Settlement of larvae

Rather than attempt an exhausting review of this literature, this chapter focuses mainly on papers published after 1990 that offer new insights into the role(s) of biofilms on hard surfaces in inducing settlement of larvae of marine invertebrate animals. See Pawlik3 for a good summary of earlier literature on the role of biofilms in the recruitment of invertebrate larvae. It is probably valid to say that most, if not all, members of the common fouling communities that have become widely distributed around the world due to their transport on ships are initiated when their larvae respond to bacterial films on submerged surfaces.29... 

When larvae fail to settle in a particular test situation, is it due to the absence of positive cues, or are there other factors that prohibit settlement, even when positive cues may be present This is a difficult question to answer because of the possibility that a negative cue may, in fact, be a neutral substance that simply makes the positive cue undetectable by a larva, rather than a substance that causes a larva to reject a potential settlement site. Much effort to demonstrate negative cues to settlement has come from the search for antifouling natural products from marine organisms (reviewed by Pawlik 3 see also Chapters 10 and 17 in this volume). However, there is little reason to believe that extracted compounds which are toxic or aversive to invertebrate larvae have any such function in nature. The best evidence to date for chemical deterrence of larval settlement comes from the work of Woodin and co-workers.212 214 Focusing on halogenated compounds released by many marine polychaete and enteropneust worms,212 they have shown inhibition of settlement of larvae of other species in the presence of the compounds.213 214... 

Gee, J. M., Chemical stimulation of settlement of larvae of Spirorbis rupestris (Serpulidae), Anim. Behav., 13, 181, 1965. 

The adsorption of biopolymers onto a surface 190], the attraction and adhesion of bacteria to that surface, their subsequent multiplication and exopolymer production leads to the formation of biofilms 191]. The original conditioning film can influence the type and number of settling microorganisms, which in turn can affect the settlement of larvae of marine fouling organisms (92, 93]. 

For many years the use of exogenous chemicals to influence settlement and metamorphosis in a range of marine invertebrate species has been studied. In an aquaculture context, the ability to influence this transitional period represents a powerful tool (Baloun and Morse, 1984 Mesfas-Gansbillar et al, 2008). The identification of simple chemical inducers could provide routine, inexpensive and effective culture techniques for the settlement of larvae onto a substrate in a controlled system (Cooper, 1982 Davis et a/., 1990). 

Table 9.3 Liothyrella uva settlement of larvae on different substrata ...

Wieczorek SK, Todd CD (1998) Inhibition and facilitation of settlement of epifaunal marine invertebrate larvae by microbial biofilm cues. Biofouling 12 81-118... 

Ecological studies indicate that the Australian sponge Stylotella aurantium inhibits the settlement of ascidian larvae. A dichloroimine metabolite, stylotellane B (132), was isolated which displayed weak P-388 activity [105],... 

Tribromo-3,4,7-trichloro-3,7-dimethyl-1,5-octadiene (133) from the Australian alga Plocamium costatum deters the settlement of Balanus amphitrite larvae at 10 pg/ml [106]. 

Elatol (134) from the red alga Laurencia rigida completely inhibits the settlement of Balanus amphitrite larvae at 0.1 pg/cm2 [107]. 

Small sedentary grazers such as amphipods appear to select chemically defended seaweeds as host plants since they would otherwise be subject to intense predation by reef fishes however, they do not sequester metabolites as do other selective grazers such as sacoglossans and opistobranch molluscs.105 109 Grazing by amphipods induces increased concentrations of acutilol A acetate and acutilol B in Dictyopteris menstrualis and makes the seaweed less susceptible to attack by other predators 112 the same terpenes acted as antifoulants which prevented the settlement of bryozoan larvae.107 This evidence for multiple roles for algal metabolites may provide an explanation of previously documented differences in chemical composition in Dictyota.113... 

FIGURE 10.2 (CONTINUED) and unattached larvae. N = six (6) replicates (dishes) were done for all treatments. The results of the assay are expressed as percentage settlement of the seawater (untreated) control. Data are mean + S.E. Treatments lacking error bars indicate 100% settlement in all replicates. Statistical analysis of the data (separate one-factor analysis of variance ANOVA for each of Figure 10.2A and 10.2B, followed by Tukey s post-hoc comparison among means) showed that only extracts from D. pulchra significantly deterred settlement (at both natural and twice natural concentrations). 

Several partially characterized inhibitors have been described from the marine bacterium Pseudoalteromonas tunicata, isolated from the tunicate Ciona intestinalis. This bacterium produces a diversity of metabolites, each of which specifically inhibits the settlement of invertebrate larvae... 

Wieczorek, S.K., Clare, A.S., and Todd, C.D., Inhibitory and facilitatory effects of microbial films on settlement of Balanus amphitrite amphitrite larvae, Mar. Ecol. Prog. Ser., 119, 221, 1995. 

Holmstrom, C., Rittschoff, D., and Kjelleberg, S., Inhibition of settlement by larvae of Balanus amphitrite and Ciona intestinalis by a surface-colonizing marine bacterium, Appl. Environ. Microbiol., 58, 2111, 1992. 

Crisp, D.J., Factors influencing the settlement of marine invertebrate larvae, in Chemoreception in Marine Organisms, Grant, P.T. and Mackie, A.M., Eds., Academic Press, New York, 1974, 177. 

Tamburri, M.N., Zimmer-Faust, R.K., and Tamplin, M.L., Natural sources and properties of chemical inducers mediating settlement of oyster larvae a re-examination, Biol. Bull., 183, 327, 1992. 

Turner, E.J., Zimmer-Faust, R.K., Palmer, M.A., Luckenbach, M., and Pentcheff, N.D., Settlement of oyster (Crassostrea virginica) larvae effects of water flow and a water-soluble chemical cue, Limnol. Oceanogr., 39, 1579, 1994. 

Daume S., Brand-Gardner, S., and Woelkerling, W.J., Preferential settlement of abalone larvae diatom films vs. non-geniculate coralline red algae, Aquaculture, 174, 243, 1999. 

Kato, T., Kumanireng, A.A., Ichinose, I., Kitahara, Y., Kakinuma, Y., Nishihara, M., and Kato, M., Active components of Sargassum tortile effecting the settlement of swimming larvae of Coryne uchidai, Experientia, 31, 433, 1975. 

Leis, J.M. and Carson-Ewart, B.M., In situ swimming and settlement behaviour of larvae of an Indo-Pacific coral-reef fish, the coral trout Plectropomus leopardus (Pisces Serranidae), Mar. Biol., 134, 51, 1999. 

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