Ultraviolet radiation (UV-C): a potential tool for the control of biofouling on marine optical instruments

Design and In Situ Validation of Low-Cost and Easy to Apply Anti-Biofouling Techniques for Oceanographic Continuous Monitoring with Optical Instruments

Biofouling is the major factor that limits long-term monitoring studies with automated optical instruments. Protection of the sensing areas, surfaces, and structural housing of the sensors must be considered to deliver reliable data without the need for cleaning or maintenance. In this work, we present the design and field validation of different techniques for biofouling protection based on different housing materials, biocides, and transparent coatings. Six optical turbidity probes were built using polylactic acid (PLA), acrylonitrile butadiene styrene (ABS), PLA with copper filament, ABS coated with PDMS, ABS coated with epoxy and ABS assembled with a system for in situ chlorine production. The probes were deployed in the sea for 48 days and their anti-biofouling efficiency was evaluated using the results of the field experiment, visual inspections, and calibration signal loss after the tests. The PLA and ABS were used as samplers without fouling protection. The probe with chlorine production outperformed the other techniques, providing reliable data during the in situ experiment. The copper probe had lower performance but still retarded the biological growth. The techniques based on transparent coatings, epoxy, and PDMS did not prevent biofilm formation and suffered mostly from micro-biofouling.

Single Ultraviolet-C light treatment of early stage marine biofouling delays subsequent community development

Past studies of Ultraviolet-C (UV-C) radiation as a marine antifoulant have focused on repeated doses. However, single or very low frequency exposures of UV-C could create more plausible applications for certain marine structures. The objective of the study reported here was to apply a single treatment of UV-C radiation to an early stage marine biofouling community to observe subsequent effects on biofouling development. Biofouling formed over a 2-week field immersion received UV-C treatments of 0 (control), 4, 20, or 120 min, and subsequent progression was then monitored weekly for 16 weeks. Analysis of acute effects and later macrofouling development suggested direct toxicity of UV-C illumination to invertebrate recruits caused reduction of subsequent biofouling (compared to controls) that persisted for up to 16 weeks following the longest UV-C treatment. Thus, UV-C treatments spaced by days or even weeks could be an option for some applications of UV-C radiation as an antifoulant.

A low-cost, long-term underwater camera trap network coupled with deep residual learning image analysis

Understanding long-term trends in marine ecosystems requires accurate and repeatable counts of fishes and other aquatic organisms on spatial and temporal scales that are difficult or impossible to achieve with diver-based surveys. Long-term, spatially distributed cameras, like those used in terrestrial camera trapping, have not been successfully applied in marine systems due to limitations of the aquatic environment. Here, we develop methodology for a system of low-cost, long-term camera traps (Dispersed Environment Aquatic Cameras), deployable over large spatial scales in remote marine environments. We use machine learning to classify the large volume of images collected by the cameras. We present a case study of these combined techniques’ use by addressing fish movement and feeding behavior related to halos, a well-documented benthic pattern in shallow tropical reefscapes. Cameras proved able to function continuously underwater at deployed depths (up to 7 m, with later versions deployed to 40 m) with no maintenance or monitoring for over five months and collected a total of over 100,000 images in time-lapse mode (by 15 minutes) during daylight hours. Our ResNet-50-based deep learning model achieved 92.5% overall accuracy in sorting images with and without fishes, and diver surveys revealed that the camera images accurately represented local fish communities. The cameras and machine learning classification represent the first successful method for broad-scale underwater camera trap deployment, and our case study demonstrates the cameras’ potential for addressing questions of marine animal behavior, distributions, and large-scale spatial patterns.

Reduction of biofilm accumulation by constant and alternating potentials in static and dynamic field experiments

The application of electric fields to conductive coatings is an environmentally friendly way to reduce biofilm formation. In particular alternating potentials (APs) have received increasing attention in recent studies. Here, an electrochemical rotating disk setup for dynamic field exposure experiments was developed to study how APs alter the attachment of fouling organisms in a multispecies ocean environment. A specific focus of the device design was proper integration of the potentiostat in the strongly corroding saltwater environment. The effect of APs on the accumulation of fouling organisms in short term field exposures was studied. Potentials on conductive gold surfaces were periodically switched between -0.3 V and 0.3 V or between -0.8 V and 0.6 V at a frequency of 0.5 Hz. APs were capable of significantly reducing the attachment of marine fouling organisms compared with the conductive samples immersed at open circuit potentials.

