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Increasing settlement and post-settlement survival during the critical transition from planktonic larvae to benthic juveniles will increase efficiency for sea urchin aquaculture. This study investigated the effects of temperature and settlement cues on the settlement and post-settlement survival of the sea urchin Tripneustes gratilla during this phase. The current commercial methodology, which utilises natural biofilm settlement plates, was tested and resulted in low settlement (<2%) and poor post-settlement survival (<1% of settled urchins). In laboratory trials, settlement was high and unaffected by temperatures between 24 and 30°C, but significantly decreased at 33°C. Development of spines, however, was significantly affected by temperatures over 29°C. Mirroring this result, post-settlement survival was optimal between 24-28°C. In laboratory assays, the macroalgae Sargassum linearifolium and Corallina officinalis, and seawater conditioned with these algae, induced significantly higher settlement (>90%) than a natural biofilm (∼25%). The addition of macroalgae-conditioned seawater to natural biofilm significantly increased settlement rates (>85%). Mixed consortia and single strains of bacteria isolated from macroalgae, biofilms and adult conspecifics all induced significant settlement, but at significantly lower rates than macroalgae. No evidence was found that higher rates of settlement to bacteria on macroalgae were generated by a cofactor from the macroalgae. Age of bacterial cultures, culturing bacteria on solid and liquid media and concentration of nutrients in cultures had little effect on settlement rates. Finally, macroalgae-conditioned seawater combined with natural biofilm settlement plates induced significantly higher settlement than to the biofilm plates alone in a commercial scale trial. However, high post-settlement mortality resulted in equivalent survival between treatments after 25 days. This study highlights that settlement studies should extend to post-settlement survival, which remains poor for T. gratilla and is a significant obstacle to increasing efficiency for aquaculture.
???displayArticle.pubmedLink???
22162755
???displayArticle.pmcLink???PMC3230603 ???displayArticle.link???PLoS One
Figure 1. Settlement and post-settlement survival of Tripneustes gratilla induced to settle using natural biofilm in a commercial scale trial.(A) Location of newly settled sea urchins at first census. Letters denote statistical differences (PERMANOVA, post-hoc pair-wise test). (B) Survival to 31 days. Data are means ± SE.
Figure 2. The effect of temperature on settlement and post-settlement survival of Tripneustes gratilla in a small scale laboratory trial.(A) Settlement and post-settlement spine development. Letters denote significant differences (PERMANOVA, post-hoc pair-wise test). (B) Survival to 24 days. * denotes significant difference between treatments (PERMANOVA, post-hoc pair-wise test). Data are means ± SE.
Figure 3. The settlement of Tripneustes gratilla to macroalgae, macroalgae-conditioned seawater, a mono-specific diatom and natural biofilm.The full species names are presented in the text. CS = Conditioned Seawater, ASW = Autoclaved Seawater. Data are means ± SE. Bars denote statistical differences (PERMANOVA, post-hoc pair-wise test).
Figure 4. The settlement of Tripneustes gratilla to mixed consortia, single strains and supernatants of bacteria isolated from macroalgae, biofilms and adult conspecifics.The full species names are presented in the text. ASW = Autoclaved Seawater. Data are means ± SE. Bars denote statistical differences (PERMANOVA, post-hoc pair-wise test).
Figure 5. The effect of (A) culture medium, (B) culture age and (C) presence of macroalgae on induction of settlement of Tripneustes gratilla by mixed consortiums of bacteria.The full species names are presented in the text. MBA = Marine Broth/Agar surface medium, MB = Marine Broth in ASW liquid medium, ASW = Autoclaved Seawater. X-axis percentages denote concentration of Marine Broth in the culture medium. Bars denote statistical differences between treatments (PERMANOVA, post-hoc pair-wise test). Data are means ± SE.
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