195 10 Ecologically Safe Protection from Biofouling 10.1 DEFENSE AGAINST EPIBIONTS The total surface area of living organisms in marine environments is really enormous. It appears to be comparable with, or even exceed, the area of non-living hard substrates on the shelf. This seems quite probable if one takes into account not only the population of benthos, including the hard-substrate communities (see Section 1.1), but also plankton and nekton. Many “living” surfaces are populated by certain organisms. The extent of epibiosis becomes evident from the following example. Out of 2254 pairwise interactions between species of multicellular algae, invertebrates, and ascidians inhabiting underwater rocks in New England (U.S.), 59% represent active interactions and are the result of the overgrowing of one organism by others (Sebens, 1985b). Competition for space is especially severe on natural substrates in coastal areas and on the shelf. The dispersal forms of micro- and macroorganisms of benthos that settle on attached or vagile animals and macroalgae (basibionts) become epibionts. The fol- lowing situations are theoretically possible. The basibiont surface or a part of it may be either chemically inert or attractive for epibionts or, conversely, repellent, toxic, or biocidal. According to many workers (Goodbody, 1961; Jackson, 1977a; Gauthier and Aubert, 1981; Bakus et al., 1986; Pawlik, 1992; Wahl, 1989, 1997; Slattery, 1997; Targett, 1997), negative epibiotic interrelations between macroorganisms are more common than are positive or neutral interrelations. This phenomenon may serve as a prerequisite for developing ecologically safe antifouling protection, based on epibiotic defense mechanisms. Let us consider in greater detail the published data on the protection of sea organisms from epibionts. Some attached macroalgae and animals, despite being surrounded by hundreds of potential foulers, have almost no macroorganisms on their surface. Such resistant species have special mechanisms of protection, which have been considered in a number of reviews (Jackson, 1977a; Gurin and Azhgikhin, 1981; Gauthier and Aubert, 1981; Bakus et al., 1986; Elyakov and Stonik, 1986; Wahl, 1989, 1997; Sammarco and Coll, 1990; Pawlik, 1992; Clare, 1996; Slattery, 1997; Steinberg et al., 1997; Targett, 1997). Similar to commercial antifouling pro- tection (see Chapter 9), biological defense against epibiosis can be divided into a chemical and a physical one on the basis of the acting factors; in this case, mechanical defense will be considered as a type of physical defense. 1419_C10.fm Page 195 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 196 Marine Biofouling: Colonization Processes and Defenses The most widespread means of direct physical (mechanical) protection of basi- bionts from epibionts are the following: release of mucus; peeling of outer teguments; molting; filtering-off of dispersal forms; and the presence of needles and other skeletal structures hampering the fouling. For relatively motile animals (for example, dolphins and fish), the speed with which they are able to swim should be added to this list, along with the mucus-rich integuments that may release toxicants (Jackson, 1977a; Wahl, 1989, 1997; Duffy and Hay, 1990; Pawlik, 1992; Slattery, 1997; Targett, 1997; Wahl et al., 1998). Means of indirect physical protection may include a high growth rate, allowing one species to avoid fouling by another, more slowly growing species (see Section 6.5). Such situations are commonly observed in those algae and invertebrates that grow preferentially along a hard surface, such as cal- careous coralline algae, sponges, corals, bryozoans, and compound ascidians. Release of mucus, peeling, and molting as a means of tegument renewal are routine mechanisms used to remove fouling from the outer surface of sea plants and animals. They make it possible to periodically cast off the biofouling and the dead cover tissues. Such methods of physical protection are widespread in nature (Wahl, 1989, 1997; Targett, 1997). In more than 20 investigated species of coralline algae, epithelial cells were shown to peel off (Johnson and Mann, 1986; Keats et al., 1997). Peeling provides a short-term antifouling effect but does not completely solve the problem of defending against epibiosis. In algae, it reduces the abundance of micro- and