Marine Fouling and Its Prevention

Volume 51 Number 2 March/April 2017

The International, Interdisciplinary Society Devoted to Ocean and Marine Engineering, Science, and Policy

Journal

P A P E R

Marine Biofouling on Moored Buoys andSensors in the Northern Indian OceanA U T H O R SRamasamy VenkatesanJagadeesh KadiyamPuniyamoorthy SenthilKumarRajagopalan LavanyaOcean Observation Systems,National Institute of OceanTechnology, Chennai, India

Loganathan VedaprakashTitanium Tantalum ProductsLimited, Chennai, India

A B S T R A C TEquipment and structures deployed in seawater and other marine environ-

ments are susceptible to marine growth. This marine biofouling is one of the crit-ical factors that affects the measurement of continuous real-time data from theoceanographic sensors deployed for long-term observations. To understand thecharacteristics of biofouling on marine sensors, an investigation was conductedon sensors deployed in a moored buoy network deployed and maintained by theNational Institute of Ocean Technology (NIOT) in the Arabian Sea and Bay of Ben-gal regions. The present paper attempts to elucidate the characteristics of biofoul-ing on sensor components deployed at seven locations in the Bay of Bengal andfive locations in the Arabian Sea, at varying depths ranging from the surface to500-m depth. Biofouling on bare sensor surfaces and surfaces with various anti-fouling measures has been studied for 2 consecutive years (2015 and 2016),and the effect of antifouling measures is discussed in this paper. Among thelocations studied, buoys deployed in the Arabian Sea exhibited a higher biofoulingload compared to the buoys deployed in the Bay of Bengal. The study showed thatthe pedunculate barnacles Lepas anatifera Linnaeus, 1758, was the predominantbiofouling species on these sensors. Furthermore, observations show that the useof copper- and zinc-based antifouling methods reduced the incidence of biofoulingby 59% on average.Keywords: marine sensors, biofouling, antifouling, marine coatings

Introduction

Marine biofouling is the rapid andundesirable biological growth (i.e.,settlement of microorganisms, plants,algae, and/or animals) on structuresexposed to the marine environment(Delauney et al., 2010; Nuriogluet al., 2015). The first event in thesequence of biofouling of a surface isthe accumulation of an organic condi-tioning film comprising chemicalcompounds (mostly protein and poly-saccharides) changing the physio-chemical properties of the surface.Adsorption of macromolecules suchas protein, polysaccharides, and sus-pended solids forms the conditioningfilm, which is the primary foulingevent that changes the physicochemi-cal properties of the surface and initi-ates the fouling process. It is followedby a secondary fouling event of colo-nization by bacteria involving twodistinct phases—a reversible phase(adsorption) where van der Waals forceshold it loosely and a nonreversiblephase (adhesion) where exopolymersare secreted forming biofilms, which

hold the bacteria to the surface(Venkatesan et al., 2006). The bio-film formation aids in recruitment ofmacrofouling organisms, which formthe tertiary event of biofouling.Macrofouling species are representedby barnacles, goose barnacles, mus-sels, and serpulids, leading to heavygrowth on the unprotected surfaces.The prevention, occurrence, and re-lapse of the fouling events appear todepend on the physicochemical andsurface properties of the substratumconcerned (Vedaprakash, 2013).

Biofouling formation is one of thecritical factors that affects the qualityof the data and increases the weight ofthe buoy hull and marine sensors,thus resulting in high mooring loads

(Det Norsok Veritas [DNV], 2010).Growth of macrofoulers obstructsthe water flow to the sensors, therebyobstructing the sensor function, whileslime formation by microfoulers onthe inner surfaces of conductivitycells drastically weakens their mea-surement capabilities, which resultsin sensor measurement drift, henceincreasing the maintenance frequency.Thus, biofouling is of utmost concernto offshore moored buoy operators,and consequently, the antifoulingmeasures assume greater significanceand are a necessity. The major bene-fit of antifouling strategies includespreservation of measurement qualityby safeguarding the measuring instru-ments from the microorganisms;

22 Marine Technology Society Journal

they should have lower power con-sumption to preserve the enduranceof the observation platform and reli-ability of the system in hostile condi-tions (Laurent et al., 2009). Thisnecessitates the development of analternative environmental-friendlyantifouling technology.

The National Institute of OceanTechnology (NIOT), having carriedout more than 600 moored buoy sys-tem deployments during the period of1997–2015, has found that biofoul-ing is one of the major challenges inthe maintenance of buoys, and collec-tion of quality data from these buoyshas been affected immensely as a re-sult of biofouling growth. Hence, at-tempts are being made to deployedsensors with antifouling measuresand to study their effect on biofoul-ing. This paper attempts to elucidatethe characteristics of biofouling onbare marine sensors, sensors installedwith antifouling protection mountedon moored buoys that are deployed byNIOT.

