Bryozoan Bugula Neritina Research Articles

Antibacterial and antilarval compounds from marine bacteriumPseudomonas rhizosphaerae

In order to obtain non-toxic, antifouling natural products from marine organisms, we studied on the marine bacterium Pseudomonas rhizosphaerae isolated from deep sea sediment. Bioassay-guided column chromatography techniques were used to separate and purify compounds. Extensive spectral analyses including 1D NMR spectra and GC-MS were employed for structure elucidation of the compounds. Antibacterial activity of the isolated compounds towards eight marine bacterial strains was measures by optical density, while antilarval activity was evaluated in settlement inhibition assays with laboratory-reared Balanus amphitrite and Bugula neritina larvae. In total, nine compounds including six diketopiperazine were obtained. Among them, cyclo-(Tyr-Pro), cyclo-(Tyr-Ile), cyclo-(Phe-Pro), cyclo-(Val-Pro), 3-phenyl-2-propenoic acid, and uracil had various antibacterial activities towards five marine fouling bacteria, furthermore, bis(2-ethylhexyl)phthalate, cyclo-(Tyr-Ile), cyclo-(Phe-Pro), cyclo-(Val-Pro), and 3-phenyl-2-propenoic acid showed antilarval effect on larval settlement of barnacle Balanus amphitrite and bryozoan Bugula neritina. The results suggested that marine bacterium Pseudomonas rhizosphaerae could produce potent antibacterial and antilarval diketopiperazine and benzene-type secondary metabolites.

2D Gel-Based Proteome and Phosphoproteome Analysis During Larval Metamorphosis in Two Major Marine Biofouling Invertebrates

Larvae of some benthic invertebrates respond (metamorphose or not) to chemical cues within minutes or hours and often without excessive transcription or translation. Although protein phosphorylation is one of the most important molecular switching mechanisms that govern variety of rapid cellular responses in higher organisms, this is the first study to analyze the global protein expression and protein phosphorylation status during larval metamorphosis in two major marine biofouling invertebrates (a bryozoan Bugula neritina and a barnacle Balanus amphitrite). Results indicate that larval proteomic response to metamorphosis (inhibiton or induction) involves substantial change in the phosphorylation status of proteins rather than de novo protein synthesis. An abundantly expressed and an unnamed phosphoprotein that appears to play key regulatory role in larval metamorphosis was identified. When larvae of bryozoan and barnacle were challenged with a metamorphosis (and kinase) inhibitor, the genistein, the number of phosphoproteins in bryozoan were substantially reduced but drastically increased in barnacle. Taken together, this is the first time that the usefulness of employing 2DE-based proteomic and phosphoproteomic approaches was demonstrated for us to understand the molecular mechanisms of larval metamorphosis and to study the mode-of-action of chemical cues in marine organisms.

The native rock shrimp Rhynchocinetestypus as a biological control of fouling in suspended scallop cultures

Scallop aquaculture in Chile suffers from intense fouling on culture facilities by invasive species such as the ascidian Ciona intestinalis and the bryozoan Bugula neritina. We examined the grazing effect of the rock shrimp Rhynchocinetes typus on fouling species, which colonize scallop pearl nets. We placed different densities of shrimp (0, 2, 5 and 10 individuals) in pearl nets with juvenile scallops (mean shell height 4.9 cm) at Tongoy Bay in northern-central Chile. We sampled the nets after 4 months (January–May 2007) and recovered 35–50% of the shrimp from the different treatments. The nets with 10 initial shrimp had a lower cover of the bryozoan B. neritina and lower densities of the ascidians C. intestinalis and Pyura chilensis, which resulted in a 50% decrease in biomass of fouling on nets. Low scallop mortality and slightly higher (yet not significant) growth in treatments with high shrimp densities suggest a positive interaction between the shrimp and scallops. The native rock shrimp is therefore considered a good candidate as a biological control of fouling communities and this could have a potential for polyculture.

Antifouling Sesterterpenes from the New Zealand Marine SpongeSemitaspongia Bactriana

Three antifouling (AF) sesterterpenes have been isolated from the New Zealand marine sponge Semitaspongia bactriana with toxicity against the diatom Nitzschia closterium and bryozoan Bugula neritina. The three metabolites have been characterised by spectroscopic techniques as 7E,12E,20Z-variabilin (1), cavernosolide (2) and lintenolide A (3) (also called spongianolide C) and have low micromolar activity against our two test species. The gamma-hydroxybutenolide containing sesterterpenes (2 and 3) show the most promise, with relative stability and suitable lipophilicity for incorporation of either these metabolites, or synthetic analogues, as biocides to produce paints or plastics with AF properties.

