Dataset Information

Seabirds supply nitrogen to reef-building corals on remote Pacific islets.

ABSTRACT: Seabirds concentrate nutrients from large marine areas on their nesting islands playing an important ecological role in nutrient transfer between marine and terrestrial ecosystems. Here we investigate the role of guano on corals reefs across scales by analyzing the stable nitrogen isotopic (?15N) values of the scleractinian coral Pocillopora damicornis on fringing reefs around two Pacific remote islets with large seabird colonies. Marine stations closest to the seabird colonies had higher nitrate?+?nitrite concentrations compared to more distant stations. Coral and zooxanthellae ?15N values were also higher at these sites, suggesting that guano-derived nitrogen is assimilated into corals and contributes to their nitrogen requirements. The spatial extent of guano influence was however restricted to a local scale. Our results demonstrate that seabird-derived nutrients not only spread across the terrestrial ecosystem, but also affect components of the adjacent marine ecosystem. Further studies are now needed to assess if this nutrient input has a positive or negative effect for corals. Such studies on remote islets also open fresh perspectives to understand how nutrients affect coral reefs isolated from other anthropogenic stressors.

SUBMITTER: Lorrain A

PROVIDER: S-EPMC5473863 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Seabirds supply nitrogen to reef-building corals on remote Pacific islets.

Lorrain Anne A Houlbrèque Fanny F Benzoni Francesca F Barjon Lucie L Tremblay-Boyer Laura L Menkes Christophe C Gillikin David P DP Payri Claude C Jourdan Hervé H Boussarie Germain G Verheyden Anouk A Vidal Eric E

Scientific reports 20170616 1

Seabirds concentrate nutrients from large marine areas on their nesting islands playing an important ecological role in nutrient transfer between marine and terrestrial ecosystems. Here we investigate the role of guano on corals reefs across scales by analyzing the stable nitrogen isotopic (δ<sup>15</sup>N) values of the scleractinian coral Pocillopora damicornis on fringing reefs around two Pacific remote islets with large seabird colonies. Marine stations closest to the seabird colonies had hi ...[more]

PMID: 28623288

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Project description:Reef-building corals in the genus Porites are one of the most important constituents of Indo-Pacific reefs. Many species within this genus tolerate abnormally warm water and exhibit high specificity for particular kinds of endosymbiotic dinoflagellates that cope with thermal stress better than those living in other corals. Still, during extreme ocean heating, some Porites exhibit differences in their stress tolerance. While corals have different physiological qualities, it remains unknown whether the stability and performance of these mutualisms is influenced by the physiology and genetic relatedness of their symbionts. We investigated two ubiquitous Pacific reef corals, Porites rus and Porites cylindrica, from warmer inshore and cooler offshore reef systems in Palau. While these corals harbored a similar kind of symbiont in the genus Cladocopium (within the ITS2 C15 subclade), rapidly evolving genetic markers revealed evolutionarily diverged lineages corresponding to each Porites species living in each reef habitat. Furthermore, these closely related Cladocopium lineages were differentiated by their densities in host tissues, cell volume, chlorophyll concentration, gross photosynthesis, and photoprotective pathways. When assessed using several physiological proxies, these previously undifferentiated symbionts contrasted in their tolerance to thermal stress. Symbionts within P. cylindrica were relatively unaffected by exposure to 32℃ for 14 days, whereas P. rus colonies lost substantial numbers of photochemically compromised symbionts. Heating reduced the ability of the offshore symbiont associated with P. rus to translocate carbon to the coral. By contrast, high temperatures enhanced symbiont carbon assimilation and delivery to the coral skeleton of inshore P. cylindrica. This study indicates that large physiological differences exist even among closely related symbionts, with significant implications for thermal susceptibility among reef-building Porites.

Project description:BACKGROUND:At the forefront of ecosystems adversely affected by climate change, coral reefs are sensitive to anomalously high temperatures which disassociate (bleaching) photosynthetic symbionts (Symbiodinium) from coral hosts and cause increasingly frequent and severe mass mortality events. Susceptibility to bleaching and mortality is variable among corals, and is determined by unknown proportions of environmental history and the synergy of Symbiodinium- and coral-specific properties. Symbiodinium live within host tissues overlaying the coral skeleton, which increases light availability through multiple light-scattering, forming one of the most efficient biological collectors of solar radiation. Light-transport in the upper ~200 ?m layer of corals skeletons (measured as 'microscopic' reduced-scattering coefficient, ?'(S,m)), has been identified as a determinant of excess light increase during bleaching and is therefore a potential determinant of the differential rate and severity of bleaching response among coral species. RESULTS:Here we experimentally demonstrate (in ten coral species) that, under thermal stress alone or combined thermal and light stress, low-?'(S,m) corals bleach at higher rate and severity than high-?'(S,m) corals and the Symbiodinium associated with low-?'(S,m) corals experience twice the decrease in photochemical efficiency. We further modelled the light absorbed by Symbiodinium due to skeletal-scattering and show that the estimated skeleton-dependent light absorbed by Symbiodinium (per unit of photosynthetic pigment) and the temporal rate of increase in absorbed light during bleaching are several fold higher in low-?'(S,m) corals. CONCLUSIONS:While symbionts associated with low-[Formula: see text] corals receive less total light from the skeleton, they experience a higher rate of light increase once bleaching is initiated and absorbing bodies are lost; further precipitating the bleaching response. Because microscopic skeletal light-scattering is a robust predictor of light-dependent bleaching among the corals assessed here, this work establishes ?'(S,m) as one of the key determinants of differential bleaching response.

Dataset Information

Seabirds supply nitrogen to reef-building corals on remote Pacific islets.

Publications

Seabirds supply nitrogen to reef-building corals on remote Pacific islets.

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