Anti-pathogenic activity of graphene nanomaterials: A review

Graphene and its derivatives are promising candidates for a variety of biological applications, among which, their anti-pathogenic properties are highly attractive due to the outstanding physicochemical characteristics of these novel nanomaterials. The antibacterial, antiviral and antifungal performances of graphene are increasingly becoming more important due to the pathogen's resistance to existing drugs. Despite this, the factors influencing the antibacterial activity of graphene nanomaterials, and consequently, the mechanisms involved are still controversial. This review aims to systematically summarize the literature, discussing various factors that affect the antibacterial performance of graphene materials, including the shape, size, functional group and the electrical conductivity of graphene flakes, as well as the concentration, contact time and the pH value of the graphene suspensions used in related microbial tests. We discuss the possible surface and edge interactions between bacterial cells and graphene nanomaterials, which cause antibacterial effects such as membrane/oxidative/photothermal stresses, charge transfer, entrapment and self-killing phenomena. This article reviews the anti-pathogenic activity of graphene nanomaterials, comprising their antibacterial, antiviral, antifungal and biofilm-forming performance, with an emphasis on the antibacterial mechanisms involved.

A Review of Protocols for Fiducial Reference Measurements of WaterLeaving Radiance for Validation of Satellite Remote-Sensing Data over Water

This paper reviews the state of the art of protocols for measurement of waterleaving radiance in the context of fiducial reference measurements (FRM) of water reflectance for satellite validation. Measurement of water reflectance requires the measurement of waterleaving radiance and downwelling irradiance just above water. For the former there are four generic families of method, based on: 1) underwater radiometry at fixed depths; or 2) underwater radiometry with vertical profiling; or 3) abovewater radiometry with skyglint correction; or 4) onwater radiometry with skylight blocked. Each method is described generically in the FRM context with reference to the measurement equation, documented implementations and the intramethod diversity of deployment platform and practice. Ideal measurement conditions are stated, practical recommendations are provided on best practice and guidelines for estimating the measurement uncertainty are provided for each protocolrelated component of the measurement uncertainty budget. The state of the art for measurement of waterleaving radiance is summarized, future perspectives are outlined, and the question of which method is best adapted to various circumstances (water type, wavelength) is discussed. This review is based on practice and papers of the aquatic optics community for the validation of water reflectance estimated from satellite data but can be relevant also for other applications such as the development or validation of algorithms for remote-sensing estimation of water constituents including chlorophyll a concentration, inherent optical properties and related products.

Using ultraviolet light for improved antifouling performance on ship hull coatings

A two-part study was designed to investigate the efficacy of using UVC to prevent biofouling in the context of ship hull coatings. The first study determined the frequency of UVC required for a coating that does not have any additives (epoxy). It was found that 1 min/day was effective at preventing hard fouling but not biofilm development. The second study addressed several variables: coating type (epoxy, copper, fouling release), frequency of UVC (no exposure, continuous exposure, 1min/6h, 1 min/day), and distance from the lamp (25 and 50 mm). Continuous UVC exposure resulted in no biofouling settlement but it did damage the copper coating. Intermittent UVC exposure was effective at preventing biofouling recruitment to both the copper and the fouling release coatings. Variations were observed with regards to the fouling composition, especially biofilms, sedimentary tubeworms and barnacles, suggesting tolerances within the community.

Periodic ultraviolet-C illumination for marine sensor antifouling

Ultraviolet light has intriguing potential as a marine antifoulant, targeting almost any species and applicable to almost any surface, while not accumulating in the environment. This study field-tested the effects of periodic ultraviolet-C illumination on marine macrofouling. Across four experiments, several UV illumination duty cycles were tested against controls with no illumination. Duty cycles between 1:2 (time with UV:total time per cycle) and 1:20 were all similarly effective, inhibiting almost all macrofouling at three different temperate Northeast Pacific and Northwest Atlantic sites. Susceptible taxa included barnacles, bryozoans, tunicates (colonial and solitary), and, to a slightly lesser extent, mussels. Duty cycles of 1:30 and 1:60 reduced but did not eliminate biofouling. Measurements of ultraviolet illumination on oceanographic sensors showed similar results. The results suggest further investigation of ultraviolet light as an antifoulant for marine sensors, including susceptibility of other taxa, optimizing illumination patterns, and exploring the potential for evolved resistance.

Silver-doped laser-induced graphene for potent surface antibacterial activity and anti-biofilm action

Silver nanoparticles embedded in laser-induced graphene surfaces were generated in a one step process, resulting in highly antibacterial surfaces.