Diel Variation in the Sizes of Larvae ofBugula neritinain Field Populations

The scale of planktonic larval dispersal affects a variety of ecological and evolutionary processes. Recent work suggests that the dispersal ability of obligately lecithotrophic larvae is influenced by the amount of energy supplied to each larva: larger larvae may stay in the plankton longer and thus travel greater distances than smaller larvae. We examined a prediction of this hypothesis in the bryozoan Bugula neritina, which each morning releases brooded larvae that settle within a few hours. If larger larvae stay in the plankton longer than smaller larvae, than larger larvae should increase in frequency in the planktonic population as the day progresses. However, field surveys revealed a negative relationship between time of day and the sizes of planktonic larvae. Because these results may have been complicated by prolonged larval release, we sequestered groups of brooding colonies in field mesocosms to examine release patterns. Larvae were released over a period of 8-9 h, with smaller larvae increasing in frequency as the day progressed. We conclude that populations of larvae of B. neritina may not be homogenous in energetic content throughout the day; this must be taken into consideration when designing studies of many aspects of larval biology.

In Vivo and In Vitro Trans-Acylation by BryP, the Putative Bryostatin Pathway Acyltransferase Derived from an Uncultured Marine Symbiont

The putative modular polyketide synthase (PKS) that prescribes biosynthesis of the bryostatin natural products from the uncultured bacterial symbiont of the marine bryozoan Bugula neritina possesses a discrete open reading frame (ORF) (bryP) that encodes a protein containing tandem acyltransferase (AT) domains upstream of the PKS ORFs. BryP is hypothesized to catalyze in trans acylation of the PKS modules for polyketide chain elongation. To verify conservation of function, bryP was introduced into AT-deletion mutant strains of a heterologous host containing a PKS cluster with similar architecture, and polyketide production was partially rescued. Biochemical characterization demonstrated that BryP catalyzes selective malonyl-CoA acylation of native and heterologous acyl carrier proteins and complete PKS modules in vitro. The results support the hypothesis that BryP loads malonyl-CoA onto Bry PKS modules, and provide the first biochemical evidence of the functionality of the bry cluster.

Microbial Biofilms Facilitate Adhesion in Biofouling Invertebrates

Much interest has focused on the role of microbial layers--biofilms--in stimulating attachment of invertebrates and algae to submerged marine surfaces. We investigated the influence of biofilms on the adhesion strength of settling invertebrates. Larvae of four species of biofouling invertebrate were allowed to attach to test surfaces that were either clean or coated with a natural biofilm. Measuring larval removal under precisely controlled flow forces, we found that biofilms significantly increased adhesion strength in the ascidian Phallusia nigra, the polychaete tubeworm Hydroides elegans, and the barnacle Balanus amphitrite at one or more developmental stages. Attachment strength in a fourth species, the bryozoan Bugula neritina, was neither facilitated nor inhibited by the presence of a biofilm. These results suggest that adhesive strength and perhaps composition may vary across different invertebrate taxa at various recruitment stages, and mark a new path of inquiry for biofouling research.

Offspring Size Plasticity in Response to Intraspecific Competition: An Adaptive Maternal Effect across Life‐History Stages

When provisioning offspring, mothers balance the benefits of producing a few large, fitter offspring with the costs of decreased fecundity. The optimal balance between offspring size and fecundity depends on the environment. Theory predicts that larger offspring have advantages in adverse conditions, but in favorable conditions size is less important. Thus, if environmental quality varies, selection should favor mothers that adaptively allocate resources in response to local conditions to maximize maternal fitness. In the bryozoan Bugula neritina, we show that the intensity of intraspecific competition dramatically changes the offspring size/performance relationship in the field. In benign or extremely competitive environments, offspring size is less important, but at intermediate levels of competition, colonies from larger larvae have higher performance than colonies from smaller larvae. We predicted mothers should produce larger offspring when intermediate competition is likely and tested these expectations in the field by manipulating the density of brood colonies. Our findings matched expectations: mothers produced larger larvae at high densities and smaller larvae at low densities. In addition, mothers from high-density environments produced larvae that have higher dispersal potential, which may enable offspring to escape crowded environments. It appears mothers can adaptively adjust offspring size to maximize maternal fitness, altering the offspring phenotype across multiple life-history stages.

