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Overlooked coral predators suppress foundation species as reefs degrade.

ABSTRACT: Loss of larger consumers from stressed ecosystems can lead to trophic release of mid-level consumers that then impact foundation species, suppressing ecosystem function and resilience. For example, in coral reef ecosystems, outbreaks of coral predators like crown-of-thorns sea stars have been associated with fishing pressure and can dramatically impact the composition and persistence of corals. However, the ecological impacts, and consequences for management, of smaller, less obvious corallivores remain inadequately understood. We investigated whether reef state (coral vs. seaweed domination) influenced densities and size frequencies of the corallivorous gastropod Coralliophila violacea on its common host, the coral Porites cylindrica, within three pairs of small Marine Protected Areas (MPAs) and adjacent fished areas in Fiji. C. violacea densities were 5-35 times greater, and their size frequencies more broadly distributed, within seaweed-dominated fished areas than in adjacent MPAs dominated by corals. Tethering snails (4-9 mm in shell height) in place on their coral hosts indicated that suppression of snails in MPAs was due to predation, apparently by fishes. When tethered on the benthos (where they rarely occur), rather than on their host, mortality of larger snails (15.0-25.0 mm in shell height) was high in all areas, primarily due to hermit crabs killing them and occupying their shells. Because C. violacea is a sessile gastropod that feeds affixed to the base of corals and produces minimal visible damage, it has been considered a "prudent feeder" that minimally impacts its host coral. We assessed this over a 24-d feeding period in the field. Feeding by individual C. violacea reduced P. cylindrica growth by ~18-43% depending on snail size. Our findings highlight the considerable, but underappreciated, negative impacts of this common corallivore on degraded reefs. As reefs degrade and corals are lost, remaining corals (often species of Porites) may gain the full attention of elevated densities of coral consumers. This will further damage the remaining foundation species, suppressing the resilience of corals and enhancing the resilience of degraded, seaweed-dominated reefs.

SUBMITTER: Clements CS

PROVIDER: S-EPMC6167153 | biostudies-literature | 2018 Oct

REPOSITORIES: biostudies-literature

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Overlooked coral predators suppress foundation species as reefs degrade.

Clements Cody S CS Hay Mark E ME

Ecological applications : a publication of the Ecological Society of America 20180726 7

Loss of larger consumers from stressed ecosystems can lead to trophic release of mid-level consumers that then impact foundation species, suppressing ecosystem function and resilience. For example, in coral reef ecosystems, outbreaks of coral predators like crown-of-thorns sea stars have been associated with fishing pressure and can dramatically impact the composition and persistence of corals. However, the ecological impacts, and consequences for management, of smaller, less obvious corallivore ...[more]

PMID: 30048025

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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.

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Overlooked coral predators suppress foundation species as reefs degrade.

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Overlooked coral predators suppress foundation species as reefs degrade.

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