Inhibitory and facilitatory effects of microbial films on settlement of Balanus amphitrite amphitrite larvae

Larval settlement of the polychaete Hydroides elegans Haswell, 1883 is mediated by marine biofilms; complex agglomerates of bacteria, diatoms, fungi and protozoa enmeshed in a matrix of extracellular polymers (EPS). In our previous investigations, benthic diatoms were demonstrated to be potent mediators of larval settlement in H. elegans. The putative diatom-derived settlement cues were heat-stable components in close association with the diatom surface. For an in-depth investigation of the chemical nature of diatom-derived larval settlement cues, the EPS of the inductive (Achnanthes sp., Nitzschia constricta) and non-inductive (Amphora tenerrima, Nitzschia frustulum) diatoms were bioassayed for their effect on larval settlement. When EPS fractions larger than 100 kDa were immobilized in stable hydrogels to mimic their association to a solid substratum, they evoked an effect on larval settlement similar to that of the respective monospecies diatom films. The crude exopolymer samples mainly consisted of polysaccharides with a small proportion of proteinaceous sample components. After enzymatic removal of proteinaceous EPS components, the samples evoked an effect on larval settlement similar to that of the crude EPS samples, indicating the negligible role of large proteins or glycoproteins as settlement cues. KEY WORDS: Diatoms · Larvae · Settlement · Biofilm · Exopolymers · Hydroides elegansResale or republication not permitted without written consent of the publisher

Section: Introductionsupporting

confidence: 61%

Induction of larval settlement in the polychaete Hydroides elegans by extracellular polymers of benthic diatoms

Lam¹,

Harder²,

Qian³

2005

“…The impact of the bacterial component, which was not studied in the present study, is also known to have an effect on barnacle settlement (e.g. Strathmann et al 1981, Grosberg 1982, Wieczorek et al 1995. However, it is reasonable to believe that bacterial films probably CO-vary with microalgae.…”

Section: Selection Of Habitatcontrasting

confidence: 39%

Intertidal barnacle distribution:a case study using multiple working hypotheses

Miron¹,

Boudreau²,

Bourget³

1999

The roles of larval supply, selection of habitat, availability of space, larval physiological condition, and early post-settlement mortality in determining vertical distribution patterns of the barnacle Semibalanus balanoides (L.) were simultaneously examined in Passamaquoddy Bay, New Brunswick, Canada. Pump samples and settlement surveys showed that about 60% of planktonic cyprids were collected from 1.5 to 4.0 nl depth, whde over 90% of newly settled cyprids colonized low intertidal levels. Selection of habitat by cyprids and patterns of settlement were studied using precolonized planks that had been previously placed to obtain various perlphyton gradients. These planks precolonized at the low, mid-, and high intertidal levels and placed in different orientations, induced variations in the distribution of newly settled cyprids. For example, vertical planks turned upside down had fewer settlers at low intertidal levels compared to surfaces maintained in the same orientation at the same level. When placed horizontally at the same level, sections precolonized at the low intertidal level collected more larvae than sections initially placed at the high and mid-intertidal levels. We used the triacylglyceroVcholesterol ratio (TAG/CHOL) as a measure of physiological condition in planktonic and newly settled cyprids, and newly metamorphosed spat. The TAG/CHOL ratio in planktonic cyprids decreased over the sampling period, but there was no variability with position in the water column. For newly settled cyprids and newly metamorphosed spat, the TAG/CHOL ratio increased with decreasing intertidal level. Quadrats freed of conspecific adults were colonized by more cyprids than were uncleared controls. Early post-settlement mortality was greater in uncleared than in cleared quadrats. but this effect varied with intertidal level. Early post-settlement mortality increased with increasing intertidal level in cleared quadi-ats, while it did not significantly vary in uncleared controls. The present study shows that the vertical distribution of S. balanoides on the shore results from a complex relationship involving larval supply, selection of habitat, availability of space, and early post-settlement mortality. We also present the first evidence of correlations between larval physiological condition and early vertical distribution In S. balano~des.

“…Many decades of subsequent research have demonstrated that responses to bacterial films vary among different types of larvae (reviewed by Hadfield & Paul 2001). For example, larval settlement in Balanus amphitrite is inhibited by early, 1 to 3 d, natural biofilms, but is stimulated by 12 to 18 d films (Wieczorek et al 1995). By contrast, settlement intensity of Hydroides elegans correlates tightly with the density of bacterial cells in biofilms (Hadfield et al 1994).…”

Section: Introductionmentioning

confidence: 99%

“…Selective settlement on biofilms has been shown for larvae of many marine invertebrates, including the scleractinian corals Acropora willisae and A. millepora (Negri et al 2001), the scyphomedusae Cassiopia spp. (Hofmann et al 1996), the polychaetes Janua brasiliensis (Kirchman et al 1982) and Pomatoceros lamarkii (Hamer et al 2001), the bryozoan Bugula neritina (Maki et al 1989), the oyster Crassostrea gigas (Fitt et al 1990), the sea scallop Placopecten magellanicus (Parsons et al 1993), the mussel Mytilus edulis (Satuito et al 1995), the barnacles Balanus amphitrite (Wieczorek et al 1995), Elminius modestus and Balanus perforatus (Neal & Yule 1994), the starfish Acanthaster planci (Johnson & Sutton 1994) and the ascidian Ciona intestinalis (Szewzyk et al 1991).…”

Section: Introductionmentioning

confidence: 99%

Composition and density of bacterial biofilms determine larval settlement of the polychaete Hydroides elegans

Huang¹,

Hadfield²

2003

163

130

Larvae of the polychaete worm Hydroides elegans settle and metamorphose in response to marine biofilms. Phylogenetic relationships among 4 marine-biofilm bacterial species identified by 16S rDNA sequences were not predictive of their inductive capacity. Two bacterial species separated by a genetic distance of 30% shared the greatest capacity for inducing metamorphosis in H. elegans. Two bacterial strains with only a 3% divergence in 16S rRNA gene sequences were very different; one strain induced metamorphosis strongly while the other one did not. The percent of larvae that metamorphosed correlated positively with bacterial density in either natural biofilms or biofilms composed of a single bacterial species. When results of tests across 4 bacterial species were compared, the most inductive bacterial species was effective in much lower biofilm densities than weakly or non-inductive bacteria. Evidence presented here indicates that the cue that triggers settlement and metamorphosis in larvae of H. elegans is not unique to a single bacterial taxon and is likely to be an insoluble, surface-bound material. KEY WORDS: Biofilm bacteria · Larval settlement · Metamorphosis · Hydroides elegansResale or republication not permitted without written consent of the publisher