Materials and MethodsExperimental Systems

Biofouling observation data andsensor data were obtained frombuoys deployed by NIOT in theArabian Sea (AS) and in the Bay ofBengal (BoB), during the years 2015and 2016. The latitude, longitude,and distance from the coast for these12 buoy systems are mentioned inFigure 1, where AD and BD refer tothe AS data buoy and BoB data buoy,respectively. These buoy systems areof similar design, collect meteorologi-cal parameters above the sea surfaceand oceanographic parameters belowthe sea surface, and transmit in realtime (Venkatesan et al., 2013). Thesubsurface conductivity and tempera-

ture (CT) sensor made of titaniumcasing is placed on an inductionmooring up to 500 m at strategicdepths such as 1, 5, 10, 15, 20, 30,

50, 75, 100, 200, and 500 m. Most ofthe data buoys are moored 200 nm(nautical miles) away from the coastin both AS and BoB.

FIGURE 1

Moored buoy systems network deployed in Indian waters.

FIGURE 2

Antifouling measures taken in moored buoy systems.

March/April 2017 Volume 51 Number 2 23

As the moored buoy systems aredeployed in the deep ocean locationsfor more than a year, few antifoulingmethodologies were implemented inNIOT moored buoy systems to pro-tect the sensors from biofouling, asshown in Figure 2. Most of the tech-niques used for biofouling protectionin AS and BoB for our moored buoyswere physical methods (Lehaitreet al., 2008) such as copper tape, cop-per guards, clear packing tape wrap,antifouling coatings, protective anti-fouling sleeves, and so forth.

Copper TapeA thin copper foil wrapped over

clear packing tape was used on thecasing of CT sensors, as copper istoxic at high concentrations to micro-bial antifouling properties. The outerlayer of tape itself was largely respon-sible for the biofouling resistance, andwhen freely corroding under quietconditions, the oxide film wouldgradually convert to cupric hydro-xychloride (Parvizi et al., 1998).This layer was considered to be lessadherent; after a time, it would sloughaway leaving a protective cuprousoxide film exposed again.

After retrieval, the clear tape actsas a barrier and makes removal ofthe old copper tape much easier.

Copper Sensor GuardCT sensors supplied with titanium

protection guards by the originalequipment manufacturer have theguards replaced with pure copper tocontrol fouling; as copper corrodesin seawater, oxidized molecules re-lease into the water rather than re-main on the metal surface, whichprevents fouling organisms from at-taching effectively.

Clear Packing Tape WrapIn a few of the moored buoy sys-

tems, clear packing tape was wrappedon the casing of the CT sensor andwas tested for antifouling properties.This technique also proved good incertain ways as it makes easier the re-moval of fouling after retrieval.

Antifouling CoatingsSpecialized paint with a hybrid

TBT-free self-polishing antifoulingsystem incorporating unique copperacrylate technology has been appliedon the buoy components like thehull, instrument housing, and soforth and have proved to slow downthe growth of subaquatic organismsthat may attach to the buoy compo-nents. These coatings also have anti-corrosive properties and improve theflow of water past the buoy compo-nents due to the hard, smooth, andpolished surface.

Zinc-Based CoatingsDESITIN, a zinc oxide-based

coating, is used as a protective barrierto prevent biofouling formation onthe transducer face as well as a cou-

plant between the water and trans-ducer face.

Although the above five methodshave been applied, the present paperdiscusses observations on the antifoul-ing effects of copper tape, copper sen-sor guards, and clear packing tapewrap. Exposed components andtheir respective area of exposure aregiven in Table 1.

Biofouling Observationsand Analysis

Moored marine sensors were re-trieved for observation and mainte-nance after a period of 1 year. Thesensors of all the locations and depthsof deployment were observed for bio-fouling, and data on biofouling areacoverage (% area coverage) and bio-fouling load (kg/sensor) were recorded,according to Vedaprakash et al.(2013) and Venkatesan et al. (2017).For calculating biofouling load,weight accumulated on the sensorsas a result of fouling was estimatedby subtracting the initial weight ofthe sensors from the final wet weightof sensors along with fouled organ-isms. The data were further analyzedto compare the biofouling intensity

TABLE 1

Exposed components and their respective area of exposure.

