyclophora, Cocconeis, and Amphora. The drag forces associated with a groomed biofilm (0.75 ± 0.09 N) were significantly less than the ungroomed biofilm (1.09 ± 0.06 N). Knowledge gained from this study has helped the design of additional testing which will improve grooming tool design, minimizing the growth of biofilms and thus lowering the frictional drag forces associated with groomed surfaces.

Iodine-infused aeration for hull fouling prevention: a vessel-scale study

Biofouling is a significant economic and ecological problem, causing reduced vessel performance and increases in fuel consumption and emissions. Previous research has shown iodine vapor (I₂)-infused aeration to be an environmentally friendly method for deterring the settlement of fouling organisms. An aeration system was deployed on a vessel with hull sections coated with two types of antifoulant coatings, Intersleek^® 1100 (fouling-release) and Interspeed^® BRA-640 (ablative copper biocide), as well as an inert epoxy barrier coating, to assess the effectiveness of aeration in conjunction with common marine coatings. I₂-infused aeration resulted in consistent reductions of 80-90% in hard fouling across all three coatings. Additionally, aeration reduced the soft fouling rate by 45-70% when used in conjunction with both Intersleek^® and Interspeed^® BRA versus those coatings alone. The results of this study highlight the contribution of I₂-infused aeration as a standalone mechanism for fouling prevention or as a complement to traditional antifouling coatings.

Biofilm based attached cultivation technology for microalgal biorefineries-A review

The attached cultivation for microalga has many superiorities over the conventional aqua-suspend methods, which make it a promising pathway to supply feedstock for microalgae based bio-refinery attempts. In this review, the current reports on bioreactor, application, modeling, substratum material and engineering aspects were summarized and the future research and developments should be focused on the following aspects: 1) Build principles and guidelines for rational structure design by studying the relationship of physiological properties with typical structures and light regimes; 2) Set up theory foundation of substratum material selection by studying the physic-chemical properties of algal cells and substratum materials; 3) Further understanding the mass transfer behaviors of both CO₂ and nutrients in biofilm for enhanced growth rate and products accumulation; 4) New equipment and machines for inoculation, harvesting and moisture keeping should be developed and integrated with bioreactor structure.

Co, Zn and Ag-MOFs evaluation as biocidal materials towards photosynthetic organisms

In the present study, the biocidal activity of three different metal organic frameworks (MOFs) based on Co (Co-SIM1), Zn (Zn-SIM1) and Ag (Ag-TAZ) has been evaluated towards one green alga and two cyanobacteria. These organisms are present in fresh- and seawater and take part in the early stages of the biofouling process. The biocidal activity of these materials was evaluated by measuring chlorophyll a concentration and by inhibition zone testing. After 24h of exposure the three different MOFs caused >50% of chlorophyll a concentration inhibition towards both cyanobacteria, however, although the green alga presented a great sensitivity for Ag-TAZ (reaching 90% of chlorophyll a concentration inhibition), it was much more resistant to the rest of MOFs. Bioavailability of these metals was studied using ICP-MS, the chemical speciation program Visual MINTEQ, and a heavy metal bioreporter bioanalytical tool. We have elucidated that the biocidal activity presented by these MOFs was due to the dissolved metals released from them and more exactly, it depended on the bioavailability presented by these metal ions, which was closely related with the free ion concentration. This article highlights the potential use of different MOFs as biocidal material towards photosynthetic organisms and reveals important differences in the sensitivity between these organisms that should be taken into account in order to increase the biocidal spectrum of these materials.

What determines sclerobiont colonization on marine mollusk shells?

Empty mollusk shells may act as colonization surfaces for sclerobionts depending on the physical, chemical, and biological attributes of the shells. However, the main factors that can affect the establishment of an organism on hard substrates and the colonization patterns on modern and time-averaged shells remain unclear. Using experimental and field approaches, we compared sclerobiont (i.e., bacteria and invertebrate) colonization patterns on the exposed shells (internal and external sides) of three bivalve species (Anadara brasiliana, Mactra isabelleana, and Amarilladesma mactroides) with different external shell textures. In addition, we evaluated the influence of the host characteristics (mode of life, body size, color alteration, external and internal ornamentation and mineralogy) of sclerobionts on dead mollusk shells (bivalve and gastropod) collected from the Southern Brazilian coast. Finally, we compared field observations with experiments to evaluate how the biological signs of the present-day invertebrate settlements are preserved in molluscan death assemblages (incipient fossil record) in a subtropical shallow coastal setting. The results enhance our understanding of sclerobiont colonization over modern and paleoecology perspectives. The data suggest that sclerobiont settlement is enhanced by (i) high(er) biofilm bacteria density, which is more attracted to surfaces with high ornamentation; (ii) heterogeneous internal and external shell surface; (iii) shallow infaunal or attached epifaunal life modes; (iv) colorful or post-mortem oxidized shell surfaces; (v) shell size (<50 mm² or >1,351 mm²); and (vi) calcitic mineralogy. Although the biofilm bacteria density, shell size, and texture are considered the most important factors, the effects of other covarying attributes should also be considered. We observed a similar pattern of sclerobiont colonization frequency over modern and paleoecology perspectives, with an increase of invertebrates occurring on textured bivalve shells. This study demonstrates how bacterial biofilms may influence sclerobiont colonization on biological hosts (mollusks), and shows how ecological relationships in marine organisms may be relevant for interpreting the fossil record of sclerobionts.