macrofouling only by several times, whereas animals usually are more efficiently protected by tegument peeling or molts. The sponge Halichondria panicea , a typical inhabitant of temperate waters, regularly renews its tegument about every 3 weeks (Barthel and Wolfrath, 1989), which protects it from biofouling to a certain extent. In a similar way, peeling, along with other means of physical and chemical protec- tion, is quite efficient in maintaining the low level of biofouling in the ascidian Polysyncraton lacazei (Wahl and Lafargue, 1990; Wahl and Banaigs, 1991). Similar mechanisms were described in corals (Sammarco and Coll, 1990) and other inver- tebrates (Wahl, 1989, 1997). Peeling is a rather slow process. It occurs with certain periodicity but is not continuous. Therefore, it cannot be regarded as a radical method of protection from epibiosis. This may be said even more categorically about molting, which occurs less frequently than peeling. In addition, molting is usually accompanied by the interruption of other protective mechanisms, such as the removal of dispersal forms from the plankton in the process of feeding, which play a significant role in defending against epibiosis. Molting at the adult stage is characteristic of the animals whose growth is limited by chitinous integuments (Wahl, 1989). It is observed in cirripedes, ascidians, and some other sessile forms. Physical defense by itself appears to be insufficient for completely protecting a basibiont from epibionts. Therefore, physical protection is considered to be the main method of epibiosis control in those species that are resistant to even a considerable degree of biofouling. One of the means of physical defense against epibionts is low surface energy, i.e., hydrophoby of the basibionts’ teguments, which suppresses larval attachment to them (e.g., Wahl, 1989, 1997; Targett, 1997; Rittschof et al., 1998). Quite often this may be linked to the properties of the biofilms on their surface. The attachment of bacteria is hampered or rendered impossible at free energy values of about 20 to 1419_C10.fm Page 196 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC Ecologically Safe Protection from Biofouling 197 30 mN/m (see, e.g., Dexter, 1978). Similar critical values of surface energy have been established for the attachment of the cirripede cyprids (Rittschof et al., 1998). However, it should be noted that different parts of the body of a living organism may, generally speaking, have different wettability; and, in addition, this parameter may change in ontogenesis. Therefore, such a method of physical protection from epibiosis appears to have a restricted distribution in nature. The efficiency of physical protection in basibionts can be augmented by chemical agents. In general, chemical protection from epibionts (and predators) is more reliable and successful than physical protection, since it works continuously. It is quite widely spread and represents a more sophisticated adaptation of organisms to the changing environment. For example, damage to the thallus of Fucus distichus increases the production of phenolic compounds that are used by this brown alga for protection against feeding by the gastropod Littorina sitkana (van Alstyne, 1988). The phenol content in the plant increases by 20% within 2 weeks, not only in the damaged part, but also in the adjacent branches. As a result, the rate of consumption of such fucoids by the mollusks decreases twofold. The induction of chemical defense by physical damage has been observed in 17% of the 42 algal species studied (Cetrulo and Hay, 2000). The term “allelochemical action” will be preferentially used in the following to designate the general chemical influence of one plant or animal species over another (Gilyarov et al., 1986), whereas negative interactions involving toxic effects will be referred to as “allelopathy” (Rice, 1984). Studies performed in the 1960s to 1980s (Goodbody, 1961; Khailov, 1971; Kucherova, 1973; Jackson and Buss, 1975; Bak et al., 1981; Targett et al., 1983; Rittschof et al., 1985; de Ruyter et al., 1988, etc.) demonstrated the existence of chemical defense against epibiosis in sea plants and animals. It was found that the allelochemical action of macroalgae was based on the release of secondary metabolites of quite various natures. It should be noted that