Tracking Fish Abundance by Underwater Image Recognition

Marine cabled video-observatories allow the non-destructive sampling of species at frequencies and durations that have never been attained before. Nevertheless, the lack of appropriate methods to automatically process video imagery limits this technology for the purposes of ecosystem monitoring. Automation is a prerequisite to deal with the huge quantities of video footage captured by cameras, which can then transform these devices into true autonomous sensors. In this study, we have developed a novel methodology that is based on genetic programming for content-based image analysis. Our aim was to capture the temporal dynamics of fish abundance. We processed more than 20,000 images that were acquired in a challenging real-world coastal scenario at the OBSEA-EMSO testing-site. The images were collected at 30-min. frequency, continuously for two years, over day and night. The highly variable environmental conditions allowed us to test the effectiveness of our approach under changing light radiation, water turbidity, background confusion, and bio-fouling growth on the camera housing. The automated recognition results were highly correlated with the manual counts and they were highly reliable when used to track fish variations at different hourly, daily, and monthly time scales. In addition, our methodology could be easily transferred to other cabled video-observatories.

Fabrication of Slippery Lubricant-Infused Porous Surface with High Underwater Transparency for the Control of Marine Biofouling

Marine optical instruments are bearing serious biofouling problem, which affects the accuracy of data collected. To solve the biofouling problem of marine optical instruments, a novel instance of slippery lubricant-infused porous surface (SLIPS) with high underwater-transparency was designed over glass substrate via infusing lubricant into its porous microstructure fabricated with hydrothermal method. The advantage of SLIPS as antibiofouling strategy to marine optical instruments was proven by comparing its underwater optical and antibiofouling performances with three kinds of samples (hydrophilic glass sample, textured hydrophilic glass sample, and superhydrophobic glass sample). The modification of SLIPS enhances the underwater-transparency of glass sample within the wavelength of 500-800 nm, for the infusion of lubricant with lower refractive index than glass substrate. In contrast with hydrophilic surface, textured hydrophilic surface and superhydrophobic surface, SLIPS can significantly inhibit bacterial and algal settlements, thereby maintaining high underwater-transparency in both dynamic and static seawater. The inhibition of bacterial and algal settlements over SLIPS results from its liquid-like property. The contact angle hysteresis of water over SLIPS increases with immersion time in seawater under different conditions (static, dynamic, and vibration conditions). Both dynamic and vibration conditions accelerate the failure of SLIPS exposed in seawater. This research provides valuable information for solving biofouling problem of marine optical instruments with SLIPS.

Chemical Fouling Reduction of a Submersible Steel Spectrophotometer in Estuarine Environments Using a Sacrificial Zinc Anode

The availability of in situ spectrophotometers, such as the S::CAN spectro::lyser, has expanded the possibilities for high-frequency water quality data collection. However, biological and chemical fouling can degrade the performance of in situ spectrophotometers, especially in saline environments with rapid flow rates. A complex freshwater washing system has been previously designed to reduce chemical fouling for the S::CAN spectro::lyser spectrophotometer. In the current study, we present a simpler, cheaper alternative: the attachment of a sacrificial zinc anode. Results are presented detailing the S::CAN spectro::lyser performance with and without the addition of the sacrificial anode. Attachment of the zinc anode provided efficient corrosion protection during 2-wk deployments in a highly dynamic (average tidal range, 2.5 m) saline tidal saltmarsh creek at Groves Creek, Skidaway Institute of Oceanography, Savannah, GA.

Effect of biofilm on fluorescence measurements derived from fast repetition rate fluorometers

This study evaluates, for the first time, the influence of biofilms on single and double optical window (SOW and DOW, respectively) fast repetition rate fluorometer (FRRF) measurements of microalgal photosystem-II initial fluorescence (F0), maximum fluorescence (Fm), variable fluorescence (Fv = Fm - F0), quantum yield (Fv/Fm) and functional absorption cross section (σPSII)]. Biofilms with chlorophyll > 0.1 μg cm(-2) and > 0.3 μgcm(-2) on SOW and DOW, respectively, produced a substantial increase in fluorescence. However, the relative magnitude of biofouling effects depended on sample chlorophyll concentrations, being more critical at concentrations < 1 mg m(-3). In DOW-FRRF, biofilms affected F0 (increased) and Fv/Fm (decreased) but not Fv and σPSII, whereas in SOW-FRRF, biofilms increased fluorescence and showed a variable effect on Fv/Fm and σPSII, because only biofilms on SOW attained actual Fm. As a result, the biofilm effect was substantial on SOW-FRRF measurements. On the other hand, the neutral-density filters (representing non-chlorophyll containing biofilms) with different transmission levels reduced the fluorescence signal. Correction procedures for the above photosystem-II parameters are proposed here.