TRANSGENERATIONAL PLASTICITY IN THE SEA: CONTEXT-DEPENDENT MATERNAL EFFECTS ACROSS THE LIFE HISTORY

Maternal effects can have dramatic influences on the phenotype of offspring. Maternal effects can act as a conduit by which the maternal environment negatively affects offspring fitness, but they can also buffer offspring from environmental change by altering the phenotype of offspring according to local environmental conditions and as such, are a form of transgenerational plasticity. The benefits of maternal effects can be highly context dependent, increasing performance in one life-history stage but reducing it in another. While maternal effects are increasingly well understood in terrestrial systems, studies in the marine environment are typically restricted to a single, early life-history stage. Here, I examine the role of maternal effects across the life history of the bryozoan Bugula neritina. I exposed maternal colonies to a common pollution stress (copper) in the laboratory and then placed them in the field for one week to brood offspring. I then examined the resistance of offspring to copper from toxicant-exposed and toxicant-naïve mothers and found that offspring from toxicant-exposed mothers were larger, more dispersive, and more resistant to copper stress than offspring from naïve mothers. However, maternal exposure history had pervasive, negative effects on the post-metamorphic performance (particularly survival) of offspring: offspring from toxicant-exposed mothers had poorer performance after six weeks in the field, especially when facing high levels of intraspecific competition. Maternal experience can have complex effects on offspring phenotype, enhancing performance in one life-history stage while decreasing performance in another. The context-dependent costs and benefits associated with maternally derived pollution resistance may account for why such resistance is induced rather than continually expressed: mothers must balance the benefits of producing pollution-resistant larvae with the costs of producing poorer performing adults (in the absence of pollution).

Attachment point theory revisited: the fouling response to a microtextured matrix

This paper examines attachment point theory in detail by testing the fouling attachment of several fouling groups to a microtextured matrix. Static bioassays were conducted on polycarbonate plates with nine equal regions, comprising eight scales of microtexture (4–512 µm) and one untextured region. The microtextures examined were continuous sinusoidal ridges and troughs of defined height and width. Attachment over the microtextured plates was examined for the diatom Amphora sp., the green alga Ulva rigida, the red alga Centroceras clavulatum, the serpulid tube worm Hydroides elegans and the bryozoan Bugula neritina. It was found that the size of the microtexture in relation to the size of the settling propagules/larvae was important in the selection of attachment sites. Attachment was generally lower when the microtexture wavelength was slightly smaller than the width of the settling propagules/larvae and increased when the wavelength was wider than their width. The effect of attachment points was weak for small motile microfoulers (Amphora sp. and U. rigida) (7 µm), strong for large macrofouling larvae (H. elegans and B. neritina) (129–321 µm) and non-existent for the non-motile algal spores (C. clavulatum) (37 µm). This study reinforces the potential of using attachment points to develop surfaces with increased fouling resistance or, alternatively, surfaces which promote the attachment of selected target sizes of motile propagules or larvae.

Localization of ‘Candidatus Endobugula sertula’ and the bryostatins throughout the life cycle of the bryozoan Bugula neritina

'Candidatus Endobugula sertula,' the uncultivated gamma-proteobacterial symbiont of the marine bryozoan Bugula neritina, synthesizes bryostatins, complex polyketides that render B. neritina larvae unpalatable to predators. Although the symbiosis is well described, little is known about the locations of 'E. sertula' or the bryostatins throughout larval settlement, metamorphosis and early development. In this study, we simultaneously localized 'E. sertula' and the bryostatins in multiple stages of the B. neritina life cycle, using a novel bryostatin detection method based on its known ability to bind mammalian protein kinase C. Our results suggest that the bryostatins are deposited onto the exterior of B. neritina larvae during embryonic development, persist on the larval surface throughout metamorphosis and are shed prior to cuticle formation. During metamorphosis, 'E. sertula' remains adhered to the larval pallial epithelium and is incorporated into the preancestrula cystid tissue layer, which ultimately develops into a bud and gives rise to the next zooid in the colony. Colocalization of bryostatin signal with aggregates of 'E. sertula' in buds of ancestrulae suggested new synthesis of bryostatins in ancestrulae. In adult B. neritina colonies, symbiont microcolonies were observed in the funicular cords of rhizoids, which likely result in asexual transmission of 'E. sertula' to regenerated colonies. Furthermore, bryostatin signal was detected on the surface of the rhizoids of adult B. neritina colonies. Through simultaneous localization of the bryostatins and the 'E. sertula,' we determined how 'E. sertula' is transmitted, and identified shifts in bryostatin localization throughout the life cycle of the host B. neritina.