Exposed Components/Sensors Area of the Component (m2)

Hull 1.66

Cylinder 0.79

CT sensor 0.09

Copper guard coverage area in CT sensor 0.02

Copper tape coverage area in CT sensor 0.06

Clear tape coverage area in CT sensor 0.06

DVS sensor 0.20

Transducer face area in DVS sensor 0.01

ADCP sensor 0.69

Transducer face area in ADCP sensor 0.10

24 Marine Technology Society Journal

between the locations of deployment(AD and BD), between years ofstudy, and between bare sensors andsensors installed with antifouling de-vices. The data were analyzed withMicrosoft Excel and KYPLOT ver-sion 2.0 beta 15 (32-bit) software.Microsoft Excel 2007 was used toplot graphs.

ResultsBiofouling Observationson Sensors

Biofouling observed on sensors atdifferent depths in a moored buoysystem is shown in Figure 3. The sub-

components and sensor surfacesof the moored buoy system wereobserved to be affected by biofoul-ing settlements that led to a drift inthe measurements. Conductivitymeasurement of a sensor (AD08) at

15-m water depth from the MSB12N/69E was found to be affecteddue to biofouling (Figure 4a). Also,the output of the sensor (AD07)in MSB 15N/69E (operational for128 days from June 26, 2016, toNovember 1, 2016) installed at 10-mwater depth was affected after 3monthsof deployment (Figure 4b). In deepsea buoy systems, biofouling was ob-served on the mounted sensors till50-m depth and seldom till 75-mdepth in both the AS and BoB. Allthe sensors retrieved were fouled byLepas anatifera Linnaeus, 1758, com-monly known as the pelagic goose-neck barnacle or smooth gooseneckbarnacle.

Comparison of BiofoulingBetween AS and BoB Data Buoys

A comparative study on the bio-fouling load of sensors at differentdepths in both the AS and BoB ona spatial scale at different depths wasmade, and the data are presented inFigures 5 and 6, respectively. Amongthe sensors studied, the biofoulingload on buoys moored in the AS werehigher (5.63 ± 2.13 kg/sensor [in2015], 3.60 ± 1.93 kg/sensor [in2016]) compared to the sensors de-ployed in theBoB (0.98 ± 0.66 kg/sensor[in 2015], 0.31 ± 0.20 kg/sensor[in 2016]). The highest biofoulingload of 9 kg/sensor was observed in

FIGURE 3

Biofouling on sensors in different depths in a moored buoy system.

FIGURE 4

Sensor drift due to fouling in a moored buoy deployed at two different locations: (a) sensor driftin AD08 and (b) sensor drift in AD07.

March/April 2017 Volume 51 Number 2 25

the AS compared to the highest of4 kg/sensor in BoB, suggesting thatthe fouling in the AS is higher com-pared with the fouling in the BoB.Biofouling was very low or nil beyonda 75-m depth in both BoB and ASlocations.

Comparison of BiofoulingBetween Bare Sensorsand Sensors WithAntifouling Devices

The antifouling methods discussedwere exposed to an open ocean envi-ronment for long periods and wereable to assist in reducing fouling dur-ing retrieval. A performance compari-son of antifouling techniques used onoceanographic sensors is shown inTable 2. Observations made for the2 consecutive years 2015 and 2016,with and without antifouling mea-sures, revealed that the percentage offouling coverage over the sensor areawas reduced by 50–70% when an an-tifouling measure was implemented.

A comparison between bare sen-sors and those installed with antifoul-ing devices shows that the biofoulingload was lower in sensors installed withantifouling devices (1.00 ± 0.34 kg/sensor) compared to the sensors with-out any antifouling device (2.45 ±1.69 kg/sensor) (Figure 7). Sensorsinstalled with antifouling devices

FIGURE 5

Biofouling load on sensors moored in the BoB (BD) and AS (AD) in 2015.

FIGURE 6

Biofouling load on sensors moored in the BoB (BD) and AS (AD) in 2016.

TABLE 2

Performance comparisons of antifouling techniques for oceanographic sensors.

Sl No. Antifouling Method

Fouling Coverage Over the Sensor Area (%)

Without Antifouling Measures With Antifouling Measures

1 Copper tape 70–100% 10–20%

2 Copper sensor guard 70–100% 10–15%

3 Clear packing tape wrap 70–100% 20–50%

4 Antifouling coatings 30–80% 30–80%

5 Zinc-based coatings on transducer head 60–90% 20–30%

26 Marine Technology Society Journal

such as copper guard (Figure 8), cop-per tape (Figure 9), and zinc-basedgrease (Figure 10) demonstrated lowerbiofouling compared to bare sensors

and surfaces. Also, the copper tapingreduced the fouling on the housingof the sensor, which facilitates easycleaning of the sensors. Furthermore,

observations show that the use ofcopper- and zinc-based antifoulingmethods reduced the incidence ofbiofouling by 59%, on average.

