THE SHELLFISH CORNER

ing gear to sink or make overall gear handling more difficult. Fouling of Controlling the shellfish stock itself can create additional problems. Biofouling can not only impede the growth of the shellfish, but also affect its market- Biofouling ability as well. For instance, oysters encrusted with barnacles may not be on Shellfish and Gear as aesthetically pleasing for sale in the half-shell trade, and other bio- fouling invertebrates such as boring sponges and mud blister worms (an By Michael A. Rice* annelid worm boring into shells) can weaken the shells, making shucking very difficult without breakage. Biofouling is a complex and costly problem in most shellfish The most common method to aquaculture operations. Problem areas include fouling on gear such control biofouling around shellfish farms is by some form of mechani- as cages, mesh bags, predator control netting that may impede proper cal cleaning, such as use of brushing, water flow to the shellfish stock, resulting in reduced food supply, and scraping, or use of powered water spraying [See: Hodson et al. 1997. ultimately, growth stunting of the shellfish stock. Estimates of the effect Aquaculture 152:77-90]. However, a of not properly managing biofouling on shellfish aquaculture gear suggest drawback to power washing of gear is in some coastal areas is that farm that it can reduce growth rates in oysters in excess of 40%. neighbors object to the noise gen- erated by the machine. Often air/ sun drying of gear can aid in the ny aquaculture gear or The specific types and the inten- cleaning by killing and drying out shellfish stock placed sity of biofouling in shellfish farms some of the biofouling organisms, into marine environ- are very site-specific, depending on making their mechanical removal ments rapidly becomes local environment, season and year- easier. Cleaning of shellfish or gear Acolonized by biofouling organisms. to year climate variables. Problem can be combined with dips into In very short order upon immer- areas include fouling on gear such fresh water, high salinity brine, ace- sion, surfaces become primed for as cages, mesh bags, predator con- tic acid (vinegar) or chlorine bleach colonization by chemical adhesion trol netting that may impede proper for varying lengths of time to aid or adsorption of proteins and other water flow to the shellfish stock, -re in killing the biofouling organisms dissolved organic material (DOM) sulting in reduced food supply, and as well [see: Carver et al. 2003. J. present in the water, and these ultimately, growth stunting of the Shellfish Res. 22:621-631]. The use chemically prepared surfaces allow shellfish stock. Estimates of the ef- of some biocidal chemical coatings for bacterial colonization within a fect of not properly managing bio- such as copper oxide and tributyl tin few hours, followed by unicellular fouling on shellfish aquaculture gear on gear has been used as a means microalgae, protozoans, and fungi. suggest that it can reduce growth to avoid more labor-intensive ap- These earliest colonizing organisms rates in oysters in excess of 40 per- proaches, but this approach has form a slimy surface referred to as cent [See: Hidu et al. 1981. Aquacul- been banned in many jurisdictions a biofilm or microfouling. Finally ture 22:189-192]. A survey of shell- based upon demonstrated negative macrofouling invertebrates such as fish farmers across the United States consequences on local habitats and barnacles, mussels, and ascidians be- showed that 14.7% of shellfish farm additional regulatory concern for gun to cover the surfaces along with operating costs, amounting to over human health [See: Guardiola et al. macroalgae or seaweeds. Biofouling US$ 21 million annually [See: Ad- 2012. Int. J. Molecular Sci. 13:1541- is a complex and costly problem in ams et al. 2011. J. World Aquacul- 1560 for an excellent review]. most shellfish aquaculture opera- ture Soc. 42:242-252]. Biofouling A number of alternative meth- tions, often significantly cutting into of floats and gear suspension lines ods have been developed, such as profit margins. can add considerable weight, caus- the use of grazing fish or sea - ur

72 » APRIL - MAY 2020 chins in conjunction with shellfish farming, as a means to control bi- ofouling, particularly macroalgae [See: Hasse 1974. Prog. Fish Cultur- ist 36:160-162; Lodieros & Garcia 2004. Aquaculture 231:293-298]. Local knowledge of specific areas and past occurrences of the tim- ing of previous biofouling episodes can be used to develop strategies for moving gear temporarily to other locations to avoid a future fouling event. In more recent times the use of silicone or other smooth surface plastic coatings for gear to resist development of initial bacterial or algal biofilms, or allow for easy re- lease of freshly set biofouling or- ganisms, have been developed or are under development. Current research on biofouling prevention is focusing upon the surface prop- erties of materials and their ability to attract or resist biofouling organ- isms. The four key properties of material surfaces affecting biofoul- ing settlement include, the mechani- cal properties such as coefficient of Biofouling of oyster bags in Point Judith Pond, Rhode Island. Photo by the author.

Biofouling of floats and gear suspension lines can add considerable weight, causing gear to sink or make overall gear handling more difficult.

Unloading fouled lantern nets at a Chilean scallop farm. Photo by Ed Rhodes.

APRIL - MAY 2020 » 73 THE SHELLFISH CORNER

Local knowledge of specific areas and past occurrences of the timing of previous biofouling episodes can be used to develop strategies for moving gear temporarily to other locations to avoid a future fouling event.

Biofouled mussel spat collector line in the Black Sea near Batumi, Georgia. Photo by the author.

friction (or slipperiness); structural a thin layer of paraffin wax, or alter- properties such as porosity and topol- natively the wax infused with Chi- ogy (shapes, roughness and degree naberry seed extract or honeylocust of regularity of geometric forms on seed extracts, and then tested against the surface); polarity (nature of elec- untreated control oysters at coast- trical charges on the surface); and the al pearl farm sites. The wax-based surface chemistry, including the bioac- coatings deterred fouling-organism tivity of exposed molecular groups settlement on oysters for at least once exposed to seawater. Materials 60 days during the intensive fouling science studies of this type are ex- season, while reducing mortality and pected to point the direction to bet- not adversely affecting their growth ter biofouling technologies for the [See: Ye et al. 2019. J. Bioadhesion aquaculture industry. Promising new & Biofilm Res. 35:649-657]. Since coatings with a high degree of resis- there are a number of food-grade tance to biofouling are now under waxes and similar coatings approved development, but all too frequently by food safety authorities such as once exposed to real world condi- the Food and Drug Administration tions they fail to perform as they (FDA) in the United States for use as do in the laboratory [See: Koc et al. coating of fruits destined for human 2019. J. Bioadhesion & Biofilm Res. consumption, this approach of ap- 35:454-462]. plied wax coatings might be adapted One interesting recent practical for use in aquaculture production of Michael A. Rice, PhD, is a Professor of Fisheries, development in the control of bio- shellfish destined for human con- Animal and Veterinary Science at the University of Rhode Island. He has published extensively in the fouling on cultured shellfish them- sumption. One obvious application areas of physiological ecology of mollusks, shell- selves is the use of wax-based coat- of this technology may be for trials fishery management, molluscan aquaculture, and aquaculture in international development. ings applied to pearl oysters during with oysters to prevent biofouling by He has served as Chairperson of his department at the University of Rhode Island, and as an elected the high season for biofouling in boring sponges or mud blisters that member of the Rhode Island House China. In the study, pearl oysters frustrate many oyster farmers in the of Representatives. (Pinctada imbricata) were coated with Northeastern United States. [email protected]

74 » APRIL - MAY 2020