Novel Antifoulants: Inhibition of Larval Attachment by Proteases

We investigated the effect of commercially available enzymes (alpha-amylase, alpha-galactosidase, papain, trypsin, and lipase) as well as proteases from deep-sea bacteria on the larval attachment of the bryozoan Bugula neritina L. The 50% effective concentrations (EC(50)) of the commercial proteases were 10 times lower than those of other enzymes. Crude proteases from six deep-sea Pseudoalteromonas species significantly decreased larval attachment at concentrations of 0.03 to 1 mIU ml(-1). The EC(50) of the pure protease from the bacterium Pseudoalteromonas issachenkonii UST041101-043 was close to 1 ng ml(-1) (0.1 mIU ml(-1)). The protease and trypsin individually incorporated in a water-soluble paint matrix inhibited biofouling in a field experiment. There are certain correlations between production of proteases by bacterial films and inhibition of larval attachment. None of the bacteria with biofilms that induced attachment of B. neritina produced proteolytic enzymes, whereas most of the bacteria that formed inhibitive biofilms produced proteases. Our investigation demonstrated the potential use of proteolytic enzymes for antifouling defense.

The effect of quorum-sensing blockers on the formation of marine microbial communities and larval attachment

We studied the effect of the quorum-sensing (QS) blockers 5-hydroxy-3[(1R)-1-hydroxypropyl]-4-methylfuran-2(5H)-one (FUR1), (5R)-3,4-dihydroxy-5-[(1S)-1,2-dihydroxyethyl]furan-2(5H)-one (FUR2) and triclosan (TRI) on the formation of bacterial biofilms, and the effect of these biofilms on the larval attachment of the polychaete Hydroides elegans and the bryozoan Bugula neritina. 14-day-old subtidal biofilms were harvested from artificial substrata and were allowed to develop in the laboratory with and without QS blockers. QS blockers inhibited the production of violacein by the QS reporter strain Chromobacterium violaceum CV026 and did not affect the metabolic activity of bacteria in multispecies biofilms. At a concentration of 10(-3) M all three tested compounds inhibited the establishment of microbial communities, but at one of 10(-4) M only FUR2 inhibited establishment. The tested QS blockers caused changes in bacterial density and bacterial community structure, as revealed by terminal restriction fragment length polymorphism and FISH. The groups most affected by QS blockers were Alphaproteobacteria, Gammaproteobacteria and the Cytophagales. Larvae of H. elegans and B. neritina avoided settling on biofilms that had developed in the presence of QS blockers. Our results suggest that QS blockers directly control the formation of multi-species biofilms, and indirectly - by means of biofilm properties - affect larval attachment on these modified biofilms.

Optimized maintenance and larval production of the bryozoan Bugula neritina (Bugulidae: Gymnolaemata) in the laboratory

In recent years, bryozoans have attracted the attention of applied scientists and marine biotechnologists since bryozoa serve as a source of bioactive substances for biotechnological appliances, e.g. for cosmetic or pharmaceutical industries and for the antifouling industry. The larval production of bryozoa is of interest for both, mariculture and for developmental investigations, e.g. for settlement assays in fouling studies. We optimised maintenance conditions of the bryozoan Bugula neritina accordingly, that larvae could be harvested sustainably within a period of 4 weeks from adult brood stocks which had been kept in bulk in flow-through containers in the laboratory. Preliminary experiments showed that moderate water flow and permanent moderate light conditions without aeration were key-parameters for a maintenance regime that maximizes and prolongs larval harvest for several weeks.

Attachment of the biofouling bryozoan Bugula neritina larvae affected by inorganic and organic chemical cues