Zinc-based grease applied to theheads of an acoustic Doppler currentprofiler (ADCP) was also found to in-hibit biological growth on bottom-mounted frames. Upon recovery ofthe ADCP, it was observed that bar-nacle growth was found to be reducedconsiderably on the acoustic heads.

The sensors on moored buoy sys-tems wrapped with clear packing tapealso exhibited reduced biofoulinggrowth. This simple physical methodwould facilitate easy removal of bio-fouling growth after retrieval.

DiscussionDevelopment of fouling assem-

blages on various substrates has beenstudied for several decades, both to-ward understanding the variation incommunity succession (Butler &Connol ly , 1996; Vedaprakash,2013) and developing antifoulingmeasures (Abarzua & Jakubowski,1995; Dineshram et al., 2009), inan attempt to extend the perfor-mances of marine structures. Biofoul-ing varies enormously withoutinterruption seasonally and geograph-ically throughout the year in tropicalwaters. Several studies have been con-ducted worldwide on substrates suchas metals, glass, polymers, wood, con-crete, different types of paint coatings,and engineered surfaces with alteredsurface properties to understand thesurface dependency of the recruit-ment process or to identify thefouling-induced damage to surfacesor toward developing antifouling sur-faces (Vedaprakash, 2013). The pau-city of data on biofouling and theeffect of antifouling measures on

FIGURE 7

Variation in biofouling load on sensors moored with and without antifouling method in the year2016. (Data corresponding to the sensors moored from the surface and up to 50-m depth alonehave been taken to plot this graph to avoid errors due to statistical bias.)

FIGURE 8

Comparison of fouling on sensors with copper guards. (a) Bare sensor. (b) Sensor with copperguard.

FIGURE 9

Comparison of fouling on sensor casing after implementing copper tape. (a) Bare sensor.(b) Sensor with copper tape.

March/April 2017 Volume 51 Number 2 27

moored data buoys instigated thisstudy.

Biofouling Observationson Sensors

Biofouling is a natural process thatcan disrupt sensor measurements inless than a week (Delauney et al.,2010). Biofouling protection of ma-rine in-situ sensors is a challengingissue that necessitates the applicationof multifaceted preventive measures.Several studies have been made dur-ing the last few centuries to character-ize biofouling recruitment on variousmetals (Vedaprakash et al., 2013;Venugopalan & Wagh, 1990), poly-mers (Muthukumar et al., 2011),antifouling coating (Yebra et al.,2004), engineered antifouling surfaces(Dineshram et al., 2009; Howell &Behrends, 2006), and many othermaterials and surfaces (Vedaprakash,2013). Most of the studies were madeon the experimental panels in the coastalregion, which had shown a fouling as-semblage represented by barnacles,green mussel, serpulids, macroalgae,and so forth. In the present study, themost distinguishing observation isthat the sensors retrieved were found

to be predominantly fouled by Lepasanatifera Linnaeus, 1758, which isabundant in tropical waters and isfound attached to floating objectsand other offshore equipment (Castroet al., 1999) and is thus a nuisance tomaritime operations (Kathe, 2010).

This observation on the predomi-nance of Lepas anatifera corroboratesthe earlier observation made on theinstrumented moored buoy sensorsoperated in the Northern India Ocean(Venkatesan et al., 2017). This varia-tion in the fouling species betweenthe earlier studies on coastal envi-ronment ( Sathpathy et al., 2010;Vedaprakash et al., 2013) could be at-tributed to the availability of larvae ofthe settling species in the local ecosys-tem, presence of required food, varia-tion in the sunlight penetration overthe depth, and so forth, which playa limiting factor for recruitment ofmany biofouling organisms. Themost dominant fouling species on thebuoy hull deployed in the open oceanis gooseneck barnacle of Lepas sp.(Kathe, 2010). Generally, barnaclesare concentrated around the buoyhull, on the rubber fender and edgesof sharp corners.

Comparison of BiofoulingBetween AS and BoB Data Buoys

Biofouling load on the sensorsmoored in the AS was found to be80–90% higher compared to that ob-served in the BoB sensors during thestudies made in 2015 and 2016. Theincreased biofouling load relates tothe increased recruitment of the or-ganisms, which could be attributedto the higher sweater salinity observedin the AS (Gordon, 2015; Jensen,2001).