secondary metabolites include the compounds that are not directly associated with basic metabolism, i.e., processes of growth and reproduction, but perform regulatory, signal, protective, and some other functions. The objects of many studies were marine algae, which have little or no fouling at all. For example, Z.S. Kucherova (1973) studied the biological activity of exudates of the Black Sea macrophytes. She found that the green alga Enteromorpha linza , the brown alga Padina sp . , and the red algae Corallina officinalis and Callithamnion sp . released into sea water some compounds that, under experimental conditions, caused the cessation of movement in the larvae of such macrofoulers as the mussels Mytilus galloprovincialis and barnacles of the genus Balanus . Prolonged exposure to these compounds killed the larvae. In addition, these exudates suppressed the development of cultures of some bacteria and diatoms. A widespread group of secondary metabolites released in water by marine macroalgae is that of phenolic derivatives — tannins and tannin-like compounds (Slattery, 1997; Targett, 1997). Hydrolysable tannins represent esters of sugars and gallic acid or gallic and hexaoxydiphenic acids (Figure 10.1(1, 2)). Condensed tannins are the product of the oxidative polymerization of catechols (Figure 10.1(3)) and belong to the group of polyphenolic compounds. They are considerably more resistant to microbial destruction than hydrolysable tannins (Barashkov, 1972). Phlorotannins, 1419_C10.fm Page 197 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 198 Marine Biofouling: Colonization Processes and Defenses which are commonly present in brown algae, are polymers of 1,3,5-trihydroxyben- zene, known by the common name phloroglucinol (Figure 10.1(4)). The content of polyphenolic compounds in brown algae can reach 10 to 25% by dry weight (van Alstyne, 1988; Targett et al., 1995) and is especially high in young growing parts of the thallus — at the tips of branches, where the epibionts are routinely scarce or absent (Sieburth and Conover, 1965). Tannins are highly toxic and kill the mollusks feeding on the algae even at low concentrations (Duffy and Hay, 1990). Tannins of the brown alga Sargassum natans are toxic to various marine invertebrates, such as hydroid polyps, triclads, nematodes, sea spiders, and copepods (Sieburth and Conover, 1965), causing loss of motility followed by death. According to the data of the same authors, a paint containing tannic acid was resistant to fouling by cirripedes and algae. Other studies (Lau and Qian, 1997, 2000) showed that tannic acid, phloroglucinol, and their polymers (phlorotannins) inhibit the settlement of the larvae of the polychaete Hydroides elegans and the barnacle Balanus amphitrite amphitrite. In addition to polyphenols, algae may secrete other high-molecular compounds as well. The green alga Ulva reticulata suppresses larval settlement and metamor- phosis in the polychaete Hydroides elegans (Harder and Qian, 2000). The antifouling factor of still unknown composition (a polysaccharide, protein, glycoconjugate, or a mixture thereof) has a molecular weight of more than 100 kD. Rather high biological activity is characteristic of halogenorganic compounds, such as trichloroethylene, bromopentane, iodoethane, and others, secreted by various species of green, brown, and red algae (Gschwend et al., 1985; Abrahamsson et al., 1995; Steinberg et al., 1998; Wright et al., 2000). These compounds are toxic to micro- and macroorganisms and protect the algae from epibionts. The red alga Plocamium hamatum exerts a contact toxic effect on the coral Sinularia cruciata and the sponges inhabiting the coral reef (de Nys et al., 1991). Animal tissues undergo necrosis under the action of a specific monoterpene (Figure 10.2). Terpenoids of green algae are effective against microorganisms, sea urchins, and fish (Paul and Fenical, 1987). FIGURE 10.1 Phenolic components of tannins. (1) Gallic acid, (2) hexaoxydiphenic acid, (3) catechol, (4) 1,3,5-trihydroxybenzene (phloroglucinol). 