The bryozoan Bugula neritina L. is an important fouling organism worldwide and has been the focus of great interest for large scale culturing because of the powerful anticancer chemicals extracted from the animals. In this study, the effects of four inorganic ions and five bioactive compounds on larval attachment of the bryozoan were investigated with an aim of identifying artificial cues for prevention and mariculture of this species. K+ at 10-70 mM and NH4+ > 10 mM significantly induced larval attachment on the bottom surfaces of the culture dishes. Mg2+ at 1-50 mM significantly inhibited larval attachment, while Ca2+ showed toxicity to the larvae at 30 mM. T-Aminobutyric acid induced larval attachment to the bottom surfaces of the aquarium only at 10(-2) M. Acetylcholine at 10(-2)-10(-3) M, L-3-(3,4-dihydroxyphenyl)-L-alanine at 10(-3)-10(-5) M and dopamine at 10(-3)-10(-4) M significantly induced larval settlement but inhibited larval attachment, probably due to the restricted mobility and less active probing of the substratum surfaces during larval exploration. Serotonin at concentrations between 10(-3) and 10(-5) M significantly inhibited larval settlement and attachment by forcing the larvae to swim in the water. Our observations suggest that serotonin and its derivatives are potential candidates for the development of non-toxic antifouling substances. (C) 2007 Published by Elsevier Ltd.

Pedicellariae of the crown-of-thorns sea star Acanthaster planci are not an effective defence against fouling

This study focused on the speculative role of the pedicellariae of the sea star Acanthaster planci in fouling control, as quantitative measurements showed that this species is free of any macro-fouling organisms. The morphology and distribution of its pedicellariae were measured to determine if larvae or propagules of fouling organisms could settle between pedicellariae without being in their physical range. The elementary and straight pedicellariae of A. planci had a mean length of 0.7 mm and a mean distance of 2.6 mm. The total number of pedicellariae was proportional to the estimated surface area of A. planci. To determine how pedicellariae respond to tactile stimulation, pedicellariae were stimulated by touching either inner, outer or basal sites of pedicellariae with a hypodermic needle. Pedicellariae closed rapidly on touch and closed for significantly longer when touched at their inner sites (8.9 s) than outer (6.7 s) and basal (7.9 s) sites. Settling larvae were simulated by dropping silica beads (size: 50.2, 181.5, 255.7 and 510.7 µm, density: 2.5 g ml-1) and zirconium/silica beads (size: 191.2 and 507.6 µm, density: 3.7 g ml-1) over the pedicellariae. The percentage of responding pedicellariae increased proportionally with increasing size of the silica beads. However, the percentage also increased when zirconium/silica beads of similar size but higher density were used, demonstrating that the mass, not size, of the beads was the main driving factor for the closure of pedicellariae. Pedicellariae were also stimulated by placing larvae of the bryozoan Bugula neritina (250 µm) and fragments of the alga Chrysocystis fragilis (150-1000 µm) over the pedicellariae. However, the response of the pedicellariae to the larvae of B. neritina was consistently low and none of the pedicellariae responded to the fragments of C. fragilis. These results demonstrate that for A. planci pedicellariae offer little or no defence against fouling.

Identification of the Putative Bryostatin Polyketide Synthase Gene Cluster from “Candidatus Endobugula sertula”, the Uncultivated Microbial Symbiont of the Marine Bryozoan Bugula neritina

The bryostatins are protein kinase C modulators with unique structural features and potential anticancer and neurological activities. These complex polyketides were isolated from the marine bryozoan Bugula neritina, but recent studies indicate that they are produced by the uncultured symbiotic bacterium "Candidatus Endobugula sertula" ("E. sertula"). Here we present the putative biosynthetic genes: five modular polyketide synthase (PKS) genes, a discrete acyltransferase, a beta-ketosynthase, a hydroxy-methyl-glutaryl CoA synthase (HMG-CS), and a methyltransferase. The cluster was sequenced in two closely related "E. sertula" strains from different host species. In one strain the gene cluster is contiguous, while in the other strain it is split into two loci, with one locus containing the PKS genes and the other containing the accessory genes. Here, we propose a hypothesis for the biosynthesis of the bryostatins. Thirteen PKS modules form the core macrolactone ring, and the pendent methyl ester groups are added by the HMG-CS gene cassette. The resulting hypothetical compound bryostatin 0 is the common basis for the 20 known bryostatins. As "E. sertula" is to date uncultured, heterologous expression of this biosynthetic gene cluster has the potential of producing the bioactive bryostatins in large enough quantities for development into a pharmaceutical.