Addressing the fouling of in situ ultraviolet-visual spectrometers used to continuously monitor water quality in brackish tidal marsh waters

The introduction of portable in situ ultraviolet-visual spectrometers has made possible the collection of water quality parameters at a high frequency in dynamic systems such as tidal marshes. The usefulness of this technology is inhibited by fouling of the instrument's optics. In this study, a spectrometer fitted with manufacturer-recommended compressed air optical cleaning was installed in a brackish marsh to determine if fouling interfered with measurements between bi-weekly servicing. During a 2-wk period, the absorbance measured in air at 220 nm increased from 9 to 549 m, indicating major fouling. An antifouling system was developed that reduced the time of exposure of the optics to stream water and used a pressurized fresh water cleaning. After implementation of the system, the absorbance in air increased to at most 63 m after 2 wk of data collection. The dramatic reduction in fouling will allow quality long-term data to be collected using this technology.

Effect of chlorination on the development of marine biofilms dominated by diatoms

This study addressed the antifouling efficiency of commercially available chlorine at different concentrations (0.5%, 1%, and 2%) and exposure times (0.5 min, 1 min, 5 min, and 15 min). The rapid and non-destructive FIRe (fluorescence induction and relaxation) technique was used to evaluate the effects of the biocide on diatom dominated biofilms. The efficiency of chlorine in removing diatoms from the developed biofilms increased with an increase in concentration and exposure time. The fluorescence measurements revealed low F(v)/F(m) and high σ(PSII) values for chlorine-treated Navicula and Amphora biofilms indicating that chlorination was efficient in damaging the photosystem-II reaction centers. Chlorination also caused mortality of diatom cells by damaging the cell body. In natural biofilms, the biocidal effect of chlorine was species specific; species of Amphiphrora, Navicula, Cylindrotheca, and Coscinodiscus showed an increase in the density of the population, but species of Pleurosigma, Amphora, and Thalassionema did not increase in density after chlorine treatment. It was also demonstrated that diatoms can colonize, grow and photosynthesize on chlorine-treated surfaces. Under pulse chlorination (treatment every 6 h), irrespective of chlorine concentration, the development of biofouling decreased with an increase in exposure time. Differences between exposure times of 1 to 15 min were not significant. Additionally, transmission levels of the control (non-chlorine-treated) fouled coupons reduced significantly (∼20%) compared to the chlorine-treated fouled coupons (<2%). These results suggest that chlorine can be used as a biocide to control the development of diatom biofilms.

Biofouling control in water by various UVC wavelengths and doses

UV light irradiation is being increasingly applied as a primary process for water disinfection, effectively used for inactivation of suspended (planktonic) cells. In this study, the use of UV irradiation was evaluated as a pretreatment strategy to control biofouling. The objective of this research was to elucidate the relative effectiveness of various targeted UV wavelengths and a polychromatic spectrum on bacterial inactivation and biofilm control. In a model system using Pseudomonas aeruginosa, the inactivation spectra corresponded to the DNA absorption spectra for all wavelengths between 220 and 280 nm, while wavelengths between 254 nm and 270 nm were the most effective for bacterial inactivation. Similar wavelengths of 254-260-270 nm were also more effective for biofilm control in most cases than targeted 239 and 280 nm. In addition, the prevention of biofilm formation by P. aeruginosa with a full polychromatic lamp was UV dose-dependent. It appears that biofilm control is improved when larger UV doses are given, while higher levels of inactivation are obtained when using a full polychromatic MP lamp. However, no significant differences were found between biofilms produced by bacteria that survived UV irradiation and biofilms produced by control bacteria at the same microbial counts. Moreover, the experiments showed that biofilm prevention depends on the post-treatment incubation time and nutrient availability, in addition to targeted wavelengths, UV spectrum and UV dose.

Marine antifouling laboratory bioassays: an overview of their diversity

In aquatic environments, biofouling is a natural process of colonization of submerged surfaces, either living or artificial, involving a wide range of organisms from bacteria to invertebrates. Antifouling can be defined as preventing the attachment of organisms onto surfaces. This article reviews the laboratory bioassays that have been developed for studying the control of algae and invertebrates by epibiosis (chemical ecology) and the screening of new active compounds (natural products and biocides) to inhibit settlement or adhesion, ie fouling-release coatings. The assays utilize a range of organisms (mainly marine bacteria, diatoms, algae, barnacles). The main attributes of assays for micro- and macroorganisms are described in terms of their main characteristics and depending on the biological process assessed (growth, adhesion, toxicity, behavior). The validation of bioassays is also discussed.