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Productivity links morphology, symbiont specificity and bleaching in the evolution of Caribbean octocoral symbioses.

ABSTRACT: Many cnidarians host endosymbiotic dinoflagellates from the genus Symbiodinium. It is generally assumed that the symbiosis is mutualistic, where the host benefits from symbiont photosynthesis while providing protection and photosynthetic substrates. Diverse assemblages of symbiotic gorgonian octocorals can be found in hard bottom communities throughout the Caribbean. While current research has focused on the phylo- and population genetics of gorgonian symbiont types and their photo-physiology, relatively less work has focused on biogeochemical benefits conferred to the host and how these benefits vary across host species. Here we examine this symbiosis among 11 gorgonian species collected in Bocas del Toro, Panama. By coupling light and dark bottle incubations (P/R) with (13)C-bicarbonate tracers, we quantified the link between holobiont oxygen metabolism with carbon assimilation and translocation from symbiont to host. Our data show that P/R varied among species, and was correlated with colony morphology and polyp size. Sea fans and sea plumes were net autotrophs (P/R>1.5), while nine species of sea rods were net heterotrophs with most below compensation (P/R<1.0). (13)C assimilation corroborated the P/R results, and maximum ?(13)Chost values were strongly correlated with polyp size, indicating higher productivity by colonies with high polyp SA:V. A survey of gorgonian-Symbiodinium associations revealed that productive species maintain specialized, obligate symbioses and are more resistant to coral bleaching, whereas generalist and facultative associations are common among sea rods that have higher bleaching sensitivities. Overall, productivity and polyp size had strong phylogenetic signals with carbon fixation and polyp size showing evidence of trait covariance.

SUBMITTER: Baker DM

PROVIDER: S-EPMC4817624 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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Productivity links morphology, symbiont specificity and bleaching in the evolution of Caribbean octocoral symbioses.

Baker David M DM Freeman Christopher J CJ Knowlton Nancy N Thacker Robert W RW Kim Kiho K Fogel Marilyn L ML

The ISME journal 20150519 12

Many cnidarians host endosymbiotic dinoflagellates from the genus Symbiodinium. It is generally assumed that the symbiosis is mutualistic, where the host benefits from symbiont photosynthesis while providing protection and photosynthetic substrates. Diverse assemblages of symbiotic gorgonian octocorals can be found in hard bottom communities throughout the Caribbean. While current research has focused on the phylo- and population genetics of gorgonian symbiont types and their photo-physiology, r ...[more]

PMID: 25989369

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Project description:Disturbance events are an important component of the ecology of coral reefs and increasingly frequent disturbances coupled with a lack of population resilience may contribute to changes in the structure of coral reef communities. The harvest of the Caribbean octocoral Antillogorgia elisabethae provides an opportunity to explore the relationship between adult abundance and recruitment and the manner in which recruitment contributes to the resilience of local populations. Recruitment of A. elisabethae was monitored in 20, 1-m(2) quadrats at 8 sites along the southern edge of the Little Bahama Bank from 2004 through 2007. A. elisabethae has been harvested in The Bahamas for over fifteen years and all of the sites had been harvested three times, including a harvest during the course of the study. Abundances of adult colonies at those sites as well as a location that had not been harvested were also determined. Recruitment was highly variable, differing between sites, transects within sites, and, depending on the site, between years. Recruitment was best correlated with adult abundance averaged across the surrounding site. Regression analyses suggest abundance on smaller scales had only small effects on recruitment. The effects of the harvesting were site specific ranging from a 38 to 67% reduction in the density of mature colonies. The sites with the most abundant A. elisabethae continued to have the highest abundances after harvesting and there was no significant difference in recruitment before and after harvesting. Population size-structure at 6 of 8 sites that have been harvested multiple times exhibited an overall depletion in small colonies suggesting long term suppression of recruitment and declining populations. Severe depression of adult abundances coupled with local recruitment can create a negative feedback and lead to the decline of local populations. Populations that are dependent on self-recruitment are not resilient to large disturbance events.

Project description:BackgroundWhat are the determinant factors of community assemblies in the most diverse ecosystem in the ocean? Coral reefs can be divided in continental (i.e., reefs that develop on the continental shelf, including siliciclastic reefs) and oceanic (i.e., far off the continental shelf, usually on volcanic substratum); whether or not these habitat differences impose community-wide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown.MethodsStudying Caribbean octocorals as model system, we determined the phylogenetic community structure in a coral reef community, making emphasis on species coexistence evidenced on trait evolution and environmental feedbacks. Forty-nine species represented in five families constituted the species pool from which a phylogenetic tree was reconstructed using mtDNA. We included data from 11 localities in the Western Caribbean (Colombia) including most reef types. To test diversity-environment and phenotype-environment relationships, phylogenetic community structure and trait evolution we carried out comparative analyses implementing ecological and evolutionary approaches.ResultsPhylogenetic inferences suggest clustering of oceanic reefs (e.g., atolls) contrasting with phylogenetic overdispersion of continental reefs (e.g., reefs banks). Additionally, atolls and barrier reefs had the highest species diversity (Shannon index) whereas phylogenetic diversity was higher in reef banks. The discriminant component analysis supported this differentiation between oceanic and continental reefs, where continental octocoral species tend to have greater calyx apertures, thicker branches, prominent calyces and azooxanthellate species. This analysis also indicated a clear separation between the slope and the remaining habitats, caused by the presence or absence of Symbiodinium. K statistic analysis showed that this trait is conserved as well as the branch shape.DiscussionThere was strong octocoral community structure with opposite diversity and composition patterns between oceanic and continental reefs. Even habitats with similar depths and overall environmental conditions did not share similar communities between oceanic and continental reefs. This indicates a strong regional influence over the local communities, probably due to water transparency differences between major reef types, i.e., oceanic vs. continental shelf-neritic. This was supported by contrasting patterns found in morphology, composition and evolutionary history of the species between atolls and reef banks.

Dataset Information

Productivity links morphology, symbiont specificity and bleaching in the evolution of Caribbean octocoral symbioses.

Publications

Productivity links morphology, symbiont specificity and bleaching in the evolution of Caribbean octocoral symbioses.

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