1419_C10.fm Page 198 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC Ecologically Safe Protection from Biofouling 199 Secondary metabolites of macroalgae also serve as a defense against phytoph- ages. For example, phlorotannins of the brown alga Ecklonia stolonifera protect it from being eaten by the gastropod Haliotis discus (Taniguchi et al., 1991). Diterpe- noids rather efficiently protect green algae of the genus Halimeda from grazing by fish (Paul and van Alstyne, 1988). Terpenic compounds are secreted not only by green but also by red and brown algae (Barashkov, 1972). A mechanism that is common to 39 species of green, brown, and red algae, which protects them from being eaten by invertebrates, involves the release of acrylic acid and acrylate as a result of the metabolic transformation of dimethyl-sulfoniopropionate (van Alstine et al., 2001). It is interesting to note that allelochemical interactions between different flow- ering plants, and also between flowering plants and animals, are based on similar principles, while the protective compounds used belong to the same classes as in marine macroalgae (Harborn, 1993). This indicates both the ancient origin and the universality of the corresponding biochemical mechanisms, which have been pre- served during the long evolution from the lower to the higher plants. Among marine animals, allelochemical protection from epibiosis has been stud- ied most extensively in sponges, corals, and ascidians, which is reflected in several reviews (Wahl, 1989; Pawlik, 1992; Clare, 1996; Slattery, 1997; Targett, 1997). Compounds secreted by many sponges are toxic to microorganisms, animals, and plants. Therefore, keeping sponges in aquaria together with other organisms quite often results in the death of the latter. The antimicrobial activity of sponges is a widespread phenomenon. It was described by J.E. Thompson and his colleagues (1985), who studied 40 species of sponges and found that, for 28 of the species (i.e., 70%), the extracts of sponges suppressed the growth of bacterial and yeast cultures. More than 40 different antimicrobial substances, mostly belonging to terpenes, have so far been isolated and identified in sponges. Defense of sponges against macrofouling, though common, is still not a general rule; for example, it was revealed in only 6 of 20 studied species of Caribbean sponges, i.e., in 30% (Engel and Pawlik, 2000). The marine sponge Aplisina fistularis protects itself from fouling by bryozoans and polychaetes (Thompson, 1985). In experiments, the settlement of larvae of the bryozoan Philodophora pacifica and the polychaete Salmacina tribranchiata was impeded in water in which the sponge had been kept for 1 h. The suppression of metamorphosis and death of juveniles of the mollusk Haliotis rufescens also were observed. After several days, the water sur- rounding the sponges became toxic to mollusks and starfish. Two heterocyclic compounds, identified as aerothionin and homoaerothionin (Figure 10.3 [1,2]), were isolated from exudates of Aplisina fistularis . They proved to be responsible for protecting this sponge from epibionts (Walker et al., 1985). FIGURE 10.2 Monoterpene chloromertensine. 1419_C10.fm Page 199 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 200 Marine Biofouling: Colonization Processes and Defenses Observations of Siphonodictyon spp . , which settle on the coral Montastrea cav- ernosa near the Caribbean islands, show that a sterile zone is formed around these sponges (Jackson and Buss, 1975). Their toxic agent is siphonodictidine (Figure 10.3 [3]), which consists of a furan ring and a sesquiterpene (Sullivan et al., 1983). The sponges Aplisina fistularis , Haliclona cinerea , Dysidea amblia , Euryspongia sp . , Axinella sp . , and some others, which are capable of the simulta- neous suppression of three to six species of bacteria, have practically no macrofoul- ing on their surface (Thompson et al., 1985). The antimicrobial metabolites of sponges show a wide spectrum of actions: in particular, they suppress the growth of a red alga, the locomotion of a limpet and a starfish, and the feeding of a hydroid and a bryozoan. They also inhibit settlement and development in the propagules of the brown alga Macrocystis pyrifera , the polychaete Salmacina tribranchiata , the bryozoan Philodophora pacifica , and the abalone Haliotis rufescens . Other terpenes secreted by sponges (Figure 10.3) also have a wide spectrum of actions (Elyakov and Stonik, 1986; Clare, 1996). Sponges, like macroalgae, can defend themselves from grazing by means of secondary metabolites that they release in water (Wright et al., 1997), for