Organic matter bioavailability in tropical coastal waters: The Great Barrier Reef

Lønborg, Christian; Álvarez‐Salgado, Xosé Antón; Duggan, S.; Carreira, Cátia

doi:10.1002/lno.10717

Cited by 51 publications

(37 citation statements)

References 121 publications

(169 reference statements)

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“…Bioassay experiments are the common approach used to determine the bioreactivity of substrates under defined environmental conditions (Ogura ; Søndergaard and Middelboe ; Lønborg et al ). The term labile is used to characterize components that persist for minutes to weeks, whereas the term refractory is used to characterize components of DOM that persist in the ocean for centuries to millennia (Carlson ).…”

Section: Discussionmentioning

confidence: 99%

Molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean

Shen

Benner

2019

Limnology & Oceanography

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The global ocean sequesters a large amount of reduced carbon in dissolved organic molecules that can persist for centuries to millennia. The persistence of dissolved organic carbon (DOC) in the deep ocean has been attributed to inherently refractory molecules and to low concentrations of molecules, but the relative roles of molecular properties and molecular concentrations remain uncertain. We investigate both of these possibilities using bioassay experiments with unfiltered seawater collected from five depths (50-1500 m) at the Bermuda Atlantic Time-Series Study site. The microbial utilization of compositionally distinct forms of seawater DOC at in situ and elevated concentrations was determined. Microbial utilization of in situ organic carbon ranged from 6% to 7% in surface waters to 0% in deep water after 180 d. Additions of surface plankton-derived DOC (~18 μmol L −1 ), which was enriched in amino acids and carbohydrates, revealed substantial (50-75%) removal of the added DOC at all depths within 7 d. In sharp contrast, additions of C-18 isolated deep-sea DOC (~20 μmol L −1 ) showed insignificant or minimal utilization at all depths after 7 or 180 d, even when primed with labile substrates. These experiments demonstrate microbial communities from varying depths and environments in the ocean could rapidly utilize elevated concentrations of plankton-derived DOC, whereas these same microbes failed to utilize elevated concentrations of C-18 DOC. These results indicate molecular properties are the primary control on the microbial utilization of DOC in the ocean. Our findings imply a dynamic DOC reservoir with a flexible capacity for carbon sequestration in the global ocean.

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Section: Discussionmentioning

confidence: 99%

Molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean

Shen

Benner

2019

Limnology & Oceanography

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“…In this study, the concentration of DOM at mesophotic depths was lower than shallow depths, but the C : N ratio of mesophotic DOM (∼ 21) was greater than that of shallow DOM (∼ 14), initially suggesting a depletion of N with depth. However, only ∼ 20% of DOC is bioavailable in shallow reef waters (de Goeij and van Duyl ; Lønborg and Álvarez‐Salgado ; Lønborg et al ) and potentially even lower at mesophotic depths. If we assume 10% bioavailability for the deeper depths, and we also assume the bioavailability of DON tracks DOC, then the C : N ratios for shallow (∼ 14) and mesophotic (∼ 21) DOM are still sufficient to support metabolism in terms of the availability of carbon.…”

Section: Discussionmentioning

confidence: 99%

Depth‐dependent detritus production in the sponge, Halisarca caerulea

Lesser

Mueller

Pankey

et al. 2019

Limnology & Oceanography

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Sponges are important ecological and functional components of coral reefs. Recently, a new hypothesis about the functional ecology of sponges in organic matter recycling pathways, the sponge‐loop hypothesis, in which dissolved and particulate organic matter is taken up by sponges and shunted to higher trophic levels as detritus, has been proposed and demonstrated for shallow (< 30 m) cryptic species. However, support for this hypothesis at mesophotic depths (∼ 30–150 m) is lacking. Here, we examined detritus production, a prerequisite of the sponge loop pathway, in a reciprocal transplant experiment, using Halisarca caerulea from water depths of 10 and 50 m. Detritus production was significantly lower in mesophotic sponges compared to shallow samples of H. caerulea. Additionally, detritus production rates in transplanted sponges moved in the direction of rates observed for resident conspecifics. The microbiome of these sponge populations was also significantly different between shallow and mesophotic depths, and the microbial communities of the transplanted sponges also shifted in the direction of their new depth in 10 d largely driven by changes in Oxyphotobacteria, Acidimicrobiia, Nitrososphaeria, Nitrospira, Deltaproteobacteria, and Dadabacteriia. This occurred in an environment where the availability of both dissolved and particulate trophic resources changed significantly across the shallow to mesophotic depth gradient where these sponge populations were found. These results suggest that changes in sponge detritus production are primarily driven by differential quality and quantity of trophic resources, as well as their utilization by the sponge host, and its microbiome, along the shallow to mesophotic depth gradient.

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“…The most important allochthonous DOM sources in the GBR are mangroves and seagrasses (Maher and Eyre, ; Alongi and Mukhopadhyay, ). Changes in the relative importance of phytoplankton and these macrophytes as DOM sources (Stepanauskas et al ., ; Sawstrom et al ., ) will impact both the quantity and quality of carbon flowing through the microbial food web (Lønborg et al ., ). Although temperatures are already elevated in the GBR, they will continue to rise (IPCC, ).…”

Section: Introductionmentioning

confidence: 97%

Responses of physiological groups of tropical heterotrophic bacteria to temperature and dissolved organic matter additions: food matters more than warming

Morán

Baltar

Carreira

et al. 2020

Environmental Microbiology

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Compared to higher latitudes, tropical heterotrophic bacteria may be less responsive to warming because of strong bottom-up control. In order to separate both drivers, we determined the growth responses of bacterial physiological groups to temperature after adding dissolved organic matter (DOM) from mangroves, seagrasses and glucose to natural seawater from the Great Barrier Reef. Low (LNA) and high (HNA) nucleic acid content, membrane-intact (Live) and membrane-damaged (Dead) plus actively respiring (CTC+) cells were monitored for 4 days. Specific growth rates of the whole community were significantly higher (1.9 day -1 ) in the mangrove treatment relative to the rest (0.2-0.4 day -1 ) at in situ temperature and their temperature dependence, estimated as activation energy, was also consistently higher. Strong bottom-up control was suggested in the other treatments. Cell size depended more on DOM than temperature. Mangrove DOM resulted in significantly higher contributions of Live, HNA and CTC+ cells to total abundance, while the seagrass leachate reduced Live cells below 50%. Warming significantly decreased Live and CTC+ cells contributions in most treatments. Our results suggest that only in the presence of highly labile compounds, such as mangroves DOM, can we anticipate increases in heterotrophic bacteria biomass in response to warming in tropical regions.

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Organic matter bioavailability in tropical coastal waters: The Great Barrier Reef

Cited by 51 publications

References 121 publications

Molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean

Molecular properties are a primary control on the microbial utilization of dissolved organic matter in the ocean

Depth‐dependent detritus production in the sponge, Halisarca caerulea

Responses of physiological groups of tropical heterotrophic bacteria to temperature and dissolved organic matter additions: food matters more than warming

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