Abstract
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.
Highlights
IntroductionSince the time of Darwin, it is known that coral reefs can differ regionally due to their history of geological formation (e.g., atolls, barrier reefs, fringe reefs, banks), which in turn can lead to the formation of a diversity of local habitats (e.g., lagoon, fore-reef, slope, plateau) [1]
Since the time of Darwin, it is known that coral reefs can differ regionally due to their history of geological formation, which in turn can lead to the formation of a diversity of local habitats [1]
What are the determinant factors of community assemblies in the most diverse ecosystem in the ocean? Coral reefs can be divided in continental and oceanic; whether or not these habitat differences impose communitywide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown
Summary
Since the time of Darwin, it is known that coral reefs can differ regionally due to their history of geological formation (e.g., atolls, barrier reefs, fringe reefs, banks), which in turn can lead to the formation of a diversity of local habitats (e.g., lagoon, fore-reef, slope, plateau) [1]. Terrestrial run-off can provoke well known adverse effects on corals and coral reefs (see review in [3]), some coral reefs successfully develop along neritic coastal siliciclastic-environments [4]. Whether or not these diverse conditions impose community-wide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown. 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 communitywide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown What 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 communitywide ecological divergence or species exclusion/coexistence with evolutionary consequences, is unknown
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