example, halogenorganic compounds (Assmann et al., 2000) and triterpene glycosides (Kubanek et al., 2000). FIGURE 10.3 Terpenes of sponges with a broad action spectrum. (1) Aerothionin ( n = 4), (2) homoaerothionin ( n = 5), (3) siphonodictidine, (4) heteronemin, (5) ambiol A, (6) pallescensin A, (7) idiadione, (8) δ -cadinen cyan. 1419_C10.fm Page 200 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC Ecologically Safe Protection from Biofouling 201 Coral polyps produce a number of toxic aliphatic, heterocyclic, nitrogen-con- taining compounds (including pyridines), and terpenes. Especially noticeable among them is palitoxin (Orlov and Gelashvili, 1985; Gleibs and Mebs, 1998), which is structurally close to saponins, the triterpene derivatives known to exist in echino- derms. Palitoxin has been isolated from the coral Palythoa toxica that lives in the Caribbean Sea. This is the most powerful toxin known in marine organisms. Its lethal dose for mice is only 0.15 µ g/kg of body mass, which is 3,000 times lower than that of curare and 60,000 times lower than that of potassium cyanide. Terpenes, many of which are also toxic, are especially common in corals (Gurin and Azhgikhin, 1981; Elyakov and Stonik, 1986; Clare, 1996). Large quantities of terpenes are present in soft-bodied corals (Alcyonaria); they protect the corals from predation by fish; from other corals in the course of interspecific competition; and also from fouling by filamentous algae, bryozoans, sedentary polychaetes, and cir- ripedes (Sammarco and Coll, 1990; Puglisi et al., 2000). One of the representatives of sea fans (Gorgoniacea), Renilla reniformis , secretes diterpenes known as renillafoulins (Figure 10.4 [1]), which suppress larval settlement in the barnacle Balanus amphitrite amphitrite by acting as biocides (Keifer and Rinehart, 1986). The diterpenes pukalide and epoxypukalide (Figure 10.4 [2,3]) from the gorgonian Leptogorgia virgulata also inhibited settlement in the larvae of B. amphitrite (Gerhart et al., 1988). However, according to the data of these authors, the mechanism of suppression does not appear to be biocidal. Secondary metabolites of corals can suppress the growth of microorganisms, bacteria, and diatoms via a non-toxic mechanism (Wilsanand et al., 1999, 2001). The corals Leptogorgia virgulata and L. setacea were found to contain homarine FIGURE 10.4 Antifoulants of corals. (1) Renillafoulins (R 1 = R 2 = C 2 H 5 ; R 1 = C 2 H 5 , R 2 = C 2 H 5 CO; R 1 = C 2 H 5 , R 2 = C 3 H 7 CO), (2) pukalide, (3) epoxypukalide, (4) homarine. 1419_C10.fm Page 201 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 202 Marine Biofouling: Colonization Processes and Defenses (Figure 10.4 [4]), a pyridine derivative that is effective in protection from epiphytic diatoms (Targett et al., 1983). One of the methods of allelochemical protection from epibiosis in ascidians involves releasing substances with a low pH value onto the tunic surface (Wahl, 1989). In 13 of the 35 ascidian species from the families Ascidiidae, Didemnidae, Polycytoridae, and Polyclinidae, living near the Bermudas, the pH of the excreta was less than 2.0 (Stoecker, 1980). Such a high concentration of hydrogen ions was caused by the release of sulfuric acid from the vacuoles of special cells — vanadocytes. Another method of toxic pro- tection from epibionts and predators in ascidians is the high content of vanadium, which is also accumulated in the vanadocytes. Such a method of protection was found in 10 of the 35 ascidian species occurring on the Bermudas. As a result of chemical and possibly physical protection, or their combination, 60% of the species studied were completely free of macroscopic epibionts (Stoecker, 1980). The compound ascidian Polysyncraton lacazei has only one species of multicel- lular epibionts — a small entoproct Loxocalyx sp . — even though hundreds of potential epibiont species are present in the nearest environment (Wahl and Lafargue, 1990). Another very rare epibiont is the diatom Navicula sp. Besides physical pro- tection, which is mainly related to its filtering activity, this ascidian possesses means of chemical protection. Special studies (Wahl and Banaigs, 1991) have shown that the ascidian releases two secondary metabolites that suppress the reproduction of unicellular algae. One of them is a still unidentified lipid, while the