The biofouling weight data showthat lower depths are prone to highfouling compared to deeper waters.In the present study, the observationsshow a clear demarcation in the bio-fouling pattern along the depth ofthe study, both in the AS and BoBdata buoys. Based on the observa-tions, the distribution pattern of bio-fouling with respect to depth could bebroadly categorized into three regions,namely,■ High fouling region (from surface

to 30-m depth);■ Medium fouling region (from 30-

to 75-m depth);■ No fouling region (above 75-m

depth).This observation concurs with ear-

lier studies that have reported thatbiofouling organisms are dense onthe upper 30 m of underwater struc-tures (Miller et al., 1984; Oldfield,1980) and that biofouling load is sig-nificantly less at 42-m level and below(Venugopalan & Wagh, 1990).

Comparison of BiofoulingBetween Bare Sensorsand Sensors WithAntifouling Devices

In this study, copper has shown a59% reduction in marine biofoulingload for long-term sensor deploy-ments in open ocean environments

FIGURE 10

Comparison of fouling on ADCP acoustic heads after implementing zinc grease. (a) Bare ADCPacoustic head. (b) ADCP acoustic head with zinc-based grease.

28 Marine Technology Society Journal

and could be used as an effective re-placement for the highly toxic TBT-based methods and other less benignantifoulants that are currently in use.Copper has been widely studied forits antifouling property, which ismainly attributed to the toxicity ofcopper, although another mechanismof “gross exfoliation”—shredding offof thin parallel layers on the coppermetal surface, which causes the or-ganisms to lose their hold and getdetached—is possible (WHOI, 1952).This view is also supported by earlierstudies that copper leaching from sur-faces did not prevent barnacle settle-ment but killed the attached larvae(Crisp & Austin, 1960; Vedaprakash,2013).

Similarly, the application of zinc-based gel coat reduced the incidenceof biofouling, suggesting that thetoxic nature of the zinc element pre-vents biofouling. Despite the factthat copper- and zinc-based antifoul-ing devices release toxic chemicals,the quantum of such release fromthese tiny structures used for protect-ing sensors is relatively much lesscompared to those protecting largersurface areas on floating vessels andoff structures; hence, the effect ofthe leachates on the surrounding envi-ronment would be relatively quitenegligible. Also, other antifoulingmeasures studied, such as packingtape and plastic sleeves, either wereobserved to reduce the incidence offouling or aided in the easy removalof biofouling on retrieval from thedata buoys. Few other moored buoyoperators around the world haveimplemented copper- and zinc-basedantifouling strategies successfully inthe form of modular shutters andcopper guards for moored buoy sen-sors (Dickey et al., 2009; Manov et al.,2004).

ConclusionThis biofouling study carried out

on sensor devices deployed in theAS and BoB demonstrated that bio-fouling settlement is influenced bythe environment, depth, and chemi-cal nature of the settlement substrate.The most distinguishing observationis that biofouling on the moored sen-sors deployed both in the AS and BoBwas predominated by Lepas anatifera.This study corroborates the earlierobservation that biofouling is a highlyvarying phenomenon and that surfacechemistry, physical properties, andenvironmental properties play amajor role in the density and compo-sition of biofouling settlement. Theobservations also show that bare sen-sors are prone to biofouling, while ap-plication of antifouling methods, suchas copper guard, copper tape, and zincgel, reduced the settlement andgrowth of biofouling organisms, de-picted by a reduction in biofoulingload of 59%. Hence, the study dem-onstrates that use of copper- and zinc-based antifouling methods could beused as alternative methods to replacethe TBT-based toxic antifoulants.Furthermore, elaborate studies couldbe taken up to optimize the use ofvarious antifouling methods for sus-tainable long-term biofouling preven-tion on sensors, a problem that stillposes a big challenge.

AcknowledgmentsThe authors sincerely thank the

Ministry of Earth Sciences, Govern-ment of India, for their financial sup-port to this project. They are gratefulto the Directors of NIOT, Chennai,and INCOIS, Hyderabad, for provid-ing all the facilities and logistic sup-port. The authors are thankful tothe members of the cruise onboard

the ship ORV Sagar Nidhi for collect-ing the samples and bringing themsafely to shore. We also thank thestaff of Ocean Observation Systems(OOS) group, Vessel ManagementCell (VMC) of NIOT, and the shipstaff for their excellent help and sup-port onboard the vessel.

Corresponding Author:Ramasamy VenkatesanOcean Observation Systems,National Institute of OceanTechnology, Chennai, IndiaEmail: rvenkatin5@gmail.com

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