Availability of dissolved organic matter offsets metabolic costs of a protracted larval period for Bugula neritina (Bryozoa)

For nearly a century researchers have investigated the uptake and utilization of dissolved organic matter (DOM) by marine invertebrates, but its contribution to their growth, reproduction, and survival remains unclear. Here, the benefit of DOM uptake was assessed for the marine bryozoan Bugula neritina (Linnaeus 1758) through performance comparisons of individuals in the presence and absence of DOM. The experiments were performed using B. neritina collected from floating docks in Beaufort, NC, USA from July to September 2004. Seawater was subjected to ultraviolet irradiation to reduce naturally occurring DOM, and then enriched with either 1 μM of palmitic acid or a mixture containing 1 μM each of glucose, alanine, aspartic acid and glycine. Larvae in DOM-enriched and DOM-reduced treatments were sampled and induced to metamorphose following 1, 6, 12, and 24 h of continuous swimming at 25°C. Sampled larvae were assessed for initiation of metamorphosis, completion of metamorphosis, and ancestrular lophophore size to determine the extent to which energy acquired from DOM uptake could offset the metabolic costs of prolonged larval swimming. DOM treatment had no significant effect on initiation of metamorphosis, but did have a significant effect on completion of metamorphosis and lophophore size. Larvae swimming in DOM-enriched treatments for 24 h experienced a 20% increase in metamorphic completion rate, compared to larvae swimming for 24 h in the DOM-reduced treatment. In addition, larvae in the amino acid and sugar mixture for 24 h had a significantly larger lophophore surface area and volume (23 and 31%, respectively), compared to larvae in DOM-depleted seawater. To ensure that the increases in performance found in larvae with access to DOM were not due to a decrease in metabolic activity, the respiration rates for these larvae were compared to those of larvae in DOM-depleted seawater. There were no significant differences between these treatments, indicating that the increases in performance were due to the energy acquired from DOM. These results clearly show that for B. neritina, DOM uptake results in increased metamorphic success and in the size of the feeding apparatus following an extended larval swimming duration.

Isolation of Two Polyketide Synthase Gene Fragments from the Uncultured Microbial Symbiont of the Marine Bryozoan Bugula neritina

"Candidatus Endobugula sertula," the uncultured microbial symbiont of the bryozoan Bugula neritina, produces ecologically and biomedically important polyketide metabolites called bryostatins. We isolated two gene fragments from B. neritina larvae that have high levels of similarity to polyketide synthase genes. These gene fragments are clearly associated with the symbiont and not with the host.

Allelochemical defense against epibiosis in the macroalga Caulerpa racemosa var. turbinata

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 318:165-175 (2006) - doi:10.3354/meps318165 Allelochemical defense against epibiosis in the macroalga Caulerpa racemosa var. turbinata Sergey Dobretsov1, Hans-Uwe Dahms1, Tilmann Harder2, Pei-Yuan Qian1,* 1Department of Biology & Coastal Marine Laboratory, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR, PR China 2Institute of Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Carl von Ossiezkystr. 9–11, 26111 Oldenburg, Germany *Corresponding author. Email: boqianpy@ust.hk ABSTRACT: The abundance and diversity of microorganisms on the surface of the tropical green macroalga Caulerpa racemosa var. turbinata and the effect of algal surface and waterborne compounds on fouling organisms were investigated both in laboratory and field experiments. As shown via electron microscopic enumeration, the abundance of epibiotic bacteria and diatoms on algal frond surfaces was not significantly different from the reference biofilms harvested from stones in the C. racemosa habitat. The analysis of Terminal Restriction Fragment Length Polymorphism of DNA from algal surface-associated bacterial communities revealed that despite a similar abundance of these bacteria, the community profile on algal frond surfaces differed significantly from that of inanimate, undefended substrates. These results suggest that the alga regulate the occurrence of certain bacterial ribotypes. This result was in accordance with the fact that different bacterial communities formed on the artificial substrata (i.e. Petri dishes) placed in the C. racemosa habitat and alga-free control sites. Neither C. racemosa conditioned seawater (CCW) nor hexane surface extracts affected the growth of bacterial isolates from biofilms. However, only CCW exhibited a toxic effect on the larvae of the fouling polychaete Hydroides elegans, and evoked abnormal larval development in a concentration-dependent fashion. At sublethal concentrations, the <1 kD fraction of CCW inhibited the larval settlement of H. elegans and the bryozoan Bugula neritina. Caulerpenyne, the prominent bioactive metabolite in the genus Caulerpa, was not detected in CCW by chromatographic procedures. Our data suggest that waterborne compounds other than caulerpenyne are involved in the chemical defense of the alga C. racemosa. KEY WORDS: Caulerpa racemosa · Algae · Microbial communities · Larval settlement · Epibiosis · Antifouling · Chemical defense Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 318. Online publication date: August 03, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.