other is probably a protein. These metabolites also suppressed the development of the sea urchin Paracentrotus lividus and were toxic to its larvae. The surface of the ascidian Cystodytes lobatus was shown to be practically free of microorganisms (Wahl et al., 1994). The density of bacteria on it is about 10 to 100 cells/cm 2 , whereas on other species this value may reach up to 10 5 cells/cm 2 . Extracts and secretions of this ascidian reduce the number of attaching bacteria of various species by several times. The fractions suppressing the settlement of micro- organisms did not influence their growth, even though the growth inhibitors were present in the extracts of this ascidian. Thus, the suppression of settlement was not caused by any expressed toxic effect on the bacteria. Similar results were obtained for Aplidium californicum , Archidistoma psammion , Didemnum sp., and Trididemnum sp. (Wahl et al., 1994). Different ascidians possess protective properties to an unequal extent. The study of 12 species showed that only some of them, such as Aplidium proliferum , Botryllus schlosseri , and Morchellium argus , possessed a noticeable defense against a hydroid polyp and two species of bryozoans; M. argus also was protected against the poly- chaete Spirorbis spirorbis (Teo and Ryland, 1994). The highest mortality rate in this polychaete and the bryozoans was caused by the ascidian Clavelina lepadiformis . The same species revealed a distinct antibacterial biocidal activity. The surfaces of the ascidians Eudistoma olivaceum and E. glandulosum are pro- tected from biofouling due to the release of special compounds — eudistomins (Figure 10.5 [1,2]) — which are alkaloids that have high biological activity (Davis et al., 1991). Ascidians, like sponges and corals, also secrete deterrents that protect them from such predators as crabs and fishes (Teo and Ryland, 1994). 1419_C10.fm Page 202 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC Ecologically Safe Protection from Biofouling 203 Other groups of animals have been less thoroughly studied as potential sources of antifoulants. Of special interest are the data on the suppression of settlement in Balanus amphitrite cyprid larvae by 2,5,6-tribromo-1-methylgramine (Figure 10.5 [3]), isolated from the bryozoan Zoobotryon pellucidum (Kon-ya et al., 1994). This compound was efficient in concentrations smaller than the working concentrations of the common biocide tributyltin oxide, which is used in industrial antifouling protection (see Section 9.1). It should be emphasized that settlement was suppressed at non-toxic concentrations of the agent. Another example is the work in which exudates of two bryozoan species Bugula pacifica and Tricellaria occidentalis were shown to have a broad spectrum of antibacterial activities and to suppress the bacterial film on these animals (Shellenberger and Ross, 1998). The data on the possible suppression of biofouling by the microbial communities developing on hard surfaces (including the integuments of basibionts) are directly related to understanding the mechanisms of defense against epibiosis. In particular, films of the diatoms Stauroneis constricta and Nitzschia closterium were shown to be toxic to the prothalli of the red alga Gigartina stellata and to suppress its growth (Huang and Boney, 1985). The combined negative effects of the two species of diatoms proved to be more expressed than the separate influence of each species. Such data are especially important for understanding the protection from epibiosis in a natural environment, where multispecific communities of microorganisms, con- sisting preferentially of bacteria and diatoms, develop on the surfaces of macroalgae, invertebrates, and ascidians. Different epiphytic bacteria have different effects on the settlement of larvae. Their effects can be toxic, biocidal, neutral, or stimulating (e.g., Thompson et al., 1985; Maki et al., 1988, 1990; Rittschof and Costlow, 1989; Holmström et al., 1992; Dobretsov and Qian, 2002; see also Section 5.5). Of special interest in connection with defense against epibiosis are data on the bacterial suppression of the settlement and attachment of larvae. Toxic epiphytic bacteria are rather common and comprise about 25% of all cultures isolated from natural marine substrates. Comparison of the toxicities of some bacteria allows one to arrange them in the following sequence, in order of their increasing biocidal activity: Vibrio campbelli , Pseudomonas atlantica , Deleya (Pseudomonas) marina , and Vibrio vulnificus (Maki FIGURE 10.5 Some antifoulants from ascidians and bryozoans. (1) and (2) Eudistomins G and H (in 1, R = H, R 1 = Br; in 2, R = Br, R 1 = H); (3) 2,5,6-tribromo-1-methylgramine. 