Pyomelanin from Pseudoalteromonas lipolytica reduces biofouling

Members of the marine bacterial genus Pseudoalteromonas are efficient producers of antifouling agents that exert inhibitory effects on the settlement of invertebrate larvae. The production of pigmented secondary metabolites by Pseudoalteromonas has been suggested to play a role in surface colonization. However, the physiological characteristics of the pigments produced by Pseudoalteromonas remain largely unknown. In this study, we identified and characterized a genetic variant that hyperproduces a dark‐brown pigment and was generated during Pseudoalteromonas lipolytica biofilm formation. Through whole‐genome resequencing combined with targeted gene deletion and complementation, we found that a point mutation within the hmgA gene, which encodes homogentisate 1,2‐dioxygenase, is solely responsible for the overproduction of the dark‐brown pigment pyomelanin. In P. lipolytica, inactivation of the hmgA gene led to the formation of extracellular pyomelanin and greatly reduced larval settlement and metamorphosis of the mussel Mytilus coruscus. Additionally, the extracted pyomelanin from the hmgA deletion mutant and the in vitro‐synthesized pyomelanin also reduced larval settlement and metamorphosis of M. coruscus, suggesting that extracellular pyomelanin released from marine Pseudoalteromonas biofilm can inhibit the settlement of fouling organisms.

Diatom communities on commercial biocidal fouling control coatings after one year of immersion in the marine environment

Little is known about the effect of commercial biocidal fouling control coatings on fouling diatom communities and their growth forms after long periods of exposure in the marine tropical environment. The current study investigated the abundance and composition of fouling diatom communities developed on 11 commercially available biocidal antifouling coatings, covering the three main technology types in recent historic use (Self-Polishing Copolymers, Self-Polishing Hybrid and Controlled Depletion Polymers) after one year of static immersion at two locations in Muscat, Oman (Marina Shangri La and Marina Bandar Rowdha). Light microscopy demonstrated that the total abundance of diatoms and the relative abundance of growth forms were significantly affected by the choice of biocidal antifouling coating and experimental location. Using scanning electron microscopy, a total of 21 diatom genera were identified which were grouped into adnate, motile, plocon and erect growth forms. The adnate growth forms, mainly the genera Amphora, Cocconeis and Mastogloia, dominated the other growth forms in terms of their relative abundance. Current results revealed the importance of exposure location and choice of biocidal antifouling coating on the relative abundance of diatom growth forms.

Eelgrass Leaf Surface Microbiomes Are Locally Variable and Highly Correlated with Epibiotic Eukaryotes

Eelgrass (Zostera marina) is a marine foundation species essential for coastal ecosystem services around the northern hemisphere. Like all macroscopic organisms, it possesses a microbiome (here defined as an associated prokaryotic community) which may play critical roles in modulating the interaction of eelgrass with its environment. For example, its leaf surface microbiome could inhibit or attract eukaryotic epibionts which may overgrow the eelgrass leading to reduced primary productivity and subsequent eelgrass meadow decline. We used amplicon sequencing of the 16S and 18S rRNA genes of prokaryotes and eukaryotes to assess the leaf surface microbiome (prokaryotes) as well as eukaryotic epibionts in- and outside lagoons on the German Baltic Sea coast. Prokaryote microbiomes varied substantially both between sites inside lagoons and between open coastal and lagoon sites. Water depth, leaf area and biofilm chlorophyll a concentration explained a large amount of variation in both prokaryotic and eukaryotic community composition. The prokaryotic microbiome and eukaryotic epibiont communities were highly correlated, and network analysis revealed disproportionate co-occurrence between a limited number of eukaryotic taxa and several bacterial taxa. This suggests that eelgrass leaf surfaces are home to a mosaic of microbiomes of several epibiotic eukaryotes, in addition to the microbiome of the eelgrass itself. Our findings thereby underline that eukaryotic diversity should be taken into account in order to explain prokaryotic microbiome assembly and dynamics in aquatic environments.

Influence of hydrodynamic stress on the frictional drag of biofouling communities

The role of hydrodynamic wall shear stresses on the development of the fouling community structure and resulting frictional drag were examined using a commercially available fouling release coating. Immersed test panels were exposed to three different hydrodynamic treatments, one static and two dynamic (corresponding to an estimated wall shear stress of 7.0  and 25.5 Pa). The drag of the panels was measured in a hydrodynamic test chamber at discrete time intervals over 35 days. The fouling community composition on the static panels was significantly different from the organisms observed on the dynamic panels. Despite different fouling community composition, the drag forces measured on the panels were very similar. This suggests that the frictional drag of low form and soft fouling communities are similar and that there may be a stepwise increase in frictional drag associated with the presence of mature calcareous organisms.

The effects of substratum material and surface orientation on the developing epibenthic community on a designed artificial reef

Artificial reefs provide shelter and can be an important source of food for fish depending on the epibenthic community on the structure. The growth and diversity of this community is influenced by the substratum material and the surface orientation of the reef. Settlement plates of four materials (Perspex, sandstone, wood and steel) were deployed in three orientations (upwards, downwards and vertical) at a depth of 33 m on a designed artificial reef (DAR) off the coast of Sydney, Australia. After three months, the steel surfaces had lower invertebrate species richness, total abundance and diversity compared to other surfaces. Steel was not an ideal material for the initial recruitment and growth of epibenthic invertebrates. A longer duration would be required to develop a mature epibenthic community. Surface orientation had species-specific impacts. Surface material and orientation are important factors for developing epibenthic assemblages, and are thus likely to affect the broader artificial reef assemblage, including fish.