1419_C10.fm Page 203 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 204 Marine Biofouling: Colonization Processes and Defenses et al., 1988, 1990). According to some evaluations (Rittschof and Costlow, 1989), D. marina reduced the settlement of the cyprid larvae of Balanus amphitrite and the cyphonautes of Bugula neritina by 14 and 17 times, respectively. An exopolymer that suppresses the settlement and attachment of barnacle larvae was isolated from the culture of this bacterium (Maki et al., 1990). When adsorbed on polystyrene, this high- molecular substance reduced the number of attached juvenile barnacles by more than 10 times, whereas on glass it was reduced by only 3 times. Such differences were accounted for by the structural features of the adhesive polymer, which appears to have a greater affinity to a hydrophobic surface than to a hydrophilic one (Maki et al., 1990). According to other data (Holmström et al., 1992), the settlement and attachment of barnacles can be suppressed by a bacterial factor with an MW of only 500 D. The toxin includes a carbohydrate component and probably is a carbohydrate. Consideration of the published data allows some general conclusions to be made. Defense against epibiosis, which is widespread in nature, reduces the abundance of epibionts on marine algae and animals. This may partly explain the fact that the biomass of foulers is usually higher on non-toxic artificial substrates than on the surfaces of living objects (Zevina, 1994). As in the case of industrial antifouling protection, chemical factors prove to be the most efficient against epibiosis. They work continuously and therefore provide permanent protection. Some classes of substances and individual compounds are efficient enough to be considered as potential antifoulants in industrial protection systems. In my opinion, this group should include, first of all, the phenolic and halogenorganic secondary metabolites of sponges with a broad spectrum of biocidal activities, and also the terpenes of corals, since they have distinct toxic properties. These substances or their analogs will probably be used for this purpose in the future. Non-biocidal protection from biofouling, which will be surveyed in Sections 10.3 and 10.4, appears quite prom- ising, especially from an ecological point of view 10.2 NATURAL AND INDUSTRIAL ANTICOLONIZATION PROTECTION The concentration of foulers on natural and artificial hard substrates (see Section 1.2) is largely determined by their colonization pressure, which may be rather intensive (Wahl and Mark, 1999). However, during the course of evolution, basibionts have acquired certain mechanisms of chemical and physical defense against colonization by epibionts (see Section 10.1). In industry, special protection methods have been designed to counteract the colonization pressure (see Section 9.2). Despite the wide use of biocides (and toxicants) by basibionts, the natural defense against biofouling is ecologically safe. However, the use of biocides for protecting man-made systems has rather negative ecological consequences (see Section 9.3). The fact is that the chemical nature of antifouling agents is completely different in the two cases. Natural defenses against epibiosis involve secondary organic exometabolites: phenolic (polyphenolic) and halogenorganic compounds, terpenes, heterocyclic compounds, and other compounds. In the protection of man- made systems, heavy metals (copper, zinc, and lead oxides), low-molecular organotin compounds, chlorine, ozone, and their derivatives are used as biocides. 1419_C10.fm Page 204 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC [...]... communities Field experiments were carried out in the White Sea Copyright â 2004 CRC Press, LLC 1419_C10.fm Page 210 Tuesday, November 25, 2003 4:56 PM 210 Marine Biofouling: Colonization Processes and Defenses TABLE 10. 1 Repellent Effect of N,N,N,N-Tetramethylethylenediamine and Benzoic Acid on Planulae of Hydroids and Postlarvae of Mollusks Substance Concentration, mM Turning from the Capillary Angle , Distance,... Dynamena pumila 10 2 82 0.98 68 8 0.41 105 11 0.70 10 2 110 11 1.30 0.20 0 0 40 55 0 85 N,N,N,N-Tetramethylethylenediamine 0 43 172 Gonothyraea loveni 63 1 45 9 1.00 0.07 90 11 1.13 0 .10 0 20 70 5.11 8.18 2 .10 2.05 N,N,N,N-Tetramethylethylenediamine Benzoic acid 0 86 0 744 Mytilus edulis 82 1 90 11 1.80 0 .10 82 1 90 15 0.60 0 .10 0 85 0 45 7.44 5.45 2.02 2.02 N,N,N,N-Tetramethylethylenediamine... Antifouling ship enamel KHV-5153 8 0.1 (10. 5) 31 6 (3.8) Notes: (1) Fouling of the control vinyl-rosin coatings without additions is taken to be 100 %; (2) calculated t-test values are given in parentheses; (3) in Tables 10. 2, 10. 3, 10. 5, and 10. 6, the values signicantly (p < 0.05) different from the control are underlined; (4) dashes indicate the absence of data Based on the data of Railkin and Dobretsov, 1994... those reducing or suppressing attachment (antiadhesives), and those that block Copyright â 2004 CRC Press, LLC 1419_C10.fm Page 206 Tuesday, November 25, 2003 4:56 PM 206 Marine Biofouling: Colonization Processes and Defenses locomotion (anesthetic and narcotizing agents) work in natural systems at concentrations that do not kill the organisms and in many cases do not cause any apparent toxic effects... oxygen, and superoxide, whose toxicity is intermediate between the most toxic hydroxyl radical and the least toxic hydrogen dioxide Chemical properties of these forms are known well enough, and they can be produced as individual compounds in large quantities Copyright â 2004 CRC Press, LLC 1419_C10.fm Page 218 Tuesday, November 25, 2003 4:56 PM 218 Marine Biofouling: Colonization Processes and Defenses. .. safe protection from marine and freshwater biofouling 10. 6 PROSPECTS OF DEVELOPING ECOLOGICALLY SAFE ANTICOLONIZATION PROTECTION Antifouling protection aimed at the suppression of colonization processes employs a variety of ideas, approaches, and methods Many of them have been considered in this chapter, but the prospects and possible directions of development of ecologically safe anticolonization protection... laboratory and eld tests of antifoulants are carried out using a Copyright â 2004 CRC Press, LLC 1419_C10.fm Page 224 Tuesday, November 25, 2003 4:56 PM 224 Marine Biofouling: Colonization Processes and Defenses variety of techniques and biological objects, so that a comparative analysis of their antifouling effect is difcult It obviously would be practical to unify both the procedures used and the test... effective value These repellents were also effective enough against microfouling (Table 10. 3) The repellent suppression of all major groups of microfoulers (bacteria, diatoms, Copyright â 2004 CRC Press, LLC 1419_C10.fm Page 212 Tuesday, November 25, 2003 4:56 PM 212 Marine Biofouling: Colonization Processes and Defenses TABLE 10. 3 Suppression of Microfouling by Repellents Relative Fouling, % of Control Bacteria... tetra-(p-sulphophenyl)-porphin complex, and cobalt meso-(tetra-N-methylpiridine)-porphin complex In solutions of these substances, the swimming velocity of the ciliates decreases gradually, and subsequently the protists die At the rst stage, the toxic effect is reversible The addition of an equimolar concentration of SOD not only restores cell motility but also keeps the ciliates alive (Figure 10. 7)... 12 37 Note: Mean values and their errors are given in parentheses After Railkin, 1995a With permission of the Hydrobiological Journal Copyright â 2004 CRC Press, LLC 1239 h (30 1) h 124 h (8 2) h 0.512 h (2 1) h Time of Locomotion Recovery, h 1224 624 0.51 13 16 2448 (without rinsing) 13 36 8 312 2024 Marine Biofouling: Colonization Processes and Defenses 12 h 332 5-p-Diethylamino anilinomethylene . epoxypukalide, (4) homarine. 1419_C10.fm Page 201 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 202 Marine Biofouling: Colonization Processes and Defenses (Figure 10. 4 [4]),. the White Sea 1419_C10.fm Page 209 Tuesday, November 25, 2003 4:56 PM Copyright © 2004 CRC Press, LLC 210 Marine Biofouling: Colonization Processes and Defenses coastal area (Kandalaksha Bay, Chupa. and Vibrio vulnificus (Maki FIGURE 10. 5 Some antifoulants from ascidians and bryozoans. (1) and (2) Eudistomins G and H (in 1, R = H, R 1 = Br; in 2, R = Br, R 1 = H); (3) 2,5,6-tribromo-1-methylgramine.